Seagrasses in tropical Australia, productive and abundant for decades decimated overnight
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Australian Rivers Institute, 2School of Engineering, Griffith University, Nathan campus Q. 4111 Australia *Corresponding author (Email, [email protected])
Seagrass ecosystems provide unique coastal habitats critical to the life cycle of many species. Seagrasses are a major store of organic carbon. While seagrasses are globally threatened and in decline, in Cairns Harbour, Queensland, on the tropical east coast of Australia, they have flourished. We assessed seagrass distribution in Cairns Harbour between 1953 and 2012 from historical aerial photographs, Google map satellite images, existing reports and our own surveys of their distribution. Seasonal seagrass physiology was assessed through gross primary production, respiration and photosynthetic characteristics of three seagrass species, Cymodocea serrulata, Thalassia hemprichii and Zostera muelleri. At the higher water temperatures of summer, respiration rates increased in all three species, as did their maximum rates of photosynthesis. All three seagrasses achieved maximum rates of photosynthesis at low tide and when they were exposed. For nearly six decades there was little change in seagrass distribution in Cairns Harbour. This was most likely because the seagrasses were able to achieve sufficient light for growth during intertidal and low tide periods. With historical data of seagrass distribution and measures of species production and respiration, could seagrass survival in a changing climate be predicted? Based on physiology, our results predicted the continued maintenance of the Cairns Harbour seagrasses, although one species was more susceptible to thermal disturbance. However, in 2011 an unforeseen episodic disturbance – Tropical Cyclone Yasi – and associated floods lead to the complete and catastrophic loss of all the seagrasses in Cairns Harbour. [Pollard PC and Greenway M 2013 Seagrasses in tropical Australia, productive and abundant for decades decimated overnight. J. Biosci. 38 157–166] DOI 10.1007/s12038-013-9299-6
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Introduction
As submerged marine flowering plants, seagrass meadows are found in shallow coastal waters around the world. They provide food and shelter for invertebrates and fish, endangered species such as dugongs and turtles, and provide a critical part of the early life cycle of many species that contribute to off-shore fisheries (Greenway 1995; Green and Short 2003; Halpern et al. 2008). Recent research has shown that seagrass meadows globally store nearly three times more organic carbon than the carbon stocks of the world’s forests (Fourqurean et al. 2012). Human activity in coastal areas is limiting the extent of their distribution and with global climate change and increased water temperatures their distribution may be even further limited (Orth et al.
2006; Short et al. 2007; Waycott et al. 2009; Jorda et al. 2012; McKenzie et al. 2012). There are few places in the world where coastal seagrass ecosystems have not only survived but also flourished amidst increasing anthropogenic influences (Halpern et al. 2008). Whi
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