Disturbance influences the invasion of a seagrass into an existing meadow

Effects of a chronic impact on Cymodocea nodosa community carbon metabolism and dissolved organic carbon fluxes

Seagrass communities have been degraded worldwide experiencing elevated shoot density reduction by anthropogenic chronic pressures. This study aims to assess how a chronic (i.e., low intensity but long-lasting) impact that promotes reduced shoot density in a temperate seagrass population may affect community components and functioning. To this end, shoot density was reduced (0, 40, and 75 %) for three months in contrasting seasons (winter and summer), and assessed its effects on biotic components (i.e., seagrasses, macroalgae, macrofauna, and microphytobenthos), as well as on community carbon metabolism, dissolved organic carbon (DOC) fluxes and sediment organic matter (OM) content. Lower shoot densities enhanced the presence of macroalgae and microphytobenthos in the community, while macrofauna remained unchanged. Net community production was significantly reduced with the simulated reduction in shoot density in both seasons (up to 10-fold lower), which shifted the community in winter from being largely autotrophic (CO2 sink) to heterotrophic (CO2 source). This was due to the expected reduction in gross primary production, but also to the unexpected increase in community respiration (up to 2.2-fold higher). Since OM in the sediment was reduced in the simulated shoot density reduction treatments, the increase in sediment bacterial activity may help explain the increase in community respiration. DOC fluxes were also greatly reduced in both seasons (up to 5.5-fold lower), which coupled with the reduced net community production and loss of OM in the sediment may have a continued silent effect on blue carbon capture and storage capacity in this chronically stressed community. This study therefore highlights the importance of chronic impacts that promote the degradation of seagrass communities that may reduce their ability to provide highly valuable ecological services, including the ability to cope with the effects of climate change.

Improving Approaches to Mapping Seagrass within the Great Barrier Reef: From Field to Spaceborne Earth Observation

Seagrass meadows are a key ecosystem of the Great Barrier Reef World Heritage Area, providing one of the natural heritage attributes underpinning the reef’s outstanding universal value. We reviewed approaches employed to date to create maps of seagrass meadows in the optically complex waters of the Great Barrier Reef and explored enhanced mapping approaches with a focus on emerging technologies, and key considerations for future mapping. Our review showed that field-based mapping of seagrass has traditionally been the most common approach in the GBRWHA, with few attempts to adopt remote sensing approaches and emerging technologies. Using a series of case studies to harness the power of machine- and deep-learning, we mapped seagrass cover with PlanetScope and UAV-captured imagery in a variety of settings. Using a machine-learning pixel-based classification coupled with a bootstrapping process, we were able to significantly improve maps of seagrass, particularly in low cover, fragmented and complex habitats. We also used deep-learning models to derive enhanced maps from UAV imagery. Combined, these lessons and emerging technologies show that more accurate and efficient seagrass mapping approaches are possible, producing maps of higher confidence for users and enabling the upscaling of seagrass mapping into the future.

Recovery of a fast-growing seagrass from small-scale mechanical disturbances: Effects of intensity, size and seasonal timing

We studied the recovery of the fast-growing seagrass Cymodocea nodosa from disturbances of different intensities (shoots removal or the entire plant), plot sizes (from 0.04 to 1 m²) and in different seasons (spring and autumn) in a shallow coastal bay. We monitored recovery over 27 months and measured plant traits at the end. Shoot density and canopy height recovered faster (1 month) when only shoots were removed compared to when the entire plant was removed (10-25 months). Small areas took longer to recover than large ones, probably due to limited light availability or the accumulation of detritus. Plants disturbed in autumn took 9 months longer to recover than those disturbed in spring. After the 27-month, all plant traits were similar to those of control plots, except rhizome biomass, which was lower. Our results suggest that mechanical disturbances might exert a negative effect on the long-term resilience of seagrasses.

Over a decade monitoring Fiji's seagrass condition demonstrates resilience to anthropogenic pressures and extreme climate events

Seagrass are an important marine ecosystem of the Fiji Islands. We confirm six seagrass species from the archipelago and defined five broad categories of seagrass habitat. We report, with high confidence, seagrass meadows covering 59.19 km² of Fiji's shallow water habitats from literature and this study. Long-term monitoring of seagrass abundance, species composition, and seed banks at eight sentinel sites, found no long-term trends. Examination of key attributes that affect seagrass resilience identified meadows as predominately enduring and dominated by opportunistic species which had moderate physiological resistance, and high recovery capacity. We examined threats to Fiji's seagrass meadows from extreme climatic events and anthropogenic activities using a suite of indicators, identifying water quality as a major pressure. Based on these findings, we assessed existing protections in Fiji afforded to seagrass and their services. This understanding will help to better manage for seagrass resilience and focus future seagrass research in Fiji.

Invasive alien plant species: Their impact on environment, ecosystem services and human health

Ecological perturbations caused by biotic invasion have been identified as a growing threat to global sustainability. Invasive alien plants species (IAPS) are considered to be one of the major drivers of biodiversity loss and thereby altering the ecosystem services and socio-economic conditions through different mechanisms. Although the ecological impacts of IAPS are well documented, there is a dearth of studies regarding their economic quantification, livelihood considerations, biotechnological prospects (phytoremediation, bioenergy, phyto-synthesis of nanoparticles, biomedical, industrial applications etc.) and human health risk assessments of IAPS. In this context, the current panoramic review aimed to investigate the environmental, socio-ecological and health risks posed by IAPS as well as the compounded impact of IAPS with habitat fragmentation, climate and land use changes. To this end, the need of an integrated trans-disciplinary research is emphasized for the sustainable management of IAPS. The management prospects can be further strengthened through their linkage with geo-spatial technologies (remote sensing and GIS) by mapping and monitoring the IAPS spread. Further, the horizon of IAPS management is expanded to ecological indicator perspectives of IAPS, biosecurity, and risk assessment protocols with critical discussion. Moreover, positive as well as negative implications of the IAPS on environment, health, ecosystem services and socio-economy (livelihood) are listed so that a judicious policy framework could be developed for the IAPS management in order to mitigate the human health implications.

Changes in carbon storage and macrobenthic communities in a mangrove-seagrass ecosystem after the invasion of smooth cordgrass in southern China

The exotic smooth cordgrass (Spartina alterniflora) has invaded intertidal wetlands near the Ronggenshan tidal flats of Beihai, Guangxi, China, where historically seagrasses and mangroves coexisted. We investigated sediment organic carbon (SOC) storage and macrobenthic community structure in the existing mangroves (MG), S. alterniflora (SA), seagrass bed (SG), and unvegetated flat (UnV) habitats following the S. alterniflora invasion. SOC storage increased after S. alternifolia invasion in the SG and UnV habitats. Spartina alterniflora invasion changed the dominant species of the macrobenthos in the original habitats and reduced the diversity of macrobenthos in SG and UnV habitats. Clearly, S. alternifolia invasion can change the ecological functioning of south China's coastal ecosystems by altering carbon sequestration and affecting biodiversity.

Local trampling disturbance effects on alpine plant populations and communities: Negative implications for climate change vulnerability

Global change is modifying species communities from local to landscape scales, with alterations in the abiotic and biotic determinants of geographic range limits causing species range shifts along both latitudinal and elevational gradients. An important but often overlooked component of global change is the effect of anthropogenic disturbance, and how it interacts with the effects of climate to affect both species and communities, as well as interspecies interactions, such as facilitation and competition. We examined the effects of frequent human trampling disturbances on alpine plant communities in Switzerland, focusing on the elevational range of the widely distributed cushion plant Silene acaulis and the interactions of this facilitator species with other plants. Examining size distributions and densities, we found that disturbance appears to favor individual Silene growth at middle elevations. However, it has negative effects at the population level, as evidenced by a reduction in population density and reproductive indices. Disturbance synergistically interacts with the effects of elevation to reduce species richness at low and high elevations, an effect not mitigated by Silene. In fact, we find predominantly competitive interactions, both by Silene on its hosted and neighboring species and by neighboring (but not hosted) species on Silene. Our results indicate that disturbance can be beneficial for Silene individual performance, potentially through changes in its neighboring species community. However, possible reduced recruitment in disturbed areas could eventually lead to population declines. While other studies have shown that light to moderate disturbances can maintain high species diversity, our results emphasize that heavier disturbance reduces species richness, diversity, as well as percent cover, and adversely affects cushion plants and that these effects are not substantially reduced by plant-plant interactions. Heavily disturbed alpine systems could therefore be at greater risk for upward encroachment of lower elevation species in a warming world.