Macroepibenthic communities associated with the hydrocoral Errina antarctica from the Chilean fjord region: Does bathymetry influence community structure?

The cold-water hydrocoral Errina antarctica provides habitat for numerous macroepibenthic species and plays an important role for biodiversity in the Chilean fjord region. Gaining knowledge about the assumedly highly diverse benthic communities associated with cold-water corals such as E. antarctica is crucial for an efficient management programme for the ecosystem, which is strongly threatened by aquaculture and other human activities. In this investigation, the epizoobenthic community associated with E. antarctica in three bathymetric zones (Zone 1: 10-20 m; Zone 2: >20-30 m; Zone 3: >30-40 m) in the Chilean fjord region is described quantitatively by analysing videos recorded via remotely operated vehicle (ROV). To be able to compare communities from different diving sites, pH, salinity, temperature, depth, oxygen saturation, and oxygen concentration were measured. Videos and abiotic parameters were recorded during dives at four stations. A total of 260 images was extracted from the videos, and abundance of macroepibenthic organisms was calculated. Community composition of different bathymetric zones and stations were investigated by means of multivariate statistical methods (SIMPER, ANOSIM 1) and similarities between samples visualised by Cluster analysis and MDS-plots. Ecological indices (S, H´, d, and J´) were calculated. Distribution of differently sized E. antarctica-colonies (small [diameter < 10 cm], medium [10 cm < diameter < 20 cm], large [20 cm < diameter]) was investigated. At the southernmost station (station Is_Solar) oxygen saturation and concentration were lower than at the other stations. Other abiotic parameters measured showed no clear differences between stations. Abundances of E. antarctica-colonies of all sizes decreased with depth, the portion of small colonies was highest in Zone 1. Based on abundances, annelids dominated all bathymetric zones, followed by cnidarians, sponges, and chordates. Ecological indices were lowest in Zone 1. SIMPER identified genus spirorbis as dominant in all bathymetric zones and stations. R-values of ANOSIM 1 indicated poor distinctness between bathymetric zones (GR=0.062). Investigating each station separately provided higher distinctness between bathymetric zones 1 and 2 (R-values between 0.234 and 0.568). Neither Cluster-analysis nor MDS-plots showed clear grouping of bathymetric zones. Zone 1 was less heterogeneous than the other zones. Grouping of stations was visible on MDS-plot. No significant influence of depth on the investigated communitiy was detected. Different characteristics of the four stations might overlay bathymetric effects. The observed community composition agrees with results from former investigations, especially the dominance of polychaetes. Differences in diversity between samples from different bathymetric zones are explained by distribution of differently sized E. antarctica-colonies. Alternative sampling methods are briefly discussed. This investigation for the first time provides information on quantitative composition of benthic communities associated with E. antarctica, and it is desirable its results will help to provide efficient protection of this threatened system