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|Deep-sea predator-prey dynamics revealed by biologging and eDNA analysis
In: Oceanography. Oceanography Society: Washington DC. ISSN 1042-8275, meer
- Merten, V.
- Visser, F, meer
- Hoving, H.-J.
At depths below 200 m, the pelagic deep sea comprises the largest, but least explored, part of the ocean. In this vast environment, animals are hard to find, and interactions among them are even harder to investigate (Robison, 2009). Climate change and industrial exploitation are exerting increasing pressure on deep-sea ecosystems, causing a decline in global ecosystem health and ecosystem services. Many of these changes occur outside of the range of human observation and are unrecognized so that effective conservation is limited. Such changes can include interactions between elusive and sometimes giant deep-sea predators such as cetaceans and their prey. The use of on-animal recorders has revealed that multiple species of cetaceans make extensive use of the deep sea, specifically the meso- (200–1,000 m depth) and bathypelagic (1,000–4,000 m depth) zones, to hunt for diverse, often cephalopod-dominated prey populations (Tyack et al., 2006). Because their dives to remote depths are energy consuming, the prey reward needs to be substantial to make the dives profitable. Thus, we expect that deep-diving cetaceans selectively target distinct foraging zones that hold specific prey communities to optimize their foraging performance.Cephalopods are extremely abundant and play a pivotal role in marine food webs as both predators and prey (Hoving et al., 2014). For instance, it is estimated that sperm whales alone annually feed on as many cephalopods in terms of biomass as human fisheries catch worldwide. Yet deep-sea cephalopods, in particular, are understudied, and many have never been observed alive in their habitats or captured as adults (Hoving et al., 2014). Traditional methods for studying cetacean prey include net capture, optical methods, or stomach content analysis. Physical and optical sampling face the challenge that cephalopods show avoidance behavior and are patchily distributed. This results in a sampling bias toward less mobile, less sensorially equipped, and abundant specimens (Wormuth and Roper, 1983). Stomach content analysis of cetaceans is rare and requires stranding or capture, and does not typically represent a good average of the population. An alternative method for assessing regional cephalopod diversity and hence potential prey spectra of cetaceans is environmental DNA (eDNA) analysis, a relatively novel tool for studying deep-sea communities. This method exploits the phenomenon that every organism leaves genetic information in the form of DNA particles behind. These DNA particles can stem from shed cells, mucus, or feces and have the potential to reveal the identity of the source organism. eDNA analysis has been successfully used to reconstruct the horizontal distribution, diversity, and migration of open-ocean nekton (Beng and Corlett, 2020). Yet, to the best of our knowledge, eDNA analysis has not been used to investigate cephalopod biodiversity in the deep sea prior to the study presented here, which is adapted from Visser et al. (2021).