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Thermal sensitivity in ectothermic organisms is often contingent upon environmental factors. Nutrient availability in particular is believed to influence the physiological responses of primary producers to global warming and is thus relevant to consider when forecasting the structure and functioning of future marine ecosystems. This study measured the effect of nutrient enrichment on the thermal sensitivity of 4 genera of Galápagos seaweeds (Ulva,Caulerpa,Padina, andOchtodes), estimated as the thermal optimum (T_opt), performance maximum (P_max), activation energy, and deactivation energy. These parameters were quantified by modeling thermal performance curves for net photosynthesis under ambient and nutrient-enriched conditions. Our findings revealed variation inT_optamong genera, ranging from 27.6° to 36.0°C. Nutrient additions enhancedT_optby ~2°C for 2 (PadinaandCaulerpa) of the 4 taxa and also significantly increasedP_maxinPadina, suggesting the ability for warming-induced ocean stratification and associated effects (i.e. decreasing nutrient availability) to reduce the capacities of these populations to maintain and support new growth. No significant differences inT_optorP_maxwere observed for eitherUlvaorOchtodeswith enrichment. Ambient net photosynthesis and respiration rates were also compared across genera;P_maxrates for net photosynthesis were consistently higher than those for respiration (i.e. until just beyondT_opt); however, photosyntheticT_optvalues were lower. Thus, this study suggests that further warming could reduce overall net primary productivity, with potentially far-reaching implications for marine food webs. 

The rise of animals across the Ediacaran–Cambrian transition marked a step-change in the history of life, from a microbially dominated world to the complex macroscopic biosphere we see today.1,2,3 While the importance of bioturbation and swimming in altering the structure and function of Earth systems is well established,4,5,6 the influence of epifaunal animals on the hydrodynamics of marine environments is not well understood. Of particular interest are the oldest “marine animal forests,”7 which comprise a diversity of sessile soft-bodied organisms dominated by the fractally branching rangeomorphs.8,9 Typified by fossil assemblages from the Ediacaran of Mistaken Point, Newfoundland,8,10,11 these ancient communities might have played a pivotal role in structuring marine environments, similar to modern ecosystems,7,12,13 but our understanding of how they impacted fluid flow in the water column is limited. Here, we use ecological modeling and computational flow simulations to explore how Ediacaran marine animal forests influenced their surrounding environment. Our results reveal how organism morphology and community structure and composition combined to impact vertical mixing of the surrounding water. We find that Mistaken Point communities were capable of generating high-mixing conditions, thereby likely promoting gas and nutrient transport within the “canopy.” This mixing could have served to enhance local-scale oxygen concentrations and redistribute resources like dissolved organic carbon. Our work suggests that Ediacaran marine animal forests may have contributed to the ventilation of the oceans over 560 million years ago, well before the Cambrian explosion of animals. 

Sponge-grade Archaeocyatha were early Cambrian biomineralizing metazoans that constructed reefs globally. Despite decades of research, many facets of archaeocyath palaeobiology remain unclear, making it difficult to reconstruct the palaeoecology of Cambrian reef ecosystems. Of specific interest is how these organisms fed; previous experimental studies have suggested that archaeocyaths functioned as passive suspension feeders relying on ambient currents to transport nutrient-rich water into their central cavities. Here, we test this hypothesis using computational fluid dynamics (CFD) simulations of digital models of select archaeocyath species. Our results demonstrate that, given a range of plausible current velocities, there was very little fluid circulation through the skeleton, suggesting obligate passive suspension feeding was unlikely. Comparing our simulation data with exhalent velocities collected from extant sponges, we infer an active suspension feeding lifestyle for archaeocyaths. The combination of active suspension feeding and biomineralization in Archaeocyatha may have facilitated the creation of modern metazoan reef ecosystems. 

Seawater microorganisms play an important role in coral reef ecosystem functioning and can be influenced by biological, chemical, and physical features of reefs. As coral reefs continue to respond to environmental changes, the reef seawater microbiome has been proposed as a conservation tool for monitoring perturbations. However, the spatial variability of reef seawater microbial communities is not well studied, limiting our ability to make generalizable inferences across reefs. In order to better understand how microorganisms are distributed at multiple spatial scales, we examined seawater microbial communities in Florida Reef Tract and US Virgin Islands reef systems using a nested sampling design. On 3 reefs per reef system, we sampled seawater at regular spatial intervals close to the benthos. We assessed the microbial community composition of these waters using ribosomal RNA gene amplicon sequencing. Our analysis revealed that reef water microbial communities varied as a function of reef system and individual reefs, but communities did not differ within reefs and were not significantly influenced by benthic composition. For the reef system and inter-reef differences, abundant microbial taxa were found to be potentially useful indicators of environmental difference due to their high prevalence and variance. We further examined reef water microbial biogeography on a global scale using a secondary analysis of 5 studies, which revealed that microbial communities were more distinct with increasing geographic distance. These results suggest that biogeography is a distinguishing feature for reef water microbiomes, and that development of monitoring criteria may necessitate regionally specific sampling and analyses. 

Ernietta plateauensis is a semi-infaunal macroscopic eukaryote of unknown affinities common in latest Ediacaran (∼548–539 Ma) shallow marine settings in Namibia. The discovery of in-situ assemblages of Ernietta has demonstrated that these organisms lived in aggregated populations, while studies employing computational fluid dynamics (CFD) modeling have supported the hypothesis that these organisms were likely behaving as gregarious suspension feeders, analogous to many extant invertebrate phyla in present-day marine environments. Careful census and measurement of individuals within these in-situ populations offers an opportunity to examine how their size and location within a larger population affect nutrient delivery dynamics. In this study, we build on previous work by simulating fluid flow over aggregations of Ernietta comprising individuals of disparate sizes, and additionally reconstruct a population of Ernietta preserved in-situ from Farm Hansburg, Namibia. We use a combination of stationary and time-dependent CFD to reconstruct nutrient carrying flow paths, and compare the efficiency with which nutrients are partitioned between individuals of different shapes and sizes. Our results demonstrate that smaller Ernietta experience limited recirculation within their cavities compared to larger individuals. Furthermore, in spatially-accurate distributions, reduced recirculation is limited to isolated individuals of any size, while smaller individuals found downstream of larger ones receive enhanced cavity mixing. These reconstructed flow patterns illustrate that the disadvantage associated with small size is apparently mediated by location within the overall aggregation, suggesting a complex interplay of controls on feeding efficiency. This in turn suggests that aggregations of adult Ernietta would likely have performed a ‘nursery’ function, creating localized conditions ideal for the settlement and growth of younger individuals. 

Pteridinium simplex is an iconic erniettomorph taxon best known from late Ediacaran successions in South Australia, Russia, and Namibia. Despite nearly 100 years of study, there remain fundamental questions surrounding the paleobiology and paleoecology of this organism, including its life position relative to the sediment–water interface, and how it fed and functioned within benthic communities. Here, we combine a redescription of specimens housed at the Senckenberg Forschungsinstitut und Naturmuseum Frankfurt with field observations of fossiliferous surfaces, to constrain the life habit of Pteridinium and gain insights into the character of benthic ecosystems shortly before the beginning of the Cambrian. We present paleontological and sedimentological evidence suggesting that Pteridinium was semi-infaunal and lived gregariously in aggregated communities, preferentially adopting an orientation with the long axis perpendicular to the prevailing current direction. Using computational fluid dynamics simulations, we demonstrate that this life habit could plausibly have led to suspended food particles settling within the organism's central cavity. This supports interpretation of Pteridinium as a macroscopic suspension feeder that functioned similarly to the coeval erniettomorph Ernietta, emblematic of a broader paleoecological shift toward benthic suspension-feeding strategies over the course of the latest Ediacaran. Finally, we discuss how this new reconstruction of Pteridinium provides information concerning its potential relationships with extant animal groups and state a case for reconstructing Pteridinium as a colonial metazoan. 

ABSTRACT Stony coral tissue loss disease (SCTLD) is decimating Caribbean corals. Here, through the metatranscriptomic assembly and annotation of two alphaflexivirus-like strains, we provide genomic evidence of filamentous viruses in SCTLD-affected, -exposed, and -unexposed coral colonies. These data will assist in clarifying the roles of viruses in SCTLD. 

Abstract The Ediacara biota are an enigmatic group of Neoproterozoic soft‐bodied fossils that mark the first major radiation of complex eukaryotic and macroscopic life. These fossils are thought to have been preserved via pyritic “death masks” mediated by seafloor microbial mats, though little about the chemical constraints of this preservational pathway is known, in particular surrounding the role of bioavailable iron in death mask formation and preservational fidelity. In this study, we perform decay experiments on both diploblastic and triploblastic animals under a range of simulated sedimentary iron concentrations, in order to characterize the role of iron in the preservation of Ediacaran organisms. After 28 days of decay, we demonstrate the first convincing “death masks” produced under experimental laboratory conditions composed of iron sulfide and probable oxide veneers. Moreover, our results demonstrate that the abundance of iron in experiments is not the sole control on death mask formation, but also tissue histology and the availability of nucleation sites. This illustrates that Ediacaran preservation via microbial death masks need not be a “perfect storm” of paleoenvironmental porewater and sediment chemistry, but instead can occur under a range of conditions. 

Stony coral tissue loss disease (SCTLD) was first observed in St. Thomas, U.S. Virgin Islands (USVI) in January 2019. This disease affects at least 20 scleractinian coral species; however, it is not well understood how reef diversity affects its spread or its impacts on reef ecosystems. With a large number of susceptible species, SCTLD may not follow the diversity-disease hypothesis, which proposes that high species diversity is negatively correlated with disease prevalence. Instead, SCTLD may have a higher prevalence and a greater impact on reefs with higher coral diversity. To test this, in 2020 we resampled 54 sites around St. Thomas previously surveyed in 2017 or 2019 by the National Oceanic and Atmospheric Administration National Coral Reef Monitoring Program. These sites represented a variety of species diversity values [categorized into poor (<12 spp. rich.) and rich (12 spp. rich.)] in multiple disease zones (Endemic: disease present  9 months; Epidemic: disease present 2–6 months; Control and Emergent: disease present no disease/<2 months). We hypothesized that, contrary to the diversity-disease hypothesis, sites with high species diversity (as measured by species richness or Simpson’s index) would have higher disease prevalence within the epidemic zone, and that high species diversity sites would have a greater impact from disease within the endemic zone. Results indicated a significant positive relationship between disease prevalence and diversity in the epidemic zone, and a similar trend in the endemic zones. Additionally, a negative relationship was seen between pre-outbreak diversity and loss of diversity and coral cover within the endemic zone. This supports the hypothesis that higher diversity predicts greater disease impact and suggests that SCTLD does not follow the diversity-disease hypothesis. Within the epidemic zone, the species with the highest SCTLD prevalence were Dendrogyra cylindrus, Colpophyllia natans, and Meandrina meandrites, while in the endemic zone, Diploria labyrinthiformis, Pseudodiploria strigosa, Montastraea cavernosa, and Siderastrea siderea had the highest SCTLD prevalence. Understanding the relationship between species diversity and SCTLD will help managers predict the most vulnerable reefs, which should be prioritized within the USVI and greater Caribbean region.