Assemblage structure and trophodynamics of mesopelagic fishes in the Canary and Benguela Current
Eastern Boundary Upwelling Systems are known as highly productive areas and vital for fisheries. Because these provide about 20% of the global fish catches, it is important to understand the community assemblage and trophic interactions, since factors such as climate change and over-exploitation can have large impacts on these environments. The Benguela and Canary current are two of these highly productive areas that have seen decreases in fish stocks and changes in community composition due to over exploitation of fish. My aim is to gain a better understanding between the differences in assemblage structure and the role mesopelagic fish play in the food webs of these upwelling systems.
Although once thought of as barren and not containing much life, the mesopelagic zone (200-1000 m) contains the highest biomass of fish in the world’s oceans. Mesopelagic fish are important, as they are prey for many predatory fish such as sharks, hake, and tuna. Not only are they a vital part of the ocean’s food webs, but they also play a role in the ocean’s biological pump and contribute to the transport of carbon from the epipelagic to the mesopelagic zone. Many families of mesopelagic fish, including lanternfish (Myctophidae) perform diel vertical migrations (DVM), spending the day in deeper waters and going to the surface to feed on krill and other zooplankton at night. Because fish come to the surface to feed, they are ingesting a considerable amount of biomass, which is then transported to the mesopelagic zone. Through excretion and respiration, large amounts of carbon are transported to these deeper water layers. For these reasns, it is important to understand the role mesopelagic fish play in the food webs of these highly productive areas.
The first aim of my project is to compare the assemblage structure of mesopelagic fish in the Canary current (sections off the coast of Senegal and Mauritania) and the Benguela upwelling systems (northern and southern Benguela). In order to compare assemblage structure, I will use samples collected in 2016 in the Canary current and samples that we will collect for the project TRAFFIC (see below) in the Benguela. Fish will be identified and measured to compare community composition, richness, and the biomass size spectra for each location. My second aim is to compare the role of mesopelagic fish in the food web in these four locations. To do this, I will perform stomach content analysis and nitrogen and carbon stable isotope analysis (δ15N & δ13C) of different fish species and sizes in each location. With these methods I hope to gain a better understanding of the assemblage structure and the role mesopelagic fish play in the food web of the Canary current and Benguela upwelling system.