Littoral meiofauna community estructure in San Julián bay, Santa Cruz province, Argentina

LO RUSSO, VIRGINIA; PASTOR DE WARD, CATALINA T.; ZAIXSO, HÉCTOR

Ecología Austral

Asociación Argentina de Ecología

Año: 2023

1667-7838

Meiofauna standing stocks and community structure are reported for the first time for San Julián Bay, located in Santa Cruz Province, towards the southern tip of South America, in the sub-Antarctic district. Mean meiofauna density found was 6724 ind/10 cm2 with high dominance of nematodes (97.69%). Multivariate studies (PERMANOVA) revealed two distinct meiofauna assemblages, one in an upper-littoral salt-marsh habitat and one in a medium to low soft-bare-sediment. In the middle of the bay, in front of San Julián city, salt-marsh habitats presented the highest meiofaunal density while bare sediments (medium-low levels) were the lowest. Mean average in salt-marsh area was 12246 ind/10 cm2 with nematodes being dominant followed by oligochaetes as the subdominant taxa. Mean average in bare sediments (medium-low levels) was 3962 ind/10 cm2 with nematodes as dominant and turbellarians, mastigophorans and maxillopodos (harpacticoid copepods) as subdominant taxa. Bare-sediments related to Patagonian mussel’s populations presented the lowest meiofauna densities. Diversity showed an opposite trend, with a maximum in medium-low levels and a minimum in salt-marshes habitat. Richness in number of taxa ranged from 8 to 12, with a total number of 18 taxa. Despite dominance of nematodes in meiofauna assemblages is known, maximum density found in San Julian Bay is much higher than previously found for estuaries from North and mid-latitudes littoral sandy beaches and in the nearby region of the Straits of Magellan and Beagle Channel and other sub-Antarctic and Antarctic sites. On the other hand, the number of meiofauna taxa (no nematodes) is low and its community structure is different than in the reported papers. The meiofauna taxa assemblages provide evidence that in salt-marsh habitats, they have the highest densities but the lowest diversity when compared with lower levels. This is probably due to adaptation problems of the meiofauna communities to a semi-terrestrial habitat.