Coastal Sediment Response to the Diel Oxygen Cycle

Shallow coastal sediments are sites of intense respiration and organic matter breakdown. Macroinfauna bioturbate and bioirrigate sediments which supplies microbes with oxygen and newly deposited organic material from surface sediments, facilitating microbial remineralization of organic matter. These processes depend heavily on the concentration of dissolved oxygen in overlying water. Shallow water oxygen patterns often follow a diel cycle as dissolved oxygen decreases at night due to respiration and then increases during the day with photosynthesis, creating recurring suboxic conditions that are potentially stressful to organisms. Sediment oxygen flux is known to depend on ambient dissolved oxygen concentration, but behavioral responses of macrofauna to low oxygen can be complex and diverse, introducing variability into sediment metabolism rates. This dissertation research examined the effects of diel changes in dissolved oxygen on macrofaunal behavior and activities and corresponding changes in sediment metabolism throughout the diel cycle. I constructed a simple laboratory system to manipulate dissolved oxygen concentrations into a diel pattern and exposed sediment infauna to repeated diel oxygen cycles. Sediment mixing in all three of the tested taxa decreased overall throughout the experiment and over two diel cycles, but also varied proportionally with oxygen within each diel exposure. Behaviors did not show significant variation with the diel cycle, though this is likely because behaviors relevant to sediment x mixing activity were not easily detected or quantified with the employed methods. These results indicate that experiments quantifying sediment mixing by macrofauna that occur in fully oxygenated conditions may not be representative of in situ rates, and that it may require more even than a single diel cycle for representative rates to emerge. To better understand how natural macrofaunal assemblages affect sediment metabolism when exposed to diel cycling oxygen, I conducted a field sediment metabolism experiment. Flow-through sediment metabolism chambers were constructed and deployed to measure in situ sediment oxygen consumption. The presence of macrofauna drove overall greater and more variable rates sediment oxygen demand particularly at night, presumably due to fauna responding to low oxygen by increasing their irrigation activity. This research shows that in coastal sediments, variation on small temporal and spatial scales interact to affect sediment metabolism. Sediment metabolism, a key ecosystem function, is controlled by complex networks of interactions and feedbacks between biogeochemical and ecological processes. This research sheds new light on the connection between oxygen concentration and oxygen consumption in these dynamic, productive marine systems and improves our understanding of the role of macrofauna in modulating that relationship

Oil disturbance reduces infaunal family richness but does not affect phylogenetic diversity

Infaunal organisms are susceptible to disturbances such as hypoxia and sediment contamination; changes in infaunal community structure are therefore often used as indicators of anthropogenic disturbance. Susceptibility to disturbance varies across taxa, either due to physiological factors or to behaviors or functional roles that increase exposure. Both sources of variability are likely to be heritable and shared among related taxa. Thus, we would expect oil disturbance to disproportionately affect related taxa and therefore decrease phylogenetic diversity (PD). We test this hypothesis for a shallow water marine infaunal community using a simulation approach that iteratively removes clades with shared vulnerability to oil exposure. Infauna were sampled at two sites in the Chandeleur Islands, LA, that reflect different exposures to crude oil after the Deepwater Horizon event. Seagrass and adjacent bare sediment habitats were sampled in 2015, 5 years after initial oil exposure, and again in 2016 after an acute re-oiling event. We found that strong correlation between PD and family richness masked any detectable PD patterns with oil exposure. For our full community tree, sensitivity analysis indicated that the removal of larger clades did not disproportionately reduce PD, against our prediction. For this pair of sites, PD did not provide a better metric for assessing the impacts of oil exposure than family richness alone. It is possible, however, that finer-scale taxonomic resolution of infaunal communities may better decouple PD from taxonomic richness. More work is needed to fully evaluate the impacts of disturbance on PD

Early Career Aquatic Scientists Forge New Connections at Eco-DAS XV

A sense of kuleana (personal responsibility) in caring for the land and sea. An appreciation for laulima (many hands cooperating). An understanding of aloha ’āina (love of the land). The University of Hawai’i at Manoa hosted the 2023 Ecological Dissertations in Aquatic Sciences (Eco-DAS) program, which fostered each of these intentions by bringing together a team of early career aquatic ecologists for a week of networking and collaborative, interdisciplinary project development (Fig. 1)

Dataset: Baywide distribution of benthic ecological functions in the past decades in the Chesapeake Bay

We undertook the collection and analysis of long-term benthos data from the Chesapeake Bay Benthic Monitoring Plan. Multiple ecological function traits related to feeding and disturbance were assigned to each observed benthic species based on a thorough literature review. The spatial distributions of the ecological function groups will be utilized in a 3D hydrodynamic biogeochemistry model simulation. This approach aids in estimating the contributions of benthos to estuarine hypoxia and nutrient dynamics. Furthermore, it fosters a connection between ecologists and modelers, promoting collaborative efforts in understanding and modeling the ecosystem

Better Together: Early Career Aquatic Scientists Forge New Connections at Eco‐DAS XV

A sense of kuleana (personal responsibility) in caring for the land and sea. An appreciation for laulima (many hands cooperating). An understanding of aloha 'āina (love of the land). The University of Hawai'i at Manoa hosted the 2023 Ecological Dissertations in Aquatic Sciences (Eco-DAS) program, which fostered each of these intentions by bringing together a team of early career aquatic ecologists for a week of networking and collaborative, interdisciplinary project developmen