The development of urchin barrens in seagrass meadows at Luscombe Bay, Western Australia from 1985 to 2004.

2011 ◽  
Vol 17 (1) ◽  
pp. 48 ◽  
Author(s):  
Mark W Langdon ◽  
Eric I Paling ◽  
Mike Van Keulen
Keyword(s):  
Western Australia ◽  
Seagrass Meadow ◽  
Anthropogenic Disturbances ◽  
Present Evidence ◽  
Heliocidaris Erythrogramma ◽  
Manual Removal ◽  
Seagrass Meadows ◽  
Large Aggregation ◽  
Urchin Grazing

Herbivore grazing is a well-documented cause of habitat decline in terrestrial systems, but marine examples from seagrass meadows are rare. Here we present evidence that isolated urchin grazing events have caused further localized losses to seagrass meadows already degraded by eutrophication or other anthropogenic disturbances. By 1992 a substantial scar in Posidonia meadows at Luscombe Bay in Cockburn Sound, Western Australia, had been caused by grazing urchins. When seagrass transplants were placed at the site more than a decade later most were grazed and did not survive. GIS analyses on imagery from 1985 to 2004 indicated that rapid seagrass meadow decline coincided with the presence of an unusually large aggregation of the grazing urchin Heliocidaris erythrogramma. Evidence of some seagrass recovery after 1993 was also apparent after the manual removal of the urchins in late 1992. Restoration efforts in seagrass meadows should consider the potential for grazing damage, as is commonplace in terrestrial systems.

scholarly journals A simple mooring modification reduces impacts on seagrass meadows

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Anna L. Luff ◽  
Emma V. Sheehan ◽  
Mark Parry ◽  
Nicholas D. Higgs
Keyword(s):  
Species Richness ◽  
Seagrass Meadow ◽  
Habitat Degradation ◽  
Ecological Impacts ◽  
Sediment Composition ◽  
Simple Modification ◽  
Seagrass Meadows ◽  
Ecological Importance ◽  
Detrimental Impact ◽  
Seagrass Density

AbstractMoorings can have a detrimental impact on seagrass, fragmenting the meadows, resulting in the habitat degradation. To reduce contact of the moorings with the seabed we attached small floats along the chain of a traditional swing mooring and monitored the ecological impacts of this modified mooring, with reference to a standard swing mooring, in a seagrass meadow under high tidal influence. After three years, seagrass density surrounding the modified mooring was over twice as high as that of the standard mooring, with blade length surrounding the modified mooring also found to exceed that of the standard mooring. Seagrass-associated epifaunal species richness was twice as high surrounding the modified mooring compared to the standard mooring. Sediment composition was considerably finer at the modified mooring, indicative of increased disturbance surrounding the standard mooring. A simple modification to existing swing moorings can mitigate some of the impacts of moorings on seagrass meadows, whilst accommodating for tidal fluctuations. The scale of the differences observed between the mooring types demonstrates the susceptibility of seagrass meadows to damage from swing moorings. Given the ecological importance of these habitats, it is crucial that action is taken to reduce further degradation, such as that demonstrated here.

Ten years of conservation efforts enhance seagrass cover and carbon storage in Thailand

2018 ◽  
Vol 61 (5) ◽  
pp. 441-451 ◽  
Author(s):  
Ekkalak Rattanachot ◽  
Milica Stankovic ◽  
Supaphon Aongsara ◽  
Anchana Prathep
Keyword(s):  
Organic Carbon ◽  
Carbon Storage ◽  
Seagrass Meadow ◽  
Seagrass Meadows ◽  
Rate Of Increase ◽  
Southern Thailand ◽  
Seagrass Cover ◽  
Conservation Projects ◽  
Organic Carbon Storage ◽  
Total Coverage

Abstract Seagrasses are known as engineering ecosystems that play important roles in coastal environments. Globally, seagrass areas have been declining, and many conservation projects have been carried out to prevent further decline. The goal of this work was to determine how successful conservation efforts have been in a seagrass meadow at Koh Tha Rai in the Nakhon Si Thammarat Province of southern Thailand in terms of meadow extent, coverage and organic carbon storage. A study was conducted in 2017 and compared to a previous study from 2006 to determine the effects of the various conservation efforts devoted to this area. The results show that the total seagrass area increased by 0.7 ha with a rate of increase of approximately 0.06 ha year−1. The total coverage of seagrass increased by approximately 3 times. The organic carbon in existing seagrass meadows (2006) was 53.35 Mg ha−1, while growth was 32.34 Mg ha−1 in the areas of new seagrass. Moreover, the total organic carbon storage in the sediment increased by 26.86 MgC from 2006 to 2017 (from 211.60 MgC to 235.46 MgC). In conclusion, this study demonstrated the importance of successful conservation efforts in terms of increasing seagrass meadow areas, seagrass coverage and carbon storage within the meadow.

scholarly journals MODELLING, SIMULATION AND VISUALIZATION OF A MULTISPECIFIC PHILIPPINE SEAGRASS MEADOW

2019 ◽  
Vol XLII-4/W19 ◽  
pp. 77-82
Author(s):  
V. P. Bongolan ◽  
G. M. Torres ◽  
J. E. Branzuela
Keyword(s):  
Clonal Growth ◽  
Seagrass Meadow ◽  
Light Attenuation ◽  
Thalassia Hemprichii ◽  
Diffusion Limited Aggregation ◽  
Seagrass Meadows ◽  
Branching Angle ◽  
Coexisting Species ◽  
Cymodocea Rotundata ◽  
Model Features

Abstract. Seagrass meadows are constantly under threat from natural and man-made stresses due to its shallow existence in the coastal environment. Restoration and preservation of seagrasses by means of rehabilitation or transplanting strategies is possible, but the studies have been limited. An agent-based model of a mixed Philippine seagrass meadow is presented. Three species were used for testing: Enhalus acoroides, Thalassia hemprichii, and Cymodocea rotundata. The model features parameter-based clonal growth of seagrass species, recruitment of new seagrass apices through basic flowering/seeding, and a crowding logic for multiple coexisting species in a single meadow. Seagrass clonal growth is modeled using a modified Diffusion-Limited Aggregation (DLA) model. Each species has a preconfigured set of parameters for clonal growth including rhizome elongation, branching rate, vertical elongation rate, rhizome branching angle and shoot age. Seed recruitment is applied through occasional flowering/seeding events configurable per species. We developed a simple three-species competition model which controls the growth and direct competition effects based on a configurable population size and comparison radius. Upon further calibration and validation, the model would enable more accurate long-term predictions for different rehabilitation and transplanting strategies of mixed seagrass meadows. Further improvements can also be implemented, particularly taking into account the environmental variables within the meadows such as light attenuation and salinity, among other factors.

scholarly journals Dissolved organic carbon release by marine macrophytes

2012 ◽  
Vol 9 (2) ◽  
pp. 1529-1555 ◽  
Author(s):  
C. Barrón ◽  
E. T. Apostolaki ◽  
C. M. Duarte
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Seagrass Meadow ◽  
Gross Primary Production ◽  
The Philippines ◽  
Community Respiration ◽  
Seagrass Meadows ◽  
Macrophyte Communities ◽  
Marine Macrophytes ◽  
Doc Flux

Abstract. Estimates of dissolved organic carbon (DOC) release by marine macrophyte communities (seagrass meadows and macroalgal beds) were obtained experimentally using in situ benthic chambers. The effect of light availability on DOC release by macrophyte communities was examined in two communities both by comparing net DOC release under light and dark, and by examining the response of net DOC release to longer-term (days) experimental shading of the communities. All most 85% of the seagrass communities and almost all of macroalgal communities examined acted as net sources of DOC. There was a weak tendency for higher DOC fluxes under light than under dark conditions in seagrass meadow. There is no relationship between net DOC fluxes and gross primary production (GPP) and net community production (NCP), however, this relationship is positive between net DOC fluxes and community respiration. Net DOC fluxes were not affected by shading of a T. testudinum community in Florida for 5 days, however, shading of a mixed seagrass meadow in the Philippines led to a significant reduction on the net DOC release when shading was maintained for 6 days compared to only 2 days of shading. Based on published and unpublished results we also estimate the global net DOC production by marine macrophytes. The estimated global net DOC flux, and hence export, from marine macrophyte is about 0.197 ± 0.015 Pg C yr−1 or 0.212 ± 0.016 Pg C yr−1 depending if net DOC flux by seagrass meadows was estimated by taking into account the low or high global seagrass area, respectively.

Morphochronological variations in the genus Posidonia

1997 ◽  
Vol 48 (5) ◽  
pp. 421 ◽  
Author(s):  
G. Pergent ◽  
C. Pergent-Martini ◽  
M. Cambridge
Keyword(s):  
Primary Production ◽  
Western Australia ◽  
Leaf Blade ◽  
Leaf Sheath ◽  
Growth Rings ◽  
New Techniques ◽  
Seagrass Meadows ◽  
Foliar Tissue ◽  
Tissue Production

Morphochronological variations have been observed in five marine phanerogams of the genus Posidonia in the two regions where they occur (Mediterranean and Western Australia). The occurrence of these variations, which is comparable to that of growth rings in trees (studied in dendrochronology), has provided a basis for developing new techniques for the investigation of characteristics of these underwater seagrass meadows (e.g. primary production). The development of lepidochronology in the assessment of primary production has the advantage of being rapid and allowing the determination of the total foliar tissue production (leaf blade and leaf sheath) including that of species for which no data were hitherto available.

scholarly journals Temporal variability of a protected multispecific tropical seagrass meadow in response to environmental change

2019 ◽  
Vol 191 (12) ◽  
Author(s):  
E. Alonso Aller ◽  
J. S. Eklöf ◽  
M. Gullström ◽  
U. Kloiber ◽  
H. W. Linderholm ◽  
...  
Keyword(s):  
Species Composition ◽  
Environmental Change ◽  
Low Income ◽  
Environmental Variables ◽  
Seagrass Meadow ◽  
Spatial Scales ◽  
Temporal Changes ◽  
Climate Impacts ◽  
Seagrass Meadows ◽  
Seagrass Cover

AbstractIn a changing environment, there is an increasing interest to monitor ecosystems to understand their responses to environmental change. Seagrass meadows are highly important ecosystems that are under constant pressure from human activities and climate impacts, with marked declines observed worldwide. Despite increasing efforts, monitoring of multispecific tropical seagrass meadows is scarce, particularly in low-income regions. Based on data from a monitoring programme in a marine protected area in Zanzibar (Tanzania), we assessed temporal changes in seagrass cover and species composition during a 10-year period in relation to local variability in environmental variables. We observed a strong, gradual decline in seagrass cover and changes in species composition, followed by a period of recovery. However, the timing and length of these temporal patterns varied in space (between transects). Multiple environmental variables—cloud cover, temperature, storm occurrence, sunspot activity, and tidal amplitude and height—influenced seagrass cover, although only to a minor extent, suggesting that the monitored seagrass meadow may be influenced by other unmeasured factors (e.g. water currents and sediment movement). Our results show that seagrass meadows can be highly dynamic at small (10–50 m) spatial scales, even in the absence of major local anthropogenic impacts. Our findings suggest that high-resolution monitoring programmes can be highly valuable for the detection of temporal changes in multispecific seagrass meadows; however, to understand the causes of change, there is a need of long-term (> 10 years) data series that include direct measurements of environmental variables and extreme events.

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