Actuopaleontology on the Bonaerense coast: the anthropocene as a model to understand the fossil record and the recent evolution of current marine populations and communities

Abstract

Mollusk death assemblages actively accumulating on modern beaches along the coast of Buenos Aires are abundant and provide unique information on the current status of populations and communities during the last decades to millennia and their response to environmental changes. However, they have been little studied, and aspects related to compositional fidelity, time-averaging, and taphonomic patterns are currently unknown. The long-term aim of this line of research is to generate actualistic taphonomic models to improve palaeoecological interpretations and to discriminate between natural. and anthropogenic variations. This will allow us to assess the structure and evolution of coastal populations and communities in the face of multiple stressors on timescales longer than those of ecological studies. This will provide a historical perspective on the evolution of the current macrobenthic communities in the region and will be a fundamental and indispensable tool for the development of marine pollution mitigation strategies for the beaches of the Buenos Aires coast. In the short term, it is proposed to evaluate the compositional fidelity between life assemblages (LAs) and death assemblages (DAs) of the rocky intertidal zone of Buenos Aires and to use the live-dead mismatch to detect the impact of anthropogenic changes. Between Mar del Plata and Mar Chiquita 5 LAs and 5 DAs were sampled from 5 sites: Submarine outfall (sewage outfall) and towards the north, away from this site, Monolito, Kaskote, Atalaya and Santa Clara. Granulometry and organic matter were analyzed, and the seawater´s pH, T° and conductivity were measured. Preliminary results showed that LAs were present only in Monolito, Atalaya and Santa Clara and were dominated (>95%) by the bivalve Brachidontes rodriguezii. The Siphonaria lessoni limpet was also recorded, but in very small numbers. At least 18 species of mollusks were identified in the DAs, with Spisula spp., B. rodriguezii and Eucallista purpurata being the most abundant species. Specific diversity varied between 6 and 10 mollusk species per sample. The DAs are dominated by fragments (between 1 and 5 mm), and the mollusk individuals recovered are generally of the same size, which is to be expected as this is a highenergy abrasion platform environment. However, this makes it difficult to process the samples and identify the mollusk species due to the remains´ size and the degree of fine-scale alteration. Despite the taphonomic condition of the DAs from Mar del Plata´s rocky beaches, the diversity of mollusk species provides valuable information on ecological interactions.