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

CECILIA CARCEDO; GABRIELA BLASINA ; JUAN MANUEL MOLINA; MARCO SCOTTI; MARÍA C. MENÉNDEZ; MARÍA S. DUTTO; JOHN GARZON CARDONA; JESSICA MOYANO; ANDREA LOPEZ CAZORLA; SANDRA FIORI

Mar del Plata

Congreso; XVIII COLACMAR; 2019

The communities inhabiting the surf-zones of exposed sandy beaches have received little attention, especially neglecting trophic interactions. The objective of this study was to explore the trophic niche of co-occurring species of the surf-zone. The studied sites are sandy beaches located between Punta Tejada and Monte Hermoso (38°S-61°W). We aimed to detect similarities in resource use by characterizing the trophic positions of the organisms, their feeding preferences and the possible trophic niche overlap. Samples of zooplankton, macrobenthic invertebrates and fishes were taken from the surf-zone across 200 m transects parallel to the shore. Organisms and tissues were freeze-dried and ground into a homogeneous powder. Aliquots (0.06-0.1 mg) were transferred to tin capsules and analyzed by simultaneous analysis of nitrogen (δ15N) and carbon (δ13C) stable isotopes. Trophic position (TP) of each species was calculated with following equation: TP = δ15Nconsumer − δ15Nbase / Δδ15N + 2, using the δ15N values of the filtering clam Amarilladesma mactroides as TP=2 (mean δ15N=10.27). Isotopic niche width and overlapping were calculated using corrected standard elliptical area (SEAc). Zooplankton species presented δ13C values varying from -20.8 to -18.7. The copepods Acartia tonsa and Paracalanus parvus had δ15N values around 11.4-12.6 (TP=2.5) while Euterpina acutifrons had lower δ15N values, around 9.1 (TP=2). Two macro-epibenthic invertebrate species, the isopod Leptoserolis bonaerensis and the amphipod Phoxocephalopsis zimmeri, had δ13C mean values of -13.8 and -16.2, respectively. Both species displayed similar δ15N values around 11.5−11.9 (TP=2.5). They showed an overlap in their SEAc (~30%), which indicated the existence of shared resources. In the case of macro-hyperbenthic species, the δ13C values of mysids Arthromysis magellanica and Pseudobranchiomysis arenae ranged between -16.8 and -18.4. Trophic niches of the mysids did not overlap and the δ15N values were 10.9−11.6 (TP=2.5) and 12.4−12.7 (TP=3), respectively. Two fishes were found inhabiting the surf-zone, Odonthestes argentinensis and Ramnogaster arcuata. Their δ13C values ranged between -17.4 and -17.9 and from -18.5 to -18.9, respectively. The fishes showed similar values of δ15N (around 13.5 and 15), which correspond to similar TP: 3.5. No overlap was detected suggesting a different resource use. In summary, the δ15N values indicate the existence of up to three trophic levels and the δ13C values indicate the differential use of organic matter that support a pelagic or benthic pathway. Our study demonstrates significant niche segregation in the biological community of the surf-zone, essential for the coexistence of species inhabiting this inherently dynamic ecosystem.