Geoscience Reference
In-Depth Information
might well improve with warming seas, opening up new feeding areas in spring with the reduced ice cover and
exposing more potential breeding sites as melting snow cover exposes more seaside slopes.
Rising sea level will negatively affect several types of marine bird habitat. Coastal sandbars on Nova Sco-
tia's Atlantic coastline and the Gulf of St. Lawrence will be lost and with them the breeding habitat for en-
dangered piping plovers and many terns. If Sable Island itself disappears under a warming and rising sea, the
rare Ipswich sparrow will almost certainly become extinct, and the world's largest colony of gray seals will be
lost. Increased tides at the head of the Bay of Fundy will also put pressure on the extensive saltwater and fresh-
water marshes, which are important breeding areas for “puddle ducks” like the ubiquitous black duck as well
as rarer species in Atlantic Canada such as northern shoveler, gadwall, and American widgeon.
In pondering the consequences of warming and rising seas, the late seabird biologist and author Richard
Brown wrote that “it is hard to know how much to believe of these scenarios.” With insulating feathers and
subcutaneous fat, seabirds are well adapted to cope with extreme cold, but some have greater difficulty in
keeping cool—for instance, northern gannets, which find it harder to deal with heat stress than with the cold.
So, Brown concluded, “warm temperatures may therefore set southern limits to seabird distributions that need
have nothing to do with availability of suitable prey or breeding sites.”
The projected picture with cetaceans is different again. Deep-water whales are mobile, have large ranges,
and face few barriers to their movements. They would most likely adapt readily to system-wide changes by
moving to parts of the ocean that are more favorable and therefore would be animals of least concern related to
climate change. Long-term studies of deep-water whales, like sperm and northern bottlenose, and dolphins in
the Atlantic, Pacific, and Indian oceans, predict that in response to the global change scenarios put forward by
the Intergovernmental Panel on Climate Change, cetacean diversity would decline across the tropics and in-
crease in higher latitudes. But in the Sable Island Gully, productivity peaks at temperatures of 12° to 16°C (53°
to 61°F), then decreases substantially at higher temperatures. In addition, populations of cetaceans that have
limited ranges or specialized habitat requirements—like Arctic species such as narwhals, bowhead, and belu-
gas, or baleen whales that migrate to polar regions to feed—may be compromised by the rapidly changing con-
ditions in the north.
Overall, global warming seems to predict an increase in diversity in temperate regions of the oceans and a
decrease in the tropics, as is the case on land. But as Richard Brown pointed out, “we must not underestimate
the unpredictability of the animals themselves, however well we think we know them.”
He gave the example of the capelin, which today can be seen spawning on the gravel beaches around New-
foundland. During the last glaciation, eighteen thousand years ago, there was even more spawning habitat as
the southern tip of the Grand Banks—that “vast apron”—emerged. His Neolithic counterpart, Brown surmised,
might well have predicted that the capelin stock and the predators dependent on it would be decimated as these
beaches disappeared under the waves and the ocean climate warmed as the Gulf Stream moved north. “Yet,”
Brown pointed out, “the capelin still spawn there, 375 kilometers (230 miles) offshore, on 'beaches' 50 meters
(160 feet) underwater.” And this offshore stock of capelin—separate from the inshore stock—supports molting
greater shearwaters, lactating baleen whales, and, until very recently, a major groundfish population.
Back from the Brink
Despite these grim scenarios, some modern-day examples give hope that timely corrective human action in
concert with the resiliency of natural systems can pull us back from the edge of disaster.
According to George A. Rose, a warming ocean should benefit Newfoundland and Labrador cod stocks,
which live near the northern limits of the range of the species. In these ecosystems, cod are limited more by
cold water than by warm. If warming does occur, cod will move farther north on the Labrador coast, following
capelin, which will move north first, as has already happened in Icelandic and Greenland waters.
