Environmental Engineering Reference
In-Depth Information
underwater light intensities are also recognized as important environmental
triggers for summer and spring diatom blooms in shallow environments
(Eilertsen et al. 1995).
Salinity closely co-varies with temperature and also has important
implications in plankton physiology, affecting germination of resting stages,
growth rates and development of blooms in coastal waters (McQuoid
2005, Shikata et al. 2008). The effect of the climate warming on water
temperature and salinity appears stronger in shallow and semi-enclosed
areas where evaporation is high and river runoff is low (Guinder et al. 2010).
Phytoplankton species have different tolerances to variations in salinity
and temperature (Gebühr et al. 2009, Huertas et al. 2011), which defi ne the
water density and viscosity, and shape nutrient diffusion and cell motility
(Falkowsky and Oliver 2007, Finkel et al. 2010). Therefore, changes in
these parameters affect ecological niches and species-specifi c interactions
leading to shifts in community structure and composition (Litchman et al.
2007). Changing conditions also favor the development of fast-growing
opportunistic species, able to exploit open niches and establish dominance
in the system (Cloern and Dufford 2005). Particular examples are the cases
of
Paralia sulcata
at Helgoland Roads in the North Sea (Gebühr et al. 2009)
and
Thalassiosira minima
in the Bahía Blanca Estuary, Southwestern Atlantic
coast (Guinder et al. 2012).
Indirect effects on phytoplankton
:
Enhanced growth of primary producers
is expected under future trends of temperature increase. The projected
scenario, however, becomes complex when considering indirect effects of
warming, such as grazing acceleration, which play key modulating roles
of phytoplankton biomass accumulation (Aberle et al. 2012, Sommer and
Lewandowska 2011). Hence, food web interactions need to be considered
when assessing temperature effects on phytoplankton (Klauschies et al.
2012).
Sea-surface warming lead to higher mean underwater irradiances and
nutrient depletion from the upper layers due to intensifi ed stratifi cation
(Doney 2006). The establishment of a shallow pycnocline (Fig. 2) acts
as a barrier for vertical mixing and upward transport of nutrients and
resting stages, and exposes the phytoplankton cells to more intensifi ed
irradiances, both PAR and UVR. This affects cellular photochemistry,
eventually hampering the photosynthetic carbon assimilation (Litchman
and Neale 2005, Marcoval et al. 2008), and ultimately may yield a decline
in phytoplankton productivity under the above conditions (Behrenfeld et
al. 2006, Doney 2006, Boyce et al. 2010). On the contrary, positive effects of
warming on photoautotrophic production and phytoplankton biodiversity
have been registered related to upwelling events (Chavez et al. 2011), earlier
stratifi cation and extension of the growing season with adequate resource
supply (Winder and Schlinder 2004, Sommer et al. 2012b).
