Deep‐sea demersal fish species richness in the Porcupine Seabight, NE Atlantic Ocean: global and regional patterns

Abstract

The ichthyofauna of ocean margin regions is characterised by a succession of different species occurring at different depths. This study was aimed at determining whether the resultant pattern of species richness with depth is a consequence of local factors in a given region or whether it simply reflects the global pattern of fish species distribution in the oceans. Along the ocean margin of the temperate NE Atlantic Ocean in the Porcupine Seabight and Abyssal Plain region, 48°-53°N, a total of 108 demersal fish species were identified from 187 trawls at depths from 240 to 4865 m. Fitting of species accumulation curves predicted an asymptote of 120, indicating that the fauna is 90% described. Baited cameras detected 22 scavenging species with a predicted asymptote of 24 species. Scavenging species represented a constant 22.7% (SD 3.5%) of the total species richness throughout the depth range studied. Species richness per trawl varied between a maximum of 16 at 1600 m and 4 on the abyssal plain > 4000 m with no significant influence of sea floor slope (a measure of topographic heterogeneity). Total species richness was 48 at 1600 m and 10 on the abyssal plain. There is a clear transition between slope species above 3000 m and abyssal species below. The depth at which peak species richness occurs (1100-2000 m) coincides with the depth of the permanent thermocline, presence of Mediterranean overflow water (MOW), seasonally strong currents, resuspension of particulate matter, high biomass of benthic filter feeders and pelagic biomass impinging on the slope. We suggest that these factors increase habitat and resource heterogeneity, thus supporting a wider range of fish species. The local pattern of species richness was compared with the global distribution of maximum depths of marine fish species from FishBase. Globally all three Classes of fishes, Agnatha, Chondrichthyes and Osteichthyes, showed a logarithmic decrease in species with depth, with the deepest observed species in each class occurring at 3003 m, 4156 m and 8370 m, respectively. In contrast, the local distribution of species maximum depths is idiosyncratic with a mean of 16.6 species maxima per 500 m at 1000-3000 m depth followed by three species per 500 m at 3500-4000 m and 11 species per 500 m at 5000 m. It is concluded that global patterns of species richness, as a source of recruitment, exert a weak influence on local patterns of species richness. Rather, global species richness is the sum of numerous regional and local patterns, each determined by characteristic environmental conditions.

Baited-camera observations of deep-sea megafaunal scavenger ecology on the California slope

“…n max : peak abundance; %frames: percentage of frames in which at least 1 individual was observed; t 0 : time of first arrival; na: not applicable suggests an increasing importance of carrion in the diets of demersal fishes and a shift to an opportunistic foraging strategy at deeper portions of continental margins. This finding contrasts with observations in the NE Atlantic where Priede et al (2010) found scavenging fish to comprise a constant proportion of the fish fauna (22.7%) from 240 to 4965 m. This result was an average across depths. If the data presented in Fig.…”

“…If the data presented in Fig. 4 are averaged, the resulting value of 22% would be very close to that presented by Priede et al (2010). It is interesting to note that at depths <1000 m, the data in Priede et al (2010) yield percentages of <10%, similar to our own findings.…”

Use of Remotely-Derived Bathymetry for Modelling Biomass in Marine Environments

“…Although the fit and model predictions computed for GAMM_depth_lat-also those based on a cross-validation procedure-are superior over the other models under study, the resulting distribution of roundnose grenadier as a function of depth is bimodal, with the first (lower) modal value around 1,000 m and the second (upper) mode at 1,600 m of depth. The bimodal distribution of roundnose grenadier is biologically improbable (PRIEDE et al 2010;REX and ETTER 2010), and a potential explanation should be sought in the relatively limited number of data points available in each period. Indeed, the sparse data points are spatially clustered and thus it is difficult to unequivocally confirm the bimodal pattern of the distribution curve.…”

“…50°N, 13°W) were surveyed by scientific bottom trawl from 1977 to 2002. For the present analysis we used trawls at depths ranging from 800 to 4,865 m [=146 trawls, GODBOLD et al (2013)], which is a subset of the full data described by BAILEY et al (2009) andPRIEDE et al (2010). Trawls from depths \800 m were excluded from the analysis as no shallow water trawling was carried out after 1989.…”

“…Most deep-sea species are confined to characteristic depth zones (REX and ETTER 2010). In bottom-living fishes, this kind of zonation is manifested as a succession of different species with increasing depth (PRIEDE et al 2010). As depth has been found to be a strong predictor of probability of species occurrence and relative abundance, using information on patterns of species abundance with depth it is possible to estimate stock biomass in a given area by extrapolation using known bathymetry.…”