Spatial variability of microbenthos in intertidal waters of Scotia Bay (Laurie Island), with emphasis in benthic diatoms

.ALDER VA; ABBEDUTO M.L.

Leuven

Simposio; XIIth SCAR Biology Symposium; 2017

SCAR

Besides contributing significantly to coastal primary production and providing a key source of food for both primary and secondary consumers, the importance of microbenthos lies also on its dampening sediment resuspension and serving as a shelter to algal propagules and larvae of invertebrates. The current study is the first one addressing the microbenthos of Scotia Bay (Laurie Island, South Orkney Islands), and its main goal was to detect differences between the communities living on rocky and sandy bottoms (epilithon and epipsammon, respectively). Samples of these two communities were taken by triplicate from four different sites within the intertidal zone during low tide conditions. Sites were selected based not only on the type of bottom but also on the degree of protection from wind and the influence of glacier melting runoff.The richest site in terms of benthic fauna and macroalgae proved to be the most protected from wind (site S1), located near Mount Mossman and characterized by a bottom mostly made up of rocky blocks. At the inlet of the bay (S2 y S3) and next to the glacier (S4), the intertidal sea bottom was predominantly sandy. The communities living on both types of bottom included diatoms, flagellates, dinoflagellates, and unidentified cysts, while epipsammon also comprised ciliates and exoskeletons of silicoflagellates. Within the total area sampled, the epipsammic community reached average abundances over three times higher than the epilithic (4.8 107 cells.m-2 vs. 1.4 107 cells.m-2). Diatoms were the dominant group in both communities, with a majority of their taxa belonging to the genera Navicula, Licmophora, Amphora, and Cocconeis. Planktonic genera were mainly represented by Thalassiosira, which occurred at all sampling sites, plus Rhizosolenia, Chaetoceros, and Corethron, which showed highest concentrations at sites S1, S2 and S3, respectively. Highest diatom abundances corresponded to the epipsammon from S4, in the vicinity of the glacier (8.9 107 cells.m-2). Epilithic diatoms, on the other hand, showed maximum concentrations at S1 (5.3 107 cells.m-2). Flagellates exhibited a similar trend, with higher numbers in the epipsammon (mean: 0.2 107 cells.m-2 vs 0.06 107 cells.m-2 for epilithon). The rest of the groups always showed abundances below 0.1 107 cells.m-2 in both communities, although with highest figures at S1. The only exception was dinoflagellates, for which highest concentrations were found in the epipsammon of site S2. A comparative assessment of benthic vs. planktonic diatom species will be discussed.S01: Taxonomy Systematics, Biogeography of Antarctica Biota