Diversity, density and vertical distribution of benthic meiofauna in muddy sediments off central Peru (12°S)

Abstract

The presence of tiny, benthic organisms living on extremely oxygen-deficient sediments has been observed in several ocean regions worldwide. In order to analyze, quantify and describe the vertical distribution of the benthic meiofauna, it was collected sediment cores at two stations: E2 (94 m) and E5 (178 m) off Callao shelf break (~ 12° S), during February-2015. Five phyla were identified: Nematoda (96.9%, E2) and 44% (E5); Gastrotricha, which was only registered at station E5 (47.4%); Platyhelminthes 1.9% (E2) and 2.3% (E5); Granuloreticulosa 0.3% (E2) and 5.2% (E5), and Annelida that obtained 0.9% (E2) and 1.1% (E5). Station E2 accounted 777 Ind/10 cm2, free-living nematodes (753 Ind/10 cm2) were numerically dominant in the community. The Platyhelminthes (15 Ind/10 cm2), polychaetes (7 Ind/10 cm2) and allogromids individuals (2 Ind/10 cm2) exhibited densities generally more than one order of magnitude below that of the nematodes. A more detailed taxonomic analysis showed that taxonomic richness fluctuated between 10 (E2) and 12 (E5). The E2 station showed the very high relative dominance of Desmodora sp. (> 80%) within the community, followed by the poor dominance of Turbellaria (1.9%) and nematodes of the Comesomatidae family (1.9%). At station E5 the dominant group was Gastrotricha (47.4%), followed by the family of nematodes Comesomatidae (10.3%), the nematode Desmotersia levinae (8.2%), nematodes of the genus Desmodora (7.5%) and the family Chromadoridae (7.1%). Polychaetes, turbellarians worms and other families of free-living nematodes were, in general, below 5% of the total registered. The first results about the dominance of some important families of free-living nematodes in Callao sediments are discussed. Likewise, the vertical distribution found and the new depth strata recorded for D. levinae are analyzed, which extend the latitudinal and bathymetric distribution originally reported for this species.