Taphonomic fidelity and the detection of anthropic impacts in shallow water marine benthic communities of San Antonio Bay, northern Patagonia, Argentina

ARCHUBY, FERNANDO M; ROCHE, ANDREA

Río Grande do Sul

Workshop; 2nd Workshop on Actualistic Taphonomy; 2021

Centro de Estudos Costeiros, Limnológicos e Marinhos, CECLIMAR, UFRGS Litoral Norte

https://doi.org/10.5281/zenodo.5114543In a recent paper we found a surprisingly high mollusc diversity recorded in the intertidal death assemblages of Punta Mejillón, in the atlantic coast of northern Patagonia, Argentina, that were close to figures found in studies based on living fauna across the whole San Matías Gulf (SMG). In this contribution we intend to provide the first evaluation the taphonomic fidelity of the death assemblages in the Gulf. Fot that sake, we sampled the living (LA) and dead (DA) mollusc assemblages of two channels affected by tides in San Antonio Bay (SAB), northwestern side of the SMG. The channels were sampled in three sites at different distances from the bay. The West Channel (WSACh) passes along San Antonio town where it receives organic content of seawage and industries that process the fish since the middle of the XX century. At its proximal sampling site there is a popular beach with high influx of tourists. The East Channel (ESACh), in turn, has a low charge of human impact. Distal ends of both channels are charaterized by several hours of subaerial exposure per day, with high temperatures in summer, low temperatures in winter and strong winds. We expect lowered fidelity due to harsh climatic conditions, that destroy shells, and to human impacts. Human impact along the WSACh consists of pollution with high organic content that caused eutrophication since few decades ago. The proximal sampling site of WSACh is probably also impacted by tourism. Our data matrix consists of abundances per species of the six localities, divided by dead (n=12954) and alive (n= 56860). To test our hypothesis we used nMDS and permanova tests with BC distance on the sqrt transformed abundance matrix. Ordination axes were correlated with distance (1, proximal samples to 3, distal samples) with Spearman rank correlation index. Living communities showed a distal to proximal pattern that is mimicked by the death assemblages. In 2/3 cases of WSACh (polluted) LAs differ from DAs but in none of ESACh. Although not identical, DAs are aproppriate proxies of benthic communities and proper tools to help identifying impacted communities. [The field work was supported by a Research Project of Universidad Nacional del Comahue UNCO-04P001. The attendance to the 2TAAS was possible due to a AUGM program Escala Docente 2020, supported by Universidad Nacional de La Plata and Universidade Federal do Rio Grande do Sul]