Using new ocean observing technologies in two contrasting locations, this research is combining measurements of biological and environmental conditions to understand highly productive ocean shelf food webs. Within marine food webs, a diverse community of small animals, referred to collectively as zooplankton, serve as prey for larger animals including fishes and marine mammals. Zooplankton can also influence lower trophic levels, such as marine microbes that in turn, affect nutrient and gas cycling throughout the oceans. This project is also supporting graduate and undergraduate students, including several from Savannah State University, a Historically Black University with undergraduate and graduate programs in marine sciences. The field research is providing authentic oceanographic experiences for K-12 educators, who will participate in the planned research cruises, as well as research opportunities for juniors and seniors at a local high school with high enrollment of groups underrepresented STEM. Public outreach includes annual open house events at the University of Georgia’s Skidaway Institute of Oceanography.
This project addresses fundamental questions in ocean sciences regarding how environmental conditions affect the structure and composition of zooplankton communities in continental shelf ecosystems. Biologically productive shelf ecosystems can oscillate between extremes of vertically mixed waters during windy and colder seasons and vertically stratified waters during warmer and calmer conditions. Warm, calm conditions favor the formation of dense layers or aggregations of plankton and particulate material, generating hot spots of biological activity that potentially allow marine organisms to feed at much higher rates than water-column-average abundances might suggest. Although physical mechanisms of layer formation and plankton groups associated with them have been described in several shelf environments, less is known about the influence of layers on zooplankton community composition and trophic transfer. For fast-reproducing pelagic tunicates such as salps, pyrosomes, appendicularians, and doliolids, these layers or aggregations may serve as rich food resources that prime pelagic tunicates to form dense blooms which then ultimately serve as food for gelatinous predators. This sequence of events, from layer formation to pelagic tunicate reproduction and predation on the bloom, may generate high abundances of gelatinous organisms throughout the marine food web. The investigators will test this hypothesis by measuring fine-scale abundances of gelatinous zooplankton with in-situ imaging, gelatinous zooplankton diets using molecular gut content analysis, and food web properties using compound-specific stable isotopes in both vertically mixed and stratified conditions. To determine if food web interactions are generalizable to water columns with and without vertical structure, these processes will be compared in the South Atlantic Bight and northern Gulf of Mexico shelf ecosystems. Both provide favorable conditions for doliolid blooms yet differ in drivers of vertical stratification.
Funder: National Science Foundation
PI: Adam Greer, Franklin College of Arts and Sciences, Department of Marine Sciences