Examining the dynamic nature of epiphytic microalgae in the Florida Keys: What factors influence community composition?

The factors that influence the composition of marine epiphytic microalgal assemblages are poorly-understood. To address this short-coming, 93 samples were collected from four distinct regions in the Florida Keys National Marine Sanctuary (FKNMS) during winter and summer months to test the model that epiphytic microalgal communities are influenced by environmental gradients related to different sites, seasons, and host macrophyte species. One hundred and eighty-three morphotypes from 13 classes (7 phyla) were identified, dominated by 106 Bacillariophyta (77 identified to species equivalent or below), 37 Cyanophyta (13 identified to species equivalent or below), and 30 Dinophyta (21 identified to species equivalent or below). The largest proportion of variability in epiphytic communities was related to physico-chemical parameters (37%), followed by site location (ocean-versus bayside; 15%), seasonal differences (11%), and host macrophyte species (10%). Four physico-chemical variables were found to be most influential: wave height, temperature, ammonium concentration, and salinity. Only six out of 616 epiphyte - host comparisons exhibited significant differences in individual epiphyte taxon abundance between different host species (within site and season), further demonstrating that host-specificity was not strongly evident in this study. Overall, the results of this (sub)tropical study indicate that changing environmental characteristics between sites and seasons were the primary drivers influencing epiphyte community composition. Similar findings were found in an accompanying study of phytoplankton and other studies from temperate and (sub)polar regions, suggesting that common, underlying processes exist among these disparate environments.

Microphytobenthos spatio-temporal dynamics across an intertidal gradient using Random Forest classification and Sentinel-2 imagery.

Microphytobenthos (MPB) provides important ecosystem functions and services, contributing significantly to the total primary production in shallow coastal ecosystems. However, determining the factors that regulate the seasonal changes of MPB and its distribution patterns at larger scales is hindered by the considerable spatial and temporal variability in these environments. Here, we studied the dynamics of intertidal MPB biomass, cover, and net growth rates in a south European tidal flat (Cadiz Bay, Spain) over a four-year period using the Normalized Difference Vegetation Index (NDVI) calculated from Sentinel-2 satellite images. Pixels dominated by different benthic communities (MPB, Zostera sp., Caulerpa sp. and green macroalgae) were identified at a 10-m resolution using a Random Forest (RF) machine learning classification algorithm. MPB dominated the intertidal zone. MPB cover did not show a clear seasonal pattern and was clearly higher in the middle of the intertidal range of sea level. Despite interannual variability, MPB biomass was always higher during winter, coinciding with observations from other low latitude intertidal flats with temperate climate, and in the upper-middle intertidal. Net rates of MPB biomass change, calculated from the differences in MPB NDVI over time, showed maximal net growth rates from autumn to winter and maximum loss rates during spring and summer, although with high variability. Our study demonstrates that RF algorithms allow mapping MPB and other intertidal communities from Sentinel-2 multispectral satellite imagery accurately obtaining invaluable information from large areas at very high spatio-temporal resolution. The dissimilarities observed in the patterns of MPB variables over time or sea level, indicate differences in their ecological regulation, still largely unknown both here and in other temperate climate intertidal flats. High resolution remote sensing can aid in their detailed and systematic study producing a more integrated view of these systems and contributing to their science-based management and conservation.

Stranding events of drift organisms (Arribadas) in southern Brazil and the spread of invasive bryozoan in South America.

The accumulation of drift organisms (Arribadas, constituted by benthic microalgae, macroalgae and bryozoans) on Central Beach in Balneário Camboriú (SC) has drawn attention since the early 2000s. However, historical surveys suggest an ancient phenomenon that has been increasing in intensity, promoted by urbanization and the eutrophication of the bay in recent years, leading to changes in the taxonomic composition. Previously, these Arribadas were comprised of two species of benthic microalgae (Amphitetras antediluviana and Biddulphia biddulphiana) and the bryozoan Arbocuspis ramosa. However, since 2019, a substantial increase in biomass has been observed on the beach and the dominance of the macroalgae Bryopsis plumosa strongly suggests an increase in the load of organic matter and nutrients in the bay. Recently (2022) the presence of a new invasive bryozoan species (Amathia alternata) was detected, highlighting the need to continue investigating the Arribadas to monitor the ecological evolution of this process.

Temporal and spatial distribution of epibenthic dinoflagellates in the Kattegat-Skagerrak, NE Atlantic-Focus on Prorocentrum lima and Coolia monotis.

Epibenthic dinoflagellates occur globally and include many toxin-producing species of concern to human health and benthic ecosystem function. Such benthic harmful algal blooms (BHABs) have been well described from tropical and sub-tropical coastal environments, but assessments from north temperate waters, e.g., northern Europe, and polar regions are scarce. The present study addressed the biodiversity and distribution of potentially toxic epibenthic dinoflagellate populations along the west coast of Sweden (Kattegat-Skagerrak) by morphological and molecular criteria. Morphological analysis conducted by light- and electron-microscopy was then linked by DNA barcoding of the V4 region of 18S rRNA gene sequences to interpret taxonomic and phylogenetic relationships. The presence of two potentially toxigenic epibenthic dinoflagellates, Prorocentrum lima (Ehrenberg) F.Stein and Coolia monotis Meunier was confirmed, along with a description of their spatial and temporal distribution. For P. lima, one third of the cell abundance values exceeded official alarm thresholds for potentially toxic BHAB events (>1000 cells gr-1 of macroalgae fresh weight). The same species were recorded consecutively for two summers, but without significant temporal variation in cell densities. SEM analyses confirmed the presence of other benthic Prorocentrum species: P. fukuyoi complex, P. cf. foraminosum and P. cf. hoffmannianum. Analyses of the V4 region of the 18S rRNA gene also indicated the presence P. compressum, P. hoffmannianum, P. foraminosum, P. fukuyoi, and P. nanum. These findings provide the first biogeographical evidence of toxigenic benthic dinoflagellates along the west coast of Sweden, in the absence of ongoing monitoring to include epibenthic dinoflagellates. Harmful events due to the presence of Coolia at shellfish aquaculture sites along the Kattegat-Skagerrak are likely to be rather marginal because C. monotis is not known to be toxigenic. In any case, as a preliminary assessment, the results highlight the risk of diarrhetic shellfish poisoning (DSP) events caused by P. lima, which may affect the development and sustainability of shellfish aquaculture in the region.

Heteroaggregates of Polystyrene Nanospheres and Organic Matter: Preparation, Characterization and Evaluation of Their Toxicity to Algae in Environmentally Relevant Conditions.

The environmental fate and behavior of nanoplastics (NPs) and their toxicity against aquatic organisms are under current investigation. In this work, relevant physicochemical characterizations were provided to analyze the ecotoxicological risk of NPs in the aquatic compartment. For this purpose, heteroaggregates of 50 nm polystyrene nanospheres and natural organic matter were prepared and characterized. The kinetic of aggregation was assimilated to a reaction-limited colloid aggregation mode and led to the formation of heteroaggregates in the range of 100-500 nm. Toxicities of these heteroaggregates and polystyrene nanospheres (50 and 350 nm) were assessed for a large range of concentrations using four benthic and one planktonic algal species, in regards to particle states in the media. Heteroaggregates and nanospheres were shown to be stable in the exposure media during the ecotoxity tests. The algal species exhibited very low sensitivity (growth and photosynthetic activity), with the noteworthy exception of the planktonic alga, whose growth increased by more than 150% with the heteroaggregates at 1 µg L-1. Despite the lack of a strong direct effect of the NPs, they may still impair the functioning of aquatic ecosystems by destabilizing the competitive interactions between species. Moreover, further work should assess the toxicity of NPs associated with other substances (adsorbed pollutants or additives) that could enhance the NP effects.

Succession pattern and phylotype analysis of microphytobenthic communities in a simulated oil spill seagrass mesocosm experiment.

Microphytobenthic communities play a significant role in nutrient modulation, sediment stabilization, and primary production in seagrass beds, which provide various ecosystem services. We hypothesized that microphytobenthic communities in sediments of chronically oil-exposed seagrass beds will exhibit increased resiliency to stressors associated with oil exposure as opposed to seagrass beds never exposed to oil spills. We prepared 14-liter seawater mesocosms, each containing a submersed macrophyte Ruppia maritima collected from the Chandeleur Islands, Louisiana, and Estero Bay, Florida. Mesocosms were initially exposed to 50% water-accommodated oil fractions (WAF) and subsequently diluted by 50% with daily artificial seawater exchanges over 8 days to simulate tidal dilution. High-throughput amplicon sequencing based on 23S rRNA gene targeting cyanobacteria and chloroplasts of eukaryotic microphytobenthos was conducted to assess the impact of oiling on microphytobenthic communities with additional assessment via microscopy. High-throughput sequencing in combination with traditional microscopic analysis provided a robust examination in which both methods roughly complemented each other. Distinct succession patterns were detected in benthic algal communities of chronically oil-exposed (Louisiana) versus unexposed (Florida) seagrass bed sediments. The impact of oiling in microphytobenthos across all samples showed that benthic diatoms dominated all algal communities with sample percentages ranging from 42 to 97%, followed by cyanobacteria (2 to 50%). It is noteworthy that drastic changes in microphytobenthic community structure in terms of the larger taxonomic level were not observed, rather change occurred at the phylotype level. These results were also confirmed by microscopy. Similarity percentages (SIMPER) analysis identified seven phylotypes (Cyanobacteria, Bacillariophyceae, and Mediophyceae) in the Louisiana samples and one phylotype (Bacillariophyceae) in the Florida samples that increased in relative sequence abundance after oil exposure. The detailed phylotype analysis identifying sentinel microphytobenthic indicators provides a base for future research on benthic microalgae response to ecosystem disturbance.

Hydrological connectivity and herbivores control the autochthonous producers of coastal salt marshes.

Sea-level rise and overfishing could enhance the strength of hydrological connectivity and the presence of herbivores, resulting in salt marsh loss through physical stress and trophic cascade effects. Our aim was to estimate the effects of these two stresses on autochthonous producers. Survivorship and biomass of Suaeda salsa (S. salsa) were the lowest in areas with high hydrological connectivity, whereas the highest biomass was observed in the areas with moderate connectivity. The biomass of benthic microalgae was higher under low hydrological connectivity and no herbivores. The interactive effects between hydrological connectivity and herbivores on S. salsa but not on benthic microalgae were observed. Herbivores were somewhat (28%) important for the survival of initial S. salsa seedlings, while hydrological connectivity controlled (50%) the biomass of benthic microalgae. Our study highlights that, the autochthonous producers in coastal salt marshes may disappear due to strong hydrological connectivity and the excessive presence of herbivores.

Diversity and Toxicity of the Genus Coolia Meunier in Brazil, and Detection of 44-Methyl Gambierone in Coolia tropicalis.

Coolia is a genus of marine benthic dinoflagellates which is widely distributed in tropical and temperate zones. Toxicity has been reported in selected Coolia species, although the identity of causative compounds is still controversial. In this study, we investigated the taxonomical and toxicological aspects of Coolia species from Brazil. Since light- and electron microscopy-based morphology was not enough to distinguish small-celled species, ITS and LSU D1-D3 phylogenetic analyses were used for species definition. Cultures of Coolia palmyrensis and Coolia santacroce were established from samples collected along the northeastern Brazilian coast, the first record of both species in South Atlantic waters. Cultures of Coolia malayensis and Coolia tropicalis were also established and exhibited acute in vivo toxicity to adults of Artemia salina, while C. palmyrensis and C. santacroce were non-toxic. The presence of 30 yessotoxin analogues, 7 metabolites of Coolia and 44 Gambierdiscus metabolites was screened in 14 strains of Coolia. 44-methyl gambierone (formerly referred to as MTX3) and a new isomer of this compound were detected only in C. tropicalis, using both low- and high-resolution LC-MS/MS. To our knowledge, this is the first report of gambierone analogues in dinoflagellates other than Gambierdiscus; the role of C. tropicalis in ciguatera poisoning thus deserves to be considered in further investigations.

Spatiotemporal variability in microphytobenthic primary production across bare intertidal flat, saltmarsh, and mangrove forest of Asia and Australia.

The ecological role of intertidal microphytobenthos (MPB) is increasingly recognized in coastal production systems. MPB primary production (PP) measured in coastal wetlands of Korea, Cambodia, and Australia confirmed large variability at the global scale. Surprisingly, MPB biomass in mangrove forests almost doubled those measured in nearby bare tidal flats. However, MPB productivity (Pb) in vegetated habitats was significantly reduced (by ~50%) compared to that on bare tidal flats. Extensive measurements of MPB biomass, PP, and Pb across 12 Korean tidal flats revealed large spatiotemporal variations, suggesting complex sediment-MPB coupled dynamics. The key factors included sediment type, tide, bed elevation, irradiation, temperature, and vegetation. Winter MPB blooms and the elevated Pb seem to be unique characteristics of the Korean intertidal flats. The present study provides the baseline data of MPB PPs in mudflat, saltmarsh, and mangrove habitats in the highly productive zones of the Western Indo-Pacific Rim.

Ostreopsis cf. ovata Bloom in Currais, Brazil: Phylogeny, Toxin Profile and Contamination of Mussels and Marine Plastic Litter.

Ostreopsis cf. ovata is a toxic marine benthic dinoflagellate responsible for harmful blooms affecting ecosystem and human health, mostly in the Mediterranean Sea. In this study we report the occurrence of a summer O. cf. ovata bloom in Currais, a coastal archipelago located on the subtropical Brazilian coast (~25° S). This bloom was very similar to Mediterranean episodes in many aspects: (a) field-sampled and cultivated O. cf. ovata cells aligned phylogenetically (ITS and LSU regions) along with Mediterranean strains; (b) the bloom occurred at increasing temperature and irradiance, and decreasing wind speed; (c) cell densities reached up to 8.0 × 104 cell cm-2 on fiberglass screen and 5.6 × 105 cell g-1 fresh weight on seaweeds; (d) and toxin profiles were composed mostly of ovatoxin-a (58%) and ovatoxin-b (32%), up to 35.5 pg PLTX-eq. cell-1 in total. Mussels were contaminated during the bloom with unsafe toxin levels (up to 131 µg PLTX-eq. kg-1). Ostreopsis cells attached to different plastic litter, indicating an alternate route for toxin transfer to marine fauna via ingestion of biofilm-coated plastic debris.