Environmental Engineering Reference
In-Depth Information
The euphotic zone of the continental shelf that is not uncovered by
tides is called the subtidal zone. In shallow subtidal areas, benthic algae can
form extensive communities such as the giant kelp forests, if hard substrata
is available. At greater depths, light becomes limited and algal diversity
and abundance are limited to shade-tolerant forms (Dawes 1998). Subtidal
seaweeds communities form important habitats and are the primary source
of food for many organisms (Littler and Littler 1984).
Seaweed Communities under Stress
Rocky shores are subjected to considerable natural environmental change,
the most obvious one is tidal amplitude that varies on short (daily to
monthly) and long-term (annual and decadal) time scales. Occasional
natural catastrophic events such as cold winters, hot summers, extreme
storms, toxic algal blooms, earthquakes and volcanic events also occur
(Denny and Paine 1998). Similarly, increased freshwater input from fl ooding
rivers can also infl uence adjacent coastlines (Thompson et al. 2002). Rocky
shore organisms have mechanisms to deal with stresses associated with
alternating submersion and emersion in air (desiccation, temperature
extremes, osmotic stress) (Karsten et al. 1996). The tolerance mechanisms
involved are also effective for withstanding some anthropogenic stresses.
Anthropogenic stress is the response of a biological entity to an anthropogenic
disturbance. Many coastal ecosystems are subjected to a variety of stresses
caused by human activities ranging from subsistence collection of food
through the discharge of domestic and industrial effl uents and occasional
catastrophic oil spills. These anthropogenic stresses are superimposed on
the stress caused by natural environmental factors (Harvell et al. 1999).
Anthropogenic stresses infl uence the metabolism, activity patterns,
respiration, growth, reproductive output and immune responses of
intertidal organisms (Harvell et al. 1999). Numerous studies have examined
mortality of intertidal organisms in relation to environmental stresses and
attempted to relate these to their distribution (Lüning 1984). For most
species, the distribution falls well within their ultimate physiological
tolerances and is determined by interactions among several physical and
biological factors (Raffaelli and Hawkins 1996). Hence the consequences
of anthropogenic stress are often expressed by sub-lethal effects, which
alter the competitive balance between species and indirectly infl uence their
population distribution and abundance.
Climate change and global warming occurring on Earth are recognized
phenomena within the public and scientific communities. The IV
Intergovernmental Panel on Climate Change (IPCC 2007) reported changes
in the abundance of seaweed and phytoplankton, a higher acidity of the
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