Abstract
Patterns in benthic megafauna diversity in littoral and intertidal zones in the Gulf of California has been associated as a function of habitat heterogeneity and substrate type. Current knowledge of invertebrate communities in hard bottom habitats at depths >200 m in the Gulf is poor due to the methodological limitations inherent in sampling deep habitats. Using benthic imagery recorded on video coupled with environmental data from the Remotely Operated Vehicle Doc Ricketts, we documented variation in the diversity and community composition of the benthos from 849-990 m depth in the NW limit of the Guaymas Basin in relation to dissolved oxygen and substrate characteristics. This area is affected by the incidence of an oxygen minimum zone where oxygen drops to levels <0.5ml L-1 and strong gradients in a narrow depth range occur. Dissolved oxygen varied along our benthic survey from 0.200 to 0.135 ml L-1. We observed a great taxonomic richness across an area of rocky outcrops through the lower transitional zone. This megafaunal pattern is different to that reported in other oxygen minimum zones where they are characterized by a great abundance of a few species. Taxonomic richness diminished at depths with reduced dissolved oxygen in the lower boundary of the oxygen minimum zone with increasing soft sediment cover. We found that rocky outcrops (including structure-forming organisms such as corals, sponges and oyster aggregations also provide a hard substrate for other fauna) supported a higher diversity (H’= 0.8) than soft sediment (H´=0.7) as have been observed in other habitats such as seamounts. Environmental variables that explained most of the megafaunal variation were substrate type (18.4%), depth (1.14%) and temperature (0.9%). Salinity (0.45%) and dissolved oxygen (0.3%) were less important factors to explain the megafaunal composition variance. Substrate type played a key role in the diversity and composition of benthic megafauna. These results broaden our understanding concerning the potential roles of substrate characteristics in the community composition of the deep-sea benthic megafaunal assemblages in the Gulf of California and oxygen minimum zones in general.
Highlights
Habitat is defined by the space and abiotic factors in which an organism, population or species assemblage lives (Norse, 1993; Davies et al, 2004; Tapia de la Yossellin, 2018)
The findings of this study support the hypothesis that taxonomic richness in the NW limit of Guaymas Basin are highest in rocky benthic habitats with the greatest structural complexity in comparison with soft sediment habitats, and, we found that diversity, composition and cover of benthic megafauna vary among soft sediment and rocky outcrops
The present study documented that diversity, taxonomic richness, composition and cover of benthic megafauna within the Oxygen Minimum Zone (OMZ) from 849 to 990 m depth in the NW limit of the Guaymas Basin varied among rocky outcrops and soft sediments
Summary
Habitat is defined by the space and abiotic factors in which an organism, population or species assemblage lives (Norse, 1993; Davies et al, 2004; Tapia de la Yossellin, 2018). ROV video surveys have been used more commonly for hard, steep, and rugged substrate and in areas of cold-water corals (CWC’s) (Du Preez and Tunnicliffe, 2012; Ayma et al, 2016). Traditional methods of sampling, such as dredge and sledges are difficult to use in hard and rugged substrate and cannot be used in areas inhabited by delicate and vulnerable structure forming-organisms (Tyler et al, 2016). The analysis of images recorded by ROVs has become a non-invasive and complementary method (to conventional methodologies) for sampling deep water fauna in all habitats and substrate types (Cuvelier et al, 2012; Ayma et al, 2016; Tyler et al, 2016)
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