Megabenthic assemblages in the lower bathyal (700–3000 m) on the New England and Corner Rise Seamounts, Northwest Atlantic

doi:10.1016/j.dsr.2020.103366

Deep Sea Research Part I: Oceanographic Research Papers

Volume 165, November 2020, 103366

https://doi.org/10.1016/j.dsr.2020.103366 Get rights and content

Highlights

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The New England and Corner Rise Seamount groups in the NW Atlantic have different megabenthic assemblages.
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Megabenthos assemblage composition is correlated with latitude and water depth.
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Megabenthos assemblages are determined by the physical characteristics of the water masses.

Abstract

Using a combination of data obtained from high-definition still images, video, and specimens collected during human-occupied submersible and remotely-operated vehicle dives spanning the period 2003 to 2014, we provide the first detailed characterization of the megabenthic assemblages in the lower bathyal on the New England and Corner Rise Seamounts in the Northwest Atlantic. Over all, the New England Seamounts east from Retriever to Nashville have a more diverse megabenthic fauna than Corner Rise, but the lowest diversity was observed on the three seamounts located closest to the continental margin. The megabenthic assemblage structure varies both within and across seamounts, and hierarchical cluster analysis revealed groups dependent on location (as measured by longitude) and depth, with substrate composition an additional but less significant factor at the regional scale. We conclude that the megabenthos assemblages in the bathyal Northwest Atlantic are determined, at the regional scale, by the water masses in which they reside.

Introduction

Seamounts comprise a significant component of the hard substrate areas in the lower bathyal (700–3000 m) and although estimates of the exact number of seamounts vary significantly depending on the methodology and thresholds used, one robust assessment concludes that there are at least 14,000 seamounts globally (Kitchingman and Lai, 2004). Seamounts have been found to be hotspots of biomass and biodiversity in the deep sea (Samadi et al., 2006; Rowden et al., 2010), and deep-sea corals on seamounts form complex structures that provide habitat to a diversity of organisms, including invertebrates and fishes, with some abundant species economically valuable (Watling et al., 2011). Seamounts are threatened by several anthropogenic activities, the most widespread being bottom trawling by commercial fisheries, which can occur to depths of ~1800 m (Haedrich et al., 2001; Ramirez-Llodra et al., 2011). The detrimental impacts of trawling on seamount fauna have been well documented (Koslow et al., 2001; Clark and O'Driscoll, 2003; Waller et al., 2007; Althaus et al., 2009; Clark and Rowden, 2009; and others), and more recent studies have also been undertaken to examine the possible impacts of proposed mining of seafloor massive sulfide (SMS) and cobalt-rich manganese crusts (Schlacher et al., 2014; Boschen et al., 2016). Consequently, an increased understanding of variation in seamount community composition and regional biodiversity is imperative for developing and implementing conservation strategies.

Although numerous studies have focused on single taxonomic groups on seamounts and other hard substrate habitats in the bathyal (canyons, ridges, etc.), the literature on benthic assemblages as a whole is limited. Due to the logistic difficulties of sampling deep-sea hard substrates, much research on seamount assemblages has been based on video and still-image data obtained from underwater vehicles (i.e., towed cameras, human-occupied submersibles - HOVs, and remotely operated vehicles - ROVs), occasionally combined with genetic and morphological analyses of a limited number of collected specimens.

Here we provide the first detailed characterization of the lower bathyal (700–3000 m) megabenthic assemblages on the seamounts of the New England and Corner Rise chains in the Northwest Atlantic. Using a combination of data obtained from high-definition still images, video, and specimens collected during HOV and ROV dives spanning the period 2003 to 2014, we examine the heterogeneity of the megabenthic assemblages both within and among seamounts, and the assemblage composition related to multiple physical parameters including depth, temperature, and salinity.

Section snippets

Study site and video data

The New England and Corner Rise seamount chains in the Northwest Atlantic extend an approximate total of 1700 km from the vicinity of the Mid-Atlantic Ridge to the continental slope southeast of George's Bank (Fig. 1). The New England Seamount Chain extends 1200 km from Bear Seamount in the west to Nashville Seamount in the east (Uchupi et al., 1970), while the Corner Rise Seamounts are located about 300 km east of the New England Seamounts near the boundary of the Sohm abyssal plain and

Megabenthic taxa

A total of 183 taxa were recorded (Supplemental Table 1) in the 91 sample units (100 m depth interval); 86 taxa were rarely seen, observed in only one or two sampling units, while 38 taxa were found in 10 or more sample units (Fig. 2). The most ubiquitous taxon was the black coral genus, Bathypathes, which was found in 58 sample units. Taxon accumulation curves based on the observed species (Sobs) and the Chao1 estimator of species richness (Fig. 3) show that additional sampling in these depth

Discussion

The major factors correlated with the composition of the assemblages on the New England and Corner Rise seamounts are depth, temperature, position along the chain (using “longitude” as a factor in the analyses), and substrate composition. It is likely that slope, or a derivative of slope, is also an important factor (Guinotte et al., 2017) but that variable cannot easily be determined at an ecologically meaningful scale from the existing multibeam data (some dive tracks were short enough that,

Conclusions

This study produced the first detailed characterization of the megabenthic assemblages on the New England and Corner Rise seamount chains in the Northwest Atlantic. The assemblages vary both within and across seamounts, and we observed changes in assemblages dependent on location (longitude), depth (temperature), and substrate. The New England and Corner Rise Seamounts are influenced by three main water masses, as well as the Gulf Stream in water shallower than 1000 m. Our results suggest that

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We gratefully acknowledge the NOAA National Undersea Research Program and Office of Ocean Exploration and Research for the many years of support for cruises to the New England and Corner Rise Seamounts. Each cruise involved detailed mapping of the seamounts, as well as dives with submersibles and ROVs, requiring the expertise of a host of crew and technicians on the R/V Atlantis and NOAA Ships Ronald H. Brown and Okeanos Explorer, as well as pilots and technicians for the HOV Alvin and ROVs

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View full text

Megabenthic assemblages in the lower bathyal (700–3000 m) on the New England and Corner Rise Seamounts, Northwest Atlantic

Highlights

Abstract

Introduction

Section snippets

Study site and video data

Megabenthic taxa

Discussion

Conclusions

Declaration of competing interest

Acknowledgements

Mar. Environ. Res.

Deep Sea Res. Oceanogr. Res. Pap.

Fish. Res.

Seafloor Geomorphology as Benthic Habitat

Mar. Geol.

Deep Sea Res. Oceanogr. Abstr.

Adv. Mar. Biol.

Impacts of bottom trawling on deep-coral ecosystems of seamounts are long-lasting

Mar. Ecol. Prog. Ser.

An ordination of the upland forest communities of southern Wisconsin

Ecol. Monogr.

Nonparametric estimation of the number of classes in a subpopulation

Scand. J. Stat.