Spatial pattern and scale of Everglades macroinvertebrate communities along
nutrient and hydroperiod gradients
Shawn E. L. Smith, Joel C. Trexler,
Florida International University, Miami, FL
The periphyton mat and its associated
invertebrate community are an integral part
of the Everglades food web, so it is
important to understand their distribution
and response to variation in the physical
environment. While several groups have
described macroinvertebrate community
dynamics across a nutrient gradient, the
consistency of these patterns across a range
of hydroperiods has not been addressed. In Fig 1: Floating periphyton mat in
wet prairie Eleocharis sp. slough.
this study we sought to determine the
spatial scale and distribution of the floating
periphyton mat and its associated macroinvertebrate community. We used this
information to design a sampling study that sought to describe the response of the
community to both enrichment and variation in hydroperiod. A deeper
understanding of these community dynamics will enable researchers to better
identify trophic interactions and determine the impact of environmental stressors
on this system.
In the wet-season of 2000
we conducted an intensive
sampling survey in
10 m
northern Shark River
Slough, ENP to describe
the densities of
macroinvertebrates in the
90 m
floating mat and to detect
2
1m
any spatial patterns that
may exist between 0.5 and
90 m. Four sites were
established approximately
Fig 2: Nested-L sampling design for
1 km apart along a transect
each site (each dot represents 1 sample)
parallel to slough flow. At
each site, approximately
100 6-cm diameter cores were taken from the periphyton mat in a nested-L
pattern (Fig. 2) in both July and November 2000. Epiphytic algae in the water
column was sampled in the absence of a floating periphyton mat. All animals
greater than 1 mm in length were removed and identified to lowest feasible
taxonomic resolution. Epiphytic algae samples differed from periphyton samples
in both physical structure and community composition. We found that periphyton
from the floating mat contained more inorganic CaCO3 than epiphytic algae from
the water column (P=0.054), while it contained 350-550% more amphipods and
50-175% more Dasyhelia spp. Epiphytic algae, however, contained 25-50% more
chironomids than surface periphyton. From July to November we saw an increase
in water depth, periphyton percent cover, and abundance of all major invertebrate
groups (P<0.01). While we saw more spatial variation in July when abundances
were lower, a nested ANOVA revealed no general patterns in spatial variation at
any scale. Analysis of semivariance also failed to detect significant spatial
patterns at a scale smaller than 25 m.
Total number of invertebrates /g AFDW
In December 2002 we sampled sites at two levels of phosphorus enrichment
(enriched and unenriched) and three hydroperiods (short: <200 days since last
dry-down; long: >400 days since last dry-down; and very long: >4000 days since
last dry-down) in a factorial design. This was replicated in WCA-3A and Shark
River Slough, ENP, although no ‘very long’ sites were available in Shark River
Slough. At each site, 15 6-cm diameter periphyton mat cores and 15 6-cm
diameter benthic floc cores
were taken within a 10 x 10 m
600
area. Soil, floc, and periphyton
Hydroperiod
were also collected and
500
Short (<200 days)
analyzed for total phosphorus.
Long (>400 days)
We failed to find any
400
Very Long (>4000 days)
significant differences in the
total number of invertebrates
300
from the two areas, or
consistent patterns in the total
200
number of invertebrates in sites
with different hydroperiods. It
100
was clear, however, that
enrichment caused almost a
three-fold increase in the total
0
Enriched
Unenriched
number of invertebrates in each
Nutrient Level
sample (P<0.001). We also
Fig 3: Effect of the interaction of enrichment
saw a significant interaction
and hydroperiod on the density of macrobetween hydroperiod and
invertebrates in the periphyton mat
enrichment. We found that
when short hydroperiod sites were enriched, they experienced almost a six-fold
increase in the total number of invertebrates (P<0.001), with more than twice as
many invertebrates as any other enriched sites (Fig. 3). Similar results were
found when most taxonomic groups were treated individually.
This research was funded in part by the NSF Florida Coastal Everglades LongTerm Ecological Research Program and a US EPA STAR Fellowship.
Shawn, Smith, Department of Biological Sciences, Florida International
University, University Park, Miami, FL 33199, Phone: 305-348-4032, Fax: 305348-1986, slisto01@fiu.edu