In the ocean, microscopic plants called phytoplankton form the basis of the marine food chain. Production and species diversity of phytoplankton varies depending on environmental conditions (e.g., water temperature, nutrients, and light availability). This, in turn, has a significant influence on the survival of the animals that feed on the phytoplankton: zooplankton.
The most abundant zooplankton found in the Bering Sea are copepods (crustaceans) and euphausiids (krill). Zooplankton are the primary food source for larval and juvenile fish during their first year of life, a critical period where fish experience high mortality. Quality, quantity, and distribution of zooplankton prey therefore have a strong impact on fish survival.
Understanding how zooplankton respond to changing ocean conditions is an active area of research. In general, higher ocean temperatures increase growth and secondary production rates, and reduce development times of zooplankton. However, these higher temperatures also reduce body mass and can change the overall species composition of zooplankton. Through years of observation, scientists have determined that the species of copepods that are most abundant in warm years are different than those seen in cold years.
Studies have shown that juvenile fish need abundant lipid-rich (fatty) copepods in summer to put on enough body mass to make it through their first winter. Copepods and euphausiids are also important components of adult fish diets. For example, the stomach contents of commercially important pollock are comprised of roughly 27 percent copepods and 40 percent euphausiids by weight.
Models Fill in Data Gaps
A lot of data have been collected over the years through field observations. However, inaccessibility and limited surveys, particularly during winter months, means that some areas and times of the year are not sampled.
“By comparing and better integrating direct observations of plankton species, abundance and distribution in the marine environment with the model results, we hope to improve the models,” said David Kimmel, NOAA Fisheries biologist and project lead at the Alaska Fisheries Science Center. “It is critical to understand how zooplankton populations will respond to future warming as it will significantly impact fisheries production.”
Kimmel and his collaborators at NOAA Research’s Pacific Marine Environmental Laboratory hope to develop projections for zooplankton abundance under varied climate conditions out to 2035.
Better Forecasting Leads to Better Fisheries Management
Improved forecasting capabilities allows managers to make decisions about fisheries production or development tools that will address expected changes in marine ecosystems. For instance, they will be able to provide more reliable short-term and potentially long-term estimates for pollock recruitment (the number of young that will reach an age when they are capable of reproducing and contributing to the population).
“Projects like this are really important to help the Alaska Fisheries Science Center advance our science as ecosystems change,” said Alaska Fisheries Science Center Director Bob Foy. “Enhanced modeling capabilities is part of a strategic science portfolio that includes long-term field research and surveys to collect essential biological, ecological and oceanographic data, sophisticated processing capabilities to interpret the field study results, and innovative technologies to further expand our monitoring capacity.”