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<P PLOS Io h .
Complex Effects of Ecosystem Engineer Loss on Benthic
Ecosystem Response to Detrital Macroalgae
Francesca Rossi1*, Britta Gribsholt2, Frederic Gazeau3'4, Valentina Di Santo5, Jack J. M iddelburg2'6
1 Laboratoire Ecologie des Systèmes marins côtiers, Université Montpellier 2, Montpellier, France, 2 D epartm ent of Ecosystems, Royal Netherlands Institute for Sea
Research, Yerseke, th e Netherlands, 3 Centre National d e la Recherche Scientifique-lnstitut National des Sciences d e l'Univers, Laboratoire d' O céanographie d e
Villefranche, Villefranche-sur-mer, France, 4 Université Pierre e t Marie Curie, Observatoire O céanologique de Villefranche, Villefranche-sur-mer, France, 5 D epartm ent of
Biology, Boston University, Boston, M assachusetts, United States o f America, 6 D epartm ent of Earth Sciences - Geochemistry, Faculty of Geosciences, Utrecht University,
Utrecht, The Netherlands
Abstract
Ecosystem e n g in e e r s c h a n g e a bio tic c on ditio ns, c o m m u n i ty a s s e m b ly a n d e c o s y s t e m function ing. C o n se q u e n tly , their loss
m ay modify t h r e s h o ld s o f e c o s y s t e m r e s p o n s e t o d i s t u r b a n c e a n d u n d e r m i n e e c o s y s t e m stability. This s t u d y in vestiga te s
h o w loss o f t h e b i o tu r b a tin g l u g w o rm Arenicola m arina modifies t h e r e s p o n s e to m acroalgal detrital e n r ic h m e n t o f
s e d i m e n t b io g e o c h e m ic a l propert ies, m i c r o p h y t o b e n t h o s a n d m a c r o fa u n a a s s e m b la g e s . A field m anip u lativ e e x p e r i m e n t
w a s d o n e o n an intertidal sa nd flat (O o s te rsc h eld e estuary, The Netherlands). L u g w o rm s w e r e de libe ra tely e x c lu d e d from
1 X m s e d i m e n t plots a n d different a m o u n t s o f detrital Ulva (0, 200 o r 600 g W et Weight) w e re a d d e d twice. S e d im e n t
b i o g e o c h e m is tr y c h a n g e s w e re e v a lu a te d t h r o u g h b e n th i c respiration, s e d i m e n t o rg a n ic c a r b o n c o n t e n t a n d p o r e w a t e r
inorganic c a r b o n as well as de trital m a c r o a lg a e re m a in ing in t h e s e d i m e n t o n e m o n t h a fte r e n r ic h m e n t. Microalgal b io m a ss
a n d m a c r o fa u n a c o m p o s it i o n w e r e m e a s u r e d at t h e s a m e tim e. Macroalgal c a r b o n m ineralization a n d tran sfer t o t h e
b e n th i c c o n s u m e r s w e r e also in v e s tig a te d d u rin g d e c o m p o s i t io n a t low e n r i c h m e n t level (200 g WW). T he interaction
b e t w e e n lu g w o r m exclusion a n d detrital e n r ic h m e n t did n o t m odify s e d i m e n t o rg a n ic c a r b o n o r b e n th i c respiration. W eak
b u t significant c h a n g e s w e r e in stea d fo u n d for p o r e w a t e r inorg an ic c a r b o n a n d m icroalgal biom ass. L ug w o rm exclusion
c a u s e d a n increase o f p o r e w a t e r c a r b o n a n d a d e c r e a s e o f microalgal biom ass, while detrital e n r i c h m e n t d ro v e t h e s e values
b a ck t o values typical o f lu g w o r m - d o m i n a te d se d im e n ts. L u g w o rm exclusion also d e c r e a s e d t h e a m o u n t of m a c r o a lg a e
re m a in ing into t h e s e d i m e n t a n d a c c e le ra te d detrital c a r b o n m ineralization a n d C 0 2 release t o t h e w a t e r c o lu m n .
Eventually, t h e interactio n b e t w e e n l u g w o rm exclusion a n d detrital e n r i c h m e n t a ffected m a c r o f a u n a a b u n d a n c e a n d
diversity, which c olla p sed a t high level o f e n r ic h m e n t only w h e n t h e lu g w o r m s w e re p re sen t. This s t u d y reveals t h a t in
n a tu re t h e role of this e c o s y s t e m e n g i n e e r m ay b e variable a n d s o m e t i m e s have no o r e v e n n e g a tiv e effects o n stability,
c on versely t o w h a t it s h o u ld b e e x p e c t e d b a se d o n c u rre n t research kn o w le d g e.
C itation : Rossi F, Gribsholt B, Gazeau F, Di Santo V, Middelburg JJ (2013) Complex Effects of Ecosystem Engineer Loss on Benthic Ecosystem Response to Detrital
Macroalgae. PLoS ONE 8(6): e66650. doi:10.1371/journal.pone.0066650
Editor: Andrew Davies, Bangor University, United Kingdom
Received Septem ber 25, 2012; A ccepted May 10, 2013; Published June 21, 2013
C opyrigh t: © 2013 Rossi e t al. This is an open-access article distributed under th e term s of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided th e original author and source are credited.
Funding: This work was funded by a PIONIER grant o f th e Netherlands Organization for Scientific Research to JJM. The funders had no role in study design, data
analysis, decision to publish, or preparation o f th e manuscript.
C om peting Interests: The authors have declared th a t no com peting interest exist.
* E-mail: francesca.rossi@univ-montp2
Introduction
response to disturbances [10-12]. O n e or few species can be key
contributors to ecosystem functions to the extent th a t their loss can
outw eigh the effect o f species richness o n ecosystem functions,
resilience o r resistance [10,13,14], Such overw helm ing effect can,
how ever, vary w ith the e nvironm ental context a n d change w ith
increasing ecological com plexity [15]. It seems thus evident th at
un d erstan d in g the role o f species loss in m arin e systems m ight
req u ire a large body o f know ledge o f the functional role o f
individual species a n d o f the consequences o f losing particu lar
species for ecosystem functions a n d for their response to
disturbance.
Ecosystem engineer species strongly m odify resource availability
a n d en v ironm ental conditions, w hich in tu rn can alter c o m m u ­
nities a n d ecosystem functions [16,17]. T hese species are thus ideal
candidates to test hypotheses o n how local extinction o f key
contributors to ecosystem functions can m odulate the response o f
ecosystem s to disturbance. In m arin e sedim ents a n d terrestrial
soils, ecosystem engineers are often species th a t c ontribute to
It is w idely recognized th a t species loss m ay affect ecosystem
stability and, in tu rn , have im p o rta n t social a n d ecological
consequences [1—3]. O verall, w hen m ore species are presen t in a
com m unity, ecosystem functions are m ore stable in tim e a n d
increase their resistance o r resilience against disturbance, due to
a n increased variety o f life strategies, functional traits a n d
responses to e nvironm ental d isturbance [4—6], D ifferent species
con trib u tin g to sim ilar ecosystem functions can occur u n d e r
different e nvironm ental conditions a n d ensure th a t functions are
p erfo rm ed even w h en som e o th er species are displaced [4,5,7].
E m pirical evidence has show n th a t som etim es species loss can
have com plex, often idiosyncratic effects on the stability o f
ecosystem functions a n d o n b o th th eir resistance a n d resilience
against d isturbance [8,9], T his is especially tru e for the m arine
coastal ecosystem , w here species identity, functional traits a n d
e nvironm ental con text m ay rule ecosystem functions a n d their
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Complex Effects o f Ecosystem Engineer Loss
o f lugw orm s w ould increase the m agnitude o f changes caused by
the d isturbance o f m acroalgal detritus for (i) carb o n availability
a n d b enthic respiration; (ii) m icroalgal biom ass a n d (iii) m acrofauna assem blages. R ecycling o f the organic carb o n derived from
detrital decom position was also investigated to explore som e o f the
m echanism s th a t m ight regulate the effect o f el. marina o n benthic
responses to m acroalgal detritus.
particle m ixing a n d solute p e n etratio n into the sedim ent th ro u g h
the process o f b io tu rb atio n , w hich includes sedim ent rew orking
a n d b u rro w ventilation [18], T hese b io tu rb a tin g engineer species
can be g reat contributors to diagenetic reactions, to the recycling
o f sedim entary organic m atter, a n d to benthic com m unity
structure a n d biodiversity [18-21]. T h ey also have the p otential
to strongly m odify the response to d isturbance o f benthic
com m unities a n d functions [22]. F or instance b io tu rb a tio n by
Marenzellaria viridis has b e en found to decrease hypoxic crises in the
Baltic Sea [23]. It has also b e en found th a t in soil, rew orking
activity o f d o m in a n t c o ntributors to b io tu rb atio n , such as
earthw orm s, m odulates the response o f p lan t com m unities to
invasions [24]. Surprisingly, how ever, ecosystem engineer loss has
b e en poorly considered in studies investigating ecosystem response
to disturbance.
In m arin e coastal systems, a large p o rtio n o f seaweeds a n d
seagrasses is n o t consum ed by herbivores b u t retu rn s to the
env iro n m en t as decaying organic m a tte r [25]. In shallow -w ater
coastal habitats, d etrital seaweeds a n d seagrasses can supply
im p o rta n t am ounts o f organic m a tte r to b enthic ecosystem s. T h ey
represent a n im p o rta n t source o f d isturbance because du rin g
decom position they can alter sedim ent biogeochem istry and, in
tu rn , b enthic com m unities o f consum ers. D espite detrital seaw eed
a n d seagrass supply is often a n a tu ra l event, proliferation a n d
bloom s o f seaweeds as a consequence o f e u tro p h icatio n can
dram atically increase detrital seaw eed biom ass a n d exacerbate the
effects on benthic ecosystem s [26-29]. Biom ass decom position can
induce hypoxia follow ed b y the release o f red u ced toxic
com pounds such as sulphides, w hich are toxic for several benthic
species a n d can therefore strongly reduce species a b u n d an c e a n d
diversity [26,27,29-33]. D etrital decom position can also provide
food, directly for detritivores o r indirectly, b y stim ulating bacterial
m etabolism , thereby altering the b enthic food w eb [28,34]. T hese
effects strongly d e p en d o n the a m o u n t o f d etrital inputs a n d o n its
decom position p atterns, w hich m ay strongly v ary as a conse­
quence o f b enthic invertebrate com position a n d identity [35].
B ioturbating fauna can m odulate the recycling o f detrital
m acroalgae en h an c in g organic m atter m ineralization a n d m icro­
bial activity [36-38]. Som e b u rro w in g b io tu rb a tin g species, such
as certain crabs o r polychaetes, can also in co rp o ra te detritus into
th eir b u rro w wall lining a n d represent im p o rta n t sinks for detrital
m acroalgae [39]. In addition, often b io tu rb a tin g infauna are also
detritivores th a t c an consum e directly detritus a n d c o n trib u te to its
recycling in the food w eb. In a lab o rato ry experim ent, for instance,
it was found th a t nitro g en a n d c arb o n fluxes at the sedim ent-w ater
interface ch an g ed following b o th the addition o f the d etrital green
m acroalgae Chaetomorpha linum a n d the presence o f the b io tu rb a tin g
polychaete Nereis diversicolor. T his polychaete ingested m acroalgal
fragm ents, e n h an c ed m icrobial m etabolism a n d co n trib u ted to
diffuse solutes in the interstitial sedim ent a n d at the sedim entw ater interface [36],
O n e co m m o n w ell-recognized b io tu rb a tin g species typical o f
tem p erate w aters is the bu rro w in g lugw orm Arenicola marina. T his
w orm lives h e a d dow n in J-sh a p e d burrow s w here it ingests
sedim ent a n d defecates o n the surface. Its activity has been
recognized to destabilize sedim ent a n d co u n te rac t the effect o f
m icrophytobenthos, increase sedim ent m icrohabitats a n d alter
sedim ent biogeochem istry, b y e n h an cin g solute p e n etratio n into
sedim ent d e p th a n d re-distributing organic m aterial along the
vertical profile [40], C onsequently, this species m ay alter o th er
fau n a a n d vegetation [36,37,41], T his study reports o n how the
loss o f this b io tu rb a tin g lugw orm m ay alter the response to detrital
m acroalgae o f intertidal benthic m acro fau n a a n d sedim ent
biogeochem istry. It was hypothesized th a t the deliberate exclusion
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M aterials and Methods
S tu d y Site a n d E x p e rim e n ta l D esig n
T w o m anipulative experim ents w ere done o n a n intertidal flat
o f the O osterschelde estuary (T he N etherlands) d o m in a ted by the
b io tu rb a tin g lugw orm Arenicola marina, du rin g sum m er 2006. T h e
study intertidal flat, n a m e d Slikken van V iane (51" 3 7 ' 0 0 " N , 4"
0 1 ' 0 0 " E), was a sheltered a re a situated on the u p p e r intertidal
close to a salt m arsh. S edim ent grain-size was 65% fine sand a n d
35% very fine sand (Rossi F., u n p ublished data). T h e O os­
terschelde estuary is a natio n al p a rk designated as zone V I by the
In tern a tio n a l U n io n for C onservation o f N a tu re (IU CN ). T his
IU C N classification has a m o n g its objectives the facilitation o f
scientific research a n d e nvironm ental m onitoring, m ainly related
to the conservation a n d sustainable use o f n a tu ra l resources
(h ttp ://w w w .iu c n .o rg ). N o specific perm its w ere therefore re ­
q u ired for p erfo rm in g these scientific experim ents, w hich did not
involve en d an g e red o r p ro tec te d species. T h e first experim ent
tested the effect o f el. marina exclusion o n the response o f
m acro fau n a assem blages a n d sedim ent biogeochem istry to differ­
ent am ounts o f d etrital m acroalgae. T h e second experim ent
m easured the changes in detrital recycling follow ing el. marina
exclusion. F or the first ex p erim ent (Fig. 1), all lugw orm s w ere
excluded from 15 ran d o m ly chosen sedim ent plots o f l x l m,
som e m eters ap art, by bu ry in g m osquito nets to the d e p th o f
approxim ately 7 cm (hereafter exclusion A — treatm ent), following
the m eth o d p ro p o sed by [41] in a m ore extensive area. A
p ro c ed u ra l control for the effect o f the n et a n d o f the b u rial was
done for o th er 15 sedim ent plots o f 1 x i m by bu ry in g m osquito
nets w ith 1 0 x 1 0 cm holes (hereafter p ro c ed u ra l control A +
treatm ent).
O n e m o n th after lugw orm exclusion, the sedim ent plots w ere
organically-enriched b y ad dition o f d etrital Ulva spp. Fresh Ulva
thalli w ere previously collected in the O osterschelde estuary a n d
w ashed to rem ove anim als a n d sedim ent. T halli w ere th en
w eighted a n d frozen in separate plastic bags. F reezing is
■ L ugw orm excluded plots (A -)
□ Procedural control plots (A + )
600
0
200 600
0
200
200
0
600 600
0
200
0
200
0
200 600
0
600
0
200 600 600
0
200 600
600 200
0
200
Figure 1. Schematic experim ental design fo r ex p erim ent 1. Each
rectangle co rre sp o n d s to 1 m 2 plot. N um bers refers to th e detrital
enrichm ent. (0: no addition; 200:200 g WW w ere a d d ed tw ice a t a 1
w eek interval; 600:600 g WW w ere ad d e d tw ice with a 1 w eek interval).
D istance am o n g plots are n o t in scale.
doi:10.1371/journal.pone.0066650.g001
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Complex Effects of Ecosystem Engineer Loss
3 111111 in n er diam eter (i.d.). F o r chlorophyll a, the sedim ent was
collected to 1 cm depth, kept in the d ark a n d preserved at —80°C.
T h e sedim ent for O C was collected to the d ep th o f 6 cm,
sectioned into 0- 1, 1-2 a n d 2 -6 cm depths a n d preserved freezedried. Ulva detritus was rem oved from this sedim ent u n d e r the
stereo-m icroscope. T h e sedim ent for p o re w ate r D IC extraction
was collected w ith cores o f 5 cm i.d. a n d sectioned into 0 -1 , 1-2
a n d 2 -6 cm d epth intervals at the lowest a n d highest levels o f
organic en rich m en t (0 a n d 600) in b o th the control a n d the
exclusion treatm ents. T w o cores w ere collected from each plot a n d
th en pooled to reach the a m o u n t o f w a ter need ed for the analyses.
P orew ater was extracted by centrifugation (1344 g, 15 m in) a n d
the su p e rn ata n t was filtered on M illipore 45 |Im . T h e extracted
w ater was stored in glass vials, sealed, im m ediately poisoned w ith
satu rated H g C F to stop bacterial activity a n d analyzed w ithin 3 d.
O nly 3 out o f 5 random ly-chosen replicate plots w ere sam pled for
O C an d T C O 2.
T h e sedim ent for m acro fau n a was collected using 11 cm i.d.
PV C core. T h is sedim ent was sieved (0.5 n in i m esh) a n d
m acro fau n a fixed in 4% buffered form ol. Before sam pling, all
plots w ere p h o to g rap h e d to estim ate the ab u n d an c e o f A. marina
using visible m ounds. In the laboratory, all plots w ere in d ep e n ­
dently exam ined by four researchers to reduce estim ate bias. Five
random ly-chosen n a tu ra l plots w ere also p h o to g rap h e d a n d th en
sam pled using 11 cm i.d. cores to test for the effect o f the
p ro c ed u ra l control A + on the n a tu ra l a b u n d an c e o f A. marina a n d
o f the o th er benthic m acrofauna. N o differences w ere detected
betw een n a tu ra l a n d p ro c ed u ra l control treatm en ts (see Results
section) a n d this latter was used for evaluating the effect o f detrital
en rich m en t an d lugw orm exclusion.
S edim ent cores w ere also used to m easure fluxes o f inorganic
c arb o n (TCCF) a n d oxygen (CF) at the sedim ent-w ater interface.
In tac t sedim ent cores w ere collected by p ushing Plexiglas cores
(11 cm i.d.) into the sedim ent to a d e p th o f 20 cm at each o f th ree
replicate plots for the lowest a n d the highest levels o f organic
en rich m en t (0 an d 600) in b o th the control a n d the exclusion
treatm ents. T h e n e t w as carefully cut a ro u n d the cores to allow the
core p e n etratio n into the sedim ent. C ores w ere sealed w ith ru b b e r
stoppers a n d d ug out o f the sedim ent. All cores w ere b ro u g h t to a
clim ate controlled ro o m w ithin 2 h, a n d kept in the d ark at in situ
tem p e ra tu re (10°C) before fu rth er handling. T h e sam e day, the
cores w ere in cu b ated in the d ark for 12 h. In c u b atio n in the dark
com m only used in experim ents th a t aim s at testing effects o f
detrital m acroalgae a n d decom position patterns. T his trea tm e n t is
necessary in o rd e r to create detritus a n d ensure th a t Ulva is d ead
w hen bu ried since this seaw eed can survive for very long periods in
the d ark [30]. T h e thalli w ere left defrosting a t air tem p e ra tu re
an d th en ad d ed to the top 1 cm o f the sedim ent by gently h andch u rn in g the detritus w ith the sedim ent. E n ric h m en t was done
twice, on Ju ly 3 a n d Ju ly 10, 2006. E ach tim e either 200 o r 600 g
o f w et w eighted Ulva (hereafter treatm en ts 200 a n d 600,
respectively) w ere ad d ed to 10 exclusion (A —) a n d 10 pro ced u ral
control (A—) plots. T hese am ounts corresponded to 40 a n d 120 g
dry weight. O th e r 10 plots (5 A — a n d 5 A+) w ere n o t enriched
(hereafter trea tm e n t 0), b u t the sedim ent was h a n d -ch u rn e d to
control for the m anipulation. T h e re was no p ro c ed u ra l control for
the physical presence o f detritus as previous experim ents h a d
dem o n strated no effects [28-30]. T h e a m o u n t o f Ulva spp. was
based on the available literature to cause m ed iu m a n d high levels
o f disturbance (e.g. [27,30,32,33]).
T h e second ex p erim ent was ru n at the sam e tim e o f experim ent
1. T w o additional p ro c ed u ra l control plots for b urial a n d 2
exclusion plots w ere enrich ed w ith 200 g loC -labelled Ulva twice,
resem bling the tre a tm e n t “ 2 00” . T hese four plots w ere used to
trace the fate o f the carb o n released from detrital Ulva. T h e
labeling o f Ulva was done in the laboratory. Leaves w ere w ashed
an d carefully cleaned to elim inate epiphytes a n d anim als. T h en ,
thalli w ere transferred to a q u aria c o ntaining filtered seaw ater
supplem ented w ith N a H loC 0 3 (99% loC) to the con cen tratio n of
0.2 g L \ T h e a q u aria w ere oxygenated a n d covered w ith
tran sp are n t PV C to lim it 1 'C b acterial respiration.
Field S a m p l in g
F o r the first experim ent, sam pling was done on Ju ly 30 a n d
A ugust 1, 2006, one m o n th after detrital enrichm ent. T his tim ing
was chosen because previous studies suggested th a t effects o f algal
m ats on m acro fau n a occur w ithin 2 to 10 weeks from the
deposition [31-33,42] a n d th a t decom position o f Ulva occurs
w ithin a m o n th (e.g. [43,44]).
S edim ent sam ples w ere taken for organic c arb o n (hereafter
O C ), p o re w ate r total inorganic c arb o n (D IC —H 2C O 3+
H C O 3 + C O 32 ), m icroalgal biom ass (chlorophyll a) a n d m ac ro ­
fauna species com position, a b u n d an c e a n d diversity. T h e sedim ent
for chlorophyll a a n d O C was collected using a cut syringe of
Arenicola-Qxeluded sediment
Procedural control sediment
(A-)
(A+)
Figure 2. Comparison o f sedim ent surface appearance a fte r Arenicola m arina exclusion a t low tid e . A - rep resen t th e sed im en t after 1
m o n th from th e burial of net to exclude burrow ing species. A+ is th e procedural control tre a tm e n t (see Materials and M ethods for details).
doi:10.1371/journal.pone.0066650.g002
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Complex Effects o f Ecosystem Engineer Loss
□ 0
■ 200
■ 600
Table 1. T w o-w ay analyses o f variance for s e d i m e n t o rga nic
c a r b o n (OC) a n d p o r e w a t e r DIC a t different s e d i m e n t d e p t h s
o n e m o n t h a fte r detrital e n r ic h m e n t.
01 cm
A+
lcm
A-
A+
A-
2 cm
A+
6 cm
(b)
26 cm
1 -2 cm
S edim ent OC
d f MS
F
MS
F
MS
F
Exclusion = E
1 0.67
10-3
0.40
1.60 10~3
3.80
0.09
10-3
0.52
Detrital
enrichm ent = D
2 0.61
10-3
0.96
0.09 10~3
0.40
0.62
10-3
2.22
ExD
2
1.7 10 " 32.64
0.42 10~3
1.90
0.17
10-3
0.62
Residual
12 0.63
10-3
0.22 10~3
0.28
10-3
P orew ater DIC
y
1
Id Id i
A+
lcm
A+
2 cm
A-
1 1.89
17.50 5.06
1.03
10.15
4.80
Detrital
enrichm ent = D
1 0.06
2.00
1.28
5.12
0.15
0.28
ExD
1 0.11
3.43
4.93
19.71
0.30
0.57*
Residual
8 0.03
1.00
2.11
A+
Significant values (P<0.05) are n bold. Data were not-transformed (PC-cochran
>0.05). Asterisk indicates pooling of interaction w hen P>0.25.
6 cm
Figure 3. M ean (+1SE) fo r (a) b u lk sedim ent organic carbon
(OC) and (b) p orew ater dissolved inorganic carbon (DIC) at
d iffe re n t sedim ent depths { I c m surface sedim ent to 1 cm
d epth; 2 cm. from th e d ep th o f 1 to 2 cm; 6 cm: from the d ep th
o f 2 to 6 cm). In th e g raphs, A—: A. marina excluded; A+: procedural
control for burial; th e legend indicate th e levels o f detrital addition (0:
no addition; 200:200 g WW w ere ad d e d tw ice a t a 1 w eek interval;
600:600 g WW w ere ad d e d tw ice with a 1 w eek interval). Data w ere
sam pled o n e m o n th after detrital addition. Asterisk indicates significant
differences.
doi:10.1371/jo u rn al.pone.0066650.g003
(a)
150.00
•3
100.00
P
50.00
0.00
did n o t allow to g ath er ad ditional inform ation con cern in g the
(auto)trophic state o f the sedim ent, w hich w ould need a light
incubations o f o th er sedim ent cores. O u r system was how ever
lim ited to carry 12 cores a t a tim e a n d no fu rth er analyses could b e
done. P rio r to incubations, cores w ere in u n d ate d w ith welloxygenated O osterschelde w ater collected the sam e day
([N H 4+] = 20 pm o l L", [ N 0 3~] = 110 pm o l L “ 1, salinity = 22)
a n d left to acclim atize in the d ark for 6 -8 h. D u rin g incubation,
the overlying w ater-colum n (25-30 cm) was continuously stirred
w ith a m agnetic stirrer, m ain tain in g continuous w ater circulation
at a ra te well below the resuspension lim it. Dissolved 0 2 never
decreased below 65% o f saturation. W ater sam ples for T C 0 2 a n d
0 2 w ere collected in glass vials a n d sealed avoiding a ir bubbles. All
sam ples w ere im m ediately poisoned w ith satu rated H g C l2 to stop
b acterial activity a n d th en analyzed w ithin 3 d.
F o r ex p erim ent 2, sedim ent sam ples w ere taken from the four
plots w ith labelled Ulva. Sam pling was done on four occasions, 6 ,
8, 15 a n d 17 days after d etrital enrichm ent. E ach tim e, one
plexiglass intact sedim ent core (11 cm i.d.) was collected to 20 cm
d epth, follow ing the m odality used to sam ple the cores for
estim ating b enthic respiration. T o reduce plot dam age d u rin g core
collection, the central p a rt o f the plot (20 cm from the edges) was
divided into 4 q u a d ran ts o f 3 0 x 3 0 cm . E ach sam pling occasion, a
sedim ent core was taken from a different q u a d ran t. A n a rea o f
1 5 x 1 5 cm was thus dam ages each tim e, correspondin g to 2.25%
o f the entire plot area. T h e sam pled sedim ent was replaced w ith
plexiglass tubes to avoid any collapse a n d to leave the rem ain in g
PLOS ONE I www.plosone.org
Exclusion = E
ΠI
-50.00
o<1
-
100.00
A-
(b)
A+
2.5
1.5
0.5
A-
A+
Figure 4. M ean (+1 SE) fo r (a) benthic oxygen ( 0 2) consum ption
and total carbon d io x id e (T C 0 2) released d uring 12 hours d ark
incubation; (b) Respiratory q u o tie n t (RQ). In th e graphs, A : A.
marina excluded; A+: procedural control for burial; th e leg en d indicate
th e levels of detrital addition (0: no addition; 200:200 g WW w ere ad d ed
tw ice a t a 1 w eek interval; 600:600 g WW w ere ad d e d tw ice w ith a
1 w eek interval). Data w ere sam pled o n e m o n th after detrital addition.
doi:10.1371/journal.pone.0066650.g004
4
June 2013 | Volume 8 | Issue 6 | e66650
Complex Effects o f Ecosystem Engineer Loss
Table 2. T w o-w ay analyses o f variance for s e d i m e n t - w a t e r
e x c h a n g e s of 0 2 a n d T C 0 2 a n d for t h e b e n th ic respiratory
coefficient RQ.
tc o 2
o2
d f MS
F
F
MS
F
Exclusion = E
1 8.8 10-6 2.38
252.08
0.78
0.29
2.39
Detrital
enrichm ent = D
1 8.0 10-9 0.00
102.08
0.31
0.02
0.18
0.22*
0.00
0.01*
1 4.38 1 ~7 0.11* 70.08
Residual
8 4.10 1-6
325.08
m
M)
0
[
D 200
■ 600
25
RQ
MS
ExD
30
A-
A+
0.14
Figure 5. M ean (+1SE) fo r chlorophyll a concentration a t the
surface sedim ent (1 cm d ep th ). In th e graphs, A - : A. marina
excluded; A+: procedural control for burial; th e legend indicate th e
levels of detrital addition (0: no addition; 200:200 g WW w ere ad d ed
tw ice a t a 1 w eek interval; 600:600 g WW w ere ad d e d tw ice w ith a 1
w eek interval). Data w ere sam pled o n e m o n th after detrital addition.
Asterisk indicates significant differences.
doi:10.1371/journal.pone.0066650.g005
Significant values (P<0.05) are in bold. Data w ere not-transformed (Pc-cochran
>0.05), except for O2, which was arc-tangent transform ed to hom ogenise the
residual variances. Asterisk indicates pooling o f interaction w hen P>0.25.
doi:10.1371 /journal.pone.0066650.t002
p a rt o f the plots u ndisturbed. T h e cores w ere h a n d le d like the
cores used for evaluating oxygen a n d carb o n exchange at the
sedim ent-w ater interface for the ex p erim ent 1. H ow ever, before
incu b atin g for w et respiration a n d determ in in g release o f T C 0 2
in the w ater colum n, the labelled cores w ere in cu b a ted for dry
fluxes d u rin g 6 h. A t the b eginning a n d a t the e n d o f the
incubation, air sam ples w ere collected using syringes a n d p u m p ed
into tubes co n tain in g soda lim e to trap C 0 2 a n d m easure the
C 0 2 derived from Ulva decom position. A L IC O R au to m a te d
C 0 2 analyzer was used to quantify C 0 2 release every hour.
Sedim ent-w ater exchange ra te a n d m acro fau n a d a ta w ere
gen erated as for ex p erim ent 1 (see “ A nalytical m easures” section).
Follow ing flux incubations for b o th experim ents, the cores w ere
sieved at 0.5 nin i to collect the m acrofauna. N o lugw orm was
included in the cores, m ea n in g th a t any observed p a tte rn
rep resen ted the result o f sedim ent a n d m acro fau n a alteration
due to Arenicola, b u t not the direct activity o f the lugw orm du rin g
incubation.
W ater T C 0 2 (wet fluxes), gaseous C 0 2 (dry flux), bulk sedim ent
a n d m acro fau n a collected in the labelled plots w ere analyzed for
carb o n isotope com position (8 C). T h e gaseous C 0 2 (dry flux)
c ap tu red using soda lim e was analyzed after acidification. T h e 13C
isotope signature for T C 0 2 dry a n d w et fluxes was analyzed using
a G C colum n coupled to a F in n in g an delta S m ass spectrom eter
IR M S . T h e carb o n isotopic com position for sedim ent, residual
detritus a n d anim als was d e term in ed using a Fisons elem ental
analyzer coupled to a F inningan delta S mass spectrom eter. 13C to
*~C ratio was referred to V ie n n a PD B a n d expressed in units o f %o.
R eproducibility o f the m easurem ents is b e tte r th a n 0.2%o [45].
T h e excess o f the heavy isotope o f carb o n (above background) was
expressed as total uptake (I) in m illigram s o f 13C. I was calculated
as the p ro d u c t o f excess 13C (E) a n d carb o n or biom ass (C):
I =E XC
A nalytical M e a s u r e s
In the laboratory, m acro fau n a w ere identified to the species
level, co u n te d a n d d ried a t 60"C for 48 h to o b tain dry w eight
biom ass to be used for stable isotope analyses relative to the
experim ent 2. T h e d etrital Ulva rem ain in g in the sam ples was also
collected, d ried a n d w eighed. C hlorophyll a was ex tracted in
darkness for 24 h a t 0 -4 "C using a 90% acetone solution. T h e
sedim ent was h om ogenized a n d sub-sam ples o f ab o u t 1 g dry
w eight w ere taken. Pigm ents w ere m easured spectrophotom etrically before a n d after 0.1 N HC1 acidification. Pre-com busted
(450"C for 3 h) sedim ent was used as a blank. M easurem ents for
bulk sedim ent O C w ere m ad e using a P erkin-E lm er C H N elem ent
analyzer o n freeze-dried m aterial, after c arb o n a te rem oval w ith
HC1.
Flux rates o f T C 0 2 a n d 0 2 b etw een the sedim ent a n d the
overlying w ater w ere estim ated as difference b etw een the initial
a n d the final T C 0 2 or 0 2 concentrations d u rin g d a rk incubation,
assum ing constant solute exchange w ith tim e. T h e oxygen
dissolved into the w ater sam ples was analyzed using the sta n d ard
m eth o d o f W inkler titration, while w ater T C 0 2 a n d po rew ater
D IC w ere d e term in ed by the flow in jection/diffusion cell
technique, w hich is based o n the diffusion o f C 0 2 th ro u g h a
hydrophobic m em b ran e into a flow o f deionized w ater, thus
gen eratin g a grad ien t o f conductivity p ro p o rtio n al to the
co n cen tratio n o f C 0 2.
PLOS ONE I www.plosone.org
E = F control
F¡¡„„pie
w here F indicates the fraction o f isotope a d d ed a n d it is calculated
as:
F = R /R +
1
w here R can be calculated from the m easured S 13C using R
referen ce o f 0.0112372:
4 f
\R sam ple / ^referen ce
I
X
10'
Statistical A n aly ses
F o r ex p erim ent 1, d a ta w ere analyzed w ith tw o-w ay orthogonal
m ixed m odel o f analysis o f variance (AN OVA ), w ith exclusion (2
levels: p ro c ed u ra l control A + a n d exclusion o f .4. marina, A —) a n d
d etrital e n rich m en t (3 o r 2 levels: 0, 200 a n d 600) as fixed a n d
ra n d o m factors, respectively. D etrital e n rich m en t was considered a
ra n d o m factor because the a m o u n t o f detritus to a d d was chosen
w ithin a range o f values to sim ulate conditions o f low a n d high
5
June 2013 | Volume 8 | Issue 6 | e66650
Complex Effects o f Ecosystem Engineer Loss
Table 3. T w o-w ay analyses o f variance for chlorophyll a, m a c r o fa u n a a b u n d a n c e a n d n u m b e r (N) of species.
C hlo ro phyll a
A bundance
N o f species
df
MS
F
MS
F
MS
F
Exclusion = E
1
72.23
1.27
0.48
0.69
0.03
0.00
Detrital enrichm ent = D
2
53.74
4.02
0.29
0.56
30.00
7.11
ExD
2
56.80
4.25
2.34
4.81
17.73
4.21
Residual
24
13.37
0.49
4.22
Significant values (P<0.05) are in bold. Data w ere sqrt-transformed for macrofauna abundance.
doi:10.1371 /journal.pone.0066650.t003
e nrichm ent, b u t no specific hypothesis con cern ed the chosen
am ounts. A significant interaction b etw een exclusion a n d detrital
e n rich m en t was expected if the exclusion o f A. marina ch an g ed the
response to d etrital enrichm ent. T hese analyses w ere done for the
total a b u n d an c e o f m acro fau n a individuals, n u m b e r o f m acrofau­
n a species, chlorophyll a, sedim ent O C , p o re w ate r D IC , w ater 0 2
a n d T C 0 2 exchange rate. C-cochran test was used to test for
residual v ariance hom ogeneity before ru n n in g the analyses. W h en
this test was significant (iP<0.05), d a ta w ere transform ed. Pooling
was done w h en P > 0.25. A posteriori m ultiple com parison S N K test
was ru n w h en interaction term was significant.
T h e variables collected for evaluating the recycling o f detrital
13C (experim ent 2) w ere analyzed w ith re p ea te d m easure
A N O V A , w ith tim e (6 , 8, 15 a n d 17 sam pling days from the
e n d o f detrital addition) as the re p ea te d m easure ra n d o m factor
a n d A. marina exclusion as fixed factor. Plots (2 levels) was nested in
exclusion. T h e interaction o f tim e w ith the exclusion trea tm e n t
was m easured over the interaction tim e x p lo t. W h en significant
interaction was found, the m ain effect exclusion was not
interp reted . A ssum ption ab o u t the correlation a m o n g the different
observations o f the re p ea te d m easure factor (time) was tested w ith
M au ch ley ’s sphericity test.
D ecom position rate o f m acroalgal detritus was estim ated by
fitting the first-order m odel:
Results
A fter the exclusion o f A. marina, no burrow s w ere visible in the
excluded plots (Fig. 2) a n d the n u m b e r o f burrow s in the
p ro c ed u ra l control (treatm ent A+) was com p arab le to th a t o f
na tu ra l sedim ent (m e a n ± S E , n = 5:8.7 2 ± 1.77 a n d 1 0 .3 3 ± 1 .1 7
burrow s m 3 for the n a tu ra l a n d the p ro c ed u ra l control,
respectively). O verall, th ere w ere no differences in m acro fau n a
species com position betw een the n a tu ra l sedim ent a n d the
p ro c ed u ra l control plots. M a c ro fa u n a a b u n d an c e (m ean ± SE,
n = 5) was 2 9 4 ± 4 2 a n d 2 2 0 ± 5 3 individual m 3, w hereas the
n u m b e r o f species was 1 0 ± 0 .2 a n d 1 0 ± 0 .5 for A + a n d n a tu ra l
sedim ent, respectively. T h erefo re, A + could be used as a control
for the effect o f lugw orm exclusion a n d d etrital m acroalgae.
O verall, in the n a tu ra l sedim ents a n d in the A + plots the
gastropod Hydrobia ulvae was num erically d o m inant, representing
90% o f m acro fau n a ab u n d an c e. T h e rem ain in g 10% was m ad e up
by oligochaetes (3%), deposit feeder polychaetes (3%) such as
spionids, nereids, capitellids a n d cirratulids a n d bivalves (3%),
m ainly Macoma balthica a n d Cerastoderma edule.
C a r b o n Availability a n d B e n th ic R e sp iratio n
A t the tim e o f sam pling, sedim ent organic carb o n (OC) did not
vary follow ing detrital enrichm ent, the exclusion o f A. marina or
their interactions (T able 1, Fig. 3a; A N O V A , T > 0 .05). M acroalgal
debris was still presen t in the sedim ent w here d etrital m acroalgae
w ere ad d ed a t the highest e n rich m en t level (treatm ent 600). T h e
biom ass o f this m acroalgal debris was sm aller in the lugw orm excluded sedim ent th a n in p ro c ed u ra l controls (m e a n ± SE:
lugw orm exclusion, trea tm e n t A —: 2 .3 ± 1 .4 gD W m 3; A+:
1 2 .0 ± 6 .6 gD W m - 3 ; A N O V A : F lt „ = 6.19, P = 0.038).
T h e re was a significant effect o f the in teractio n betw een
lugw orm exclusion a n d detrital e n rich m en t on p o re w ate r D IC to
the d e p th o f 1-2 cm (T able 1; Fig. 3b). In the n o n -en rich ed
sedim ent, p o re w ate r D IC c o n ce n tra tio n was h igher in the
lugw orm exclusion th a n in the control plots (SN K test at
P = 0.05: n o n -en rich ed plots, trea tm e n t 0: A —> A + ). M oreover,
in the lugw orm -exclusion plots, p o rew ater D IC was low er in the
en rich ed th a n in the n o n -en rich ed plots (SN K test at i 5= 0 .0 5 :
Arenicola exclusion, A —: 0 > 6 0 0 ). V alues in detrital-enriched,
lugw orm -excluded sedim ent w ere sim ilar to those m easu red for
the A+ trea tm e n t (Fig. 3b). A sim ilar p a tte rn was observed for
superficial (0-1 cm) a n d d eep er sedim ent (2-6 cm in Fig. 3b), b u t
no significant changes w ere m easured.
B oth A. marina exclusion a n d d etrital e n rich m en t o r their
interaction did n o t significantly change sedim ent-w ater exchanges
o f T C 0 2 a n d 0 2 n o r the RQ^ respiration coefficient ( T C 0 2: 0 2
ratio) (T able 2; Fig. 4).
B, = B0ek'
W h ere Bt is the g o f d etrital biom ass a t tim e t (days), B0 is the initial
biom ass, a t tim e 0 , a t the m o m e n t o f the second d etrital addition
a n d k is the specific decom position constant. T h e two detrital
additions w ere done at a distance o f one week, w hich m ay greatly
affect the estim ates o f B0. W e therefore considered the estim ates o f
residual Ulva as the sum o f two decom position curves, w ith the
sam e constant k b u t different decom posing time:
B t = B (0_ 1)ekl't+1) + B (0)ekt
T h e curves o f 13C b enthic inco rp o ratio n (including loss due to
respiration) w ere fitted to the logistic curve:
It= Y /(\+ q e -" )
q = ( Y - I 0) / I 0
W h ere Y is the 13C loss from m acroalgal decom position a n d r is
the capacity o f b e n thos to inco rp o rate C.
PLOS ONE I www.plosone.org
6
June 2013 | Volume 8 | Issue 6 | e66650
Complex Effects of Ecosystem Engineer Loss
(a)
60
□ 0
400
■ 200
■ 600
30 0
^
200
100
50
bù
40
I
£
30
-0.06
-0.08
-
H? 20
S
a
10
16
18
A significant interactio n betw een A. marina exclusion a n d detrital
en rich m en t was also found for m ac ro fau n a a b u n d an c e a n d
n u m b er o f species (T able 3). A b u n d an ce was low ered by the
highest level o f detrital en rich m en t in the plots w here A. marina was
present (Fig. 6a; S N K test: A+: 0 = 20 0 > 6 0 0 ). O verall, b o th the
d o m in a n t gastropod Hydrobia ulvae a n d all o th er rem aining
m ac ro fau n a decreased in a b u n d an ce, especially nereids, spionids
a n d bivalves (AN OVA : F 2, 94 = 4.26, P — 0.026 for H. ulvae, Fig. 6b;
F 2, 24 = 4.65, P — 0.019 for rem aining taxa, d a ta w ere square-root
transform ed; S N K tests for both: A+: 0 = 20 0 > 6 0 0 ). N u m b e r o f
species show ed a sim ilar p a tte rn , decreasing in response to the
highest level o f en rich m en t in the A + plots (Fi. 6G; S N K test: A+:
0 = 20 0 > 6 0 0 ). D etrital en rich m en t seem ed to not affect the
a b u n d an c e o f the lugw orm s as the n u m b er o f Arenicola burrow s
rem a in e d relatively stable at different levels o f detrital en rich m en t
(2 w ay A N O V A : F2t 12 = 0.88, P = 0.34, Fig. 6d).
20
£
0
b
15
2
10
tw
5
0
14
a n d a re re la tiv e to e x p e r im e n ts 2.
d o i:1 0 .1 3 7 1 /jo u rn a l.p o n e .0 0 6 6 6 5 0 .g 0 0 7
12
<N
12
Figure 7. Decom posing curves fo r Ulva detritus in lugw orm
excluded (tre atm en t A - ; square symbols in th e graphs) or
procedural control sedim ents (treatm en t A+; tria n g le symbols
in th e graph). S y m b o ls In d ic a te m e a n ( ± SE) for m a c ro a lg a l b io m a s s
o
C/3
•2h
"o
(U
Qh
GO
(d)
0.2
Tim e (days)
Hi
100
o
-
10
200
(c)
io
0.1
Ul
0
A-
T h e F a te o f D etrital C a r b o n
A+
T h e re w ere differences in the rate o f Ulva decom position
following A. marina exclusion. T h e decom position constant k was
—0.2 for the detritus ad d ed to the A. marina excluded sedim ent
(A— plots in Fig. 7). Interestingly, the A + plots did not fit well the
exponential curve using the sam e constant k th ro u g h the
decom position. R a th e r, at the beginning o f decom position, they
fitted k values betw een —0.06 a n d —0.08, w hereas at the en d they
fitted a K constant o f —0.1 (Fig. 7). T h e re w as a significant
interactio n betw een exclusion trea tm e n t a n d tim e after detrital
en rich m en t for the flux rate o f T C 0 2 from the sedim ent to the
w ater colum n (Table 4). M o re T 13C 0 2 was released by the
sedim ent in the exclusion trea tm e n t w ithin 6 days from burial
(Fig. 8a). R espiration rates w ere (m ean ± SE) 0 .8 4 ± 0 .2 5 a n d
0 .1 2 ± 0 .0 3 m g 13C m 2 day 1 for dry a n d w et fluxes, respectively.
P a rt o f the 13C rem a in e d in the b e nthos a n d it was in co rp o ra te d
in the bulk sedim ent a n d in the m acrofauna. T h e a m o u n t
in co rp o ra te d was variable am o n g plots, b u t it did not significantly
vary betw een exclusion treatm en ts or tim e (Table 4; Fig. 8 b —c). H.
ulvae in co rp o ra te d the largest a m o u n t o f G am o n g all m ac ro ­
fauna tax a (m ean ± SE: 3 .2 ± 0 .8 a n d 1 .2 ± 0 .4 m g 13C m 2, for
H . ulvae a n d rem ain in g fauna, respectively).
Figure 6. M ean (+1SE) for (a) to tal n um ber o f m acrofauna
individuals, (b) abundance o f Hydrobia ulvae, (c) n um ber of
m acrofauna species and (d) num bers o f Arenicola marina
burrows in th e plots w here th e m osquito net was buried
(A —) and in th e procedural control plots (A+) at th e end o f the
experim ent, e.g; 1 m onth from the second add itio n o f detrital
Ulva (0: no add itio n; 200:2 0 0 g W W w ere added tw ice at a 1
w e e k interval; 600 :6 0 0 g W W w ere added tw ice w ith a 1 w eek
interval). D ata w e re s a m p le d o n e m o n th a fte r d e trita l a d d itio n .
A sterisk in d ic a te s s ig n ific a n t d ifferen c e s.
d o i:1 0 .1 3 7 1 /jo u r n a l.p o n e .0 0 6 6 6 5 0 .g 0 0 6
Microalgal B iom ass a n d M a c r o f a u n a
T h e re w as a significant interactio n betw een A. marina exclusion
a n d detrital e n rich m en t for m icroalgal biom ass (T able 3; Fig. 5).
L ugw orm exclusion h a d a negative effect on m icroalgal biom ass in
the non -en rich ed plots (SN K test: 0: A + > A —). In the lugw orm excluded sedim ent, detrital en rich m en t en h an c ed m icroalgal
biom ass (SN K test: A —: 0 < 2 0 0 = 600). V alues w ere sim ilar to
those m easu red for the A + control plots (treatm ents 200 a n d 600
in Fig. 5).
PLOS ONE I www.plosone.org
7
June 2013 | Volume 8 | Issue 6 | e66650
Complex Effects o f Ecosystem Engineer Loss
Table 4. R e p e a te d m e a s u r e analyses of v ariance a n d sphericity t e s ts for t h e 13C in co rp o ra tio n in m a c r o f a u n a a n d bulk s e d im e n t,
a n d for t h e 1SC 0 2 released from t h e b e n t h o s ( b e n th ic respiration) d u rin g detrital d e c o m p o s i t io n a t a n in te r m e d i a t e level o f detrital
e n r i c h m e n t (200 gW W p l o t _1a d d e d twice).
M acrofaun a
df
MS
B ulk sed im e n t
F
MS
B enthic respiration
F
MS
F
Exclusion = E
1
5.97 1CT7
0.12
4.27
1CT4
0.22
1.52
1CT5
9.73
Time = T
3
3.13 10 -7
0.60
8.78
1CT4
1.02
1.84
1CT5
14.45
Residual (Plots)
2
4.96 1CT6
TxE
3
6.21
Residual (TxPlots)
6
5.21 10 -6
Sphericity test (y2) n = 6
7.80
IO-7
1.96 10 -3
0.12
8.79
1CT4
8.59 1CT4
4.83
1.56 1CT6
1.02
8.98
1CT6
7.07
1.27 1CT6
8.06
Significant values (P<0.05) are in bold. Sphericity te st was not significant.
doi:10.1371 /journal.pone.0066650.t004
Discussion
B ioturbation c an en h an ce solute p e n etratio n in d eeper
sedim ents, th eir exchange betw een the sedim ent a n d the overlying
w ater a n d re-distribute organic m aterial along the vertical profile
[36,37,41], As such, the loss o f species th a t are im p o rta n t
contributors to b io tu rb a tio n m ay greatly change the response to
d etrital decom position o f sedim ent biogeochem istry. In lab o rato ry
experim ents, for instance, A. marina a n d the polychaete Nereis
diversicolor w ere found to increase tu rn o v er o f carb o n a n d n utrients
d u rin g d etrital m acroalgal decom position [19,36], T h e exclusion
o f A. marina from intertidal sedim ents was thus expected to m odify
the biogeochem ical response to m acroalgal d etrital enrichm ent.
C onversely, a t the e n d o f decom position (1 m o n th after the second
enrichm ent) b enthic respiration ( 0 2 a n d T C 0 2 sedim ent-w ater
exchanges) a n d sedim ent organic c arb o n content did n o t change
as a n effect o f lugw orm exclusion.
Ulva a m o u n t a n d tim e o f sam pling (one m o n th after enrichm ent)
allow ed decom position a n d release o f a large q u a n tity o f organic
m atter, w hich could b e m ineralized o r accu m u lated in the
sedim ent, thereby m odifying sedim ent organic c arbon, inorganic
c arb o n dissolved in the interstitial w ater a n d fluxes a t the
sedim ent-w ater interface. Ulva halftim e decom position rate is
w ithin 15 days [30], By considering the range o f k constant
calculated for this study (betw een —0.06 a n d —0.2), a t least 85%
Ulva w ould b e decom posed at the tim e o f sam pling for b o th
e n rich m en t levels. If one considers th a t d ried sedim ent weighs
ab o u t 1600 g I- a n d Ulva organic c arb o n c o n te n t is a ro u n d 40%
o f d ried tissues [34], this decom posed detritus corresponds to
organic carb o n concentrations ra nging betw een 0.15 a n d 1.2%
sedim ent dry w eight for the top first cm , roughly 2 -1 0 tim es the
co n cen tratio n o f organic carb o n found in n a tu ra l sedim ents for
low a n d high enrichm ent, respectively (see the n o n -en rich ed
sedim ent in Fig. 2a). T h e lack o f sedim ent carb o n accum ulation
a n d changes in T C 0 2 fluxes a t the sedim ent-w ater interface
indicated th a t the b enthic system was able to rem ove the carb o n
derived from in situ decom position a n d th a t b io tu rb a tio n did not
play a cen tral role in d etrital carb o n recycling.
It is im p o rta n t to re-iterate th a t fluxes w ere m easured du rin g
12 h d ark incubation o f sedim ent cores w ithout lugw orm s, w hich
indicated the overall indirect effect o f lugw orm s on d etrital benthic
m ineralization, b u t did not include any direct effects o f lugw orm s
due to b u rro w ventilation d u rin g the p e rio d o f incubation. T h e
im p o rtan ce o f ventilation was instead assessed in the field by
PLOS ONE I www.plosone.org
m easuring p o re w ate r D IC , w hich increased after lugw orm
rem oval, in dicating a decreased solute exchange due to A. marina
loss. Interestingly, these changes w ere variable along the vertical
sedim ent profile a n d w ere offset b y the add itio n o f detrital
m acroalgae, w hich supported the idea th a t fast m ineralization o f
d etrital c arb o n in these sedim ents is only in p a rt due to
b io tu rb atio n . T h e com plexity o f the relationships betw een species,
functions a n d response to d isturbance c an increase w ith increasing
ecological realism [15,46], O u r experim ents w ere done in situ a n d
they w ere designed to test effects o f A. marina u n d e r n a tu ra l
e nvironm ental conditions. D etrital m acroalgae w ere deliberately
a d d ed to the sedim ent, w ithout using artificial nets th a t could lim it
d etrital loss. T his m eth o d exposed decom posing detritus to tides
a n d waves, especially w h en detritus re m a in e d at the sedim ent
surface. T h e role o f b io tu rb a tio n on sedim ent biogeochem istry has
b e en m ainly assessed th ro u g h lab o ra to ry studies. T h e few field
studies o n the role o f Arenicola on porew ater, fluxes a n d organic
m atter decom position have revealed th a t its role m ay vary a n d
decrease considerably in n a tu re [19,37,47]. By co m p arin g field to
lab o ra to ry experim ents, it was found, for instance, th a t solute
exchange was m o re variable in the field because it was n o t only
ruled by b io tu rb a tio n b u t also by advection related to waves a n d
tides a n d b y differences in the reactivity o f sedim ent organic
m atter related to the com plexity o f biological com m unities o f
p rim a ry p roducers a n d consum ers [47]. T h is is p articularly true
w hen experim ents are done in p erm eab le sedim ent, w here A.
marina is often a d o m in a n t species [48], In these sedim ents,
hydrodynam ics can e n h an c e advective flow from the p o rew ater to
the overlying w ater colum n, rule the exchange o f solutes a n d
organic m a tte r a t the sedim ent-w ater interface a n d overw helm the
biological effect o f b io tu rb a tio n [49]. A lthough o u r experim ents
w ere done in a relatively sheltered sand flat, as indicated b y the
dom inance o f fine-grained sand, num erous ripple m arks w ere
visible at low tide (Fig. 2) a n d they p ro bably indicated strong
hydrodynam ics gen erated b y w aves a n d tides. In these sedim ents,
hydrodynam ics could accelerate the exchange o f solutes p ro d u c ed
d u rin g d ecom position, the rem oval o f m acroalgal detritus from the
sedim ent a n d override the effect o f b io tu rb a tio n o n the response o f
sedim ent biogeochem istry to d etrital m acroalgae.
T h e decom position ra te o f Ulva in these sedim ents was fast, as
indicated b y the estim ated k constants (k = —0.2 a n d —0.1 for A —
a n d A+, respectively; Fig. 7). T hese values w ere at the lim it o r even
exceeded the range o f values typical o f Ulva detritus, w hich varies
betw een —0.04 a n d —0.1 [34], M o re im portantly, the estim ated k
June 2013 | Volume 8 | Issue 6 | e66650
Complex Effects o f Ecosystem Engineer Loss
b enthic response to detrital m acroalgae, A. marina could represent
an im p o rta n t sink for detritus a n d it could m odify in situ
decom position rate, as found for o th er burro w in g b ioturbators
[39,50]. T hese species can m echanically b u ry m acroalgae in their
funnels, th ereb y decreasing detritus availability to surface sedim ent
a n d slowing dow n decom position rate, while m ain tain in g a pool o f
organic m atter in the sedim ent. B uried detritus a n d slowed
decom position rate could, in tu rn , m odify m ineralization process­
es. In this study, a peak in T ’CCE release to the w ater colum n
was identified at an early stage o f decom position in A. marinaexcluded sedim ent plots, suggesting th a t the loss o f A. marina
accelerated the m ineralization o f d etrital Ulva at an early stage o f
decom position. T his explanation o f increased m ineralization
following A. marina loss was su pported by the finding th a t
p o re w ate r D IC decreased in response to detrital addition in A.
marina excluded sedim ents. In addition, sim ultaneously to this
decrease, m acroalgal biom ass increased. Probably, w ithout the
m echanical action o f burying m acroalgal fragm ents by Arenicola,
detrital m acroalgae rem ain in g on sedim ent surface a n d deco m ­
posing faster released nutrients th a t en h an c ed bacterial m eta b o ­
lism a n d th eir c arbon consum ption. E vidence for increased c arbon
consum ption d uring biom ass decom position has b een fo und for
p la n t litter in freshw ater ecosystem s [51,52]. In addition, benthic
m icroalgae are often regulated by botto m -u p processes [53] an d
they could greatly benefit from n u trie n t release, thereb y co n trib ­
u ting to recycling the m ineralized detrital carbon. Interestingly,
detrital en rich m en t a n d lugw orm s h a d sim ilar effects on m icro ­
algal biom ass. P robably, b o th lugw orm bioirrigation a n d detrital
decom position can provide nutrients necessary to regulate
m icroalgal grow th [19,28,37,47].
A. marina is believed to influence the assem bly rules a n d the
distribution o f m acro fau n a and, as such, th eir pa tte rn s o f response
to disturbances by altering the sedim entary h a b ita t (e. g. [37,41]).
O u r results show ed a negative effect o f A. marina on m acro fau n a
response to detrital addition since bo th m acro fau n a abu n d an ce
a n d diversity decreased following the highest level o f en rich m en t
in presence o f lugw orm s. T h e increased detrital burial b y T . marina
could play a central role in d eterm ining this response. Patches o f
detrital m acroalgae in sedim ents can govern the spatial an d
tem p o ral variability o f m acro fau n a pa tte rn s o f distribution. T h e
presence o f detritus m ay decrease nu m b ers o f individuals an d
diversity because o f hypoxia d u rin g decom position. O n c e detritus
has decom posed, fast recolonizing taxa can p rom ptly occupy the
previously d isturbed patches a n d benefit from increased food
supply [29]. D etrital burial due to lugw orm activity pro b ab ly
prolo n g ed hypoxic conditions a n d slowed dow n m acro fau n a
recovery. T h e decrease in a b u n d an c e com m on to all taxa an d
the loss o f diversity could co rro b o rate this explanation as anoxic
conditions related to detrital decom position deplete m ost taxa
a b u n d an c e a n d diversity [29]. M oreover, burial could decrease
detrital availability to surface consum ers a n d therefore prev en t
th eir colonization, once hypoxia ceases. M acroalgal supply to
sedim ent surface can rep resen t an im p o rta n t source o f food for
surface grazers a n d detritivores, such as the g a stropod Hydrobia
ulvae [34,54], P a rt o f detrital c arbon was tran sferred to m ac ro fau ­
na, especially to H. ulvae (experim ent 2, Fig. 7c), w hich was the
num erically d o m in a n t species in these area. Its im p o rta n t role for
detrital c arb o n tran sp o rt to the food w eb was found previously in
the surro u n d in g area [34], T his species is highly m obile a n d it
crawls on sedim ent surface for feeding. Its local a b u n d an c e m ight
thus vary rapidly following food availability on surface sedim ent.
In sum m ary, ou r field ex p erim ent show ed th a t A. marina can be
an im p o rta n t sink for detrital Ulva. H ow ever, conversely to w h at it
should be expected based on cu rre n t research know ledge, this
(a)
5.0
"b
(N
4.0
a
ÖD
(N
O
3.0
2.0
O
1.0
H
0.01
m
0
2
4
LO 12
14
16
18
6
8
10
12
14
16
18
6
8
10
12
14
16
18
(c)
10
O
co
bû
8
6
4
Ö
¡3
f o3
2
ou
0
H—I
o
03
0
2
4
Time (days)
Figure 8. M ean ± SE fo r (a) T 13C 0 2 released from th e sedim ent
to th e w a te r colum n (sum o f d ry and w e t fluxes); (b) am o u n t of
13C organic carbon in th e b u lk sedim ent (averaged o ver d ep th
p ro file ) and (c) a m o u n t o f 13C carbon in c o rp o ra te d by
m acrofauna. D ata a re fitte d to th e LOESS s m o o th in g w ith a n interv al
o f 4 a n d 1 p o ly n o m ia l d e g re e . V alu es a re a v e r a g e d o v e r th e tw o p lo ts
w h e re A. m arina w a s e x c lu d e d (tr e a tm e n t A —; s q u a r e sy m b o ls in th e
g ra p h s ) a n d th e tw o p ro c e d u ra l c o n tro l p lo ts (tr e a tm e n t A+; tria n g le
sy m b o ls in th e g ra p h ). D ata refers to th e e x p e r im e n t 2. A sterisk
in d ic a te s s ig n ific a n t d ifferen c e s.
d o i:1 0 .1 3 7 1 /jo u rn a l.p o n e .0 0 6 6 6 5 0 .g 0 0 8
constant for the lugw orm -exclusion sedim ent was twice th a t o f the
control plots. In addition, the biom ass o f m acroalgal debris was, on
average, 6 tim es larger in controls th a n in lugw orm -excluded
sedim ents (2 a n d 12 g D W p e r p lot 1 for A + a n d A —,
respectively). T his m ay brin g to the conclusion th a t despite
hydrodynam ics could play an im p o rta n t role in d eterm ining
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9
June 2013 | Volume 8 | Issue 6 | e66650
Complex Effects o f Ecosystem Engineer Loss
species has m o d erate, som etim es negative effects on the response
to d etrital en ric h m e n t o f sedim ent biogeochem istry a n d m acro ­
fauna. A. marina loss causes the sedim entary ecosystem to becom e a
faster recycler o f detrital m acroalgae, en h an c in g d etrital loss,
c arb o n consum ption a n d m ineralization. T his m ay b rin g to the
conclusion th a t the loss o f this species m ig h t be u n im p o rta n t or
som ew hat beneficial for certain intertidal ecosystem s. H ow ever,
fast recycling a n d d etrital dispersal could u n d e rm in e carb o n
storage capacity o f benthos an d , in tu rn , the stability o f w hole
estuarine ecosystem facing organic en ric h m e n t a n d eu tro p h ica ­
tion.
T hese findings clearly dem onstrate th a t u n d e r n a tu ra l c ondi­
tions, the local extinction o f a n ecosystem engineer m ay have
com plex effects on the ecological stability o f m arin e sedim ent
biogeochem istry a n d b en th ic com m unities o f consum ers. T h ey
also highlight the im p o rtan ce o f p erform ing experim ents u n d e r
na tu ra l conditions if w e are to u n d e rstan d a n d p re d ic t the response
o f ecosystem s to p e rtu rb a tio n a n d species loss.
Acknowledgments
T he authors wish to thank the technicians for their invaluable help in the
chem ical analyses and E. W eerm an, JJ Jan sen and F M ontserrat and
num erous other students for their help in the field. S. T hrush is kindly
thanked for his critical revision o f an early version of this MS. This study is
p a rt of the B IO FU SE project, w ithin the M A RBEF network of excellence.
Author Contributions
Conceived an d designed the experim ents: F R BG. Perform ed the
experiments: F R BG FG VDS. Analyzed the data: F R BG FG VDS.
C ontributed reagents/m aterials/analysis tools: TTM. W rote the paper: FR
BG FG V D S JJM .
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
G rim e J P (1997) E c o lo g y - B io d iv ersity a n d e c o sy ste m fu n c tio n : T h e d e b a te
d e e p e n s. S c ien c e 277: 1 2 6 0 -1 2 6 1 .
M c C a n n K S (2000) T h e d iv ersity -sta b ility d e b a te . N a tu re 405: 2 2 8 -2 3 3 .
W o rm B, B a rb ie r E B , B e a u m o n t N , D u ffy J E , F o lk e C , e t al. (2006) Im p a c ts o f
b io d iv e rsity loss o n o c e a n e c o sy ste m services. S c ien c e 314: 78 7 —790.
T ilm a n D , D o w n in g AT. (1994) B io d iv ersity a n d sta b ility in g rasslan d s. N a tu re
367: 3 6 3 -3 6 5 .
Y a c h i S, L o re a u M (1999) B io d iv ersity a n d eco sy stem p ro d u c tiv ity in a flu c tatin g
e n v iro n m e n t: T h e in s u ra n c e h y p o th esis. P ro c e e d in g s o f th e N a tio n a l A c a d e m y
o f S cien ces o f th e U n ite d S ta te s o f A m e ric a 96: 1463—1468.
D o w n in g A , L e ib o ld M (2010) Sp ecies ric h n e ss fac ilitate s e co sy stem resilie n c e in
a q u a tic f o o d w ebs. F re sh w a te r B io lo g y 55: 2 1 2 3 —2137.
Ives A , C a r p e n te r S (2007) S ta b ility a n d d iv ersity o f eco sy stem s. Scien ce: 5 8 —62.
R a ffa e lli D G , R a v e n J A , P o o le L J {1998) E c o lo g ic a l im p a c t o f g re e n m a c ro a lg a l
b lo o m s. O c e a n o g r a p h y a n d M a rin e B iology, a n A n n u a l R e v ie w 36: 9 7 —125.
27.
F o r d R B , T h r u s h SF, P r o b e r t P K {1999) M a c r o b e n th ic c o lo n is a d o n o f
d istu rb a n c e s o n a n in te rtid a l san d flat: th e in flu e n ce o f se aso n a n d b u r ie d algae.
28.
29.
P fiste re r A , S c h m id B (2002) D iv e rs ity -d e p e n d e n t p r o d u c tio n c a n d e c re a se th e
sta b ility o f e c o sy ste m fu n c tio n in g . N a tu re 4 1 6 : 8 4 —86.
Allison G (2004) T h e in flu e n ce o f sp ecies d iv ersity a n d stress in te n sity o n
c o m m u n ity re sista n c e a n d resilien ce. E c o lo g ic a l M o n o g ra p h s 74: 117—134.
E m m e r s o n M C , S o la n M , E rn es C , P a te rs o n D M , R a ffa e lli D (2001) C o n s is te n t
R o ssi F {2006) S m all-scale b u r ia l o f m a c ro a lg a l d e tritu s in m a r in e se d im e n ts:
E ffects o f U lv a sp p . o n th e sp a tia l d istrib u tio n o f m a c r o fa u n a assem blages.
J o u r n a l o f E x p e rim e n ta l M a rin e B io lo g y a n d E c o lo g y 332: 8 4 —95.
31.
B o la m S G , F e r n a n d e z T F , R e a d P , R a ffa e lli D {2000) E ffects o f m a c ro a lg a l m ats
o n in te rtid a l san d flats: a n e x p e rim e n ta l stu d y . J o u r n a l o f E x p e rim e n ta l M a rin e
33.
resp o n se s o f a lg a e to d is tu rb a n c e in m o n o - a n d m u lti-sp e cie s assem b lag es.
O e c o lo g ia 157: 5 0 9 - 5 1 9 .
R o ssi F , V o s M , M id d e l b u r g J (2009) S p ecies id e n tity , d iv ersity a n d m ic ro b ia l
34.
35.
e ffe c t o f d e c o m p o s in g
a c c u m u la to in s
A b s tra c ts o f P a p e rs o f th e A m e ric a n C h e m ic a l S o ciety 221: U 5 3 8 —U 5 3 8 .
B ra e c k m a n U , P ro v o o s t P , M o e n s T , S o e ta e rt K , M id d e l b u r g J , e t al. (2011)
B iological vs. P h y sica l M ix in g E ffects o n B e n th ic F o o d W e b D y n a m ic s. Plos O n e
6: : - e l 8 0 7 8 . d o i:1 0 .1 3 7 1 /jo u rn a l.p o n e .0 0 1 8 0 7 8 .
21. L o h r e r A M , T h r u s h SF, G ib b s M M (2004) B io tu rb a to rs e n h a n c e eco sy stem
fu n c tio n th ro u g h c o m p le x b io g e o c h e m ic a l in te ra c tio n s . N a tu r e 4 3 1 : 1092—1095.
o f se a w e e d . J o u r n a l o f
E x p e r im e n ta l M a rin e B iology a n d E c o lo g y 96: 199—212.
R o ssi F {2007) R e c y c le o f b u r ie d m a c ro a lg a l d e tritu s in se d im e n ts: use o f d u a l­
lab e llin g e x p e rim e n ts in th e field. M a rin e B io lo g y 150: 1073—1081.
G o d b o ld J A , S o la n M , K illh a m K {2009) C o n s u m e r a n d re s o u rc e d iversity
effects o n m a r in e m a c ro a lg a l d e c o m p o s itio n . O ik o s 118: 77—86.
36.
H a n s e n K , K riste n s e n E {1998) T h e im p a c t o f th e p o ly c h a e te N e re is d iv ersic o lo r
a n d e n ric h m e n t w ith m a c ro a lg a l { C h a e to m o rp h a lin u m ) d e tritu s o n b e n th ic
m e ta b o lis m a n d n u trie n t d y n a m ic s in o rg a n ic -p o o r a n d o rg a n ic -ric h se d im e n t.
J o u r n a l o f E x p e rim e n ta l M a rin e B io lo g y a n d E c o lo g y 231: 2 0 1 —223.
37.
O ’B rie n A , V o lk e n b o rn N , v a n B eu se k o m J , M o rris L , K e o u g h M {2009)
I n te ra c tiv e effects o f p o r e w a te r n u trie n t e n ric h m e n t, b io tu r b a tio n a n d s e d im e n t
c h a ra c te r is tic s o n b e n th i c a s se m b la g e s in s a n d y
E x p e r im e n ta l M a rin e B iology a n d E cology: 5 1 —59.
s e d im e n ts . J o u r n a l
of
38.
D ’A n d r e a A , D e W itt T {2009) G e o c h e m ic a l eco sy stem e n g in e e rin g b y th e m u d
s h rim p U p o g e b ia p u g e tte n s is { C ru stacea: T h a la s s in id a e ) in Y a q u in a B ay,
O re g o n : D e n s ity -d e p e n d e n t effects o n o rg a n ic m a tte r re m in e ra liz a tio n a n d
n u trie n t cycling. L im n o lo g y a n d O c e a n o g r a p h y 54: 1911—1932.
39.
V o n k J , K n e e r D , S ta p e l J , A sm u s H {2008) S h rim p b u r ro w in tro p ic a l seagrass
m ea d o w s: A n i m p o r ta n t sin k fo r litte r. E s tu a rin e C o a s ta l a n d S h e lf S c ien c e 79:
40.
20.
41.
7 9 -8 5 .
M e y sm a n F JR , G a la k tio n o v E S , G rib s h o lt B, M id d e lb u r g J J {2006) B io irrig a tio n
in p e rm e a b le sed im en ts: A d v e c tiv e p o r e - w a te r t ra n s p o rt in d u c e d b y b u r ro w
v e n tila tio n . L im n o lo g y a n d O c e a n o g r a p h y 51: 142—156.
V o lk e n b o rn N , R e ise K {2006) L u g w o rm ex c lu sio n e x p e rim e n t: R e sp o n se s b y
d e p o s it f e e d in g w o rm s to b io g e n ic h a b it a t tra n s fo r m a tio n s . J o u r n a l O f
E x p e r im e n ta l M a rin e B iology A n d E c o lo g y 330: 169—179.
22.
E k l o f J , v a n d e r H e id e T , D o n a d i S, v a n d e r Z e e E , O ’H a r a R , e t al. (2011)
H a b i ta t- M e d ia te d F a c ilita tio n a n d C o u n te r a c tin g E c o s y s te m E n g in e e r in g
In te ra c tiv e ly In flu e n c e E c o sy ste m R e sp o n se s to D is tu rb a n c e . Plos O n e 6:
e 2 3 2 2 9 .-d o i: 1 0 .1 3 7 1 /jo u r n a l.p o n e .0 0 2 3 2 2 9 .
23. N o rk k o J , R e e d D C , T im m e r m a n n K , N o rk k o A , G u sta fsso n B G , e t al. {2012) A
w e lc o m e c a n o f w o rm s? H y p o x ia m itig a tio n b y a n in vasive species. G lo b a l
42.
43.
C h a n g e B iology 18: 4 2 2 - 4 3 4 . d o k lO .l 1 1 1 / j . 1 3 6 5 - 2 4 8 6 .2 0 1 1 .0 2 513.x.
E is e n h a u e r N , M ilc u A , S a b a is A , S c h e u S {2008) A n im a l E c o sy ste m E n g in e e rs
M o d u la te th e D iv e rsity -In v asib ility R e la tio n s h ip . Plos O n e 3.
C e b r ia n J {2004) R o le o f firs t-o rd e r c o n su m e rs in e co sy stem c a rb o n flow.
E c o lo g y L e tte rs 7: 2 3 2 -2 4 0 .
PLOS ONE I www.plosone.org
B io lo g y a n d E c o lo g y 249: 123—137.
H u ll S C {1987) M a c ro a lg a l m a ts a n d sp ecies a b u n d a n c e : a field e x p e rim e n t.
E s tu a rin e C o a s ta l a n d S h e lf S c ien c e 25: 5 1 9 - 5 3 2 .
T h r u s h S F {1986) T h e su b litto ra l m a c r o b e n th ic c o m m u n tiy s tru c tu re o f a n irish
s e a -lo u g h :
16. J o n e s C G , L a w to n J H , S h a c h a k M (1994) O rg a n is m s as e c o sy ste m e n g n e ers.
O ik o s 69: 3 7 3 -3 8 6 .
17. B erke S (2010) F u n c tio n a l G ro u p s o f E c o sy ste m E n g in e ers: A P ro p o s e d
C la ssific a tio n w ith C o m m e n ts o n C u r r e n t Issues. In te g ra tiv e a n d C o m p a ra tiv e
B iology 50: 1 4 7 -1 5 7 .
18. K ris te n s e n E , P e n h a -L o p e s G , D elefo sse M , V a ld e m a r s e n T , Q u i n ta n a C O , e t
al. (2012) W h a t is b io tu r b a tio n ? T h e n e e d fo r a p re c is e d e fin itio n fo r f a u n a in
a q u a tic sciences. M a rin e E c o lo g y P ro g re ss S eries 446: 28 5 —302.
19. K ris te n s e n E (2001) I m p a c t o f p o ly c h a e te s {Nereis a n d A re n ic o la ) o n s e d im e n t
b io g e o c h e m is try in c o a sta l a re a s: P a st, p re s e n t, a n d f u tu re d e v e lo p m e n ts.
25.
2 9 -3 9 .
K e la h e r B P , L e v in to n J S {2003) V a r ia tio n in d e trita l e n ric h m e n t c a u se s sp atio te m p o r a l v a ria tio n in so ft-se d im e n t a ssem b lag es. M a rin e E c o lo g y P ro g re ss S eries
261: 8 5 -9 7 .
30.
32.
c a rb o n flow in re a s s e m b lin g m a c r o b e n th ic c o m m u n itie s. O ikos: 5 0 3 —51 2 .
13. S o la n M , C a r d in a le BJ, D o w n in g A L , E n g e lh a r d t K A M , R u e s in k J L , e t al.
(2004) E x tin c tio n a n d e co sy stem fu n c tio n in th e m a r in e b e n th o s . S c ien c e 306:
1 1 7 7 -1 1 8 0 .
14. B o la m S G , F e rn a n d e s T F , H u x h a m M (2002) D iv e rsity , b io m a s s , a n d eco sy stem
pro ce sse s in th e m a r in e b e n th o s . E c o lo g ic a l M o n o g ra p h s 72: 5 9 9 —6 1 5 .
15. R o m a n u k T , V o g t R , K o la s a J (2009) E c o lo g ic a l re a lism a n d m e c h a n ism s b y
w h ic h div ersity b e g e ts stab ility . O ik o s 118: 8 1 9 - 8 2 8 .
24.
M a rin e E c o lo g y P ro g re ss S eries 191: 163—174.
R o ssi F , U n d e r w o o d A J {2002) S m a ll-sc a le d is tu rb a n c e a n d in c re a se d n u trie n ts
a s in flu e n ce s o n in te rtid a l m a c r o b e n th ic assem b lag es: e x p e rim e n ta l b u r ia l o f
w ra c k in d iffe re n t in te rtid a l e n v iro n m e n ts . M a rin e E c o lo g y P ro g re ss S eries 241:
p a tte rn s a n d th e id io sy n c ra tic effects o f b io d iv e rsity in m a r in e ecosystem s.
N a tu r e 411: 7 3 -7 7 .
11. G o o d se ll I J , U n d e r w o o d A J (2008) C o m p le x ity a n d id io sy n c ra sy in th e
12.
26.
44.
N o rk k o A , B o n s d o rff E {1996) P o p u la tio n resp o n se s o f c o a sta l z o o b e n th o s to
stress in d u c e d b y d riftin g a lg a l m ats. M a rin e E c o lo g y P ro g re ss S eries 140: 141—
151.
B u c h s b a u m R , V a lie la I, S w ain T , D z ie rz e sk i M , A lle n S {1991) A v a ila b le A n d
R e fra c to ry N itro g e n I n D e tritu s O f C o a s ta l V a s c u la r P la n ts A n d M a c ro a lg a e .
M a rin e E co lo g y -P ro g ress S eries 72: 131—143.
N e d e r g a a r d R I , R is g a a rd -P e te rs o n N , F in s te r K {2002) T h e im p o r ta n c e o f
s u lfate re d u c tio n a sso c ia te d w ith U lv a la c tu c a th alli d u r in g d e c o m p o s itio n : a
m eso c o sm e x p e rim e n t. J o u r n a l o f E x p e rim e n ta l M a rin e B io lo gy a n d E c o lo g y
275: 1 5 -2 9 .
10
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Complex Effects o f Ecosystem Engineer Loss
45.
H e r m a n P M J. M id d e lb u rg J J . W id d o w s J , L u c a s C H . H e ip C H R (2000) S ta b le
iso to p es as tro p h ic tra c e rs: c o m b in in g field s a m p lin g a n d m a n ip u la tiv e lab e llin g
o f f o o d reso u rc e s fo r m a c ro b e n th o s . M a rin e E c o lo g y P ro g re ss S eries 204: 79—92.
46. M c k ie B. S c h in d le r M . G e ssn e r M . M a lm q v is t B (2009) P la c in g b io d iv e rsity a n d
e c o sy ste m fu n c tio n in g in c o n te x t: e n v iro n m e n ta l p e rtu r b a tio n s a n d th e effects o f
species ric h n e ss in a s tre a m field e x p e rim e n t. O e c o lo g ia : 7 5 7 —770.
4 7 . P a p a s p y r o u S, K r is te n s e n E , C h r i s t e n s e n B (2 0 0 7 ) A r e n ic o la m a r i n a
(P o ly c h a e ta ) a n d o rg a n ic m a tte r m in e ra lisa tio n in s a n d y m a r in e se d im e n ts: I n
situ a n d m ic ro c o s m c o m p a ris o n . E s tu a rin e C o a s ta l a n d S h e lf S c ien c e 72: 2 13—
222.
4 8 . N e e d h a m H , P ild itc h C , L o h r e r A , T h r u s h S (2 011) C o n te x t-S p e c ific
B io tu rb a tio n M e d ia te s C h a n g e s to E c o sy ste m F u n c tio n in g . E co sy stem s 14:
1 0 9 6 -1 1 0 9 .
49. H u e tte l M , R o y H . P r e c h t E. E h re n h a u s s S (2003) H y d r o d y n a m ic a l im p a c t o n
b io g e o c h e m ic a l p ro ce sse s in a q u a tic se d im e n ts. H y d ro b io lo g ia 4 9 4 : 23 1 —236.
PLOS ONE I www.plosone.org
50.
51.
52.
53.
54.
R e tr a u b u n A , D a w s o n M , E v a n s S (1996) T h e ro le o f th e b u r ro w f u n n e l in
fe e d in g p ro ce sse s in th e lu g w o rm A re n ic o la m a r in a (L). J o u r n a l o f E x p e rim e n ta l
M a rin e B io lo g y a n d E c o lo g y 202: 1 0 7 -1 1 8 .
F o n ta in e S, B a r d o u x G . A b b a d ie L. M a rio tti A (2004) C a r b o n in p u t to soil m a y
d e c re a s e soil c a rb o n c o n te n t. E c o lo g y L e tte rs 7: 314—320.
L e n n o n J T (2004) E x p e rim e n ta l e v id e n c e th a t te rre s tria l c a rb o n subsidies
in c re a se C 0 2 flu x fro m lak e eco sy stem s. O e c o lo g ia 138: 5 8 4 —591.
H ille b r a n d H . W o rm B. L o tz e H (2000) M a rin e m ic ro b e n th ic c o m m u n ity
s tru c tu re r e g u la te d b y n itro g e n lo a d in g a n d g ra z in g p re ssu re . M a rin e E c o lo g y
P ro g re ss S eries 204: 2 7 -3 8 .
R ie ra P (2010) T r o p h ic p lastic ity o f th e g a s tro p o d H y d r o b ia u lv ae w ith in a n
in te rtid a l b a y (R oscoff. F ra n ce ): A stab le iso to p e ev id e n c e . J o u r n a l o f Sea
R e s e a rc h 63: 78—83.
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