Photosynthetic responses of seven tropical seagrasses to elevated seawater temperature

Long-term climate-associated dynamics of a tropical seagrass meadow: implications for the future

“…The investment in aboveground biomass is not necessarily directly related to spatial cover, as a large meadow could have a high or low biomass, and the area could have expanded whilst the biomass declined (or vice versa) and reflects how the plant (or plants) has invested its resources. The result of a positive correlation between area and daylight tidal exposure is, however, unexpected given the potential for such periods to result in heat, desiccation and UV stress (Björk et al 1999, Campbell et al 2006 and is in contrast to results of analysis of an Enhalus acoroides meadow, also located in north Queensland (Chartrand & Rasheed 2009). In contrast to the largeleaved E. acoroides, Halodule uninervis at Karumba is narrow and small leaved, enabling leaves to potentially lie flat on wet sediment and avoid some of the desiccation risk.…”

“…Such meadows are often spatially expansive , Coles et al 2003 and are particularly important food sources for dugong Dugong dugong and green turtles Chelonia mydas (Bjorndal 1985, Preen & Marsh 1995. The intertidal and coastal location of these meadows makes them susceptible to large climatic events, such as flooding , Campbell & McKenzie 2004, drought (Cardoso et al 2008) and elevated temperature (Campbell et al 2006). Such meadows can be highly dynamic , McKenzie 1994, Rasheed 1999, and changes in assemblage biomass and plant growth can commonly vary by up to a factor of 4 (Brouns 1985, Erftemeijer & Herman 1994, Lanyon & Marsh 1995.…”

“…Air temperature has a large effect upon intertidal seagrass, both when the seagrass is exposed and when very shallow water becomes 'super-heated' because of warm air temperatures (Campbell et al 2006). At present the responses of seagrass to variable in situ temperature are virtually unmeasured, especially within tropical environments (Thorhaug 1978, Agawin et al 2001, Waycott et al 2007).…”

“…Predictions of the influence of climate change scenarios on seagrass (Short & Neckles 1999, Harley et al 2006, Poloczanska et al 2007, Waycott et al 2007) are largely based on incidences of seagrass loss associated with extreme weather (Cardoso et al 2008, Micheli et al 2008 as reported in short-term experimental studies (Campbell et al 2006). Long-term studies directly measuring seagrass changes and how they are correlated with climate are rare.…”

“…The biomass of the small colonising species Halophila ovalis, which was a minor assemblage component, was positively correlated with rainfall; temperature was not a correlate with H. ovalis. Although incidences of high short-term rainfall and flooding have commonly resulted in detrimen- (Campbell et al 2006). Temperature stress can result not just from seagrass being subjected to elevated seawater temperatures, but additionally, intertidal seagrass can be subjected to desiccation stress during periods of low tide during daylight hours (Dawson & Dennison 1996, Stapel 1997, Durako & Kunzelman 2002.…”