Influence of Water Masses on the Biodiversity and Biogeography of Deep-Sea Benthic Ecosystems in the North Atlantic

Abstract

Circulation patterns in the North Atlantic Ocean have changed and reorganized multiple times over millions of years, influencing the biodiversity, distribution, and connectivity patterns of deep-sea species and ecosystems. In this study, we review the effects of the water mass properties (temperature, salinity, food supply, carbonate chemistry, and oxygen) on deep-sea benthic megafauna (from species to community level) and discussed in future scenarios of climate change. We focus on the key oceanic controls on deep-sea megafauna biodiversity and biogeography patterns. We place particular attention on cold-water corals and sponges, as these are ecosystem-engineering organisms that constitute vulnerable marine ecosystems (VME) with high associated biodiversity. Besides documenting the current state of the knowledge on this topic, a future scenario for water mass properties in the deep North Atlantic basin was predicted. The pace and severity of climate change in the deep-sea will vary across regions. However, predicted water mass properties showed that all regions in the North Atlantic will be exposed to multiple stressors by 2100, experiencing at least one critical change in water temperature (+2 • C), organic carbon fluxes (reduced up to 50%), ocean acidification (pH reduced up to 0.3), aragonite saturation horizon (shoaling above 1000 m) and/or reduction in dissolved oxygen (>5%). The northernmost regions of the North Atlantic will suffer the greatest impacts. Warmer and more acidic oceans will drastically reduce the suitable habitat for ecosystem-engineers, with severe consequences such as declines in population densities, even compromising their long-term survival, loss of biodiversity and reduced biogeographic distribution that might compromise connectivity at large scales. These effects can be aggravated by reductions in carbon fluxes, particularly in areas where food availability is already limited. Declines in benthic biomass and biodiversity will diminish ecosystem services such as habitat provision, nutrient

Rapid deep ocean deoxygenation and acidification threaten life on Northeast Pacific seamounts

“…Individual, or groups of similar, species are influenced by their local environment—even if they are not near an identified threshold. While temperature change drives important changes in Atlantic seamounts (Puerta et al., 2020), temperature trends in the NEP are much weaker (<0.5°C/century below 500 m, Cummins & Ross, 2020), and thus, we have focused on chemical trends. With strong chemical gradients at many depths, the narrow depth distributions of the indicator taxonomic groups identified here (Figures 4 and 5) suggest that their ranges are already limited by their chemical environment (Clark et al., 2010; Wishner et al., 1990).…”

“…These deep‐water chemical stressors have a remote source and cannot be prevented by any spatial management plan. However, impacts from these large‐scale stressors would be compounded by others that the MPA can mitigate—eliminating the controllable impacts may allow these ecosystems to withstand climate‐forcing changes better or for longer (Puerta et al., 2020).…”

“…These deep-water chemical stressors have a remote source and cannot be prevented by any spatial management plan. However, impacts from these large-scale stressors would be compounded by others that the MPA can mitigateeliminating the controllable impacts may allow these ecosystems to withstand climate-forcing changes better or for longer(Puerta et al, 2020).Our documentation of relatively rapid large-scale chemical changes and their potential ecological effects suggests an impending threat to seamount ecosystems within and beyond the study area and highlights the importance of precautionary management and conservation efforts. For instance, seamount chains to the north (the SGaan Kinghlas-Bowie seamounts) and in the international waters of the NEP, which border the southwestern edge of the proposed MPA(Figure 1) are all bathed in the OMZ(Curtis et al, 2015;Gale et al, 2017).…”

Diversity, Distribution and Phylogenetic Relationships of Deep-Sea Lithistids (Porifera, Heteroscleromorpha) of the Azores Archipelago

“…The major North Atlantic water masses and current pathways have been shown to structure the diversity and distribution of deep-sea sponges and corals, as well as the habitats they form (Puerta et al, 2020;Roberts et al, 2021). The large-scale circulation of the temperate northeast Atlantic is dominated 2) 11 ( 5) 3 ( 1) 16 ( 7) 6 ( 3) 3 ( 0 by the Azores Current (AzC) that flows eastwards toward the Iberian margin (Carracedo et al, 2014).…”

3-D ocean particle tracking modeling reveals extensive vertical movement and downstream interdependence of closed areas in the northwest Atlantic

“…The large-scale distributions of deep-sea invertebrate species are strongly associated with hydrographic features, largely the water mass characteristics of temperature and salinity 1 , 2 . This relationship has underpinned the adoption of species distribution models to predict the presence, abundance or biomass of these species through both space and time 3 .…”