New technology helps Delaware Sea Grant researcher characterize ecologically significant marine organisms in Delaware Bay

by Karen B. Roberts, Delaware Sea Grant

Delaware Sea Grant researcher Jonathan Cohen is using a new technology to analyze and quantify zooplankton in the Delaware Bay.
Zooplankton are millimeter to centimeter scale organisms that live in water. A diverse and ecologically significant group of animals, they range in size from small copepods the size of a grain of rice to large jellyfish. 
In the Delaware Bay, zooplankton contain the larvae of commercially important species, including oysters, crabs, shrimp and various finfish, and are considered an important measure of fishery sustainability. They are also a key food source in the marine food web.
Despite their ecological importance, zooplankton have been understudied in the Delaware region.
“People forget that marine organisms aren’t just adults; they are eggs and larvae that are dispersed in the water column, then become juveniles and adults,” explains Cohen, assistant professor of marine science and policy in University of Delaware’s College of Earth, Ocean, and Environment.
Supported with Delaware Sea Grant College Program (DESG) funding, Cohen’s study establishes a baseline for future zooplankton studies in the region in the context of climate change.
The research team is using Zooscan, a waterproof optical scanning system, to identify and characterize zooplankton species in the Delaware Bay.
The work builds on an early zooplankton study conducted in the 1950s by Joanne Daiber, UD’s first female marine biologist. Cohen will compare his results to Daiber’s to understand what biological changes have occurred in Delaware Bay over the past half-century. He also is looking at the physical and chemical properties of the water column.
Cohen’s team recently collected zooplankton samples from 16 stations in the bay; the second of six planned research cruises on the R/V Joanne Daiber. They created a library of zooplankton Delaware Bay specific images to identify and characterize the new samples. 
The samples are poured onto the optical scanner and a high-resolution picture is taken of the zooplankton. Computer algorithms extract individual images, characterize specific species, including their size and biomass, and place them in files, which the researchers later verify.
“Delaware Bay has improved a fair amount since the 1950s and ’60s, particularly in the upper bay where it previously had a lot of nutrient pollution from sewage and sediment,” he says.
Cohen is curious about what unexpected new species the study will detect. He suspects increased ship traffic has brought invasive species to the area. One example is the Asian shore crab, Hemigrapsus, which can be found near Lewes and is thought to have arrived in ballast waters discharged into the bay as ships come into port. 
Sharing the science with others
Cohen is collaborating with DESG’s education specialist Chris Petrone to develop a website and a teacher-training workshop for teachers to learn how to use zooplankton in the classroom to address Next Generation Science Standards. The team also is partnering with the UD Citizen Monitoring program to explore viable ways they can assist with collecting zooplankton data.
Other project collaborators include partners from Delaware Department of Natural Resources and Environmental Control and other DESG-funded researchers.