Evidence of microplastics from benthic jellyfish (Cassiopea xamachana) in Florida estuaries.

Plastic pollution is a concern in many nearshore ecosystems, and it is critical to understand how microplastics (plastics <5 mm in length) affect nearshore marine biota. Here, we report the presence of microplastics in the benthic, upside-down jellyfish (Cassiopea xamachana) across three estuaries in south Florida. Microplastics were recovered from Cassiopea using an acid digestion, then enumerated via microscopy, and identified using micro Fourier-transform interferometer (µFTIR) analysis. Out of 115 specimens analyzed, 77% contained microplastics. Bell diameter and number of plastics per individual varied significantly across locations with the highest plastic densities and bell diameter observed in individuals from Big Pine Key, followed by Jupiter, and Sarasota. µFTIR analysis confirmed that synthetic microfibers were the dominant microplastic measured at all three locations and may indicate Cassiopea as potential sinks of microplastic. Cassiopea may be used as bioindicators of microplastic contamination in the future, allowing for potential plastic pollution mitigation.

Effects of chronic pesticide exposure on an epibenthic oyster reef community.

In recent decades, oyster reefs have been deteriorating throughout North America as a result of multiple interacting anthropogenic stressors, including pesticide pollution. Here we elucidated the potential chronic effects of the commonly utilized pesticide, carbaryl, on oyster reef communities in the Loxahatchee River Estuary in southeast Florida. Though carbaryl had a limited effect on total epifaunal community diversity, species richness and evenness, the results of this experiment indicate that carbaryl significantly shifted crustacean community composition, resulting in a substantial loss in total crustacean abundance. One crustacean in particular, Americorophium spp. (tube building amphipod), was significantly less abundant within the carbaryl treatment, driving the shift in crustacean community composition. Ultimately, our results signal that pesticide pollution in estuaries will negatively impact crustaceans. Over time, this may shift benthic community composition, potentially disrupting species interactions and threatening valuable economic and ecosystem services.

Does landscape context mediate the nature of density dependence for a coral reef fish?

Over-harvest and landscape change are two of the greatest threats to marine ecosystems. Over-harvest may directly affect key population regulation mechanisms (e.g., density dependence), with the magnitude of the effects being further influenced by changes in landscape structure and associated resource availability. Because resource availability and conspecific density often co-vary within the natural landscape, manipulative experiments are needed to understand how changes in these two drivers may affect density dependence in wild populations. We used a common, shoaling, coral reef fish (white grunt, Haemulon plumierii) as our model species, and manipulated fish densities and landscape context of artificial reef habitats to assess the effects of each on fish condition. We found evidence of inverse density dependence, where individual condition was positively related to conspecific density; landscape context had little effect. Mean grunt condition on natural patch reefs was similar to that for our low grunt density treatment artificial reefs, possibly due to differences in fish densities or landscape context. These findings suggest that over-harvest may have detrimental effects on wild populations that extend beyond mere reductions in population size, especially for group-living species.

Thresholds of ecosystem response to nutrient enrichment from fish aggregations.

Biogeochemical hotspots can be driven by aggregations of animals, via excretion, that provide a concentrated source of limiting nutrients for primary producers. In a subtropical seagrass ecosystem, we characterized thresholds of ecological change associated with such hotspots surrounding artificial reef habitats. We deployed reefs of three sizes to aggregate fishes at different densities (and thus different levels of nutrient supply via excretion) and examined seagrass characteristics that reflect ecosystem processes. Responses varied as a function of reef size, with higher fish densities (on larger reefs) associated with more distinct ecological thresholds. For example, adjacent to larger reefs, the percentage of P content (%P) of seagrass (Thalassia testudinum) blades was significantly higher than background concentrations; fish densities on smaller reefs were insufficient to support sharp transitions in %P. Blade height was the only variable characterized by thresholds adjacent to smaller reefs, but lower fish densities (and hence, nutrient input) on smaller reefs were not sufficient for luxury nutrient storage by seagrass. Identifying such complexities in ecological thresholds is crucial for characterizing the extent to which biogeochemical hotspots may influence ecosystem function at a landscape scale.

Effects of anthropogenic disturbance on the abundance and size of epibenthic jellyfish Cassiopea spp.

Jellyfish blooms in pelagic systems appear to be increasing on a global scale because of anthropogenic impacts, but much less is known about the link between human activities and epibenthic jellyfish abundance. The aim of this study was to investigate whether the epibenthic jellyfish, Cassiopea spp., were found in greater abundance, and attained larger sizes, in coastal habitats adjacent to high human population densities compared to sites adjacent to uninhabited areas on Abaco Island, Bahamas. Cassiopea spp. were found to be significantly more dense and larger in areas with high human population densities. Ambient nutrient levels and nutrient content of seagrass were elevated in high human population density sites, and may be one mechanism driving higher abundance and size of Cassiopea spp. Cassiopea spp. may have important effects on community structure and ecosystem function in critical coastal ecosystems (e.g., seagrass beds), and their impacts warrant further study.