Effect o f induced anoxia on nematode densities, vertical d istrib u tio n
patterns and recovery at the G ulf o f Trieste (Northern A d riatic Sea)
T a h e ri M e h rs h a d 12, M ateja G re g o 3, B e ttin a Riedel4, M agda V in c x ' and Jan V a n a ve rb e ke 1
1 M arine B io lo g y Research G roup, B io lo g y D e p a rtm e n t, G hent U n ive rsity, K rijg sla a n 2 8 1 , S8,
B-9000 G hent, B elgium
E-mail: m e h rs h a d .ta h e ri@ u q e n t.b e
2 Iranian N a tio n a l In s titu te fo r O ce a n o g ra p h y, 9 E tem adzadeh Ave, W est Fatem i Str, T e h ra n , Iran
3 M arine B io lo g y S ta tio n Piran, N a tio n al In s titu te o f B iology, Fornace 41, 6 3 3 0 Piran, S lovenia
4 D e p a rtm e n t o f L im n o lo g y and O cea n o g ra p h y, U n iv e rs ity o f V ienna, A lth a n s tra s s e 14, 1090
V ienna, A u s tria
O xyg en stress, in c lu d in g h y p o x ia and a n o x ia , is in cre a sin g w o rld w id e due to n a tu ra l and
a n th ro p o g e n ic im p a c ts and has se rio us consequences fo r b e n th ic eco syste m fu n c tio n in g (Chan e t
al., 2 0 0 8 ; Diaz and R osenberg, 2008).
Response and re co ve ry o f n e m a to d e c o m m u n itie s to in d u ce d a n o x ia w ere in v e s tig a te d a t th e G u lf o f
T rie ste , N o rth e rn A d ria tic Sea. A n o x ia was in d u c e d fo r 7 days, 1 and 10 m o n th s in b e n th ic
ch a m b e rs in s ta lle d a t 2 4 m d e p th in s ilty sand s e d im e n t using th e E xp e rim e n ta l A n o x ia G e n e ra ting
U n it (EAGU, see Riedel e t al., 2 0 1 2 ). A t each tim e , th re e cores (i.d. 4 .6 c m ) w ere c o lle c te d in b oth
e x p e rim e n ta l tre a tm e n ts and c o n tro l s itu a tio n s . C ores w ere sliced in to 7 d e p th layers: 0 -0 .5 ; 0 .5 -1 ;
1 -1 .5 ; 1 .5 -2 ; 2 -3 ; 3-4 and 4 -5 cm , sto re d in 4% fo rm a ld e h y d e and a fte r e x tra c tio n , n e m a to d e s were
c o u n te d in each layer.
T o ta l n em a to d e d e n s ity , and th e v e rtic a l d is trib u tio n in th e u p p e r 2cm (0 .5 c m in te rv a l) and up to
5cm (1cm in te rv a l) w ere n o t s ig n ific a n tly a ffe c te d by a n o x ia a fte r 7 days. In c o n tra s t, to ta l d e n s ity
was c le a rly reduced a fte r one m o n th a n o xia , and v e rtic a l d is trib u tio n p a tte rn s w ere a lte re d . O ur
re su lts fu r th e r in d ica te th a t re co ve ry o f n e m a to d e d e n s itie s was n o t fu lly achieved a fte r a recovery
pe rio d o f 10 m o n th s.
O u r re su lts in d ica te th a t n e m a to d e s w ere to le ra n t to s h o rt te rm a n o x ia (7 days). T h is m ay relate to
a d a p ta tio n m e ch a n ism s o f n e m a to d e s to live in n a tu ra lly lo w o x y g e n e n v iro n m e n ts . On th e o th e r
hand th e negative e ffe c t on n e m a to d e c o m m u n itie s a fte r one m o n th o f a n o x ia can be related to
in creasin g c o n c e n tra tio n o f h y d ro g e n s u lp h id e (Riedel e t al., 2 0 1 2 ) w h ic h can increase th e negative
e ffe cts o f a n o xia . It seem s th a t c o m p le te re co ve ry o f n e m a to d e s d e n s ity re q u ire s a re la tiv e ly long
pe rio d o f tim e . T h is can be due to p e rs is te n t u n fa v o u ra b le c o n d itio n s in th e se d im e n t, o r a u to e co lo g ica l fe a tu re s in c lu d in g n e m a to d e re p ro d u c tio n ca p a city. H ow ever, m ore d e ta ile d (b u t
o n g o in g ) analyses are needed to increase o u r u n d e rs ta n d in g o f th e e ffe c t on a n o x ia on n e m atode
c o m m u n itie s (e.g. a t species level).
References
Chan F. J.A. B arth, J. Lubchenco, A. K irin c ic h , H. W eeks, W.T. P eterson and B.A. M enge. 2 0 0 8 .
Em ergence o f A n o x ia in th e C a lifo rn ia C u rre n t Large M arine Ecosystem . Science 3 1 9 :9 2 0 .
Diaz R.J and R. R osenberg. 2 0 0 8 . S p reading dead zones and co nsequences fo r m a rin e e cosystem s.
Science 3 2 1 :9 2 6 -9 2 9 .
Riedel B., M. Z u sch in and M. S ta ch o w itsch . 201 2. T o le ra n ce o f b e n th ic m a c ro fa u n a to h y p o x ia and
a n o x ia in s h a llo w co a sta l seas: a re a lis tic scenario. Mar. Ecol. Prog. Ser. 4 5 8 :3 9 -5 2 .
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