9.3.1.2. Mangrove Communities
The capacity of mangrove forests to cope with sea-level rise is higher where
the rate of sedimentation approximates or exceeds the rate of local sea-level
rise. Indeed, Hendry and Digerfeldt (1989) have shown that mangrove communities
in western Jamaica were able to keep pace with mid-Holocene sea-level rise (ca.
3.8 mm/yr). However, the adaptive capacity of mangroves and other coastal wetlands
to sea-level rise (usually by landward migration) is now severely limited in
many localities by increasing human activities. It has been suggested, for instance,
that a 1-m rise in sea level in Cuba will drastically affect the viability of
333,000 ha of these wetland communities (approximately 93% of Cuba's mangroves)
(Perez et al., 1996). Additionally, adaptive capacity will vary among species;
some species of mangroves appear to be more robust and resilient than others
to the effects of climate change and sea-level rise (Ellison and Stoddart, 1991;
Aksornkaoe and Paphavasit, 1993).
Some ecologists believe that mangrove communities are more likely to survive
the effects of sea-level rise in macrotidal, sediment-rich environments-such
as northern Australia, where strong tidal currents redistribute sediment (Semeniuk,
1994; Woodroffe, 1995)-than in microtidal, sediment-starved environments like
those in many small islands (e.g., in the Caribbean) (Parkinson et al., 1994).
Most small islands fall within the latter classification; therefore, they are
expected to suffer reductions in the geographical distribution of mangroves.
Furthermore, where the rate of shoreline recession increases, mangrove stands
are expected to become compressed and suffer reductions in species diversity
in the face of rising sea levels.
On the other hand, Snedaker (1993) argues that mangroves in the Caribbean are
more likely to be affected by changes in precipitation than by higher temperatures
and rising sea levels because they require large amounts of fresh water to reach
full growth potential. He hypothesizes that a decrease in rainfall in the Caribbean
would reduce mangroves' productive potential and increase their exposure to
full-strength seawater. Thus, peat substrates would subside as a result of anaerobic
decomposition by sulfate-reducing microorganisms, leading to the elimination
of mangroves in affected areas (Snedaker, 1993).
9.3.1.3. Seagrasses
It has been postulated that seagrass meadows-which exist in shallow, intertidal
coastal environments-are the ecosystems most likely to be negatively affected
by climate change effects, particularly sustained elevation of sea-surface temperature
or increases in freshwater runoff from land (Edwards, 1995). There is a growing
consensus, however, that the main threats to seagrasses in the future are likely
to come not from the effects of climate change but from anthropogenic disturbances-such
as dredging, overfishing, water pollution, and land reclamation.
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