Project: Do fine-scale water column structure and particle aggregations favor gelatinous-dominated food webs in subtropical continental shelf environments?

Overview: 

The proposed project aims to answer a fundamental question about continental shelf systems: Does layer formation and dissipation control the structure and composition of zooplankton communities? Although thin layer physical formation mechanisms and plankton groups associated with them have been described in several shelf environments, less is known about their influence on zooplankton community composition and trophic transfer. This project will address this critical knowledge gap. We hypothesize that in productive continental shelf environments, stratification generates thin layers of aggregated particles favorable for stimulating subsurface blooms of small gelatinous grazers, namely doliolids, along with predators feeding on doliolids and proliferation of microbial communities. Alternatively, in well-mixed environments lacking layers or patches, non-gelatinous zooplankton communities are favored, resulting in different food web properties. Bringing together an interdisciplinary team with expertise in biological and physical interactions, gelatinous zooplankton and microbial ecology, and stable isotope biogeochemistry, we propose a field intensive program that will combine several innovative technologies and methods to test this hypothesis.

Intellectual Merit: 

Because predators and prey are often abundant and overlapping spatially within and around thin layers, these features have been hypothesized to be trophic ‘hotspots’ that contribute to higher trophic level production in shelf ecosystems. However, most studies of thin layer ecology consist of one or more snapshots of organism distributions correlated with physical oceanographic parameters. While these studies have generated valuable insights into physical and biological coupling, supporting measurements of food web structure and trophic interactions are often lacking, leaving many questions unanswered about the trophic consequences of layering. For example, does the formation of thin layers create water-column habitat that is optimal for certain grazers and to which other organisms respond, shaping broad properties of the food web? In this project, we will assess the degree to which layers fundamentally alter the trophic structure of zooplankton communities, favoring the dominance of gelatinous grazers, which enhances microbial interactions and supports gelatinous-dominated higher trophic level populations. We will examine these dynamics in the South Atlantic Bight (SAB) and northern Gulf of Mexico (nGOM) – two subtropical shelf seas with frequent doliolid blooms yet differing oceanographic mechanisms generating stratification. Through this comparative approach quantifying the relationship between the spatiotemporal distribution of plankton/particles, trophic interactions, and food web structure in the context of oceanographic properties, including the persistence and extent of thin layers, we will advance our understanding of how productive continental shelf communities are structured. Specifically, we hypothesize that the presence of thin layers favors gelatinous (doliolid) dominated zooplankton communities over non-gelatinous dominated zooplankton communities.

Broader Impacts: 

Because the degree to which copepods or doliolids dominate the mesozooplankton community influences transfer of energy either to higher trophic levels or to the microbial loop, understanding the mechanisms causing these shifts is fundamental to our understanding of ocean ecology and, ultimately, fisheries production. Zooplankton remain a poorly resolved component of ecosystem models, and a better understanding of how these communities are coupled to the ocean environment will improve societally relevant predictions of ecosystem responses to the myriad of environmental stressors that are increasingly impacting the oceans.

In addition to the scientific and societal impacts, this proposal will support 3 graduate and several undergraduate students and will provide authentic oceanographic experiences for at least 50 K-12 educators who will participate in the planned research cruises and in a well-established annual week-long educator workshop (NOAA Rivers to Reefs). The project will also support two investigators at the beginning their academic career (Greer and Treible). The PIs also will also use innovative citizen science approaches to engage local high school students (total of ~600, predominantly African American) in the process of identifying zooplankton and interactions within the in situ images, with the broad goal of diversifying the STEM and ocean science workforce. The principles derived from the project will also be shared with the public through annual open house events at the UGA Skidaway Institute of Oceanography campus (~2,000 visitors annually).