Quantifying and partitioning spatiotemporal variability in secondary production and trophic transfer efficiency in pelagic marine ecosystems

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This research aims to measure two factors that, although critically important to understanding marine food chains, have rarely been measured in Canadian waters. The first is known as "secondary production", which is the rate at which zooplankton are produced. Zooplankton are tiny animals (mostly less than 1 cm in size) that feed on single-celled plants (called "phytoplankton") at the base of most marine food chains. Zooplankton are consumed by larger animals - including many young and adult fish, certain marine mammals, and even seabirds. The second factor is referred to as the "trophic transfer efficiency" (TTE). In short, this is an estimate of how much energy is transferred between different levels of the food chain (e.g. from phytoplankton to zooplankton). The higher the TTE the more energy that is transferred up the food chain, and the greater the amount of fish, marine mammals, etc. that can be supported. These two factors are essential components that underlie the mathematical models that oceanographers use to study marine food webs, and to predict how such food webs may change in the future. However, mainly for technical reasons, neither factor is measured directly in the ocean. Instead, modelers have relied on numbers drawn from simplified lab experiments or theoretical studies. My lab has developed a method to directly measure secondary production, based on measuring an enzyme (called chitobiase) that most zooplankton release into the water as they grow. When put together with measures of the rate of phytoplankton growth (known as "primary production" - something that oceanographers have been able to do since the 1960s), we have been able to produce the first direct estimates of TTE in a natural field setting. Over the next five years we will expand our work to begin exploring how secondary production and TTE vary between locations and at different timescale (i.e. seasonally, between years, etc.) off Canada's west coast. The data we generate will be used by researchers at Fisheries and Oceans Canada (and elsewhere) to refine their ecosystem models and improve their ability to forecast how Canada's marine resources may respond to changing ocean climates in the future.