Insights into the abundance and diversity of abyssal megafauna in a polymetallic-nodule region in the eastern Clarion-Clipperton Zone

Abstract

There is growing interest in mining polymetallic nodules in the abyssal Clarion-Clipperton Zone (CCZ) in the Pacific. Nonetheless, benthic communities in this region remain poorly known. The ABYSSLINE Project is conducting benthic biological baseline surveys for the UK Seabed Resources Ltd. exploration contract area (UK-1) in the CCZ. Using a Remotely Operated Vehicle, we surveyed megafauna at four sites within a 900 km2 stratum in the UK-1 contract area, and at a site ~250 km east of the UK-1 area, allowing us to make the first estimates of abundance and diversity. We distinguished 170 morphotypes within the UK-1 contract area but species-richness estimators suggest this could be as high as 229. Megafaunal abundance averaged 1.48 ind. m−2. Seven of 12 collected metazoan species were new to science, and four belonged to new genera. Approximately half of the morphotypes occurred only on polymetallic nodules. There were weak, but statistically significant, positive correlations between megafaunal and nodule abundance. Eastern-CCZ megafaunal diversity is high relative to two abyssal datasets from other regions, however comparisons with CCZ and DISCOL datasets are problematic given the lack of standardised methods and taxonomy. We postulate that CCZ megafaunal diversity is driven in part by habitat heterogeneity.

Abundance and morphology of Paleodictyon nodosum, observed at the Clarion-Clipperton Zone

“…Paleodictyon traces very similar to those observed in APEI-6 were identified during the ABYSSLLINE project in images from the UK-1 exploration claim area and the BEPIRB^area situated 250 km to the east of UK-1 (C.R. Smith, D. Amon and A. Ziegler personal communication; site locations in Amon et al 2016). Rona and Merrill (1978) reported a similar size (∼50 mm) for Paleodictyon at the MAR, although the number of holes in the arrays was greater (10 × 10 × 10 to 13 × 13 × 12).…”

Major impacts of climate change on deep-sea benthic ecosystems

“…Pressure from fishing has also increased since the mid-20 th century on seamounts and along continental margins, and there is now strong evidence that many deepwater fish species (e.g., rockfish, Greenland halibut, lings and tusks, orange roughy, sablefish and blue grenadier) have been severely exploited through trawling and longlining, with some species having been fished to commercial extinction (e.g., pelagic armourhead; Koslow et al 2000). There is also extensive interest in mineral mining at hydrothermal vent systems along mid ocean ridges and back arc basins, bathyal seamounts and polymetallic nodule areas at abyssal depths, as well as for phosphorites on margins (Mengerink et al, 2014;Thurber et al, 2014;Wedding et al, 2015;Amon et al, 2016;Levin et al, 2016;Vanreusel et al, 2016). Deep-sea sediments and organisms are also sinks for a variety of chemical pollutants, including persistent organochlorine pollutants (e.g., PCBs), which may have toxic effects for a variety of fauna at high concentrations (Froescheis et al, 2000;Looser et al, 2000;Ramirez Llodra et al, 2011).…”

Editorial: Biodiversity of the Clarion Clipperton Fracture Zone

“…3; Thiel et al 1993;Veillette et al 2007;Vanreusel et al 2016). A recent study by Amon et al (2016b) suggested that more than half of megafaunal species in the CCZ depend on nodules as a hard substrate. Furthermore, nodule areas seem to contain higher densities of mobile megafauna compared to those lacking nodules (Amon et al 2016b;Vanreusel et al 2016).…”

“…The variety of habitats has been thought to promote higher diversity of associated benthic communities compared to abyssal areas elsewhere (Ramirez-Llodra et al 2010;Janssen et al 2015;Amon et al 2016b;Vanreusel et al 2016).…”