Environmental Engineering Reference
In-Depth Information
as diatoms). Such shifts in the plankton can produce a trophic mismatch in
the food web (Edwards and Richardson 2004).
The occurrence of harmful algae in coastal waters is of most importance
from several points of view. They impact coastal fi sheries and are known
for their detrimental effects on human health (approximately 10% of
all foodborne disease outbreaks in the US result from the consumption
of poisoned seafood; van Dolah 2000). Other than the very obvious
consequences from poisoning or sub-lethal effects, harmful algae can
have more subtle infl uences on fi sh populations, such as habitat quality
deterioration and may exert changes in the food web structure (Burkholder
1998).
In the past ~ 35 years, harmful or toxic algal incidents have increased in
frequency and geographical extent. Even though paleontological evidence
indicates that red tide-producing dinofl agellates occurred throughout the
Holocene with characteristic periodicities, the variability and concurrence
of species in the past 60 years is unmatched in the past and suggests an
ecosystemic disequilibrium (Mudie et al. 2002). Such observations have led
researchers to agree that human impacts on the environment are responsible
for the increase in frequency and expansion of harmful algae (van Dolah
2000).
The increased geographical extent of harmful algal blooms, can be
explained by unintentional introductions by ballast water and fouling, and
the transport of stocks for aquaculture (Burkholder 1998, Thompson et al.
2002). As an example, Martin and LeGresley (2008) reported that together
with the expansion of salmonid aquaculture industry in the Bay of Fundy,
harmful algal blooms increased in intensity, frequency and geographic
distribution. Additionally, a number of non-indigenous phytoplankton
species have been detected since 1995. From an ecosystem viewpoint,
introduced harmful microalgae have been involved in the loss of habitat
for other phytoplankton and benthic algae species, and the disruption of
the microbial food web. The introductions and the ecosystemic changes
they trigger are in most cases irreversible.
Other factors have been invoked to explain the increase in frequency
of harmful blooms. Eutrophication in estuaries and coastal waters (already
discussed) is surely the most obvious (Burkholder 1998). Anomalous
weather events (e.g., the increase in frequency, persistency and intensity
of ENSO events; van Dolah 2000) and the warming trend of surface waters
are also related to harmful blooms (Burkholder 1998, Mudie et al. 2002,
van Dolah 2000).
The experimental evidence also points that toxic algal blooms will
probably increase as a result of global change (Peperzak 2003, Peperzak
2005). Simulations of future environmental conditions for the coastal zone
of The Netherlands for the year 2100 (i.e., increased stratifi cation of shallow
