Monitoring the Responses of Freshwater Ecosystems to Climate Change - Climate Change Impacts on Freshwater Ecosystems - page 92

With increasing spring water temperature and light availability, spring
phytoplankton species may grow earlier (Chen & Folt 1996; Müller-Navarra
et al . 1997; Elliott et al . 2006; Adrian et al . 2006). The spring peak may also be
more heavily grazed (Chen & Folt 1996; Müller-Navarra et al . 1997; Straile
2000). In summer, nutrient limitation may occur earlier. For example, the
summer cyanobacteria peak may decline earlier because of nutrient limitation
from increased spring growth at higher water temperatures (Bleckner et al .
2002; Elliott et al . 2005). Larger growths can be expected in autumn and
winter, benefitting from higher temperatures and delayed light-limitation before
ice forms (Bleckner et al . 2002).
Increased temperatures may result in greater macrophyte biomass or changes
in macrophyte community composition (Rooney & Kalff 2000; McKee et al .
2002; Feuchtmayr et al . 2007).
Secondary production
Trends in average temperature sometimes correlate significantly with changes in
zooplankton community composition, even over comparatively short periods of
10-15 years (Burgmer et al . 2007). Water temperature increase may be associated
with a shift of zooplankton assemblages from larger to smaller bodied forms, a
shift in food availability to inedible Cyanobacteria and possibly a heightened
sensitivity to algal toxins (Moore et al . 1996). Individual taxa have very different
threshold or maximum temperatures for growth that are species specific rather
than functional group specific. A shift from the dominance of large-bodied
Daphnia galeata to smaller D. cucullata has been observed with higher spring
temperatures (Adrian & Deneke 1996). Slow-growing summer zooplankton with
more complex life cycles responded specifically to seasonal warming, depending
on its timing (Adrian et al . 2006). Changes in the vertical temperature gradient
of a lake may affect zooplankton vertical migration. In warmer months,
zooplankton occurred closer to the surface (Helland et al . 2007). There are,
however, powerful effects of predation on zooplankton communities that may
mask any direct climate effects.
Community composition and species richness in lake fish communities is
strongly related to air temperature. In a study in third-order catchments, the
presence or absence of 33 out of 61 fish species was related to temperature, as
well as to geographic factors (Minns & Moore 1995). For many species, the
relationships with temperature have long been investigated: for instance,
Coregonus albula , an autumn spawning fish species, is vulnerable to spring
temperature increases because of a timing mismatch of hatching and the spring
development of zooplankton, in combination with higher rates of predation by
warm-water predatory fish species (Nyberg et al . 2001). Another threat for this
species is a general reduction in occurrence of the cold, oxygen-rich hypolimnetic
conditions that it requires in summer (George et al . 2006). Generally, higher
water temperatures increase growth and production for warm water fish and
inhibit growth and production for fish at or above their thermal optimum
(DeStasio et al . 1996; Petchey et al . 1999; Mackenzie-Grieve & Post 2006).