Abstract
Ferromanganese crusts occurring on seamounts are a potential resource for rare earth elements that are critical for low-carbon technologies. Seamounts, however, host vulnerable marine ecosystems (VMEs), which means that spatial management is needed to address potential conflicts between mineral extraction and the conservation of deep-sea biodiversity. Exploration of the Tropic Seamount, located in an Area Beyond National Jurisdiction (ABNJ) in the subtropical North Atlantic, revealed large amounts of rare earth elements, as well as numerous VMEs, including high-density octocoral gardens, Solenosmilia variabilis patch reefs, xenophyophores, crinoid fields and deep-sea sponge grounds. This study focuses on the extensive monospecific grounds of the hexactinellid sponge Poliopogon amadou (Thomson, 1878). Deep-sea sponge grounds provide structurally complex habitat, augmenting local biodiversity. To understand the potential extent of these sponge grounds and inform spatial management, we produced the first ensemble species distribution model and local habitat suitability maps for P. amadou in the Atlantic employing Maximum Entropy (Maxent), General Additive Models (GAMs), and Random Forest (RF). The main factors driving the distribution of the sponge were depth and maximum current speed. The sponge grounds occurred in a marked bathymetric belt (2,500 – 3,000 m) within the upper North Atlantic Deep Water mass (2.5∘C, 34.7 psu, O2 6.7–7 mg ml-1), with a preference for areas bathed by moderately strong currents (0.2 – 0.4 ms-1). GAMs, Maxent and RF showed similar performance in terms of evaluation statistics but a different prediction, with RF showing the highest differences. This algorithm only retained depth and maximum currents whereas GAM and Maxent included bathymetric position index, slope, aspect and backscatter. In these latter two models, P. amadou showed a preference for high backscatter values and areas slightly elevated, flat or with gentle slopes and with a NE orientation. The lack of significant differences in model performance permitted to merge all predictions using an ensemble model approach. Our results contribute toward understanding the environmental drivers and biogeography of the species in the Atlantic. Furthermore, we present a case toward designating the Tropic Seamount as an Ecologically or Biologically Significant marine Area (EBSA) as a contribution to address biodiversity conservation in ABNJs.
Highlights
Most of the deep seabed lies in areas beyond national jurisdictions (ABNJ), areas where the biogeography of vulnerable marine ecosystems (VMEs) has received relatively little attention and where governance is limited
The Tropic Seamount harbors diverse and near pristine benthic communities that include several VMEs such as reef-building coral species Solenosmilia variabilis, several species of octocorals and black corals that formed diverse animal forests, crinoid fields, and sponge grounds. This diversity is most likely related to the specific oceanographic characteristics and hydrography of the Tropic Seamount
The phytoplankton-enriched waters from the Sahara upwelling events extend offshore reaching the Tropic Seamount (Hernández-Guerra et al, 2005), that is fed by the iron-rich dust coming from the Sahara desert making the NW waters off Morocco a very productive oceanographic area (Henderiks, 2001)
Summary
Most of the deep seabed lies in areas beyond national jurisdictions (ABNJ), areas where the biogeography of vulnerable marine ecosystems (VMEs) has received relatively little attention and where governance is limited. Such ecosystems are often characterized by slow-growing, long-lived and late-maturing species, traits that limit their potential for resilience and recovery from human disturbances such as bottom-contact fishing and, in the future, deep-sea mining (Ramirez-Llodra et al, 2011). In the case of deep-sea mining applications, the International Seabed Authority (ISA)— the body that regulates activities on the seabed in ABNJs—is to develop policy tools on the exploitation of minerals that consider VMEs and ecologically or biologically significant marine areas (EBSAs) that may include VMEs (Miller et al, 2018). Little is known about the distribution of most VMEs, and every effort to improve the understanding of marine VME biogeography may lead to better ocean governance
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
