A Dark Hole in Our Understanding of Marine Ecosystems and Their Services: Perspectives from the Mesopelagic Community

Abstract

In the face of increasing anthropogenic pressures acting on the Earth system, urgent actions are needed to guarantee efficient resource management and sustainable development for our growing human population. Our oceans-the largest underexplored component of the Earth system-are potentially home for a large number of new resources, which can directly impact upon food security and the wellbeing of humanity. However, the extraction of these resources has repercussions for biodiversity and the oceans ability to sequester green house gases and thereby climate. In the search for "new resources" to unlock the economic potential of the global oceans, recent observations have identified a large unexploited biomass of mesopelagic fish living in the deep ocean. This biomass has recently been estimated to be 10 billion metric tons, 10 times larger than previous estimates however the real biomass is still in question. If we are able to exploit this community at sustainable levels without impacting upon biodiversity and compromising the oceans' ability to sequester carbon, we can produce more food and potentially many new nutraceutical products. However, to meet the needs of present generations without compromising the needs of future generations, we need to guarantee a sustainable exploitation of these resources. To do so requires a holistic assessment of the community and an understanding of the mechanisms controlling this biomass, its role in the preservation of biodiversity and its influence on climate as well as management tools able to weigh the costs and benefits of exploitation of this community.

Mare Incognitum: A Glimpse into Future Plankton Diversity and Ecology Research

“…Not only the identity of major players, but also the drivers of community structure and interactions between organisms remain a "mare incognitum." In the surface ocean, plankton composed of prokaryotes (viruses, bacteria, and archaea) and eukaryotes (protists and metazoans; Figure 1) have been shown to form complex interaction networks driven by multiple biotic and abiotic factors (Lima-Mendez et al, 2015), and despite their key role as resource for higher trophic levels, mesopelagic plankton communities are some of the least studied on Earth (St. John et al, 2016).…”

Evidence of Diel Vertical Migration of Mesopelagic Sound-Scattering Organisms in the Arctic

“…Mesopelagic fishes are the main contributors to the scatterers that inhabit the twilight zone between 200 and 1,000 m depth. In the oceanic regions of North Atlantic the DSL is a well-known feature (Melle et al, 1993;Magnússon, 1996;Torgersen et al, 1997;Sigurðsson et al, 2002;Pepin, 2013;St. John et al, 2016).…”

The Structuring Role of Marine Life in Open Ocean Habitat: Importance to International Policy

“…Emerging evidence suggests that mobile marine species can transform the environment as they move through it, transferring nutrients within the water column (deep to shallow and vice versa) and across oceans (Wilson et al, 2009;Pershing et al, 2010;Roman and McCarthy, 2010;Roman et al, 2014;St John et al, 2016). For example, depletion of whales due to commercial whaling resulted in substantial deep-sea habitat loss through a reduction in dead whale "falls" (Smith, 2007), declines in primary productivity due to reduced nutrient shuttling Roman and McCarthy, 2010), changes in food-web structure and biogeochemical cycles (Lavery et al, 2010;Roman and McCarthy, 2010), and reduced potential for organic carbon sequestration (Lavery et al, 2010;Pershing et al, 2010).…”

“…Estimates suggest the global biomass of mesopelagic fish is on the order of 10 billion tones and, while there is uncertainty in this number, they likely represent the most abundant vertebrates on Earth (Irigoien et al, 2014) and the largest structuring biomass in the open sea. Their mass migration provides critical links in biogeochemical cycles across the water column, promoting carbon uptake and storage, thereby affecting climate regulation (Robinson et al, 2010;Giering et al, 2014;St John et al, 2016), modifies fluxes of nutrients and oxygen (Robinson et al, 2010;Bianchi et al, 2013a,b), and helps sustain the metabolic requirements of mesopelagic ecosystems (Burd et al, 2010;Bianchi et al, 2013b). They are also a key resource for higher trophic levels such as tunas and billfish (Potier et al, 2007;Duffy et al, 2017).…”

“…They are also a key resource for higher trophic levels such as tunas and billfish (Potier et al, 2007;Duffy et al, 2017). There is increasing interest in exploiting mesopelagic fish, particularly for fishmeal and oil, but technical and economic constraints still prevent large-scale commercial activity (St John et al, 2016). Nonetheless, licenses to fish mesopelagics have been issued by Norway and Pakistan (The Economist, 2017), although the US has proactively prohibited directed commercial fisheries in its Pacific Ocean due to concerns over potential adverse ecosystem consequences (NOAA, 2016).…”