Influence of environmental factors on the characteristics of macrobenthic communities in soft bottoms around coral reefs of Larak Island (Persian Gulf)

The effective conservation of coastal ecosystems including soft bottoms around coral reefs of Larak Island, Persian Gulf, is requiring basis data on community structure at different relevant spatial scales. In this regard, the diversity and the abundance of the macrobenthic communities in soft bottoms around coral reefs of this area were described in relation to different environmental factors. A seasonal sampling was conducted at two stations located in the east and west of Larak Island, respectively, during 4 seasons, from spring to winter 2012. A total of 20 species which belong to 20 genera and 14 families were identified. The macrobenthic density showed significant differences among seasons. The Shannon-Wiener index ranged from 2.07 to 2.89 indicating a moderate diversity in both stations. The maximum diversity of macrobenthic organisms was observed during spring. A non-metric multidimensional scaling (NMDS) analysis showed a large overlap in the macrobenthic community structure between the two stations. A principal component analysis (PCA) analysis indicated that the main environmental factors controlling macrobenthic density were phosphate, dissolved oxygen and total organic matter (TOM). Our results indicated that coral macrobenthic communities in Larak Island were characterized by low density and uniform distribution of species.

Fauna associated with shallow-water methane seeps in the Laptev Sea

Background Methane seeps support unique benthic ecosystems in the deep sea existing due to chemosynthetic organic matter. In contrast, in shallow waters there is little or no effect of methane seeps on macrofauna. In the present study we focused on the recently described methane discharge area at the northern Laptev Sea shelf. The aim of this work was to describe the shallow-water methane seep macrofauna and to understand whether there are differences in macrobenthic community structure between the methane seep and background areas. Methods Samples of macrofauna were taken during three expeditions of RV Akademik Mstislav Keldysh in 2015, 2017 and 2018 using 0.1 m2 grabs and the Sigsbee trawl. 21 grabs and two trawls in total were taken at two methane seep sites named Oden and C15, located at depths of 60–70 m. For control, three 0.1 m2 grabs were taken in area without methane seepage. Results The abundance of macrofauna was higher at methane seep stations compared to non-seep sites. Cluster analysis revealed five station groups corresponding to control area, Oden site and C15 site (the latter represented by three groups). Taxa responsible for differences among the station groups were mostly widespread Arctic species that were more abundant in samples from methane seep sites. However, high densities of symbiotrophic siboglinids Oligobrachia sp. were found exclusively at methane seep stations. In addition, several species possibly new to science were found at several methane seep stations, including the gastropod Frigidalvania sp. and the polychaete Ophryotrocha sp. The fauna at control stations was represented only by well-known and widespread Arctic taxa. Higher habitat heterogeneity of the C15 site compared to Oden was indicated by the higher number of station groups revealed by cluster analysis and higher species richness in C15 trawl sample. The development of the described communities at the shallow-water methane seeps can be related to pronounced oligotrophic environment on the northern Siberian shelf.