This project will study the role of zooplankton behavior in producing aggregations in response to ocean structure. The focus is on thin layers, a wide-spread oceanic phenomenon that may serve as an organizing element of plankton patchiness. The objective is to quantify copepod threshold responses to key properties of thin layers. The successful creation of a controlled well-defined thin layer in a laboratory setting enables a quantitative comparison of kinematic patterns of plankton in response to fine-scale biological-chemical-physical features. The specially-designed apparatus creates flow gradients at naturally-occurring strain rate, density gradient, and phytoplankton exudate concentration levels, thus mimicking the essential properties of this fine-scale oceanic feature. A unique feature of the proposed treatments is that by presenting cues separately, the dominant cue for aggregation and interactions among cues can be assessed. The proposed experimental design isolates the effect of 1. individual cues, combined cues, and combined cues that are spatially separated, 2. zooplankton size, and 3. palatable vs. toxic phytoplankton species in the thin layer. The project will also evaluate the role of copepod satiation in the threshold sensitivity of plankton to thin layer cues. The ability to observe and quantify zooplankton behavior within a well-controlled environment enables a direct link between behavior and structure. Current approaches to this problem are limited because of a technological inability to sample in the ocean at the necessary scales. To scale up from the laboratory studies to in situ behavior, the laboratory data on zooplankton behavioral responses to oceanic structure will be examined for zooplankton populations using an individual-based model. The mathematical model parameterized with measured current field data will be used to reproduce the concurrent observations (in collaboration with Tim Cowles, Mark Benfield, Carin Ashjian, and Malinda Sutor) of zooplankton associated with physical-chemical oceanic features can be predicted using. Thus, fine-scale zooplankton behavior will be connected to their field distribution with respect to features in the ocean.
Broader Impacts: The biological and physical mechanisms underlying zooplankton behavioral responses are important to interpret and predict energy and material cycling and productivity of ocean ecosystems. The proposed research will be valuable to fisheries management by advancing our understanding of the impact of environmental change on the distribution and availability of prey items for managed living marine resources, such as juvenile salmon and other small pelagic fish. This research relies on an interdisciplinary collaboration between biology and fluid mechanics. The continued collaboration at Georgia Tech brings innovative tools to the oceanographic community and contributes to instrument development for in situ imaging. This proposal also represents a new collaboration between Gerogia Tech and NOAA Fisheries through the participation of Andrew Leising, who is a de facto Co-PI. The students involved in this project will experience a rich interdisciplinary research environment. This training will be further enhanced by on-going educational efforts, within existing NSF IGERT and REU programs in the area of aquatic chemical and hydromechanical signaling.
