Environmental Engineering Reference
In-Depth Information
18.1
Introduction
Marine phytoplankton are ideal indicators of environmental change. These micro-
scopic algae form the base of the oceanic food web and respond rapidly to changes in
their environment. Individuals of most phytoplankton species are short-lived and
react quickly to varying ambient conditions caused by both short-term weather and
long-term climate (Hays et al.
2005
). As the cells essentially function as an
integrated, nonlinear sensor of environmental conditions, they may be more sensitive
to change than mechanical sensors measuring only one environmental variable. Also,
because phytoplankton are not commercially important, any observed changes can be
attributed to changes in the environment and not to harvesting.
Excluding physiological change and adaptation, the response by phytoplankton
and other organisms to environmental changes can be manifested by alterations in
both their spatial distribution pattern and their phenology, i.e., the timing of events
in seasonal life cycle (Hughes
2000
). Recent studies have begun to explore the
observed variability in marine phytoplankton phenology and its effect on higher
trophic levels (Platt and Sathyendranath
2008
; Platt et al.
2009
,
2010
; Vargas et al.
2009
; Sapiano et al.
2012
). An examination of the spatial distribution pattern was
conducted for the cosmopolitan species
Emiliania huxleyi
(Fig.
18.1
), an important
member of the phytoplankton group that generates calcareous plates called
coccoliths, for which they are known as coccolithophorids.
Coccolithophorids are an abundant and widely distributed type of marine phyto-
plankton and play an important role in the oceanic carbon and sulfur cycles through
their production of CaCO
3
coccoliths and dimethyl sulfide (DMS), the dominant
precursor for cloud condensation nuclei in the maritime atmosphere. As one of the
principal producers of DMS among phytoplankton, coccolithophorids act as a
significant biogenic source of sulfur to the atmosphere and may influence regional
albedo via increased cloud formation. Coccolithophorids generate as much as two-
thirds of open ocean calcification through their generation of calcareous coccoliths,
and
E
.
huxleyi
is considered to be the largest current producer of calcite (Westbroek
et al.
1989
,
1993
).
Blooms of
E
.
huxleyi
profoundly affect the biogeochemical and optical
properties of the waters they occupy. For example, generation and export of their
calcareous coccoliths alter the equilibrium of the regional ocean carbonate system
and the sea-air flux of carbon dioxide. The influence of
E
.
huxleyi
blooms also
cascades to upper trophic levels of the food chain, including fish and marine
mammals (Napp and Hunt
2001
; Tynan et al.
2001
). As a consequence,
documenting the seasonal to decadal variability of these blooms is important to
assess climate variability and environmental conditions and to better understand
their potential impact on the carbon cycle and regional ecosystems.
Several environmental conditions appear to be favorable to
E
.
huxleyi
bloom
development, including increased stratification of the upper ocean (Tyrrell and
Merico
2004
). Smyth et al. (
2004
) found a strong correlation between bloom pre-
sence with warm sea-surface temperatures and reduced salinities in the Barents Sea.
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