The distribution, production, and many other aspects of species and biodiversity in coastal ecosystems are highly sensitive to variations in weather and climate (Section 6.4.1), affecting the distribution and abundance of the plant and animal species that depend on each coastal system type. Human development patterns also have an important influence on biodiversity among coastal system types. Mangroves, for example, support rich ecological communities of fish and crustaceans, are a source of energy for coastal food chains, and export carbon in the form of plant and animal detritus, stimulating estuarine and nearshore productivity (Jennerjahn and Ittekkot, 2002). Large-scale conversions of coastal mangrove forests to shrimp aquaculture have occurred during the past three decades along the coastlines of Vietnam (Binh et al., 1997), Bangladesh and India (Zweig, 1998), Hong Kong (Tam and Wong, 2002), the Philippines (Spalding et al., 1997), Mexico (Contreras-Espinosa and Warner, 2004), Thailand (Furakawa and Baba, 2001) and Malaysia (Ong, 2001). The additional stressors associated with climate change could lead to further declines in mangroves forests and their biodiversity.
Several recent studies have revealed that climate change is already impacting biodiversity in some coastal systems. Long-term monitoring of the occurrence and distribution of a series of intertidal and shallow water organisms in south-west Britain has shown several patterns of change, particularly in the case of barnacles, which correlate broadly with changes in temperature over the several decades of record (Hawkins et al., 2003; Mieszkowska et al., 2006). It is clear that responses of intertidal and shallow marine organisms to climate change are more complex than simply latitudinal shifts related to temperature increase, with complex biotic interactions superimposed on the abiotic (Harley et al., 2006; Helmuth et al., 2006). Examples include the northward range extension of a marine snail in California (Zacherl et al., 2003) and the reappearance of the blue mussel in Svalbard (Berge et al., 2005).
Patterns of overwintering of migratory birds on the British coast appear to have changed in response to temperature rise (Rehfisch et al., 2004), and it has been suggested that changes in invertebrate distribution might subsequently influence the distribution of ducks and wading birds (Kendall et al., 2004). However, as detailed studies of redshank have shown, the factors controlling distribution are complex and in many cases are influenced by human activities (Norris et al., 2004). Piersma and Lindstrom (2004) review changes in bird distribution but conclude that none can be convincingly attributed to climate change. Loss of birds from some estuaries appears to be the result of coastal squeeze and relative sea-level rise (Hughes, 2004; Knogge et al., 2004). A report by the United Nations Framework Convention on Biodiversity (CBD, 2006) presents guidance for incorporating biodiversity considerations in climate change adaptation strategies, with examples from several coastal regions.