The importance of amphipods in the selective benthic feeding of the sister species Notothenia rossii and N. coriiceps (Pisces, Nototheniidae) in West Antarctica

MOREIRA E.; QUARTINO L; BARRERA ORO E. R.; VALLI FRANCIONE M.; SEEFELDT M.

Leuven

Simposio; XIIth SCAR (Scientific Committee on Antarctic Research) biology symposium; 2017

SCAR

The feeding selectivity of the congeners Notothenia rossii (NOR) and N. coriiceps (NOC) was studied at Potter Cove, South Shetland Islands, in January-March of 2016, by means of a comparative analysis of the benthic organisms found in the fish diets with those collected along a depth gradient in rocky bottom with macroalgae (Ivlev index). Among the algae associated epifauna and in line with its high abundance and high energetic value, benthic amphipods, mainly the pontogeneiid Gondogeneia antarctica and the lysianassid Cheirimedon femoratus constituted the most important and frequent prey for the two nototheniids (IRI index). Macrolgae were the second important food source, represented by Palmaria decipiens and Desmarestia sp. as dominant species. Although NOR and NOC are both benthic feeders with broadly similar diets, a statistical test between their prey (by weight) indicated a significant difference. Likewise, the diet was significantly affected by fish size and depths in both species. NOC fed more intensively on a wider diversity of benthic organisms such as algae and some algal-associated groups like gastropods and bivalves; whereas NOR fed on a higher proportion of amphipods than algae. Nevertheless, and despite their distinct morphology and ecological habits, the feeding selectivity tested with the more general Ivlev index for the primary food items, algae and amphipods, and other benthic groups was similar in NOR and NOC. No substantial distinction for preference or rejection of any particular prey species between the two nototheniid species was found. Present results are compared with studies carried out at Potter Cove in the 1990s about feeding selectivity in NOC on epifauna and macroalgae. The abundance and vertical distribution of macroalgae in the sampling site in the outer cove did not change significantly over a period of two decades and probably were not greatly influenced by the retreating calving front of a glacier in the inner cove. Nevertheless, the differences in the feeding selectivity of NOC on amphipods, observed nearly three decades later, which could apply also for the ecologically similar NOR, may be explained by variations in the assemblage of the associated epifauna during this period. We hypothesize on factors that may have produced these changes in Potter Cove.