Mote Marine Laboratory

Coastal acidification is being exacerbated by terrestrial organic inputs, especially after high precipitation events. Florida’s rainy season coincides with stone crab (Menippe mercenaria) reproduction, and pH extremes could limit future harvests by reducing reproductive output. Populations that experience pH variability can serve as “natural laboratories” for estimating the tolerance of a species to coastal acidification. Here, we conducted a series of experiments to determine if ovigerous stone crabs conditioned in more variable pH habitats (seagrass) would result in faster embryonic development, greater hatching success, and higher larval survival relative to crabs conditioned in habitats with lower pH variability (sandy habitats). After field conditioning, crabs were transported to the laboratory and randomly acclimated to either a control pH (pH = 7.90) or a reduced pH condition (pH = 7.60) until larval release. The rate of embryo development was slower in the laboratory reduced pH treatment, however, there were no observable field condition effects on embryo development rate. Crabs conditioned in the more pH variable seagrass habitat did have greater hatching success and higher larval survival than crabs in less pH variable sandy habitats; however, larval survival was low across all treatments. These results suggest that the pH variability experienced in seagrass habitats during brooding may serve as a mechanism for stone crabs to acclimatize to extremes in seawater pH.

Stony coral tissue loss disease (SCTLD) affects at least 22 Western Atlantic coral species and presents as focal or multifocal lesions, which swiftly expand across the colony, resulting in rapid tissue loss and mortality. Previous histopathological examinations have noted necrosis, body wall breakage, gastrodermal separation, exocytosis, and vacuolization of the symbiont as pathological signs; however, the same signs are present to some degree in otherwise apparently healthy coral tissues processed for histology. Here, we quantify the degree of symbiont vacuolization, symbiont size change, exocytosis, and gastrodermal separation in apparently healthy and diseased coral tissues of eight coral species in association with SCTLD transmission experiments in Florida (USA) and the United States Virgin Islands. We describe a characteristic progression of disease signs which support the hypothesis that coral-algal dysbiosis contributes to SCTLD-associated tissue loss. Progression begins with symbiont cell vacuolization, followed by symbiont cell exocytosis and gastrodermal cell lysis. The lysing of gastrodermal cells leads to separation of the gastrodermis from the mesoglea, and finally to liquifying necrosis. Disease signs varied by coral species and symbiont genus following known hierarchy in disease susceptibility across coral and algal genera. SCTLD histological dynamics were also associated with differential expression of genes considered indicative of stress and dysbiosis and further influenced by both coral species and algal symbiont genus.

Blooms of the toxigenic dinoflagellate Karenia brevis are an almost annual occurrence in the eastern Gulf of Mexico, typically initiating in late summer and early fall months and terminating in late spring or earlier. The question of whether blooms have been expanding in frequency or duration has long been debated. Recently, a Bloom Severity Index (BSI) was developed that captures changes in bloom magnitude based on cell concentrations normalized to maximum observed values. Here, changes in the BSI (severity and bloom duration) were examined for the period from 1970-2019, a period of rapid climate change and increased anthropogenic pressures. This time period encompassed several changes in the Oceanic Niño Index (the El Niño-Southern Oscillation), including a shift from a highly positive to a negative North Atlantic Oscillation in the mid 1990s, bringing with it increased precipitation and more intensive storms. Annual BSI and bloom duration have increased with increasing temperatures, and blooms have also become longer in duration in relation to increased temperatures and river flows since the mid 1990s. As increased precipitation is related to increased nutrient runoff, regional fertilizer use and the anthropogenic nitrogen (N) footprint based on population census data as proxies of nitrogen loads were examined. The duration of severe blooms was highly correlated with the increasing anthropogenic N footprint, especially when BSI values were averaged across multiple years. These relationships highlight the importance of climate changes and of increasing population since the 1980s and help to explain why earlier analyses of nutrient loads and bloom severity were inconclusive. To reduce bloom severity or duration in the future, reductions in N loads and releases from the Caloosahatchee River are needed more than ever to counteract the increasing pressures from climate change.

Increasing ocean warming and storm-driven terrestrial inputs are reshaping subtropical coastal ecosystems. This study investigated how elevated temperature and humic acid enrichment, under both pre- and post-hurricane (Idalia, Debby, Helene and Milton) in situ and manipulated conditions, affect the metabolic rates of phytoplankton communities on the West Florida Shelf (WFS). We hypothesized that warming, combined with hurricane-driven humic inputs, would decrease primary production rates while enhancing respiration and dissolved organic matter (DOM) degradation, shifting system toward net heterotrophy. Using 18O techniques combined with oxygen concentration measurements, the differences between light-dependent respiration (hereafter Gross Respiration, GR, representing only that associated with algal respiration) and dark respiration (hereafter Community Respiration, CR, representing the sum of microbial respiration) were measured in addition to rates of Gross Primary Production (GPP), and Net Primary Production (NPP). Across stations and experiments, increasing temperature consistently reduced GPP and shifted NPP toward negative values due to enhanced GR. Rates of algal light-dependent GR compared favorably to total CR, in some cases exceeding CR. Changes in the Fluorescent Dissolved Organic Matter (FDOM) composition were also analyzed using spectrofluorometric methods. Increasing temperature was associated with enhanced biological production of labile, protein-like FDOM and concurrent shifts toward lower humification. Together, these changes increased oxygen demand while decreasing oxygen solubility, creating conditions favorable to hypoxia. These results show that warming and hurricane-driven brownification are associated with enhanced algal respiratory metabolism in addition to enhanced CR, highlighting a potential pathway through which climate change could intensify hypoxia in subtropical coastal systems.

Sea turtles are among the many wildlife species adversely affected by Florida red tide, Karenia brevis. This marine dinoflagellate blooms almost annually along Florida's west coast and produces brevetoxins, a suite of potent neurotoxins. Brevetoxins can reach carnivorous loggerhead and Kemp's ridley sea turtles via aerosols and marine food webs, leading to multi-system physiological effects. Sea turtles stranded during red tide can be rescued, transported to rehabilitation facilities, and given palliative care with the goal of return to the wild. However, there are no definitive diagnostic criteria for brevetoxicosis other than stranding in association with red tide. Often sea turtles experience delayed exposure due to the long temporal scale of trophic transfer of toxins. To identify exposure biomarkers and to better understand the mechanism of toxicity of brevetoxins, plasma samples from red-tide exposed and healthy loggerhead and Kemp's ridley sea turtles were analyzed via bottom-up TMT-labeled quantitative liquid chromatography tandem mass spectrometry-based proteomics. Multiple sea turtle plasma protein abundances were significantly altered in red tide exposed turtles, including several immune system proteins like serum amyloid A5 (SAA-5; loggerheads) and CD160 antigen (Kemp's ridley). Pro-inflammatory markers serum amyloid A (SAA) and myeloid-related protein 126 (MRP-126) were measured independently in plasma of loggerhead turtles, with significant increases in these markers with red tide toxin exposure. The two species also differed in their proteomic response to red tide, indicating distinct biomarker candidates. Amid intensifying red tide events and the endangered status of these species, our findings provide a foundation for biomarker-based diagnosis of brevetoxicosis in sea turtles.