Decline and recovery of seagrass ecosystems: The dynamics of change
Walker, D., Kendrick, G. and McComb, A.J. (2006) Decline and recovery of seagrass ecosystems: The dynamics of change. In: Anthony, W.D., Orth, R.J. and Duarte, C.M., (eds.) Seagrasses: Biology, Ecology and Conservation. Springer, Dordrecht, The Netherlands, pp. 551-565.
The distribution of seagrass beds has often been described in the literature as if these communities were naturally static components of coastal ecosystems (Larkum, 1977; McRoy and McMillan, 1977; Orth and Moore, 1983; Kirkman and Kuo, 1990), disturbed only by human influences. A paradigm of seagrass bed stability, developed for large bed-forming seagrasses such as Posidonia as in the Mediterranean Sea (Boudouresque et al., 1980), and the western and southern coasts of Australia (Larkum, 197 6; Larkum and West, 1983; Kirkman, 1978), suggested that sea level had been stable for the last 5-8,000 years and assumed that these large monospecific seagrass beds were static for that period.
Immense variations have been shown in detailed studies of such beds, on a seasonal and spatial basis (e.g. Duarte et al., 1994; Alcoverro et al., 1995; Duarte et al., 2003). Change is a naturally-occurring process, which takes place in the absence of human influence (Patriquin, 1975; Hottinger and Vischer, 1983; Clarke and Kirkman, 1989; Marba and Duarte, 1995; Marba and Duarte, f998). There have also been massive declines in seagrass due to anthropogenic effects (Orth and Moore, 1983; Walker and McComb, 1992; Short and Wyllie-Echeverria, 1996), raising the possibility that such losses may be irreversible. Recent research findings suggest this is not the case (Kendrick et al., 1999, 2002).
This chapter will detail aspects of more recent research demonstrating changes, both negative and positive, in seagrass distributions, as revealed by mapping and other detailed investigations. The extent of decline dominates the literature, but an increasing number of studies record the dynamic nature of seagrass meadows (Williams, 1988; Kendrick et al., 1999, 2000, 2002; Cambridge et al., 2000, 2002; Durako et al., 2002). The rates of decline and recovery will be compared. The evidence for large-scale recovery of seagrass beds, based on mapping projects, will then be described. A case study will be presented that compares and contrasts two regions on the Western Australian coast: Cockburn Sound, where seagrass loss has been dramatic and is continuing; and Success and Parmelia Banks where loss and recovery are in dynamic equilibrium or seagrasses are expanding into unvegetated sand habitats. Comparisons and contrasts in findings in Florida Bay (USA) will be explored. We will conclude by suggesting a way in which management of seagrass landscapes can be made proactive to match their dynamic nature.
|Publication Type:||Book Chapter|
|Murdoch Affiliation:||School of Environmental Science|
|Copyright:||© 2006 Springer|
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