Conserving Freshwater and Coastal Resources in a Changing Climate

Eelgrass (Zostera marina): A possible indicator of increased temperatures in the
Mid-Atlantic Region
Eelgrass is a critically important species for the Chesapeake Bay area, an area that is the southern limit of its natural
range. Eelgrass is considered a keystone species within its ecosystem, providing critical habitat for declining juvenile blue
crab populations, as well as preferred refuge and forage areas for soft clams and juvenile fish (Carl Hershner, personal
communication, March 21, 2007).
Eelgrass in the Chesapeake presently grows well
during the cooler months but dies back during warm
summer periods (Short & Neckles, 1999). An increase
in average annual temperature, as predicted with
climate change, is expected to decrease productivity and
distribution. Unlike longer-lived species such as some fish
that have a “storage effect” and can delay reproduction for
a better year, eelgrass is an annual crop and cannot wait for
optimal conditions. There is also almost no chance for any
physiological adaptation to warmer temperatures (David
Secor, personal communication, April 5, 2007). Because
of its critical role in the Chesapeake Bay ecosystem and
because eelgrass is at the southern edge of its range, the
Chesapeake Bay may be a good candidate to demonstrate
the shift of species due to climate change.
Photography by Richard Herrmann
Responses of Shorelands (Barrier
Islands, Beaches and Dunes) to
Climate Change
The United States Geological Survey (USGS) defines
barrier islands as long, narrow strips of sand forming
islands that protect inland areas from ocean waves and
storms. Beach dunes are defined as low hills of drifted
sand in coastal areas that can be bare or covered with
vegetation (National, 1995). In general, shorelands are
important features of the coastal zone that are vital habitat
for many species and serve to protect inland areas
from storms and storm surges.
In the last three decades, the barrier islands of the
U.S. Atlantic coast have been transformed from tranquil
fishing villages to thriving recreational centers that host
millions of visitors each weekend (Titus, 1990a). These
same sites are also habitat for many organisms. For example,
during their migration and over wintering, most
shorebirds depend on intertidal sand for their foraging
habitat. The ability of a site to support large numbers
of shorebirds is largely determined by the amount of
habitat and by the density, availability, and seasonal predictability
of their invertebrate prey. Sites with greater
densities of invertebrates typically support higher
shorebird densities (Galbraith et al., 2002) making them
ecologically valuable and a focus for protection.
Inundation of Beaches and Barrier Islands
Global warming is projected to raise sea level
approximately one meter by the end of the century.
Such a rise would inundate lowlands, erode beaches,
and increase the risk of flooding (US EPA, 1989).
Inundation, possibly the most obvious impact of sea
level rise, refers to the conversion of dry land to wetland
and the conversion of wetland into open water (EPA,
1989). Some of the most vulnerable areas are the recreational
barrier islands and spits (peninsulas) of the
Atlantic Coast. Coastal barriers are generally long and
narrow with the ocean on one side and a bay on the
other. Typically, the ocean front side of an island ranges
from five to ten feet above high tide, and the bay side
is two to three feet above high water. Thus, even a onemeter
sea level rise would threaten much of this area
with inundation (EPA, 1989). For example, with the
use of a simple shoreline inundation model in which all
land with an elevation less than 61cm was assumed to
be flooded, it was estimated that 91 km2 of Delaware
Conserving Freshwater and Coastal Resources in a Changing Climate
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