Benthic Community and Climate Change - Marine Ecology in a Changing World - page 128

the planet have been seen on rocky shores of Europe (Mieszkowska et al .
2006, Herbert et al. 2007, Lima et al . 2007), United States (Zacherl et al. 2003,
Harley et al . 2006) and South America (Rivadeneira and Fernandez 2005).
Temperature is an important determinant of rocky intertidal species
survival, and organisms living in this habitat exist at or near the edges of
their thermal tolerance limit (Davenport and Davenport 2005). Temperature
is also an important factor affecting metabolism, growth, feeding behavior,
reproduction and rates of larval development (Anil et al. 2001, Sanford 2002,
Luppi et al. 2003, Philippart et al. 2003, Phillips 2005). The physiological
function and geographic distribution of rocky intertidal species are
determined by both aerial and aquatic body temperature (Helmuth et al .
2006a, Helmuth et al . 2006b), such that organisms living on rocky shores will
show strong responses to changes associated with sea level rise, which affect
their emersion time (Harley et al . 2006); the behavior of organisms living
higher on the shore may be less predictable, whereas organisms that live at
median and low tide, exposed to periods of immersion and exposure, will be
more affected by the changes (Helmuth et al . 2006a). The body temperature
of intertidal invertebrates during aerial exposure depends upon a number
of interacting factors such as the absolute tidal height of the organism on
the shore, the amount of wave splash it receives and the local tidal cycle, all
of which affect the timing and duration of exposure to terrestrial conditions
at low tide; during exposure, the substratum angle plays a major role in
determining the amount of solar radiation received (Helmuth and Hofmann
2001). Experimental manipulation of aerial body temperature by shading
has enabled the documentation of changes in mortality, rates of predation,
relative competitive ability and species zonation patterns (Harley and
Lopez 2003). The importance of biotic interactions and behavior has also
been revealed: species are geographically limited by physiological stresses
related to aerial exposure such as when the upper limits of an organism are
squeezed down to the upper limit of a predator or dominant competitor,
resulting in the elimination of the subordinate or prey species from the
intertidal zone (Harley 2003, Harley and Helmuth 2003). The very same
climatic conditions can lead to widely differing body temperatures in two
different organisms, and hence different levels of physiological stress.
For example, Helmuth (2002) has shown that at low tide, the predatory
seastar Pisaster ochraceus may be up to 10ºC cooler than its prey, Mytilus
californianus .
Many intertidal organisms are expected to display strong responses to
changes in terrestrial climatic conditions (Somero 2002). A well-studied case
documenting changes in the abundance of intertidal rocky shore species
in response to climatic change involves two groups of acorn barnacles:
Semibalanus balanoides , a boreoarctic form that reaches its main southern
limit in the south of England and Brittany and two warm-water species of