Environmental Engineering Reference
In-Depth Information
has lower nutritional quality, supporting less production at higher trophic
levels. Summarizing, nutrients concentration in marine environment is
the main factor defi ning the confi guration of local food web, and water
temperature is a valuable proxy for nutrient enrichment. If the predictions
are true and the global temperature rises 1° to 2°C in the next 40 years
increasing stratifi cation, the impact on biological communities could be
devastating (Roemicch and McGowan 1995).
Climatic fl uctuations have had profound impacts on the abundance of
planktonic species (Mackas et al. 1998, Beaugrand et al. 2002, Stenseth et
al. 2002, Parmesan and Yohe 2003, Richardson and Schoeman 2004, Perry
et al. 2005, Chiba et al. 2006). The coincidence of oceanic temperature
rise and the decline in zooplankton densities in diverse aquatic systems
are suggestive of a direct causal relationship. Changes in the abundance
of some planktonic organisms off the coast of California have been well
documented over the past few decades (Hughes 2000). The surface waters
of the California Current have warmed by 1.2-1.6°C in approximately 40
years. This warming was accompanied by an 80% decline in zooplankton
abundance (Roemmich and McGowan 1995), possibly because increased
surface temperatures reduced the upwelling of cold, nutrient rich waters
(Hughes 2000). As a consequence,
Puffi nus griseus
, one of the top predators
in the system, suffered a 90% reduction in abundance off western North
America (1987-1994) (Hughes 2000). In the Northeast Atlantic, Richardson
and Schoeman (2004) also evidenced the effect that sea surface warming
has on stratifi cation and plankton dynamics. Phytoplankton abundances
were higher with warming of cool, windy, and well-mixed regions. Warmer
temperatures increase metabolic rates and water stratification, thus
increasing the residence time of phytoplankton cells in the euphotic zone
(Richardson and Schoeman 2004). In contrast, phytoplankton abundances
decreased in warm regions that become even warmer, probably because
heater surface water blocks further nutrient-rich deep water from rising
to the euphotic layer (Richardson and Schoeman 2004). The increased
phytoplankton abundances in cooler regions and the opposite trend in
warm regions was thus highly correlated with changes in the densities of
primary (herbivores) and secondary consumers (carnivores) (Richardson
and Schoeman 2004).
Although most of the evidence of climate impacts on zooplankton
community structure and abundance is from the Northern Hemisphere,
there are dramatic changes documented in the Southern Ocean (Richardson
2008). The Antarctic krill
Euphausia superba
is the primary prey for many
predators in Antarctic waters, supporting commercial fi sheries (Atkinson
et al. 2004). It has a key status in the Southern Ocean and occupies a central
place in commercially valuable food webs (Meyer et al. 2003). Since the
1970s, there has been a decline in krill density and a concomitant increase
