Environmental Engineering Reference
In-Depth Information
for adults, which in turn are linked to varying regimes of the principal
climate indices El Niño-La Niña Southern Oscillation Index (SOI) and
the related Pacifi c Decadal Oscillation (PDO). The tropical tuna species,
skipjack and yellowfi n have higher recruitments during El Niño events,
whereas the subtropical albacore has low recruitment during El Niño
and high recruitment during La Niña (Brander 2010). Both statistical and
coupled biogeochemical models have been developed to explore the causes
of regional variability in catches and their connection with climate.
The model area includes the Pacifi c from 40°S to 60°N and includes the
Kuroshio extension east of Japan (Taguchi et al. 2007). This is one of the
best examples linking processes and scales from climate related upwelling
and primary production to large geographic regions and decadal regime
shifts. The model captures the slowdown of Pacifi c meridional overturning
circulation and decrease of equatorial upwelling, which has caused primary
production and biomass to decrease by about 10% since 1976-77 in the
equatorial Pacifi c (McPhaden and Zhang 2002).
North Atlantic
Plankton samples collected between 1958 and 2002 showed an increase
in phytoplankton abundance in the cooler regions of the Northeast
Atlantic (north of 55°N) and a decrease in warmer regions (south of 50°N)
(Richardson and Schoeman 2004). The likely explanation for this apparently
contradictory result is that although both areas have undergone warming
over this period, with consequent reduction of vertical mixing, the nutrient
supply in the cooler, more turbulent regions remains suffi cient and plankton
metabolic rates benefi t from the increased temperature. In the warmer
regions reduced supply of upwelled nutrients limits production. The effects
of these changes in phytoplankton propagate up through herbivores to
carnivores in the plankton food web (bottom-up control), because of tight
trophic coupling (Brander 2010).
Another study attributed the observed decadal variability in
phytoplankton biomass in the Northeast Atlantic to climate forcing, as
expressed by the NAO (Edwards et al. 2001). In the North Sea this resulted
in a shift in seasonal timing of the peak in phytoplankton colour from April
to June which may have been accompanied by a taxonomic shift from
diatoms to dinofl agellates, with consequences for the food webs dependent
on them (Brander et al. 2006).
Antarctic
Antarctic krill (
Euphausia superba
) is among the most abundant animal
species on earth, providing the main food supply for fi sh, birds and whales.
They have declined since 1976 in the high latitude SW Atlantic sector,
