Population structure of Aequiyoldia eightsii (Jay, 1839) (Protobranchia, Sareptidae) in the shallow water zone of an Antarctic Specially Managed Area (Admiralty Bay, King George Island, Antarctic Peninsula)

Abstract The protobranch Aequiyoldia eightsii is one of the most common bivalves in Antarctica and for the first time, its population structure was studied in Admiralty Bay, an Antarctic Specially Managed Area (ASMA), to establish a baseline for future monitoring. Density, size structure, length-weight relationship, condition index, and shell morphometry were evaluated at the shallow coastal zone of the bay. High abundance values of A. eightsii were related to sites with greater contributions of mud particles and total organic carbon contents in the sediment, while the condition indexes were higher in Martel Inlet, possibly due to higher food availability. Individuals obtained from gravel-rich sediments were significantly larger than compressed, while rounded forms were observed in sandy and muddy bottoms of the bay. Positive allometric growth was reported in most sites, except Botany Point, where specimens presented an isometric growth. The results demonstrated that the sediment composition and its organic content influence the population structure of A. eightsi as well as biological factors such as predation and recruitment rates. It is also worth noting that the phenotypic shell plasticity observed for this protobranch species in geographically close sites (hundreds of meters) highlights the importance of local-scale heterogeneity to be considered in future monitoring programmes for Antarctic marine ecosystems.