Gelatinous zooplankton, often called jellies, play a key role in marine food webs. They can be very abundant, and some feed on the millimeter-sized eggs and larvae of fishes. Yet despite their ecological importance, jellies are often overlooked in marine research. Their fragile structures make them difficult to sample and quantify accurately, leaving scientists without answers to even basic questions about where many species live.
A study led by University of Georgia Skidaway Institute of Oceanography (SkIO) faculty member Adam Greer reveals new understanding. Using an underwater imaging system in the Gulf near Perdido Bay, Florida, Greer and his colleagues identified different jellies, mostly to genus level, and mapped where different groups live across seasons. They found that each type of zooplankton tended to live in its own specific area, with very little overlap, even during the fall when wind events and cooling temperatures cause lots of mixing.
“What we saw was that — no matter the season — when you look at the different jelly types, they don’t overlap with one another, which is surprising,” said Greer, an assistant professor in the Department of Marine Sciences at UGA’s Franklin College of Arts and Sciences. “You expect them to all be overlapping when the water column is mixed up.”
Each season brings distinctive water conditions. Summer is highly stratified, like an ocean layer cake, while fall is completely mixed up, which causes the ocean properties to become homogenous. The spring season is in between these two extremes, with moderate stratification associated with large amounts of river discharge.
Throughout three seasons — fall, spring and summer — Greer and his colleagues routinely visited the same areas near the Florida-Alabama border to collect their samples. They deployed an In Situ Ichthyoplankton Imaging System from the back of a research vessel. The instrument has wings that help it dive up and down throughout the water column and uses a technique called shadowgraph imaging that captures backlit images of zooplankton. These shadowgraph images make it easy to distinguish a wide variety of zooplankton and allow scientists to capture photos of the organisms without disturbing or displacing them, providing a clear view of how zooplankton are distributed.
The findings are detailed in a paper titled Oceanographic heterogeneity facilitates gelatinous zooplankton niche space and diversity, recently published in Limnology and Oceanography Letters.
The data for the paper was collected in 2015-16, when Greer was working as a postdoctoral researcher at the University of Southern Mississippi. The ecological questions that emerged from that work helped launch Dol-LAYER, a current project led by Greer in collaboration with SkIO faculty members Jay Brandes and Marc Frischer and Savannah State University faculty member Laura Treible, who was formerly a postdoctoral researcher in the Greer Lab.
Dol-LAYER considers the diets of the jellies as a contributing factor that may be useful for predicting where different groups live and why they don’t overlap. More on the Dol-LAYER project is available here.
About SkIO
The UGA Skidaway Institute of Oceanography (SkIO) is a multidisciplinary research and education institution located on Skidaway Island near Savannah, Georgia. The Institute was founded in 1967 with a mission to conduct research in all fields of oceanography. In 2013, SkIO was merged with the University of Georgia. The campus serves as a gateway to coastal and marine environments for programs throughout the University System. The Institute’s primary goals are to further the understanding of marine and environmental processes, conduct leading-edge research on coastal and marine systems, and train tomorrow’s scientists.