Environmental Engineering Reference
In-Depth Information
subsequently germinated under the current warmer, more saline and highly
turbid conditions (Guinder et al. 2013).
Summer blooms have notably increased in magnitude and frequency
in several coastal systems worldwide, although different underlying factors
have been identifi ed (Carstensen et al. 2007, Shikata et al. 2008, Guinder et
al. 2013). In a shallow coastal ecosystem in the north of Europe, the Kattegat
strait, summer phytoplankton blooms are thought to be related to short and
strong nutrients pulses associated to river discharge, resuspension from the
bottom and anthropogenic inputs (Carstensen et al. 2004). In contrast, in the
Hakata Bay, Japan (Shikata et al. 2008) and in the Gullman Fjord, Sweden
(McQuoid 2005) the occurrence of summer blooms seems to result from the
germination of resting stages of different phytoplankton species (mainly
diatoms) in response to environmental stimulus, i.e., increase in radiation
and water temperature and climate related changes in sea-surface salinity.
These cases evidence that the responses of phytoplankton bloom phenology
to climate change largely depend on the life strategies of the community.
The metabolism of heterotrophic organisms is more sensitive to
temperature than photosynthesis rates. In consequence, the zooplankton
grazing activity will be more affected than the primary production as
warming progresses, thereby enhancing the top-down control on the timing
and magnitude of phytoplankton blooms (Irigoien et al. 2005, Aberle et al.
2012, Klauschies et al. 2012). For instance, in mesocosms studies, Aberle
et al. (2012) demonstrated that an increase in the winter temperature
produces accelerated growth and large ciliate biomass, altering the specifi c
composition and creating an asynchrony between the components of the
plankton. Additionally, Sommer and Lengfellner (2008) found higher
grazer activities in the warmer mesocosms due to enhanced metabolic
demand of copepods at higher temperatures, which could explain both
the decreased phytoplankton biomass during the spring bloom and the
shift towards smaller phytoplankton at higher temperatures. It is therefore
plausible that released predation pressure on small phytoplankton cells
under warmer conditions may promote their outburst with a potential
reduction in the matter transfer through the trophic chain (Sommer and
Lewandowska 2011, Winder et al. 2008, Guinder et al. 2012). The dominance
of smaller phytoplankton may cause a shift in the pelagic food web away
from the biological pump dominated by copepods and rapid sedimentation
of particulate matter towards rapid carbon cycling in the microbial loop
(Finkel et al. 2010). The path of carbon fl ow between primary producers
and mesozooplankton may become longer through heterotrophic fl agellates
and ciliates, which can reduce productivity of higher predators.
Elemental stoichiometry and food quality
:
As previously described, ongoing
anthropogenic increases in atmospheric CO
2
levels and global warming of
