Conserving Freshwater and Coastal Resources in a Changing Climate

prey species or introduction of competitors. It may also
reduce the population size of the migrant group, because
deeper waters will not support the same biomass
as more productive surface waters (Fields et al., 1993).
Photography by Alan Eckert
commercially important soft clam, Mya arenaria) could
be eliminated from the Bay if water temperatures reach
levels that inhibit successful reproduction or that are
lethal. Meanwhile, lower-latitude or warm-tolerant species
may expand their ranges poleward, however, these
shifts may not be as rapid as poleward range contractions,
because successful invasions of new habitat require
not only physically tolerable habitat but also suitable
food supply and no unfamiliar predators, pathogens,
or competitors to impede the invaders (Kennedy,
1990). For example, if prey species are more heat sensitive
than predator species, the prey may be eliminated
from portions of the predator’s range. Stressed organisms
may fall prey to more robust predators or pathogens,
face competition from invasive species or may be
unable to produce viable young (Kennedy, 1990). The
negative effects of disease are likely to become more
severe, as pathogens are generally favored by warmer
temperatures relative to their hosts. Direct climatic impacts
on one or a few “leverage” species could drive the
response of an entire system (Harley et al., 2006).
In addition, distributional shifts in response to increased
temperature may not necessarily be latitudinal
but may include vertical displacements to deeper, cooler
waters. Many marine species occur in shallow or intertidal
waters in the cooler reaches of their ranges, but are
found progressively deeper near the warmer limits of
their distributions. In an analogous manner, as temperatures
change in response to anthropogenic warming,
the current shallow water populations of these species
may retreat into cooler deep waters. Such submergence
in response to global warming, however, may disrupt
community-wide trophic interactions, including loss of
As temperatures change, not all populations will
necessarily shift their ranges in response. Some that
stay in place may either adapt genetically or live under
suboptimal conditions. Because most marine organisms
have body temperatures that differ little from the surrounding
water temperature, they will need to adapt to
environmental warming if they do not migrate to cooler
areas (Fields et al., 1993). There are changes in enzymes
and proteins that can help adjust the metabolism of the
organism and allow it to survive higher temperatures.
These adjustments may allow species to survive in their
current habitats despite an increase in ambient temperature
(Fields et al., 1993).
Historically, fish have been able to adapt and survive
in other stressful times. For example, the white perch
(Morone americana) has been in existence for roughly
1,000 to 2,000 years, which required them to overcome
other environmental obstacles (David Secor, personal
communication, April 5, 2007). The presence of genetic
variability within the species will allow some level of
adaptation to changing temperatures and species occurring
over a wide thermal range will generally have a
broader range of genetic variability from which to draw
(Fields et al., 1993). Although data are sparse, studies
suggest that changes in average habitat temperature of
only a few degrees Celsius are sufficient to favor selection
for adaptive differences (Fields et al., 1993).
Photography by Bill Silliker Jr.
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Conserving Freshwater and Coastal Resources in a Changing Climate