Mobile Epifauna Associated To Artificial Substrates In Offshore Qatari Waters

Abstract

Offshore human-made structures including oil and gas platforms and other energy producing structures, such as foundations of windfarms, serve as hard substratum supporting diverse marine communities of invertebrates both sessile and motile. Stainless-Steel Plates were used to study the spatial distribution and connectivity among mobile invertebrate assemblages in the North of the Qatari EEZ. Thirty plates were deployed, at depths between 10 and 44 m, in each of six offshore sites, along a transect defined between natural and artificial reefs (i.e., oil platforms). After one year, two replicate plates per 5 m depth interval were retrieved and analyzed for each site. A total of 2302 specimens, belonging to 42 operational-taxonomic-units and 32 families were identified. These were comprised of 14 families of annelids, 8 arthropods, 5 echinoderms, 2 gastropods, 2 platyhelminths and 1 sipunculid. Multivariate analysis for abundance and biomass showed that both Site and Depth, as well as their interaction, had significant effects on the mobile macrofaunal community. A general trend of total abundance and average number of taxa decreasing with depth was observed, although with some notable exceptions. Cumulative dominance was consistently larger for biomass, relatively to abundance, at all depths and sites, resulting in positive values of the W statistic, which suggest low levels of disturbance. Nevertheless, an increasing trend of the W statistic with distance from the oil field was also observed, with the minimum value at the site closest to the oil platforms. Strong positive correlations were observed between some groups of mobile and sessile taxa, such as sipunculids and polyclads with bivalves and decapods with barnacles. These mobile-sessile relationships are believed to be mainly driven by trophic interactions and habitat provision. These results highlight the important ecological role of oil platforms in the Arabian Gulf as it has demonstrated the capacity of offshore stainless-steel surfaces to be rapidly colonized by diverse assemblages of mobile macrofauna. Accordingly, knowledge gathered in this project is expected to contribute to reconcile the planning, operation and decommissioning stages of oil platforms with sustainable management of marine ecosystems in the Arabian Gulf.