THE RESILIENCE OF TROPICAL SEAGRASSES TO CHRONIC STRESS AND PHYSICAL DISTURBANCES

Ph.DDOCTOR OF PHILOSOPH

Geomorphic Gradients in Shallow Seagrass Carbon Stocks

Seagrass meadows are important sinks of organic carbon (Corg), in particular the near-surface Corg pool (≤ 15 cm) compared to deeper sediments. Near-surface carbon is highly susceptible to disturbance and loss to the atmosphere, however, inadequate accounting for variability in this pool of carbon limits their uptake into carbon accounting frameworks. We therefore investigated the spatial variability in seagrass near-surface Corg and biomass Corg across different geomorphic (estuary, lagoonal and reef-associated) and community typologies (pioneer and persistent). Near-surface Corg stock in vegetated areas (25.78 Mg Corg ha−1 ± 26.64) was twice that from unvegetated areas (14.27 Mg Corg ha−1 ± 15.86), reinforcing the paradigm that the presence of seagrass enhances carbon stocks. Lagoonal and reef-associated meadows showed similar Corg stocks (p \u3e 0.05), which were substantially higher (p \u3c 0.05) than estuary meadows. Likewise, persistent seagrass communities (Cymodocea dominance) stored higher (p \u3c 0.05) stocks of Corg than pioneer communities (Halophila and Halodule dominance). Linear regression models showed significant but weak relationships between seagrass cover, shoot density and standing biomass with near-surface Corg stocks, whereas significant and strong relationships were observed for organic matter, dry bulk density and median grain size. The results highlight the need for higher resolution carbon assessments to better understand local and regional variability, in order to better inform carbon accounting and conservation policy

Seagrass in Southeast Asia: a review of status and knowledge gaps, and a road map for conservation

Southeast Asia has the highest diversity of seagrass species and habitat types, but basic information on seagrass habitats is still lacking. This review examines the known distribution, extent, species diversity, and research and knowledge gaps of seagrasses in Southeast Asia by biogeographic region of the Marine Ecoregions of the World (MEOW). The extent of seagrass meadows in Southeast Asia is ~36,762.6 km2 but this is likely an underestimate as some ecoregions were not well-represented and updated information was lacking. There is a paucity of information from the Western Coral Triangle Province, with no areal extent data available for the Indonesian regions of Kalimantan, Central and Southeast Sulawesi, the Maluku Islands, and West Papua. Regional research output has increased in the last two decades, with a trend towards more experimental, rather than descriptive research. However, there are knowledge gaps in socio-cultural-economic themed research, despite growing awareness of the importance of seagrass-human relationships in this region. Obstacles to advancing seagrass research, knowledge and conservation are rooted in either lack of expertise and training or the failure of effective management and policies. We propose a roadmap for seagrass conservation, with suggested solutions, including 1) encouraging collaboration between research institutions and scientists in the region to build capacity and share knowledge; 2) engaging with policymakers and governments to encourage science-based policies; 3) engaging with communities to raise awareness and foster stewardship of seagrass in the region

Blue Carbon Science, Management and Policy Across a Tropical Urban Landscape

The ability of vegetated coastal ecosystems to sequester high rates of “blue” carbon over millennial time scales has attracted the interest of national and international policy makers as a tool for climate change mitigation. Whereas focus on blue carbon conservation has been mostly on threatened rural seascapes, there is scope to consider blue carbon dynamics along highly fragmented and developed urban coastlines. The tropical city state of Singapore is used as a case study of urban blue carbon knowledge generation, how blue carbon changes over time with urban development, and how such knowledge can be integrated into urban planning alongside municipal and national climate change obligations. A systematic review of blue carbon studies in Singapore was used to support a qualitative review of Singapore’s blue carbon ecosystems, carbon budget, changes through time and urban planning and policy. Habitat loss across all blue carbon ecosystems is coarsely estimated to have resulted in the release of ∼12.6 million tonnes of carbon dioxide since the beginning of the 20th century. However, Singapore’s remaining blue carbon ecosystems still store an estimated 568,971 – 577,227 tonnes of carbon (equivalent to 2.1 million tonnes of carbon dioxide) nationally, with a small proportion of initial loss offset by habitat restoration. Carbon is now a key topic on the urban development and planning agenda, as well as nationally through Singapore’s contributions to the Paris Agreement. The experiences of Singapore show that coastal ecosystems and their blue carbon stocks can be successfully managed along an urban coastline, and can help inform blue carbon science and management along other rapidly urbanizing coastlines throughout the tropics

Mimicry of emergent traits amplifies coastal restoration success

Contains fulltext : 221224.pdf (publisher's version ) (Open Access

Distribution, temporal change, and conservation status of tropical seagrass beds in Southeast Asia: 2000–2020

Although Southeast Asia is a hotspot of global seagrass diversity, there are considerable information gaps in the distribution of seagrass beds. Broad-scale seagrass distribution has not been updated in the global seagrass database by UNEP-WCMC since 2000, although studies on seagrasses have been undertaken intensively in each region. Here we analyze the recent distribution of tropical seagrass beds, their temporal changes, causes of decline and conservation status in Southeast Asia (plus southern mainland China, Taiwan and Ryukyu Island of Japan) using data collected after 2000. Based on the 195 literature published since 2000, we identified 1,259 point data and 1,461 polygon data showing the distribution of seagrass beds. A large discrepancy was found in the seagrass bed distribution between our updated data and the UNEP-WCMC database, mostly due to inaccurate and low resolution location information in the latter. Temporal changes in seagrass bed area analyzed for 68 sites in nine countries/regions demonstrated that more than 60% of seagrass beds declined at an average rate of 10.9% year–1, whereas 20% of beds increased at an average rate of 8.1% year–1, leading to an overall average decline of 4.7% year–1. Various types of human-induced threats were reported as causes for the decline, including coastal development, fisheries/aquaculture, and natural factors such as typhoons and tsunamis. The percentage of seagrass beds covered with existing marine protected areas (MPAs) varied greatly among countries/regions, from less than 1% in Brunei Darussalam and Singapore to 100% in southern Japan. However, the degree of conservation regulation was not sufficient even in regions with higher MPA coverage. The percentage of seagrass beds within EBSAs (Ecologically and Biologically Significant Area determined by the Convention of Biological Diversity) was higher than that within MPAs because EBSAs cover a greater area than MPAs. Therefore, designating EBSAs as legally effective MPAs can greatly improve the conservation status of seagrass beds in Southeast Asia

Effects of shading on seagrass morphology and thermal optimal of productivity

10.1071/MF19173MARINE AND FRESHWATER RESEARCH718913-92

Seagrass habitats of Singapore: environmental drivers and key processes

Seagrasses are an important component of the marine ecosystems of Singapore. Using various assessment activities, we confirm 10 seagrass species within the waters of Singapore, with an additional two species under review for synonymy. Using long-term monitoring we examined the key attributes that affect the resilience of Singapore's seagrasses. We defined five broad categories of seagrass habitat in Singapore as estuary, coast, rocky fringing reef, sandy fringing reef, and patch reef. We identify the key features of the habitats and provide some insight into the drivers of change. In their natural state, seagrasses appear to follow a unimodal pattern of growth annually, which peaks in the late intermonsoon period prior to the onset of the southwest monsoon. Light availability appears to be the critical factor for seagrass growth in Singapore, and environmental factors, which modify the interactive effect of light availability and temperature are possibly the main drivers of change. Finally, we synthesised our understanding of seagrass ecosystems by classifying the attributes of the species present, meadow structure, and their possible drivers into a framework to assist ongoing monitoring and management decision-making. We also discuss the implications of seasonal growth in the Singapore context and identify research gaps that need to be urgently addressed. This understanding will help to better focus seagrass management and research in Singapore

Contribution of epiphyte load to light attenuation on seagrass leaves is small but critical in turbid waters

10.1071/MF19178MARINE AND FRESHWATER RESEARCH718929-93

Seagrass habitats of Singapore: environmental drivers and key\ud processes

Seagrasses are an important component of the marine ecosystems of Singapore. Using various assessment activities, we confirm 10 seagrass species within the waters of Singapore, with an additional two species under review for synonymy. Using long-term monitoring we examined the key attributes that affect the resilience of Singapore's seagrasses. We defined five broad categories of seagrass habitat in Singapore as estuary, coast, rocky fringing reef, sandy fringing reef, and patch reef. We identify the key features of the habitats and provide some insight into the drivers of change. In their natural state, seagrasses appear to follow a unimodal pattern of growth annually, which peaks in the late intermonsoon period prior to the onset of the southwest monsoon. Light availability appears to be the critical factor for seagrass growth in Singapore, and environmental factors, which modify the interactive effect of light availability and temperature are possibly the main drivers of change. Finally, we synthesised our understanding of seagrass ecosystems by classifying the attributes of the species present, meadow structure, and their possible drivers into a framework to assist ongoing monitoring and management decision-making. We also discuss the implications of seasonal growth in the Singapore context and identify research gaps that need to be urgently addressed. This understanding will help to better focus seagrass management and research in Singapore