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Infectious disease can shape community structure, particularly when pathogens affect foundation species. Seagrasses are foundation species that form meadows along coasts worldwide, controlling sediment deposition and biogeochemical cycling while supporting a diverse community of fish and invertebrates. These plants are hosts to wasting diseases that cause necrotic tissue lesions, which could alter seagrass value as food, habitat and mediators of ecosystem processes. However, such biotic interactions and influences on disease dynamics are still not well understood. We investigated whether a common herbivore affected the development of wasting disease on eelgrass. We measured the severity and prevalence of eelgrass wasting disease in a meadow across two summers through repeated field surveys. We assessed the role of the eelgrass herbivore on disease spread and growth using microcosm and mesocosm experiments. We further explored herbivore feeding preferences in a choice trial, which was paired with chemical analysis of plant tissue and analysed using a structural equation model. While the herbivore facilitates the growth of new disease lesions among isolated leaves, on balance they reduce lesion severity by more than 50% in comparison with no-herbivore controls in field-realistic settings. This was likely because the herbivore strongly prefers to eat diseased rather than healthy tissue, consuming nearly twice as much lesion area in choice trials. This preference arises from pathogen-driven changes in the host plant; lesioned tissue requires less force to penetrate than non-lesioned tissue. Additionally, as lesions increase in size, their polyphenolic concentrations drop, which further increases the magnitude of preference for lesioned tissue. Synthesis: These results suggest that these herbivores could help maintain disease in this system at a high prevalence (by facilitating disease development) but low severity (through preferential consumption), which is consistent with our field observations of nearly 100% prevalence and low severity in a natural bed where herbivore density is high. Describing such multi-species interactions in marine systems will advance our predictions of future disease states, as current understandings focus primarily on how environmental change contributes to pathogen outbreaks.

Malaysia hosts some of the most productive blue carbon ecosystems globally. Here we review the status of and known threats faced by local mangroves and seagrass and examine conservation prospects using carbon financing. Based on lessons learnt from blue carbon projects worldwide, Malaysia needs to address governance and financing hurdles that include clarifying land tenureship, ensuring local community involvement and benefits, and obtaining sustainable financing for long-term success. Research to clarify uncertainties on extent of seagrass and trajectories of both seagrass and mangrove ecosystems is needed to determine baseline scenarios and demonstrate additionality in carbon projects. Clear, definitive national approach to blue carbon is essential to streamline accounting and inventory of carbon stocks and benefits. Addressing these barriers and gaps requires a whole of society approach and public-private partnerships and ultimately allow Malaysia to fully tap into the global voluntary carbon market, local businesses, philanthropy, and multilateral carbon financing. [ABSTRACT FROM AUTHOR]

Tracking symptoms of eutrophication over time with multiple lines of evidence provides critical information to support environmental management and restoration efforts. For this case study of the Greater Charlotte Harbor estuary system in southwest Florida (USA), we assembled and curated 22 years of monthly water quality data from a spatially stratified random sampling design; estimated trends in annual mean concentrations of nitrogen, phosphorus, and chlorophyll-a across 13 monitoring strata over a sliding 5-year window between 2000 and 2021; identified hot spots where annual mean concentrations were increasing or elevated between 2017 and 2021, relative to stratum-specific thresholds informed by regulatory criteria; and summarized concurrent data from long-term surveys of macroalgal abundance and seagrass acreage. The water quality trend analysis methodology, based on generalized additive models (GAMs), captured seasonality and nonlinear inter-annual tendencies while accounting for uncertainty. Throughout the system, concentrations of total nitrogen increased and exceeded stratum-specific thresholds during the 2010 decade, while concentrations of total phosphorus and chlorophyll-a typically decreased to levels near or below thresholds. Low concentrations of inorganic nitrogen fractions indicated rapid biological assimilation consistent with eutrophication, while low chlorophyll-a concentrations indicated that nitrogen enrichment did not translate into excessive phytoplankton production. Instead, macroalgal proliferation and substantial seagrass losses were observed following Hurricane Irma (September 2017). We speculate that nitrogen enrichment during the 2010s increased the system’s vulnerability to Irma’s effects and helped tip the system toward these profound ecological changes. This work provides a broadly applicable framework for documenting and evaluating symptoms of eutrophication in estuaries. [ABSTRACT FROM AUTHOR]

Understanding the long-term effects of elevated temperatures on foundational species like seagrasses is critical for predicting and managing the impacts of warming coastal ecosystems worldwide. Seagrasses exhibit plasticity in response to a range of environmental stressors, so the effects of climate change are likely to be context dependent. This study investigated differences in the growth and morphology of Zostera muelleri inside versus outside a warm water plume generated by a power station operating for ~ 26 years in Lake Macquarie, New South Wales, Australia. The effects of other factors, including sediment organic matter, season and seagrass density were also examined to ascertain their importance relative to elevated temperatures. Despite water temperatures in the thermal plume being equivalent to conditions predicted by 2090 under future climate scenarios (1.5–2.7 °C above ambient), there were no consistent effects of these elevated temperatures on Z. muelleri growth and morphology. Instead, growth at all sites (ambient and warm water) was greater by 40.3% in spring and 74.3% in summer when compared to winter. Increasing organic matter content in sediments was associated with a 69.8% rise in below-ground biomass and a subsequent 73.8% reduction in the ratio of above- to below-ground biomass. There was also evidence for seagrass density effects, with denser meadows having shorter leaves and reduced growth rates, likely due to self-shading. Overall, these findings demonstrate that Z. muelleri in the centre of its distribution in eastern Australia can tolerate moderate temperature increases over decadal scales. [ABSTRACT FROM AUTHOR]

Biogenic habitats, including eelgrass, support productive and diverse species assemblages in spatially heterogeneous seascapes. Eelgrass-associated faunal diversity depends not only on conditions within each eelgrass meadow but also on their probability of dispersing among eelgrass meadows in a seascape in which meadows are separated by soft sediments, kelp, or rocky habitats. Experiments are required to establish dispersal limitation in communities. Here, we experimentally tested the hypothesis that dispersal limitation and edge effects influence local faunal diversity in eelgrass meadows. We manipulated habitat spacing and exposure of standardized substrate and quantified invertebrate colonization. We predicted that species richness of invertebrates would decline with increasing distance from the meadow edge and that mobility traits would covary with species’ responses to distance. We also predicted that eelgrass edges would harbor communities distinct from the interior of the meadow and that these differences would covary with species’ trophic traits. We found that species richness decreased by 0.3 species per meter from the meadow edge, and this pattern was not explained by reduced abundance or filtering of species based on traits, consistent with dispersal limitation of diversity. Edges did not affect total community richness or abundance, and the only trait that varied with meadow position was average body size, which was larger within the meadow interior. These results indicate that even short-distance dispersal limitation can structure the eelgrass invertebrate community but that communities of similar richness, trait profiles, and abundance will colonize all available habitat in the absence of dispersal barriers. [ABSTRACT FROM AUTHOR]

The wave attenuation properties of seagrasses are key to accurately predict how effective these plants are at protecting coasts from erosion and floods. While recent studies have significantly advanced the understanding of seagrass wave attenuation in pure-wave conditions, the presence of a current introduces several complications that have yet to be fully explored. In the present study, we quantify the wave attenuation of seagrass canopies in the presence of a current parallel to the direction of wave propagation via experiments conducted with dynamically scaled mimics of seagrass installed in a laboratory flume facility. The dataset we present is the largest of its kind and spans a broad range of wave properties, current velocities, water depths, and plant densities for a total of over 300 experiments. Using our experimental results, we show that the commonly employed approach of modeling wave attenuation as a result of vegetation drag works well for a range of conditions but underpredicts systematically when turbulence generated by the interaction between the seagrass canopy and the current is sufficiently strong. We then employ phenomenological arguments and experimental data to identify a nondimensional parameter that effectively quantifies the relative importance of turbulence and drag in dictating the overall observed wave attenuation. Moreover, we propose a simple but physically based modeling approach that is consistent with the proposed phenomenology and can be used for applications in coastal waters. [ABSTRACT FROM AUTHOR]

Though there is mounting evidence that climate warming is altering trophic interactions between organisms, its effects on non-trophic interactions remain relatively undocumented. In seagrass systems, the bioturbating activity of infauna influences annual seagrass patch development by influencing seed burial depth and germination success as well as sediment properties. If bioturbation is altered by warming, consequences on seagrass may result. Here, we assessed how heatwaves alter seagrass seed burial depth and germination rates when no bioturbators (control), single bioturbators and mixtures of bioturbators of contrasting feeding activities are present. The three bioturbators manipulated were surface (top 1-2 cm of sediment) biodiffusor, the brown shrimp (Crangon crangon), the shallow (top 3–8 cm) diffusor, the common cockle, (Cerastoderma edule) and the upward (5–15 cm) conveyor, the polychaete, Cappitellidae spp. We applied two temperature treatments: (1) a present-day scenario set at the average summer temperature of seagrass habitat (17ºC); and (2) a heatwave scenario modelled on the maximum recorded temperature (26.6ºC). Under present-day conditions, seed burial was greater in the presence of bioturbators than the control where no infauna was added (42–74% vs. 33 ± 7%, respectively). Cockles had the greatest impact on seed burial amongst all the bioturbators. Under the heatwave scenario, seed burial in the mixed bioturbator treatment increased to match that of the cockle treatment. Cockles and polychaetes elevated the germination rates of buried seeds under present-day temperature, but not under the heatwave scenario. Overall, these results indicate that heatwaves have the potential both to amplify and disrupt non-trophic interactions, with implications for seagrass seed germination. [ABSTRACT FROM AUTHOR]

Seagrasses are globally threatened due to increasing environmental stressors in coastal ecosystems. Excessive accumulation of algal epiphytes is suggested to be harmful to seagrasses, but an understanding of the dynamics of epiphyte accumulation relative to host leaf growth and senescence is still limited, owing to poor spatiotemporal resolution of biomass measures. This study developed and validated color scanning and image analysis methods to characterize epiphyte accumulation relative to Thalassia testudinum seagrass host morphology. Spectral Angle Mapper (SAM) algorithms within the ENVI Program distinguished the pixels of many epiphytes collectively from epiphyte-free leaf areas based on each pixel's spectral vector, derived from Red, Green, and Blue color channels (RGB). Classification accuracy was evaluated by the misclassified pixels and the correlation of biomass and morphology metrics vs. image-based metrics for more than 2,000 seagrass and epiphyte images. Many variations of four major color groups of epiphytes on the seagrass surface were identified. Misclassified pixels were < 10% in 94% of the analyzed images. Image-derived seagrass metrics strongly correlated with seagrass biomass and leaf area. Linear regressions of epiphyte biomass vs. epiphyte area (pixels), and of biomass ratio of epiphyte to seagrass vs. epiphyte coverage (epiphyte pixels/leaf pixels), were only moderate and suggestive of environmental influences. The robust validation result indicated that this image analysis method can provide insight into the spatiotemporal accumulation of epiphytes on the seagrass host and has the potential to be adapted to detect environmentally-induced changes in the community composition of epibiota. [ABSTRACT FROM AUTHOR]

Context: Ruppia thickets and their impact on zooplankton in a hypersaline shallow lake. Aims: To investigate the long-term dynamics of seagrass Ruppia , zooplankton and abiotic parameters and evaluate the relationships among them in Lake Moynaki. Methods: Quantitative assessment of Ruppia thickets, zooplankton within them and outside, temperature, salinity, wind speed and direction from 2019 to 2023. Key results: The first young Ruppia shoots appeared in the lake during March, and their number and biomass increased, most rapidly during spring. From 2019 to 2023, the average spring number of Ruppia shoots gradually increased exponentially. From 2019 to 2023, there was a gradual decrease in the average spring abundance of zooplankton within the Ruppia meadows. A significant positive relationship was noted between the Gammarus aequicauda abundance and the number of Ruppia shoots in all years, but there was a negative relationship for Moina salina and Cletocamptus retrogressus with Ruppia. Conclusions: This study presents the largely neglected effect of seagrass on zooplankton in small hypersaline water bodies. Implications: This information is valuable for the management of hypersaline water bodies and the development of sustainable polyaquaculture in them. Hypersaline waters are some of the most extreme habitats but have high productivity, and the potential to support bird diversity as well as develop multi-species aquaculture. We provide new information on interactions between seagrass Ruppia and zooplankton in those waters, which gives a better understanding of unique ecosystems and is valuable for the management of hypersaline water bodies and the development of sustainable polyaquaculture in them. (Photographs by N. Shadrin.) [ABSTRACT FROM AUTHOR]

Background: Zostera marina is an important ecosystem engineer influencing shallow water environments and possibly shaping the microbiota in surrounding sediments and water. Z. marina is typically found in marine systems, but it can also proliferate under brackish conditions. Changes in salinity generally have a strong impact on the biota, especially at the salty divide between salinity 6 and 9. To better understand the impact of the salty divide on the interaction between Z. marina and the surrounding sediment and water microbiota, we investigated the effects of Z. marina meadows on the surrounding microbiota across a salinity range of 6–15 in the Baltic Sea during the summer using 16S and 18S rRNA gene amplicon sequencing. Results: Salinity was the most important factor for structuring the microbiota within both water and sediment. The presence of Z. marina affected the composition of the bacterial and eukaryotic community and bacterial alpha diversity in the sediment. However, this effect was confined to alpha-mesohaline conditions (salinity 9–15). The impact of Z. marina below salinity 9 on water and sediment microbiota was insignificant. Conclusions: Increasing salinity was associated with a longer leaf length of Z. marina, causing an increased canopy height, which affects the sediment microbiota through reduced water velocity. Hence, we propose that the canopy effect may be the major predictor explaining Z. marina's interactions with the surrounding microbiota at salinity 9–15. These findings emphasize the importance of the physical effects of Z. marina meadow ecosystem services and have important implications for Z. marina management under brackish conditions in a changing climate. [ABSTRACT FROM AUTHOR]