The Effects of Seamounts on the Abundance of Vertically Migrating Zooplankton
Zooplankton are an important part of seamount ecosystems. They are a major food source for seamount fish species. Commercially valuable fish species are often concentrated over seamounts, leading to seamount fisheries. However, many seamount fisheries over-exploited the local fish populations, depleting the fish stocks they were harvesting. Seamount fisheries can be made sustainable more easily if the link between seamount fish stocks and their prey are better understood. Seamount fish might benefit from zooplankton diel vertical migration if migrating zooplankton descend to the summit where benthopelagic fish could feed on them more easily than in deep waters. Finding if there is a connection between zooplankton proximity to seamount and diel vertical migration behavior will add to the knowledge of seamount ecosystems and allow for better environmental planning. A study of Cross Seamount using plankton net tows and acoustic backscatter data can provide more information about how seamounts affect zooplankton distributions. Day and night net tows up-current, down-current, and over the seamount can reveal how the population of small zooplankton in the water passing the seamount is affected. Day and night acoustic transects using a 75kHz ADCP and a 30kHz EM302 across the seamount can reveal the position and strength of the scattering layers from fish and large zooplankton and how they change. The ADCP transects will also reveal the current structure around the seamount and help determine what role currents might play in the observed zooplankton distributions. I expect to find that migrating zooplankton will be less abundant over the seamount than in waters up-current of the seamount. If this is true, then currents or predation are acting on the abundance of migrating zooplankton. The ADCP current structure data will determine if currents are responsible for any differences in the seamount zooplankton population, and the echosounder backscatter layer will provide an idea of where the seamount fish are feeding, indicating what role predation has on zooplankton populations. This will indicate whether or not migrating zooplankton are acting as a significant food source for Cross seamount’s fish population, and expand knowledge of seamount ecosystems.