Seaweeds Ecology and Climate Change - Marine Ecology in a Changing World - page 168

ocean waters and an increase in the surface seawater temperature. Another
phenomenon associated to climate change is the increase of UV radiation
on aquatic ecosystems.
Thermal stress
Temperature and distribution
Temperature is one of the most fundamental abiotic factors for organisms as
it affects all levels of biological organization from molecular to community
level, e.g., the physiology, ontogeny, trophic interactions, biodiversity,
phenology and biogeography of organisms.
The geographical distribution of seaweeds depends upon habitat
temperature regime and temperature requirement for growth, reproduction
and survival (van den Hoek 1982a, b, Breeman 1988). Four critical
temperatures are important determining factors in this distribution:
the minimum temperature for survival, the minimum and maximum
temperature for reproduction, and the maximum temperature for survival
(Hutchins 1947). Such temperatures vary widely between species; as a
general rule, seaweeds with a wide geographical range are eurythermal,
that is, they are able to tolerate a wide range of temperature conditions,
whereas stenothermal species have relatively limited geographical ranges
since they are unable to tolerate large fl uctuations in temperature. For
example, the stenothermal Antarctic endemic red seaweed Palmaria decipiens,
grows at temperatures from 0 to 10°C (Wiencke and tom Dieck 1989). On the
contrary, the eurythermal brown seaweed Fucus vesiculosus shows a wide
geographical distribution from -2.1°C to 27.8°C, and has been recorded in
several shores worldwide.
Seaweed communities are important indicators of climate change not
only on a long time-scale but also on a short time - scale because of several
reasons: a) generally, intertidal species respond more rapidly than their
terrestrial equivalents to environmental changes because they usually have a
shorter life-span associated with sessile adult stages (Southward et al. 2004);
b) they are periodically exposed to temperature and weather extremes so
many intertidal species live close to their thermal tolerance (Helmuth et
al. 2002, Tomanek and Helmuth 2002); c) even when temperatures are not
suffi ciently high to directly cause the death of the organisms (Denny et al.
2006), they may have sublethal effects that eventually lead to death, limited
growth and reproduction (Breeman 1988, Somero 2002), increase in desease's
susceptibility or indirectly set limits on distribution by determining the
outcome of biotic interactions (Sanford 1999, 2002); d) because of their
position in the base of the marine food webs, changes in the composition of
seaweed communities can substantially restructure food-web interactions
amplifying their effect on the entire ecosystem.