Marine Ecosystem Assessment in a Patchy World: Are AUVs the Solution to Quantify Zooplankton?

Lead Research Organisation: University of East Anglia
Department Name: Environmental Sciences

Abstract

Cefas are the UK agency tasked with providing scientific advice to government on marine issues, informing decisions on how best to manage the marine ecosystems in UK waters. The data underpinning this advice have traditionally been collected by a network of fixed-point ocean observatories and several ship-based monitoring surveys, that provide temporally- and spatially resolved data respectively. These platforms provide the data needed to quantitatively assess the marine environment including on fish, zooplankton and physical drivers. However ship time in particular is costly. New methods using autonomous underwater vehicles (AUVs), especially ocean gliders, are now being devised. To interpret the data collected on these new platforms and facilitate comparison with existing methods, Cefas require new sampling strategies. This project is designed to explore these new techniques to benefit future Cefas scientific surveys, whilst also addressing exciting scientific questions of global relevance on why zooplankton distributions are patchy. Zooplankton are one of the key components of the marine ecosystem. They play an important role in marine foodwebs, transferring energy from the primary producers to larger organisms, for example commercially important whitefish. In the Southern Ocean they form an exploitable resource (krill) in their own right. As such, zooplankton are important indicators of ecosystem health, yet they are generally poorly sampled. Unlike plankton that contain chlorophyll, they cannot be quantified from satellite imagery. Ship-based sampling often involves deployment of nets which struggle to capture the patchiness in zooplankton distribution. Increasingly, effort is devoted to the use of acoustics for estimating zooplankton abundance from ship-borne echo sounders, already a traditional tool to monitor small fish. This project will assess and optimise the use of glider-borne echo sounders for ecosystem assessment, and apply this technology to study the patchiness of zooplankton in the marine environment and its causes. AUV technologies are revolutionising the way we collect environmental data, but we need to know how to convert these observations into statistically robust assessments of the ecosystem.
Many ocean characteristics are patchy. For example, temperature or current speed can vary over scales of a few hundred metres. Biological distributions are even more complex, driven not only by physical processes, but also by factors such as food availability or a tendency to form a school or swarm. This project will use high-resolution, coincident measurements of the patchy zooplankton distribution together with its physical and biogeochemical drivers, determine why it is patchy, how that patchiness varies, and whether it is predictable. Building on exciting recent developments in observing, understanding and modelling the submesoscale in physical marine science, this PhD project seizes the same opportunity to advance biological marine science at the submesoscale.
The project has four interlinked objectives: (i)optimise AUV assessment of zooplankton and fish distribution and biomass by exploiting existing acoustic data sets and ocean model output
(ii)conduct a glider deployment in conjunction with a ship-based survey using these newly-developed strategies
(iii)interpret the observed zooplankton and fish distribution in the context of physical, biogeochemical and bathymetric controls and predator-prey dynamics
(iv)synthesise the implications for design of future ocean monitoring systems.
The PhD student will be supervised by research leaders in the field at Cefas, BAS and UEA, bringing together expertise in
fisheries acoustics, ocean gliders, marine biology, physical oceanography, and ocean observing systems. He/she will be trained in multidisciplinary seagoing oceanography, zooplankton ecology, fisheries acoustics and the use of ocean gliders, benefiting from embedding in the NERC EnvEast DTP.

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