Trophic interactions of two sympatric small pelagic fishes off the southern coast of Angola

Quiatuhanga, Domingas; Morais, Pedro; Teodosio, Maria

http://hdl.handle.net/10400.1/27685

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Authors

Quiatuhanga, Domingas

Morais, Pedro

Teodosio, Maria

Abstract(s)

Numerous small pelagic fish species are of great economic importance and link the lower and upper levels of the marine food web. The round sardinella Sardinella aurita and flat sardinella S. maderensis coexist along their distribution range in the southeastern Atlantic Ocean, where we hypothesise that they compete for similar prey. Thus, this study aimed to compare the trophic ecology of these species off the southern coast of Angola during the austral summer and winter, by determining their diet composition and overlap, feeding strategies, trophic positions, and evaluating the correlation between their feeding intensity and remote-derived chlorophyll a concentration (Chl-a) and sea surface temperature. The results demonstarte that both species are generalists and ingest a wide range of protistoplankton and metazooplankton taxa of distinct sizes. Both sardinellas show high flexibility and adaptability to prey availability, using both filter-feeding and particulate-feeding modes. The diets were dominated by diatoms and calanoid copepods in terms of relative abundances and frequencies of occurrence, respectively, in the stomach contents. Tintinnid ciliates, fish eggs, decapod larvae, euphausiids, cladocerans and cnidarians had high wet weight contributions. The diets overlapped by 64% overall, indicating moderate competition for food, with S. maderensis exhibiting a lower trophic position than S. aurita (2.98 versus 3.49). The feeding intensity of S. maderensis was positively correlated with Chl-a, and moderately negatively correlated with SST, suggesting that species is more influenced by environmental variables owing to its lower trophic position. Trophic interactions between the two species appear to be mediated by prey sizes and availability. These findings demonstate the value of satellite-derived data as proxies to estimate the feeding intensity of these species, which will be useful to formulate regional ecological models or to predict the stock trends of S. maderensis in particular.