Otolith morphology as a tool to discriminate climate-driven growth variations in populations of black rockcod (Notothenia coriiceps) sampled over the last three decades off the Antarctic Peninsula

Abstract

The west Antarctic Peninsula is one of the most impacted areas of the Southern Ocean by global climate change in the last decades. With the aim to evaluate the effect of increasing temperature on fish community, the black rockcod Notothenia coriiceps, which is the dominant demersal species in terms of abundance and biomass in the local shallow waters, was selected. Under the hypothesis of temperature-related potential effect on growth rate and morphology of sagittal otoliths, these structures were used as a proxy of climate change to discriminate populations of this species sampled in different years (i.e. 2002, 2006, 2012, 2018) over the last three decades in the Bransfield Strait. The internal pattern of otolith growth rings allowed to estimate the individual age of fish. Otolith standard measurements and external morphology were summarized in a series of shape indices and Elliptic Fourier descriptors and a linear discriminant analysis applied to the whole dataset. Four well-defined groups of fish were discriminated in the scatter plots according to their own sampling year, with otolith roundness and weight being the most important contributors to the spatial distributions of the specimens. The analysis of otolith growth trajectories, in conjunction with the annual mean sea surface temperature trends experienced throughout the fish life cycle, revealed a generally consistent, although not unequivocal, negative effect of rising temperatures. This observation aligns with the expected response in black rockcod, a species distinguished by its striking and unique stenothermic characteristics when compared to other nototheniid fish.