Global dataset on seagrass meadow structure, biomass and production

Seagrass meadows provide valuable socio-ecological ecosystem services, including a key role in climate change mitigation and adaption. Understanding the natural history of seagrass meadows across environmental gradients is crucial to deciphering the role of seagrasses in the global ocean. In this data collation, spatial and temporal patterns in seagrass meadow structure, biomass and production data are presented as a function of biotic and abiotic habitat characteristics. The biological traits compiled include measures of meadow structure (e.g. percent cover and shoot density), biomass (e.g. above-ground biomass) and production (e.g. shoot production). Categorical factors include bioregion, geotype (coastal or estuarine), genera and year of sampling. This dataset contains data extracted from peer-reviewed publications published between 1975 and 2020 based on a Web of Science search and includes 11 data variables across 12 seagrass genera. The dataset excludes data from mesocosm and field experiments, contains 14271 data points extracted from 390 publications and is publicly available on the PANGAEA® data repository (10.1594/PANGAEA.929968; Strydom et al., 2021). The top five most studied genera are Zostera, Thalassia, Cymodocea, Halodule and Halophila (84 % of data), and the least studied genera are Phyllospadix, Amphibolis and Thalassodendron (2.3 % of data). The data hotspot bioregion is the Tropical Indo-Pacific (25 % of data) followed by the Tropical Atlantic (21 %), whereas data for the other four bioregions are evenly spread (ranging between 13 and 15 % of total data within each bioregion). From the data compiled, 57 % related to seagrass biomass and 33 % to seagrass structure, while the least number of data were related to seagrass production (11 % of data). This data collation can inform several research fields beyond seagrass ecology, such as the development of nature-based solutions for climate change mitigation, which include readership interested in blue carbon, engineering, fisheries, global change, conservation and policy

Plant-herbivore interactions in a changing climate and implications for seagrass resilience

Climate change is affecting herbivore distributions and abundance, resulting in intensified grazing pressure on foundation species such as seagrasses. This, coupled with other, rapid changes in estuarine ecosystems, may threaten the resilience of seagrass. While the overall resilience of seagrasses is generally well-studied, the timeframes of recovery have received comparatively little attention, particularly in temperate estuaries. This study investigated the recovery time of two colonising seagrasses (Halophila ovalis and Ruppia megacarpa) following various intensities of simulated grazing in two southwestern Australian estuaries. Simulated grazing treatments (25%, 50%, 75%, and 100% removal from 1 m2 plots) were applied in field experiments replicated at four locations in each estuary during summer. Seagrass cover was used as the main measure of recovery, and was monitored over 3 months following the simulated grazing while excluding swans. The results showed that Halophila ovalis recovered within 4–6 weeks from lower grazing intensities (25% and 50%), and within 7–19 weeks from higher grazing intensities (75% and 100%). Furthermore, the variability in recovery time among experimental locations increased with grazing intensity. Ruppia megacarpa recovered from 100% grazing within 2-9 weeks. The recovery time for R. megacarpa was faster than for other colonising species, but this cannot be assumed to always be the case, as recovery did not occur within the timeframe of the experiment in one location. The overall conclusion is that colonising seagrasses, represented by H. ovalis and R. megacarpa, can recover rapidly following simulated grazing and through multiple mechanisms. Vegetative growth, and particularly regrowth from the surrounding meadow, appears instrumental in recovery for both species at the scale of disturbance simulated. A novel finding is that recovery occurred via recruitment from fragments in both species. No recovery was observed by recruitment from seed germination. These results indicate that these species in these systems, are likely resilient to current and increased levels of grazing pressure. However, estuarine ecosystems will have to remain resilient to other pressures in a changing world. Estuaries worldwide are subjected to anthropogenic impacts and climate change pressure, which is not only affecting grazing dynamics, but also introducing altered physio-chemical conditions and feedbacks. These pressures may act synergistically and could alter the resilience of seagrass and make it difficult to predict their recovery capacity. Intervention strategies such as future-proofing existing populations or restoration of lost meadows, or a combination of both, may be required to prevent reductions or loss of seagrass. The study provides a baseline for understanding grazing pressure as a singular disturbance. Future work can examine how grazing and other potentially interacting pressures in a changing climate could impact seagrass recovery timescales or trajectories