Increases in sea level are an expected consequence of rising temperatures. The Intergovernmental Panel on Climate Change has forecast sea level rises ranging from 15 centimetres to almost one metre. The lower limit of these estimates corresponds to the rate of sea-level rise that has been occurring for the past century or two. The upper-limit estimate represents a substantial acceleration that may happen but for which, as yet, there is no strong evidence (IPCC 1995).

 

The main issue for marine invertebrates is the loss or change in coastal habitats. In particular, the biota restricted to or dependent on the narrow band of habitat close to sea level will be subjected to rising sea levels from below as well as increased pressure from development above (Reid and Trexler 1992). Rising seas will stress coastal habitats including wetlands, barrier islands, coral reefs, coastal lagoons, mangroves and saltmarshes. The areal extent of some of these habitats could well be contracted, if the rate of change is faster than the adoption of new available habitats.

 

There is an extensive literature on how mangroves might be affected by sea level change.  Nevertheless, stable sea levels are required for the formation of extensive mangrove swamp forests and have occurred only intermittently over the late Quaternary (Crowley 1996). Semeniuk (1994) discussed the effects of sea-level rise on mangroves in north-western Australia and concluded that the mangroves’ response would depend on the environmental setting, including the homogeneity (geomorphologically and sedimentologically) of the coast, its tidal range, stability, and history, as well as the variety of species present and their reproductive strategies. In some places (e.g. King Sound in WA, where natural erosion, progressing at 1-3 cm/yr, simulates the effects of a rising sea), mangroves are able to migrate landwards, generally keeping pace with the retreat, through colonisation (by seedling recruitment) of habitats made available by increased inundation. However, mangroves in other parts of NW Australia, where more heterogeneous assemblages have developed, are not likely to adjust so rapidly, and hence would be disrupted (Semeniuk 1994).

 

Changes in storm patterns etc  

The effect that global warming might have on circulation patterns in the major oceans has been a topic of much speculation and research (Rahmstorf 1999), in part because of the link between the major current systems and global and regional climate. Recently, Wood et al. (1999) presented a new climate model and greenhouse scenarios that suggest possible dramatic changes in the large-scale circulation patterns and currents in the Atlantic in response to increases in greenhouse gas concentrations.

 

Property and other damage from cyclones, storms and associated wind, erosion and flood hazards appear to have increased markedly in recent years (e.g., David et al. 1999). In Australia, cyclones currently cause periodic damage to coral reefs (e.g., Connell et al. 1997) and – due to increased rainfall and river flows – sedimentation events, which impact on marine invertebrate communities (see Section 6.6.1). A greater frequency or intensity of such events could, in combination with other anthropogenic stresses, reduce the opportunities for normal recovery leading to long-term changes in habitat type and community compensation (Hughes and Connell 1999).



Copyright © Environment Australia, 2002
Department of Environment and Heritage