Regional-scale compositional and size fidelity of rocky intertidal communities from the Patagonian Atlantic coast

FERNANDO ARCHUBY; MARIANA ADAMI; SANDRA GORDILLO; MARIANO MALVÉ

PALAIOS

SEPM-SOC SEDIMENTARY GEOLOGY

Lugar: Lawrence; Año: 2015 vol. 33 p. 498 - 507

0883-1351

The use of rocky intertidal assemblages in paleoecology and conservation paleobiology studies is limited because these environments have low preservation potential. Here, we evaluate the fidelity between living intertidal mussel bed communities (life assemblages or LAs) and mollusk shell accumulations (death assemblages or DAs) from the environmentally harsh Patagonian Atlantic Coast. Patagonian shores are characterized by a pronounced macrotidal regime and frequent strong winds, allowing us to explore live/dead agreement in environmentally and temporally variable conditions. Living assemblages (n = 6) were sampled from rocky mid-intertidal and mussel-dominated habitats. Since dead shells do not accumulate in rocky mid-intertidals, live-dead mismatch cannot be assessed at local scale at the same sites. Therefore, death assemblages (n = 10) were collected from the high water mark at beaches in close proximity to the living intertidal community to assess live-dead mismatch at regional scales. Shells from DAs in beach environments belonged to species inhabiting upper intertidal to Subtidal habitats and hard- and soft-bottom habitats. To ensure comparability with LAs, we used the subset of species in the DAs that inhabit rocky intertidals. A total of 37,193 mollusk specimens from intertidal species were included in the analysis. Ten species were present in LAs, in DAs, and nine were shared by LAs and DAs. DAs showed higher diversity, less dominance and more rare species than LAs. Despite finding a good agreement in species composition between DAs and mussel-dominated LAs within the same region, smaller species are underrepresented, as shown by differences in intraspecific size-frequency distributions. Our findings indicate that the composition of DAs is a result of the combined effects of spatial and temporal averaging, size-related biases and biases related to low detectability of boring and vagile species in LAs. Thus, DAs do not accurately detect within-provincial latitudinal gradients in composition. However, DAs clearly capture differences between the Argentine-Magellanic Transition Zone and the Magellanic Province, indicating that DAs are informative tools at regional scales despite the environmental harshness they are subjected.