Environmental Engineering Reference
In-Depth Information
Changes in zooplankton phenology
. Phenology is a sensitive indicator of
global warming (Edwards and Richardson 2004, Richardson 2008). Since
the level of response to climate change varies across functional groups and
trophic levels, changes in annually recurring life cycle events may be of vital
importance to ecosystem functioning (Edwards and Richardson 2004). The
decoupling of annually recurring events will have severe consequences for
trophic interactions, changing food-web structures and leading to eventual
ecosystem-level changes (Edwards and Richardson 2004). In the case of
temperate marine environments, where the recruitment success of higher
trophic levels is highly dependent on synchronization with planktonic
pulses, these changes can dramatically affect community connectivity
(Edwards and Richardson 2004, Costello et al. 2006). More crucial than
any change in timing of a single species is the potential disruption of
coordination in timing between the life cycles of predators and their prey
(Parmesan 2006).
A fundamental concept in aquatic ecology establishes
that the fi tness of a predator depends upon its temporal and spatial
synchrony with the production of its prey (Cushing 1990). Ecologists have
also observed drastic population decline in predators when predator-prey
relationships are disrupted through climate-related perturbations (Winder
and Schindler 2004).
In the Narragansett Bay, USA, phenological alterations concerning the
copepod
Acartia tonsa
and the ctenophore
Mnemiopsis leidyi
have provided
an opportunity to examine the mechanisms that underlie species-specifi c
responses to climate warming in estuarine ecosystems (Costello et al. 2006).
The change in seasonal timing of population growth by
M. leidyi
relative to
A. tonsa
has altered summer zooplankton dynamics in the central region of
the bay (Costello et al. 2006). The advance in
M. leidyi
'
s
seasonal appearance
(59 days between 1951 and 2003) has shifted the predator's peak abundance
into a time period during which
A. tonsa
has historically enjoyed a temporal
refuge from ctenophore predation (Costello et al. 2006). Before climatic
warming,
A. tonsa
was the dominant secondary producer in the estuary
and its main period of production occurred before the seasonal appearance
of
M. leidyi
. However, since 2000, the seasonal peak abundances of the two
species have overlapped, intensifying the predator-prey relationship and
resulting in the near extirpation of the once-abundant copepod from the
estuary (Costello et al. 2006).
In the surface waters of the Subarctic North Pacifi c Ocean, the copepod
Neocalanus plumchrus
, which dominates the zooplankton biomass, has
a seasonal cycle of abundance that is tightly coupled with sea surface
temperature (Mackas et al. 1998). Its vertical distribution and development
are strongly seasonal, with an important and relatively short (<60 days)
annual maximum in spring and early summer. This peak has shifted
dramatically between 1956 and the present (Mackas et al. 1998). Population
