Optimising Seagrass Conservation for Ecological Functions

Stress responses of the seagrass Cymodocea nodosa to environmentally relevant concentrations of pharmaceutical ibuprofen: Ecological implications

Pharmaceuticals like ibuprofen (IBU) entering marine environments are of great concern due to their increasing consumption and impact on wildlife. No information on IBU toxicity to seagrasses is yet available. Seagrasses form key habitats and are threatened worldwide by multiple stressors. Here, the responses of the seagrass Cymodocea nodosa to a short-term exposure (12 days) to environmentally realistic IBU concentrations (0.25-2.5-25 µg L-1), both at organism (plant growth) and sub-organism level (oxidative status, photosynthetic efficiency, and specialized metabolites production), were assessed in mesocosm. Chemical analyses to detect the presence of IBU and its metabolites in seawater and plants were also performed. IBU did not affect plant growth but caused physiological alterations which varied in severity depending on its concentration. Concentrations of 0.25 and 2.5 µg L-1 resulted in oxidative stress, but an increased antioxidant enzyme activity enabled plants to tolerate stress. A concentration of 25 µg L-1 caused greater oxidative stress, reduced antioxidant enzyme activity and specialized metabolites production, and impaired photosynthetic machinery functioning (particularly PSII). IBU was detected in seawater but not in plants suggesting no bioaccumulation. These findings indicate that C. nodosa could not withstand high IBU stress, and this could reduce its resilience to additional environmental stressors.

Tiger sharks support the characterization of the world's largest seagrass ecosystem

Seagrass conservation is critical for mitigating climate change due to the large stocks of carbon they sequester in the seafloor. However, effective conservation and its potential to provide nature-based solutions to climate change is hindered by major uncertainties regarding seagrass extent and distribution. Here, we describe the characterization of the world's largest seagrass ecosystem, located in The Bahamas. We integrate existing spatial estimates with an updated empirical remote sensing product and perform extensive ground-truthing of seafloor with 2,542 diver surveys across remote sensing tiles. We also leverage seafloor assessments and movement data obtained from instrument-equipped tiger sharks, which have strong fidelity to seagrass ecosystems, to augment and further validate predictions. We report a consensus area of at least 66,000 km2 and up to 92,000 km2 of seagrass habitat across The Bahamas Banks. Sediment core analysis of stored organic carbon further confirmed the global relevance of the blue carbon stock in this ecosystem. Data from tiger sharks proved important in supporting mapping and ground-truthing remote sensing estimates. This work provides evidence of major knowledge gaps in the ocean ecosystem, the benefits in partnering with marine animals to address these gaps, and underscores support for rapid protection of oceanic carbon sinks.

Human modifications to estuaries correlate with the morphology and functional roles of coastal fish

Animals can respond to human impacts by favouring different morphological traits or by exploiting different food resources. We quantified the morphology and diet of four functionally different fish species (n = 543 fish) from 13 estuaries with varying degrees of human modification in Queensland, Australia. We found differences in the responses of trophic groups to the environmental conditions of estuaries; principally the extent of seagrass in the estuary, and the amount of shoreline and catchment urbanisation. Here, seagrass and urbanisation extent correlated with the diet and morphology of zooplanktivores and detritivores; thereby indicating that human modifications may modify these species functional roles. Conversely, environmental variables did not correlate with the diet or morphology of zoobenthivores or piscivores thereby indicating that human modifications may have less an effect on these species functional roles. Our findings demonstrate that anthropogenic impacts to coastal ecosystems might extend from the traditionally measured metrics of abundance and diversity.

Landscape context and nutrients modify the effects of coastal urbanisation

Estuaries are focal points for coastal cities worldwide, their habitats frequently transformed into engineered shorelines abutting waters with elevated nutrients in an urbanised landscape. Here we test for relationships between shoreline armouring and nutrients on the diversity and trophic composition of fish assemblages across 22 estuaries in eastern Australia. Urbanisation was associated with fish diversity and abundance, but there were differences in the effects of shoreline armouring and nutrient level on the trophic composition of fish assemblages. Fish diversity and the abundance of most trophic groups, particularly omnivores, zoobenthivores and detritivores, was greatest in highly urban estuaries. We show that estuarine fish assemblages are associated with urbanisation in more nuanced ways than simple habitat transformation would suggest, but this depends on the broader environmental context. Our findings have wider implications for estuarine conservation and restoration, emphasizing that ecological benefits of habitat measures may depend on both landscape attributes and water quality in urban settings.

Low redundancy and complementarity shape ecosystem functioning in a low-diversity ecosystem

Ecosystem functioning is positively linked to biodiversity on land and in the sea. In high-diversity systems (e.g. coral reefs), species coexist by sharing resources and providing similar functions at different temporal or spatial scales. How species combine to deliver the ecological function they provide is pivotal for maintaining the structure, functioning and resilience of some ecosystems, but the significance of this is rarely examined in low-diversity systems such as estuaries. We tested whether an ecological function is shaped by biodiversity in a low-diversity ecosystem by measuring the consumption of carrion by estuarine scavengers. Carrion (e.g. decaying animal flesh) is opportunistically fed on by a large number of species across numerous ecosystems. Estuaries were chosen as the model system because carrion consumption is a pivotal ecological function in coastal seascapes, and estuaries are thought to support diverse scavenger assemblages, which are modified by changes in water quality and the urbanization of estuarine shorelines. We used baited underwater video arrays to record scavengers and measure the rate at which carrion was consumed by fish in 39 estuaries across 1,000 km of coastline in eastern Australia. Carrion consumption was positively correlated with the abundance of only one species, yellowfin bream Acanthopagrus australis, which consumed 58% of all deployed carrion. The consumption of carrion by yellowfin bream was greatest in urban estuaries with moderately hardened shorelines (20%-60%) and relatively large subtidal rock bars (>0.1 km² ). Our findings demonstrate that an ecological function can be maintained across estuarine seascapes despite both limited redundancy (i.e. dominated by one species) and complementarity (i.e. there is no spatial context where the function is delivered significantly when yellowfin bream are not present) in the functional traits of animal assemblages. The continued functioning of estuaries, and other low-diversity ecosystems, might therefore not be tightly linked to biodiversity, and we suggest that the preservation of functionally dominant species that maintain functions in these systems could help to improve conservation outcomes for coastal seascapes.