TROPHIC ECOLOGY OF THE SURF-ZONE COMMUNITY IN THE SW ATLANTIC COAST: A STABLE ISOTOPES APPROACH

CARCEDO CECILIA; GABRIELA ELIZABETH BLASINA; JUAN MANUEL MOLINA; SCOTTI MARCO; MAYSA ITO; MENENDEZ CLARA; DUTTO SOFIA; MARTINEZ ANA; GARZON CARDONA JOHN; MOYANO JESSICA; ANDREA LOPEZ CAZORLA; FIORI SADRA

Mar del Plata

Congreso; XVIII Congreso Latinoamericano de Ciencias del Mar-COLACMAR; 2019

ALICMAR

The communities inhabiting the surf-zones of exposed sandy beaches have receivedlittle attention, especially neglecting trophic interactions. The objective of this study wasto explore the trophic niche of co-occurring pelagic and benthic species of the surf-zone. The studied sites are sandy beaches of the Atlantic coast (38°S-61°W). Weaimed to detect similarities in resource use by characterizing the trophic positions ofthe organisms, their feeding preferences and the possible trophic niche overlap.Samples of zooplankton, macrobenthic invertebrates and fishes were taken from thesurf-zone across 200 m transects parallel to the shore. Organisms and tissues werefreeze-dried and ground into a homogeneous powder. Aliquots (0.06-0.1 mg) weretransferred to tin capsules and analyzed by simultaneous analysis of nitrogen (δ15N)and carbon (δ13C) stable isotopes. Trophic position (TP) of each species was calculatedwith following equation: TP = δ15Nconsumer − δ15Nbase / Δδ15N + 2, using the δ15N values ofparticulate organic matter as baseline. Isotopic niche width and overlapping werecalculated using corrected standard elliptical area (SEAc). Zooplankton speciespresented δ13C values varying from -20.8 to -18.7. The copepod Acartia tonsa had δ15Nvalues between 12.1 and 12.5 (TP=3) while Paracalanus parvus and Euterpinaacutifrons had lower δ15N values, from 9.1 to 11.6 (TP=2). Two macro-epibenthicinvertebrate species, the isopod Leptoserolis bonaerensis and the amphipodPhoxocephalopsis zimmeri, had δ13C mean values of -13.8 and -16.2, respectively. Bothspecies displayed similar δ15N values around 11.5−11.9 (TP=3). They showed anoverlap in their SEAc (~30%), which indicated the existence of shared resources. In thecase of macro-hyperbenthic species, the δ13C values of mysids Pseudobranchiomysisarenae and Arthromysis magellanica ranged between -16.8 and -18.4. Trophic nichesof the mysids did not overlap and the δ15N values were 10.9−11.6 (TP=2) and12.4−12.7 (TP=3), respectively. Two fishes were found inhabiting the surf-zone,Odonthestes argentinensis and Ramnogaster arcuata. Their δ13C values rangedbetween -17.4 and -17.9 and from -18.5 to -18.9, respectively. The fishes showedsimilar values of δ15N (around 13.5 and 15), which correspond to similar TPs: 3.5 and 4,respectively. No overlap was detected suggesting a different resource use. Our studydemonstrates significant niche segregation in the biological community of the surf-zone. Such aspect is essential for the coexistence of species inhabiting this inherentlydynamic ecosystem.