The University of Southern Mississippi’s Chet Rakocinski and his students will focus their research on benthic polychaetes, small organisms that live within bottom sediments of estuaries. In a series of experiments, he and Ph.D. Student Kelsey Burns will examine how these creatures, an important part of the marine food web, respond to two of the most pressing coastal health stressors, hypoxia and increasing temperature due to climate change. Knowing how these stressors affect benthic organisms can be used as an indicator of the overall health of the Gulf estuaries. To do this, they will expose common benthic organisms to different combined levels of dissolved oxygen and temperature to see how exposures affect their respiration, growth rates and overall physiological condition. Using a Hypoxia Mass Balance Model, they will examine how the physiological costs imposed by low oxygen and high temperature help to explain changes in biomass-size distributions as a functional indicator scientists can use to gauge estuarine health.

Abstract

The project proposed herein will contribute to a functional explanation of responses by benthic organisms to changing and interacting gradients of dissolved oxygen and temperature, stressors associated with two primary coastal health concerns, namely hypoxia and climate change. Furthermore, this research will take the next logical step toward producing a functional indicator of hypoxia for coastal estuarine ecosystems. The research questions are founded on the premise that macrobenthic population responses to organic enrichment and hypoxia should entail a number of mechanistic links to individual organisms in terms of their bioenergetic capacity to respire, consume, and allocate energy. Experiments will be performed using various body sizes of several prevalent benthic polychaete taxa. In addition to acute mortality, chronic effects in terms of autecological processes, including aerobic and anaerobic respiration, tropho-energetic parameters, as well as growth and degrowth rates will be quantified at various combined levels of dissolved oxygen (DO) and temperature. Information gleaned from lab experiments will be synthesized within the context of an incipient hypoxia mass balance model (HMBM) to examine how autecological processes would interact to elicit temporal changes in biomass-size distributions under alternative scenarios of DO and temperature. In addition, incorporating parameter estimates within the HMBM will help to assess the feasibility and applicability of developing a functional indicator that can be mechanistically explained through autecological processes. An ultimate goal is to craft a model which can apprehend how effects of hypoxia and warming affects trophic transfer potential to important fisheries species, such as brown shrimp. In light of the project goal of creating a resource management tool, involvement in project planning and execution will entail annual workshops involving representatives from various state and regional coastal resource management entities. Workshops will provide a forum for conveying our progress and soliciting feedback on what elements of the study will be most useful for resource management. Workshops will conclude in an illustration of the use of the HMBM resulting from the research portion of this project as a management tool for generating alternate stressor scenarios.

Objectives

The project proposed herein will contribute to a functional explanation of responses by benthic organisms to changing and interacting gradients of dissolved oxygen and temperature, stressors associated with two primary coastal health concerns, namely hypoxia and climate change. Furthermore, this research will take the next logical step toward producing a functional indicator of hypoxia for coastal estuarine ecosystems.

Methodology

Experiments will be performed using various body sizes of several prevalent benthic polychaete taxa. In addition to acute mortality, chronic effects in terms of autecological processes, including aerobic and anaerobic respiration, tropho-energetic parameters, as well as growth and degrowth rates will be quantified at various combined levels of dissolved oxygen (DO) and temperature. Information gleaned from lab experiments will be synthesized within the context of an incipient Hypoxia Mass Balance Model (HMBM) to examine how the processes would interact to elicit temporal changes in biomass-size distributions under alternative scenarios of DO and temperature. In addition, incorporating parameter estimates within the HMBM will help to assess the feasibility and applicability of developing a functional indicator that can be explained through autecological processes.

Rationale

The research questions are founded on the premise that macrobenthic population responses to organic enrichment and hypoxia should entail a number of mechanistic links to individual organisms in terms of their bioenergetic capacity to respire, consume, and allocate energy. An ultimate goal is to obtain a model which can apprehend how effects of hypoxia and warming affects trophic transfer potential to important fisheries species, such as brown shrimp. In light of the project goal of crafting a resource management tool, involvement in project planning and execution will entail annual workshops involving representatives from various state and regional coastal resource management entities. Workshops will provide a forum for conveying our progress and soliciting feedback on what elements of the study will be most useful for resource management. Workshops will conclude in an illustration of the use of the HMBM resulting from the research portion of this project as a management tool for generating alternate stressor scenarios.