Climate Change and Marine Zooplankton - Marine Ecology in a Changing World - page 96

Metabolic rate of ectothermic organisms rises exponentially with
temperature, leading to higher rates of physiological processes, including
photosynthesis and respiration, within the range of temperatures that
an organism tolerates (Doney et al. 2012). The effect of temperature on
a biological process is traditionally expressed as Q 10 , which quantifi es
temperature dependence across a limited temperature range (i.e., 10°C)
(Gillooly et al. 2001). It might be expected that primary production, as well
as the growth rates of ectothermic animals will increase in a warmer ocean
(Doney et al. 2012). However, nutritional status, thermal tolerance, oxygen
availability, elemental stoichiometry, food availability, among other factors
may limit growth and production, or other biological processes, regardless
of metabolic rate (Doney et al. 2012). In heterotrophic organisms, warmer
temperatures raise basal metabolic rates but can also raise respiratory
demand, potentially reducing their aerobic capacity (e.g., feeding,
predator avoidance, digestion) and leading to less energy for growth and
reproduction (Portner and Knust 2007).
At the population and community levels, individual physiological
responses to global warming are evident as shifts in structure and
abundance, spatial distribution of organisms and timing of annually
recurring events (e.g. , phenology) (Doney et al. 2012):
Changes in zooplankton community structure and abundance. Hydroclimatic
changes can exert signifi cant effects on the size structure, taxonomic
composition and diversity of zooplankton communities since these features
are regulated by their physical and chemical environment (Richardson 2008).
On a global scale, plankton community would exist in a continuum of states
between two extremes, the cold, well-mixed, high-nutrient environment
and the warm, stably stratifi ed, nutrient-poor environment (Schultz 2008).
Falkowski (2003) used the terms “ perturbed regime ” and “ balanced regime ”
to distinguish between these two systems. In cool waters with relatively
strong turbulence and well-mixed conditions, surface waters are full-up of
nutrients. In this perturbed regime , plankton community is dominated by
large centric diatoms and large crustaceans like copepods. The food chain
is short and highly effi cient, and supports a large number of planktivorous
and piscivorous fi shes, seabirds and mammals (Ryther 1969, Iverson 1990,
Pauly and Christensen 1995, Richardson 2008). In the balanced regime ,
the warmer and more stratifi ed waters have limited concentrations of
nutrients. Increased heating can enhance existing stratifi cation, reducing
the availability of nutrients in the surface (Richardson and Schoeman 2004).
Under such conditions, plankton community is dominated by picoplankton
and fl agellates, which are mostly grazed by heterotrophic protist, small
crustaceans and gelatinous zooplankton (Ryther 1969, Iverson 1990, Pauly
and Christensen 1995, Richardson 2008). This long and ineffi cient foodweb