Spatial and temporal distribution dataset of benthic macroalgae during the 2015-2016 tropical monsoonal cycle in Malaysia.

Background: The effects of small-scale disturbances, such as monsoon, are understudied in tropical regions. The storms associated with monsoon events not only modify the local macroalgal community structure, but also reveal the continuation of short-term recolonisation. Thus, this study aims to determine the variation in species, assemblage and cover of macroalgae during the monsoonal cycle from 2015 to 2016. This paper presents data on the spatial and temporal distribution of benthic macroalgae along the coastline of Johor, Malaysia. The information is presented as raw and partially-processed data, which summarises the cover and frequency of macroalgae at the respective study sites. This paper describes an important set of data that can be used further for in-situ experiments on the effects of environmental disturbances towards pioneer and climax species in tropical areas. New information: This study provides a description of the east coast shore of Peninsular Malaysia, specifically in Johor coast in 2015-2016. The spatial and temporal distribution and abundance of a total of 41 taxa were assessed at four monsoon-exposed locations. These data provide a comprehensive baseline against disturbance and recolonisation of macroalgal community can be effectively and objectively evaluated.

Quantification of blue carbon in seagrass ecosystems of Southeast Asia and their potential for climate change mitigation.

Seagrasses have the ability to contribute towards climate change mitigation, through large organic carbon (Corg) sinks within their ecosystems. Although the importance of blue carbon within these ecosystems has been addressed in some countries of Southeast Asia, the regional and national inventories with the application of nature-based solutions are lacking. In this study, we aim to estimate national coastal blue carbon stocks in the seagrass ecosystems in the countries of Southeast Asia including the Andaman and Nicobar Islands of India. This study further assesses the potential of conservation and restoration practices and highlights the seagrass meadows as nature-based solution for climate change mitigation. The average value of the total carbon storage within seagrass meadows of this region is 121.95 ± 76.11 Mg ha-1 (average ± SD) and the total Corg stock of the seagrass meadows of this region was 429.11 ± 111.88 Tg, with the highest Corg stock in the Philippines (78%). The seagrass meadows of this region have the capacity to accumulate 5.85-6.80 Tg C year-1, which accounts for $214.6-249.4 million USD. Under the current rate of decline of 2.82%, the seagrass meadows are emitting 1.65-2.08 Tg of CO2 year-1 and the economic value of these losses accounts for $21.42-24.96 million USD. The potential of the seagrass meadows to the offset current CO2 emissions varies across the region, with the highest contribution to offset is in the seagrass meadows of the Philippines (11.71%). Current national policies and commitments of nationally determined contributions do not include blue carbon ecosystems as climate mitigation measures, even though these ecosystems can contribute up to 7.03% of the countries' reduction goal of CO2 emissions by 2030. The results of this study highlight and promote the potential of the southeast Asian seagrass meadows to national and international agencies as a practical scheme for nature-based solutions for climate change mitigation.

Coralline macroalgae contribution to ecological services of carbon storage in a disturbed seagrass meadow.

Coralline macroalgae are globally distributed rhodopyhtes that remove carbon from their immediate environment and transform it into carbonate sediments through the senescence of their calcified tissues. In this study, the calcium carbonate (CaCO3) stocks in the tissue of Jania adhaerens and sediments in Tanjung Adang Shoal, Johor were quantified for a 13-month study period. The detailed maps of the geographical distribution based on the spatial and temporal variations of biomass and CaCO3 were also assessed. The highest amount of biomass, CaCO3 and organic carbon (OC) stocks in the tissues showed the highest in May 2018 and May 2019. The biomass values ranged from 65 to 143 g DW m-2, which contained 53-147 g CaCO3 m-2 and 3-11 g OC m-2. These findings provided insights into the biogeochemical cycling of these inputs, which can be used to estimate the overall carbon budget of the macrophyte meadow.

Data on sediment nitrogen loadings and nitrogen in the biomass of seagrasses from Sungai Pulai estuary (Johor, Malaysia).

This paper presents data on nitrogen characteristics in a tropical seagrass meadow located in Sungai Pulai estuary (Johor, Malaysia) and is related to the article "Nitrogen dynamics in tropical seagrass meadows under heavy anthropogenic influence" [1]. Field sampling conducted from August 2015 to May 2016 aimed to collect sediments and seagrass tissues for analysis of nitrogen elemental content and stable isotope values. Sediment samples and seagrass tissue (above-ground and below-ground parts) were collected by using PVC cores. The information is presented as unprocessed and partially data, which incorporates nitrogen content (in %) and δ15N values (‰) of sediment and seagrass tissue samples. Nitrogen loadings in the seagrass sediments, as based on down-core data of sediment samples up to 30 cm depths, should be read with [1] to comprehend the baseline nitrogen dynamics of the study area.

Nitrogen dynamics within an estuarine seagrass meadow under heavy anthropogenic influence.

Nitrogen is essential for seagrass productivity but excesses in nitrogen exposure contribute to declines in meadow health. This study reports baseline data of bulk nitrogen loadings and contents in surficial sediments and seagrass tissues to determine the extent of nitrogen inputs in meadows of Sungai Pulai estuary (Johor, Malaysia). The sediment contained relatively low nitrogen loadings (mean range of 91-94 g N m-2) with likely origins from land-based sources. At the meadow-level, Enhalus acoroides, Cymodocea serrulata and Thalassia hemprichii are the most important species as nitrogen sinks. The highest δ15N values of seagrass tissues were recorded for T. hemprichii (10.7 ±â€¯0.4‰), which indicated an elevated capacity for internal recycling of nitrogen. The data demonstrates the provision of ecosystem services by the meadows in mitigating excess nitrogen imported into the estuary. Seagrasses health, however, needs to be at optimum levels for the effectiveness of the meadow as a nutrient sink.

Australian vegetated coastal ecosystems as global hotspots for climate change mitigation.

Policies aiming to preserve vegetated coastal ecosystems (VCE; tidal marshes, mangroves and seagrasses) to mitigate greenhouse gas emissions require national assessments of blue carbon resources. Here, we present organic carbon (C) storage in VCE across Australian climate regions and estimate potential annual CO2 emission benefits of VCE conservation and restoration. Australia contributes 5-11% of the C stored in VCE globally (70-185 Tg C in aboveground biomass, and 1,055-1,540 Tg C in the upper 1 m of soils). Potential CO2 emissions from current VCE losses are estimated at 2.1-3.1 Tg CO2-e yr-1, increasing annual CO2 emissions from land use change in Australia by 12-21%. This assessment, the most comprehensive for any nation to-date, demonstrates the potential of conservation and restoration of VCE to underpin national policy development for reducing greenhouse gas emissions.

Carbon stores from a tropical seagrass meadow in the midst of anthropogenic disturbance.

Seagrass meadows provide important carbon sequestration services but anthropogenic activities modify the natural ecosystem and inevitably lower carbon storage capacity. The tropical mixed-species meadows in the Sungai Pulai Estuary (Johor, Malaysia) are impacted by such activities. In this study, we provide baseline estimates for carbon stores analysed from sediment cores. In sediment depths up to 100cm, organic (OC) and inorganic carbon (IC) stores were 43-101MgCha-1 and 46-83MgCha-1, respectively, and are in the lower end of global average values. The bulk of OC (53-98%) originated from seston suggesting that the meadows had low capacity to retain seagrass-derived organic matter. The species factor resulted in some variability in OC stores but did not appear to influence IC values. The low carbon stores in the meadow may be a direct result of sediment disturbances but natural biogeochemical processes are not discounted as possible causal factors.

Utilization of carbon substrates by heterotrophic bacteria through vertical sediment profiles in coastal and estuarine seagrass meadows.

Coastal vegetated ecosystems play an important role in carbon cycling and bacterial communities inhabiting coastal sediments are responsible for the remineralization and processing of organic carbon (OC). We collected 1 m-long sediment cores in Posidonia seagrass meadows from coastal and estuarine sites in Australia that differed in their sedimentary organic and inorganic carbon, nitrogen and mud contents. The metabolic diversity of sediment heterotrophic bacterial communities was characterized at different sediment depths, based on the utilization pattern of 31 individual carbon substrates using Biolog EcoPlatesTM . High metabolic diversity was recorded at both sites, but the carbon substrate utilization rates and the use of carbohydrates were higher at the coastal site compared to the estuarine site. The heterotrophic bacterial community in the coastal sediment appeared to metabolize a more diverse OC pool compared to the estuarine site, which might partly explain the differences in OC storage among the seagrass habitats studied. The Biolog EcoPlatesTM provided a useful tool for characterising the sediment heterotrophic bacterial communities in the meadows and sediment characteristics and biochemical composition of the organic matter played an important role in shaping heterotrophic bacterial communities and their carbon utilization rates, potentially affecting carbon accumulation and preservation within seagrass sediments.

Reconstruction of centennial-scale fluxes of chemical elements in the Australian coastal environment using seagrass archives.

The study of a Posidonia australis sedimentary archive has provided a record of changes in element concentrations (Al, Fe, Mn, Pb, Zn, Cr, Cd, Co, As, Cu, Ni and S) over the last 3000 years in the Australian marine environment. Human-derived contamination in Oyster Harbor (SW Australia) started ~100 years ago (AD ~1900) and exponentially increased until present. This appears to be related to European colonization of Australia and the subsequent impact of human activities, namely mining, coal and metal production, and extensive agriculture. Two contamination periods of different magnitude have been identified: Expansion period (EXP, AD ~1900-1970) and Establishment period (EST, AD ~1970 to present). Enrichments of chemical elements with respect to baseline concentrations (in samples older than ~115 cal years BP) were found for all elements studied in both periods, except for Ni, As and S. The highest enrichment factors were obtained for the EST period (ranging from 1.3-fold increase in Cu to 7.2-fold in Zn concentrations) compared to the EXP period (1.1-fold increase for Cu and Cr to 2.4-fold increase for Pb). Zinc, Pb, Mn and Co concentrations during both periods were 2- to 7-fold higher than baseline levels. This study demonstrates the value of Posidonia mats as long-term archives of element concentrations and trends in coastal ecosystems. We also provide preliminary evidence on the potential for Posidonia meadows to act as significant long-term biogeochemical sinks of chemical elements.

Variability in the carbon storage of seagrass habitats and its implications for global estimates of blue carbon ecosystem service.

The recent focus on carbon trading has intensified interest in 'Blue Carbon'-carbon sequestered by coastal vegetated ecosystems, particularly seagrasses. Most information on seagrass carbon storage is derived from studies of a single species, Posidonia oceanica, from the Mediterranean Sea. We surveyed 17 Australian seagrass habitats to assess the variability in their sedimentary organic carbon (C org) stocks. The habitats encompassed 10 species, in mono-specific or mixed meadows, depositional to exposed habitats and temperate to tropical habitats. There was an 18-fold difference in the Corg stock (1.09-20.14 mg C org cm(-3) for a temperate Posidonia sinuosa and a temperate, estuarine P. australis meadow, respectively). Integrated over the top 25 cm of sediment, this equated to an areal stock of 262-4833 g C org m(-2). For some species, there was an effect of water depth on the C org stocks, with greater stocks in deeper sites; no differences were found among sub-tidal and inter-tidal habitats. The estimated carbon storage in Australian seagrass ecosystems, taking into account inter-habitat variability, was 155 Mt. At a 2014-15 fixed carbon price of A$25.40 t(-1) and an estimated market price of $35 t(-1) in 2020, the C org stock in the top 25 cm of seagrass habitats has a potential value of $AUD 3.9-5.4 bill. The estimates of annual C org accumulation by Australian seagrasses ranged from 0.093 to 6.15 Mt, with a most probable estimate of 0.93 Mt y(-1) (10.1 t. km(-2) y(-1)). These estimates, while large, were one-third of those that would be calculated if inter-habitat variability in carbon stocks were not taken into account. We conclude that there is an urgent need for more information on the variability in seagrass carbon stock and accumulation rates, and the factors driving this variability, in order to improve global estimates of seagrass Blue Carbon storage.