Seagrass Removal Leads to Rapid Changes in Fauna and Loss of Carbon (original) (raw)
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International Journal of Environmental Sciences & Natural Resources, 2021
Seagrass meadows are considered as global hotspots of blue carbon stocks. However, they suffer global cover loss mainly due to anthropogenic activities. Few is known on the impact of seagrass loss on their blue carbon stocks. This study investigates the impact of seagrass removal on soil organic carbon stocks two years after initial perturbation, and the potential bioturbation activity of co-existing burrowing shrimps in Gazi Bay, Kenya. Seagrass aboveground biomass was removed for a period of 18 months and organic carbon samples were taken 24 months after the first harvested at three depth layers (0-5cm, 5-10cm, 10-15cm). Results indicated that organic carbon was significantly lower in the 15cm depth profile sampled in harvested seagrass meadows. The sediment turnover rate of Callianassidae present in the bay was estimated at 948 ± 342 (SE) g.DW.d-1. This bioturbation activity is assumed to play an important role in the potential release of sediment organic carbon stock from harvested plots. This study demonstrates the significant sub-surface organic carbon loss after seagrass removal, and the potential for burrowing shrimp to enhance organic carbon remineralisation. Further studies on tropical seagrass meadows organic carbon fate after seagrass loss to account for blue carbon budget.
Losses and recovery of organic carbon from a seagrass ecosystem following disturbance
Proceedings of the Royal Society B: Biological Sciences, 2015
Seagrasses are among the Earth's most efficient and long-term carbon sinks, but coastal development threatens this capacity. We report new evidence that disturbance to seagrass ecosystems causes release of ancient carbon. In a seagrass ecosystem that had been disturbed 50 years ago, we found that soil carbon stocks declined by 72%, which, according to radiocarbon dating, had taken hundreds to thousands of years to accumulate. Disturbed soils harboured different benthic bacterial communities (according to 16S rRNA sequence analysis), with higher proportions of aerobic heterotrophs compared with undisturbed. Fingerprinting of the carbon (via stable isotopes) suggested that the contribution of autochthonous carbon (carbon produced through plant primary production) to the soil carbon pool was less in disturbed areas compared with seagrass and recovered areas. Seagrass areas that had recovered from disturbance had slightly lower (35%) carbon levels than undisturbed, but more than twi...
The impact of sediment burial and erosion on seagrasses: A review
Estuarine Coastal and Shelf Science, 2008
Keywords: seagrass burial erosion sediment impacts disturbance sediment redistribution plant size a b s t r a c t The available information from experimental and descriptive studies on the effects of sediment burial and erosion on seagrasses was compiled to synthesize the information regarding the species-specific impacts and to relate them to plant characteristics. Burial thresholds (i.e. the burial levels causing 50% and 100% shoot mortality) and mortality-burial curves were estimated for the 15 seagrass species where the effects of experimental burial have been tested. All the species investigated reached 50% shoot mortality at burial levels ranging from 2 cm (Halophila ovalis) to 19.5 cm (Posidonia australis). P. australis was the most tolerant seagrass species to burial, while Thalassia testudinum was the most tolerant species to erosion. The relationships among plant size, growth, biomass and density with burial thresholds were examined. There were significant relationships between the burial thresholds and the shoot mass, the rhizome diameter, the aboveground biomass, the horizontal rhizome elongation and the leaf length of seagrass species. The leaf size and the rhizome diameter are the best predictors of the capacity of seagrasses to withstand burial. The burial thresholds estimated for seagrass species were in many cases in agreement with the burial impacts described by field observations (bioturbation), while in some cases was related to the species long-term colonization capacity (dune migration). Most human-induced impacts result in important changes of the sedimentary environment, with permanent negative effects on seagrass meadows (regression and complete destruction), whereas natural events, whether extreme (hurricane) or regular (dune migration), allow the recovery and/or adaptation of seagrasses to the burial/ erosion sediment dynamics. The extent of the effects of burial and erosion on seagrasses is speciesspecific and strongly size-dependent.
Seagrass litter decomposition: an additional nutrient source to shallow coastal waters
Environmental Monitoring and Assessment, 2018
Seagrass ecosystems are vital for its regulatory services yet, highly threatened by degradation due to human pressures. Decomposition of two tropical seagrass species (Cymodocea serrulata and Cymodocea rotundata) was studied and compared, to understand their potential in generating additional nutrients to coastal waters. Release of carbon, nitrogen and phosphorus during the decomposition process of seagrass wracks was estimated in bacteria-active (non-poisoned) and bacteria-inhibited (poisoned) conditions from shorewashed fresh seagrass, sampled from Palk Bay, India. Incubation experiments for 25 days indicated a near three times higher concentration of dissolved organic carbon (DOC) in bacteria-inhibited flasks compared to bacteria-active conditions for both species. The maximum leaching rates of DOC, TDN and TDP were found to be 294, 65.1 and 11.2 μM/g dry wt/day, respectively. Further, higher release of dissolved inorganic nitrogen (DIN) (> 1.3 times) was documented from the bacteriaactive flask, highlighting the significance of microbial process in generating bio-available nutrients from decaying seagrass. Faster decomposition (0.014 ± 0.004 day −1) in the initial stages (up to 8 days) compared to the later stages (0.005 ± 0.001 day −1) indicated a rapid loss of biomass carbon during the initial leaching process and its relative importance in the decomposition pathway. The decomposition rate is best described by a single-stage exponential decay model with a half-life of 41 days. It is estimated that the total seagrass litter available along the Palk Bay coast is about~0.3 Gg with high potential of additional nitrogen (0.9 ± 0.5 Mg) and phosphorus (0.3 ± 0.1 Mg) supply to the adjacent coastal waters.
Marine Pollution Bulletin, 2012
In 2005, dredging activities in Arcachon Bay (France) led in burying 320,000 m 2 of Zostera noltii intertidal seagrass. Recovery by macrobenthos and seagrass was monitored. Six months after works, seagrass was absent and macrobenthos drastically different from surrounding vegetated stations. Rapidly and due to sediment dispersal, disposal area was divided into a sandflat with a specific benthic community which maintained its difference until the end of the survey (2010), and a mudflat where associated fauna became similar to those in adjacent seagrass. Macrobenthic community needs 3 years to recover while seagrass needs 5 years to recover in the station impacted by mud. The secondary production loss due to works was low. In this naturally carbon enriched system, univariate biotic indices did not perform well to detect seagrass destruction and recovery. Multivariate index MISS gave more relevant conclusions and a simplified version was tested with success, at this local scale.
Major impacts and societal costs of seagrass loss on sediment carbon and nitrogen stocks
Ecosphere, 2021
Seagrass meadows constitute important carbon sinks, and the ongoing global loss of seagrass habitats raises concerns about the release of carbon stored in their sediments. However, the actual consequences of seagrass loss for the release of carbon and nutrients remain unclear. Here we take advantage of well-documented historic losses of eelgrass (Zostera marina) meadows along the Swedish NW coast to assess how the content of organic carbon (C) and nitrogen (N) in the sediment change when a meadow is lost. We find unusually high contents of C and N (on average 3.7 and 0.39% DW, respectively) in Swedish eelgrass sediments down to >100 cm depth, suggesting that these habitats constitute global hotspots for C and N storage. However, the C and N stocks were strongly influenced by wave exposure, and were almost twice as high in sheltered compared to exposed eelgrass meadows. The sediment composition and stable isotope values were distinctly different in areas that have lost eelgrass meadows, with on average >2.6 times lower content of C and N. The results indicate an erosion of >35 cm sediment following the historical eelgrass loss, and that sheltered meadows have more vulnerable sediment stocks. The results suggest that eelgrass loss has resulted in a release of 60.2 ton C and 6.63 ton N per hectare, with an estimated economic cost to society of 7,944 and 141,355 US$ ha-1, respectively. The value of N storage represents one of the highest monetary values presented for an ecosystem service provided by seagrasses, and show that Swedish eelgrass meadows are particularly important for mitigating eutrophication. Following a documented loss of approximately 10 km2 of eelgrass in the study area, it is estimated that over 60,000 ton of nitrogen was released to the coastal environment over a 20-year period, which constitutes over three times the annual river load of nitrogen to the Swedish NW coast. The study exemplifies the significant role of seagrass sediments as sinks for both carbon and nutrients, and that the risk of nutrient release following vegetation loss should be taken into account in the spatial management of seagrass and other coastal habitats.
Oikos, 2006
. Decay of multiple species of seagrass detritus is dominated by species identity, with an important influence of mixing litters. Á Oikos 114: 329 Á337. No studies of seagrass decay have examined effects of the number of species contained within the detrital pool. Given the importance of decay for nutrient cycling and longterm productivity, we tested how three seagrass species affected decay in litterbags. Experimental results clearly showed that species identity was the predominant driver of mass loss, with total loss not differing between bags containing one, two and three species. Furthermore, we show there were also non-additive effects of mixing litter that were not predicted from single-species decay rates. The nature of the non-predictable mass loss varied both through time and with the number of species in the mixtures. This indicates that species richness indeed plays a role in this important ecosystem function but one that is of less importance than species identity. The concordance of these results with terrestrial studies suggests that mechanisms responsible for mixed-species decay rates may be broadly applicable across ecosystems.
Ocean & Coastal Management
Seagrass meadows support high primary production rates and their canopies are efficient at filtering particles out of their water column as well as in preventing resuspension of the sediments. In addition, decomposition rates in seagrass sediments are slow, because of low nutrient concentration in seagrass detritus and low oxygen concentration in seagrass sediments. These characteristics result in high carbon burial rates in seagrass meadows, which have the capacity to accumulate large stores of carbon in their sediments, raising the seafloor. Carbon fingerprinting techniques allow to calculate both the age of these deposits and, therefore, the rate of carbon burial and identify the contribution of carbon produced by the seagrass. Yet, data on the regional cover and carbon stocks in seagrass meadows is sparse for some regions, particularly the Indo-Pacific, Africa and South America. In addition, our understanding of the factors regulating the variability in carbon sink capacity among seagrass meadows is limited. These gaps limit the capacity to formulate strategies to mitigate climate change based on the carbon sink capacity of seagrass meadows. A research strategy needs be formulated to address these gaps and provide the necessary protocols to ensure the accountability of mitigation actions involving the conservation and restoration of seagrass meadows.