Elemental composition and productivity of cyanobacterial mats in an arid zone estuary in north Western Australia

Extensive cyanobacterial mats are a feature of the high intertidal zone in the Exmouth Gulf, Western Australia. This study provides a description of the position of the mats within the intertidal zone and of the mats elemental composition and productivity. We found that the mats occupied 40 cm elevational range within the intertidal zone. They have a mean organic matter content of 1,600 g m(-2). Mean concentrations of nitrogen (N) were 1.82 g kg(-1) and phosphorus (P) 205 mg kg(-1). N:P ratio was 19.7 indicating P limitation, but N:P was variable. Rates of photosynthesis and biomass production were similar to those reported for mats in hypersaline conditions at other sites. When photosynthetic production was scaled-up for the region our data suggest that cyanobacterial mats are an important contributor to the carbon budget in the Exmouth Gulf, contributing between 5 and 15% of the total carbon fixed by primary producers. Additionally mats were observed to be a source of soluble carbohydrates in tidal waters indicating that fixed carbon from high intertidal cyanobacterial mats may enter near shore food webs through this pathway

Characterisation of polymorphic microsatellite markers in the widespread Australian seagrass, Posidonia Australis Hook. F. (Posidoniaceae), with cross-amplification in the sympatric P. Sinuosa

We developed 10 polymorphic microsatellite markers in the Australian seagrass Posidonia australis Hook. f. Markers were screened for their ability to detect within- and among-population genetic structure and variation. The markers showed a range in levels of polymorphism from fixed differences between the two sampled seagrass meadows to high levels of heterozygosity. These markers will be used to estimate gene flow across the species range, characterise the mating system through paternity analysis and pollen dispersal, characterise the nature and extent of clonality, and determine the genetic differentiation of local seagrass meadows to provide information on where to source local genetic provenance material for seagrass restoration projects. Seven of the 10 loci also amplified in the sympatric P. sinuosa and will be useful in future studies in population genetics and hybridisation. © Springer Science+Business Media B.V. 2009

Global analysis of seagrass restoration: the importance of large-scale planting

In coastal and estuarine systems, foundation species like seagrasses, mangroves, saltmarshes or corals provide important ecosystem services. Seagrasses are globally declining and their reintroduction has been shown to restore ecosystem functions. However, seagrass restoration is often challenging, given the dynamic and stressful environment that seagrasses often grow in. From our world-wide meta-analysis of seagrass restoration trials (1786 trials), we describe general features and best practice for seagrass restoration. We confirm that removal of threats is important prior to replanting. Reduced water quality (mainly eutrophication), and construction activities led to poorer restoration success than, for instance, dredging, local direct impact and natural causes. Proximity to and recovery of donor beds were positively correlated with trial performance. Planting techniques can influence restoration success. The meta-analysis shows that both trial survival and seagrass population growth rate in trials that survived are positively affected by the number of plants or seeds initially transplanted. This relationship between restoration scale and restoration success was not related to trial characteristics of the initial restoration. The majority of the seagrass restoration trials have been very small, which may explain the low overall trial survival rate (i.e. estimated 37%). Successful regrowth of the foundation seagrass species appears to require crossing a minimum threshold of reintroduced individuals. Our study provides the first global field evidence for the requirement of a critical mass for recovery, which may also hold for other foundation species showing strong positive feedback to a dynamic environment.Synthesis and applications. For effective restoration of seagrass foundation species in its typically dynamic, stressful environment, introduction of large numbers is seen to be beneficial and probably serves two purposes. First, a large-scale planting increases trial survival - large numbers ensure the spread of risks, which is needed to overcome high natural variability. Secondly, a large-scale trial increases population growth rate by enhancing self-sustaining feedback, which is generally found in foundation species in stressful environments such as seagrass beds. Thus, by careful site selection and applying appropriate techniques, spreading of risks and enhancing self-sustaining feedback in concert increase success of seagrass restoration.For effective restoration of seagrass foundation species in its typically dynamic, stressful environment, introduction of large numbers is seen to be beneficial and probably serves two purposes. First, a large-scale planting increases trial survival - large numbers ensure the spread of risks, which is needed to overcome high natural variability. Secondly, a large-scale trial increases population growth rate by enhancing self-sustaining feedback, which is generally found in foundation species in stressful environments such as seagrass beds. Thus, by careful site selection and applying appropriate techniques, spreading of risks and enhancing self-sustaining feedback in concert increase success of seagrass restoration

Radiocarbon dating and wood density chronologies of mangrove trees in arid Western Australia

Mangrove trees tend to be larger and mangrove communities more diverse in tropical latitudes, particularly where there is high rainfall. Variation in the structure, growth and productivity of mangrove forests over climatic gradients suggests they are sensitive to variations in climate, but evidence of changes in the structure and growth of mangrove trees in response to climatic variation is scarce. Bomb-pulse radiocarbon dating provides accurate dates of recent wood formation and tree age of tropical and subtropical tree species. Here, we used radiocarbon techniques combined with X-ray densitometry to develop a wood density chronology for the mangrove Avicennia marina in the Exmouth Gulf, Western Australia (WA). We tested whether wood density chronologies of A. marina were sensitive to variation in the Pacific Decadal Oscillation Index, which reflects temperature fluctuations in the Pacific Ocean and is linked to the instrumental rainfall record in north WA. We also determined growth rates in mangrove trees from the Exmouth Gulf, WA. We found that seaward fringing A. marina trees (similar to 10 cm diameter) were 48 +/- 1 to 89 +/- 23 years old (mean +/- 1 sigma) and that their growth rates ranged from 4.08 +/- 2.36 to 5.30 +/- 3.33 mm/yr (mean +/- 1 sigma). The wood density of our studied mangrove trees decreased with increases in the Pacific Decadal Oscillation Index. Future predicted drying of the region will likely lead to further reductions in wood density and their associated growth rates in mangrove forests in the region

Seagrass ecosystems as a globally significant carbon stock

5 páginas, 5 figuras, 1 tabla.The protection of organic carbon stored in forests is considered as an important method for mitigating climate change. Like terrestrial ecosystems, coastal ecosystems store large amounts of carbon, and there are initiatives to protect these ‘blue carbon’ stores. Organic carbon stocks in tidal salt marshes and mangroves have been estimated, but uncertainties in the stores of seagrass meadows—some of the most productive ecosystems on Earth—hinder the application of marine carbon conservation schemes. Here, we compile published and unpublished measurements of the organic carbon content of living seagrass biomass and underlying soils in 946 distinct seagrass meadows across the globe. Using only data from sites for which full inventories exist, we estimate that, globally, seagrass ecosystems could store as much as 19.9 Pg organic carbon; according to a more conservative approach, in which we incorporate more data from surface soils and depth-dependent declines in soil carbon stocks, we estimate that the seagrass carbon pool lies between 4.2 and 8.4 Pg carbon. We estimate that present rates of seagrass loss could result in the release of up to 299 Tg carbon per year, assuming that all of the organic carbon in seagrass biomass and the top metre of soils is remineralized.This is a contribution of the International Blue Carbon Science Working Group. We thank the contributors of unpublished data to our database, including A. Paytan, W.H. Orem and M. Copertino. Partial support for J.W.F.'s contribution was provided by a Gledden Visiting Senior Fellowship from the Institute of Advanced Studies, University of Western Australia and an Australian National Network in Marine Sciences Visiting Scholar fellowship and by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research programme under Grant No. DBI-0620409. C.M.D and N.M. were financially supported through the MEDEICG project of the Spanish Ministry of Science and Innovation (project ID CTM2009-07013). G.A.K. was supported by NHT II- Caring for our Country funding. M.H. was financially supported by the Danish Natural Science Foundation (09-071369). M.A.M. and O.S. acknowledge the Spanish Ministry of Science and Innovation (MICINN) and the High Council of Scientific Research (CSIC) for financially supporting various pioneering projects to explore the role of P. oceanica as a coastal C sink and a palaeoecological record. D.K.J. acknowledges the Danish National Monitoring and Assessment Programme for the Aquatic and Terrestrial Environment (NOVANA) and colleagues associated with the programme for support. K.J.M. was supported by the National Science Foundation through the Virginia Coast Reserve Long-Term Ecological Research programme under Grant No. 0621014. This is contribution no. 550 from the Southeast Environmental Research Center at Florida International University.Peer reviewe