Benthic Community and Climate Change - Marine Ecology in a Changing World - page 123

to environmental stress. Certain young benthic stages, for example, are
more vulnerable to stress than are adults (Harley et al . 2006). Changes in
temperature may directly infl uence mortality, reproduction, the onset of
spawning and the embryonic and gonad development of benthic species,
leading to phenological changes (Birchenough et al . 2011) that directly affect
trophic interactions, alter food-web structures and can lead to changes at
the ecosystem level. Since the recruitment success of higher trophic levels is
highly dependent upon synchronization with pulsed planktonic production,
temperate marine environments may be particularly vulnerable to these
changes (Edwards and Richardson 2004). For example, the spawning of
Macoma balthica in north-western Europe is timed in accordance with the
temperature; warmer trends in recent years have led to earlier spawning
but the timing of spring phytoplankton blooms has remained unchanged,
resulting in a temporal mismatch between larval production and food
supply (Philippart et al . 2003). Furthermore, the peak abundance of shrimp
has advanced to coincide more closely with the arrival of vulnerable spat,
thus intensifying shrimp predation on juvenile Macoma balthica (Philippart
et al. 2003).
Early biogeographic studies have already established a link between
the distribution of marine species and mean sea surface isotherms such that
increases in ocean temperature can be expected to change the latitudinal
distribution of species (Birchenough et al. 2011). Over decades, climate
warming may alter the composition of the resident biota by facilitating the
poleward spread of species characteristic of warmer temperature regimes
(Southward et al. 1995, Sagarin et al . 1999). However, climate change could
also produce a signifi cant expansion of the range of species across ocean
basins or continents (Stachowicz et al. 2002). The relationship between
temperature and distribution shifts, however, gets complicated by the effects
of other environmental parameters, such as physical barriers to movement
and human usage of the coastal zone (Birchenough et al. 2011). Southward
et al. (1995) reported changes in the abundance of Northeast Atlantic taxa
ranging from kelps to barnacles and from zooplankton to fi sh. The local
abundance of warm-water species increased and that of cold-water species
decreased during periods of ocean warming, whereas the opposite occurred
during a cooling period. Most changes are initially observed at the edge
of ranges, where the level of physiological stress to which organisms are
exposed is likely to be higher, but local and regional heterogeneity within
biogeographic ranges has also been observed, with infi lling of gaps or loss
of site occupancy away from range limits (Birchenough et al . 2011). In order
to predict future distributional shifts, closer attention needs to be paid to
species range boundaries and the factors that determine them (Harley et
al. 2006). Rather than—or in addition to—shifts in species ranges, several
researchers have proposed that ocean warming may result in cascading