Abstracts of Oral Presentations

Red Fish, Blue Fish, Who Eats Who Fish: Juvenile Snapper-Grouper Diet Composition.

Tutelo, GA (GPMB, University of Charleston, SC) 

Dietary studies on juvenile snapper-grouper can provide necessary ecological information such as habitat usage and trophic interactions among species. The purpose of this study is to characterize the dietary composition of juveniles in the snapper-grouper complex using visual methods. To do this, juvenile Gag Grouper (Mycteroperca microlepis), Red Snapper (Lutjanus campechanus), and Black Sea Bass (Centropristis striata) were collected from the Southeast U.S. Atlantic Coast. Methods of capture included hook and line, pinfish traps, chevron traps, and trawls. After collection, individual prey items were separated and identified down to the lowest taxon possible. This information was used to calculate the percent weight (%W), percent number (%N), percent frequency (%F), and index of relative importance (IRI). These metrics define the contribution of visually classified prey items to the diet of each species. The trophic overlap of each predator was further examined using the Morisita-Horne (MH) index by using the %N and %W of prey items. Thus far, results show that Red Snapper and Gag Grouper have diets that are dominated by fish, while Black Sea Bass are more generalists. DNA barcoding also will be used to identify individual prey items that could not be identified using visual methods alone. This information will be used to determine trophic interactions, prey usage, and dietary overlap for a very understudied life stage of economically important fish species and will inform future fisheries research in juvenile ecology and assist in the prediction of future recruitment to the fishery.

Examining Variation in Response to Marine Diesel Fuel Exposure Between Tall- and Short-Form Saltmarsh Cordgrass (Spartina alterniflora).

Ferguson, R (GPMB, University of Charleston, SC)

Within saltmarshes there are two genetically and phenotypically distinct forms of Spartina alterniflora, a tall-form (>1 m in height) which grows along the edge of tidal creeks and a short- form (<0.5 m) found further inland. Due to their locations, tall-form plants experience daily high tides while short-form plants experience high tides less frequently. This study used microcosm systems (12 gallon buckets with simulated tidal cycles) to examine the impact of marine diesel fuel on short-and tall-forms of S. alterniflora exposed to two tidal regimes. Half of the systems were dosed with marine diesel fuel to a 0.1 mm slick thickness, while half remained unoiled controls. Within each oiling condition there were two different tidal simulations; a daily simulation which received two high and two low tide events each day and a weekly simulation with two high tides every Wednesday. Short- and tall-form plants grown from seed were placed into both tidal simulations with four replicate mesocosms each resulting in 32 systems. For three months following oil exposure, measurements of plant growth, plant health, and soil and water hydrocarbon concentrations were taken. Results indicate that the fastest mortality rates among oiled treatments occurred for short-form plants exposed to weekly tides, while tall-form plants with daily tides exhibited the slowest. For the unoiled treatments, plants with weekly tides produced more stems and shorter maximum stem heights than plants in microcosms with daily tides. Data from this study will help inform spill response and marsh restoration strategies.

Physiological effects of temperature on blood chemistry, metabolism, and metabolomic profiles of the Atlantic horseshoe crab, Limulus polyphemus.

Litzenberg, K (GPMB, University of Charleston, SC)

Temperature has long been known to impact biological systems and physiological performance across the animal kingdom. Rising water temperatures are especially of concern to ectothermic marine invertebrates who cannot regulate body temperature. While the effects of temperature have been widely studied across various phyla, little is known about how it might impact metabolism, blood chemistry (e.g., amoebocyte density, and hemocyanin concentration), and metabolomic profiles in invertebrates. NMR-based metabolomics is extremely sensitive to external stressors allowing us to determine shifts in metabolic profiles caused by temperature. Due to the importance of their hemolymph in the biomedical industry, the Atlantic horseshoe crab (HSC), Limulus polyphemus, represents a unique model for investigating the effects of temperature. In this study, HSCs were collected during spawning season from April-June, 2023 and assigned to three temperature treatments (18, 23, and 28 ℃) where they acclimated for one week. A standard metabolic rate was obtained for each crab and approximately one-third of their total blood volume was collected. Temperature was found to have a significant impact on metabolic rate (p = 0.003); however, it did not affect hemocyanin concentration (p = 0.311), or amoebocyte density (p = 0.622). Preliminary results from untargeted NMR-based metabolomics analysis reveal that temperature might influence hemolymph metabolite profiles. These data will provide insight into the effects of rising temperatures on physiological stress in marine invertebrates.

Using drones to monitor the body condition of Tamanend’s bottlenose dolphins (Tursiops erebennus) spatially and seasonally in Charleston, South Carolina.

Perkins-Taylor, CM (GPMB, University of Charleston, SC)

Body condition is a measure of an animal’s energy reserves relative to its body structure that provides important information about individual and population health. Monitoring the body condition of dolphins has traditionally been difficult, but in recent years drones have made assessing dolphin body condition easier. The Charleston Estuarine System (CES) is comprised of the estuarine and coastal ecosystems surrounding Charleston, South Carolina and is utilized by Tamanend’s bottlenose dolphins (Tursiops erebennus) throughout the year. However, little is known about the body condition of free-ranging dolphins in the CES. The main hypotheses of this study are that dolphin body condition in the CES varies spatially, seasonally, and depending on age class. Drone body condition surveys were conducted between September 2022 and May 2023 at four sites. The Body Area Index (BAI) of each dolphin was calculated as the comparative body condition metric and a linear mixed effects model was constructed to determine significant differences in dolphin body condition. In total, 428 drone images of 174 dolphins were included in the final analysis. Dolphins exhibited significantly higher BAI values during the winter than the spring, most likely because dolphins store energy during the winter before investing in reproduction in the spring. Calves exhibited significantly higher BAI values than adults, indicating that calves may have more energy reserves relative to their size than adults. These findings provide an important baseline regarding how dolphin body condition in the CES differs between demographic units and in response to environmental and anthropogenic stressors. 

Exploring the Spatial Reproductive Variability of Red snapper (Lutjanus campechanus) in the Southeast, US.

Wells, CC (GPMB, College of Charleston, SC)

Red snapper (Lutjanus campechanus) are an important species both recreationally and commercially in the Southeast United States. Currently, there are regulations in place to minimize fishing pressure on these species with additional deep-water marine protected areas (MPAs) and spawning special management zones (sSMZs) that are meant to protect bottom habitat and fish within their boundaries. However, these protected areas are not the only habitats utilized. A comprehensive characterization of adult female distribution and spawning capable female distribution throughout the region would greatly improve our understanding of habitat utilization. Differences in these distributions would indicate spatial changes in habitat utilization and potential preferences with associated environmental variables. For this study, we utilized fishery-independent data from 2010-2019 to determine the location of spawning hot spots and overall adult distributions of Red Snapper from Cape Hatteras, NC to St. Lucie Inlet, FL. Boosted regression tree (BRT) analysis was used to explain complex relationships between predictor variables and fish presence/absence and abundance (CPUE). The final BRT models included latitude, longitude, bottom temperature, salinity, oxygen, and biota density as predictor variables and predicted the largest spawning hot spots based on different metrics. These results will fill knowledge gaps regarding the reproduction and distribution of adult Red Snapper off the Southeast U.S. coast and could influence management decisions relating to the protection of the spawning areas of this valuable fishery.

Reducing Uncertainty and Spatial Biases in Blue Carbon Monitoring via in-situ and Remote Sensing Techniques of Charleston, SC Salt Marshes.

Kusher, JM (GPMB, College of Charleston, SC)

Water quality monitoring by remote sensing offers a solution to traditional, spatiotemporally-constrained methodology which may be time-consuming and costly in nature. Use of satellite sensors, however, requires in situ ground-truthing and significant preprocessing adjustments to account for 1) inherent optical properties (IOP) of in situ seawater including total suspended matter (TSM) within an area of interest (AOI) which alter light scattering, and 2) atmospheric interference such as varying ozone concentrations in the air column between an AOI and satellite sensors. Coastal waters are of particular interest but are difficult to monitor remotely due to the heavy loading of IOP, including TSM from the surrounding land. Coastal ecosystems are critical areas of carbon sequestration and are highly dynamic areas experiencing new land development (LD) spurred by growing populations moving coastward. Climate change necessitates increased awareness of water quality in high LD areas. In these areas, increased runoff and nutrient loading from sea level rise (SLR) and increased precipitation events may lead to declining water quality. The present thesis aims to ground-truth satellite-observed water quality parameters including chlorophyll-a (Chl-a), chromophoric dissolved organic carbon (CDOM), and TSM in the Charleston harbor estuarine system (CHES) of Charleston, South Carolina, USA. Ground truthing will be conducted via the development of bio-optical algorithms which will increase the spatiotemporal resolution and ease of future water quality monitoring in the CHES. Successful ground-truthing of satellite data for water quality assessment will benefit future resource management and monitoring efforts, especially under increased climate change needs.

Characterizing invertebrate communities associated with the cryptogenic alga Chondria tumulosa in the Papahānaumokuākea Marine National Monument, Hawai‘i.

Radick, RM (GPMB, University of Charleston, SC)

Habitat alteration by a newly established species can change community abundance and diversity, especially in relatively undisturbed ecosystems such as the Papahānaumokuākea Marine National Monument (PMNM). A cryptogenic alga, Chondria tumulosa, was discovered in the PMNM at the atolls Manawai and Kuaihelani in 2016 and 2021, respectively. This alga forms dense mats up to 20 cm in height that overgrow native corals and macroalgae, potentially influencing the composition of associated invertebrate communities. Satellite imagery and field surveys suggest that C. tumulosa can spread rapidly, thus altering the nature of habitat available to invertebrates. The goals of this study were to characterize and compare invertebrate abundance and diversity in C. tumulosa mats across a depth gradient from 2 m to 19 m. Mat samples were collected at Manawai (n=624) from five sites in August 2019 and eight sites in July 2021. Invertebrates from each sample were sorted to the lowest identifiable taxon using a dissection scope, and DNA barcoding was used to identify representative specimens. While there was no significant change in invertebrate communities across the depth gradient, there was a trend of increasing similarity among communities at similar depths. This study, the first to describe invertebrate communities in C. tumulosa, establishes a baseline for understanding how the continued spread of this habitat-altering alga will influence invertebrate community structure in invaded coral reefs.