Abstract
Research on benthic communities in the deep sea has focused largely on habitats in isolation, with few studies considering multiple habitats simultaneously in a comparable manner. The present study aimed to determine the structural differences in benthic communities of continental slope, seamount, canyon, vent, and seep habitats, and assess their relative vulnerabilities to disturbance from bottom trawling and potential seabed mining. Megafaunal invertebrate communities of these habitats were sampled in two regions off New Zealand, in four depth strata between 700 and 1500 m, using an epibenthic sled and a beam trawl. Patterns of community and trophic structure, and the potential influence of environmental variables, were determined using multivariate analyses. The difference in community structure between regions was greater than among habitats and depth strata. Levels of food availability may explain regional differences in community structure, although some influence of fishing disturbance is also possible. Differences in community and trophic structure were most pronounced between the chemosynthetic vent and seep habitats, and other habitats. Differences among these other habitats within a region were inconsistent, except that canyon and slope communities always differed from each other. Community and trophic structural patterns were partly explained by the environmental differences observed among habitats. The relative vulnerabilities of benthic communities to human disturbance in the two regions were determined based on patterns of abundance and feeding mode of the megafauna. Communities of vent and seep habitats were assessed to be more vulnerable to disturbance than those of the other habitats based on a number of habitat-related attributes. However, the relative vulnerability of megafaunal communities at slope, canyon, and seamount habitats could not confidently be assessed on a habitat basis alone. The results of the present study have implications for how regional and habitat differences in benthic communities are incorporated into spatial management options for the deep sea.
Highlights
Research on benthic communities in the deep sea has focused largely on habitats in isolation, with few studies considering even two habitats simultaneously in a comparable manner
The present study examined the following hypotheses: (1) the benthic communities of deep-sea habitats such as seamounts, vents, canyons, and seeps are structurally and functionally different from each other and from those found on the continental slope; (2) the communities of these habitats are more vulnerable to human disturbance than are those of continental slope environments; and (3) the effects of fishing and potentially other human activities are more severe for these communities than for those on continental slopes
Variability in megafaunal community structure was partitioned in Distance-based Linear Models (DistLMs) according to the environmental predictor variables detailed above, with latitude and longitude fitted first into the models
Summary
Research on benthic communities in the deep sea has focused largely on habitats in isolation (e.g., slope, Palma et al, 2005; vents, Desbruyères et al, 2006; canyons, Schlacher et al, 2007; seeps Levin and Mendoza, 2007; seamounts, Lundsten et al, 2009), with few studies considering even two habitats simultaneously in a comparable manner (canyons and slopes: Vetter and Dayton, 1998; e.g., seamounts and slopes: O’Hara, 2007; McClain et al, 2009; slope and seeps, Zeppilli et al, 2012; De Leo et al, 2014; abyssal hills and plain, Durden et al, 2015; vents and seeps, Nakajima et al, 2015). Studies of megafaunal communities along continental margins (sampled by sleds and trawls—the focus of this study) have identified the influence of habitat heterogeneity, with variations in environmental parameters such as oxygen, temperature, overlying productivity etc., affecting broad-scale patterns of community structure (species composition and abundance) (e.g., Sellanes et al, 2010; Williams et al, 2010a). Nested within these regional environmental variations along a margin are a range of more localized topographic habitats such as canyons, seamounts, banks, and ridges as well as the open continental slope. Few studies have determined and reported the level of community similarity (species turnover or β-diversity) among the megafaunal communities that inhabit these deep-sea habitats (Cartes et al, 1994; Ramirez-Llodra et al, 2010; Rowden et al, 2010b), and only one to our knowledge has used community similarity to explicitly assess the degree of connectivity between habitats (Kelly et al, 2010—which included megafauna), and none to assess their potential vulnerability to anthropogenic disturbance
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