Climate change futures: health, ecological and economic dimensions

HARMFUL ALGAL
BLOOMS
Figure 2.32 Red Tide
in suppressing the immune systems and thus increasing
susceptibility to infections and cancers needs further
study.
Brown tides cause hypoxia and anoxia, and are contributing
to the over 150 “dead zones” being reported
in bays and estuaries around the world (Rupp and
White 2003 UNEP 2005), as well as losses of seagrass
beds, nurseries for shellfish (Harvell et al. 1999).
Mangroves — whose dropped leaves feed fish and
whose roots hide them — are being removed for
aquaculture and coastal development. Mangroves are
also threatened by sea level rise. Loss of wetlands and
coral reefs, sea level rise and greater storm surges
threaten beaches, roads, homes, hotels, island freshwater
”lenses,” nutrition and livelihoods.
80 | NATURAL AND MANAGED SYSTEMS
Image: P.J.S. Franks/Scripps Institution of Oceanography
Marine red tides or harmful algal blooms (HABs) are
increasing in frequency, intensity and duration worldwide,
and novel toxic organisms are appearing
(Harvell et al. 1999). Cholera and other bacteria
harmful to humans are harbored in the phyto- and zooplankton
that form the basis of the marine food web.
The increase in nitrogenous wastes (fertilizers, sewage
and aerosolized nitrogen) provides the substrate for
HABs, while warm, stagnant waters and runoff of nutrients,
microorganisms and toxic chemicals after floods
can trigger large blooms, sometimes with toxin-producing
organisms (Epstein et al. 1993).
Most biological toxins from red tides affect the nervous
system. The effects range from temporary tingling of
the lips, to headaches, change in consciousness,
amnesia and paralysis. Repeated exposure could possibly
lead to chronic fatigue, and the role of biotoxins
The 2005 HAB outbreak of Alexandrium fundyense in
New England was associated with heavy rains in
May and two nor’easters in June. The nor'easters
(spawned by high pressure systems over cool fresh
North Atlantic waters) blew the blooms against the
coast and brought cold upwelling water with additional
nutrients. The large 1972 bloom in New England
of the dinoflagellate, Alexandrium tamarense, bearing
saxitoxins causing paralytic shellfish poisoning, first
appeared near the mouth of rivers after a drought
ended with a hurricane. The extensive 2005 bloom in
the Northeast — affecting tourism, fisheries, livelihoods,
event planners and restaurants — cost US $3
million a week and could seed cysts along many
square miles of coastline, setting the stage for harmful
algal blooms in subsequent years.
A red tide persisting at least nine months off Florida’s
west cost has taken a large toll on fisheries, livelihoods
and tourism (Goodnough 2005).
– P.E.
CASE STUDIES
ECONOMIC DIMENSIONS
Table 2.4 provides a global environmental economic
estimate of the potential new benefit streams from
coral reefs per year and the net present value (NPV) of
the world’s coral reefs in billions of US dollars. This
analysis is based upon a 50-year extrapolation at a
discount rate of 3% (Cesar et al. 2003).
Table 2.4 The “Value” of Coral Reefs
GOODS / SERVICES
Fisheries
AMOUNT (in US $BILLION)
5.7
Coastal Protection 9.0
Tourism / Recreation 9.6
Aesthetics / Biodiversity 5.5
TOTAL 29.8
NPV 797.4
Source: Cesar et al. 2003