Ecology of Glacier Bay National Park
Ecology of Glacier Bay National Park and Preserve
Located in the southeastern Alaskan panhandle along the border of Canada, Glacier Bay National Park and Preserve covers 3,283,000 acres of land including roughly 700 miles of coastline. Though it is widely known and named for its glaciers, the National Park also features several marine, terrestrial, and freshwater ecosystems such as estuaries, fjords, and forests. Because the Park is near sea level, winters are mild with temperatures reaching as low as 25 degrees F, and summers are cool, only reaching a high of 60 degrees F. Over time, the glaciers have melted and exposed new land, allowing 300 plant species, approximately 40 mammals, including wolves, whales, seals, sea lions, and sea otters, and almost 200 species of birds to move into the area.
Glacier Bay National Park and Preserve can be split into a few ecosystem types. Terrestrial ecosystems include tundra (arctic and alpine), glaciers and icefields, and coastal forest, while aquatic ecosystems include the intertidal/coastal zone, estuaries, and marine ecosystems. In Glacier Bay, the terrestrial ecosystems are in proximity to the coastal and marine ecosystems, meaning that almost every species in the National Park and Preserve relies on its highly productive coastal and marine waters. Here, we focus on three of these ecosystems: forests, intertidal/coastal, and ocean.
Forests
The southern part of Glacier Bay National Park and Preserve consists largely of temperate rainforest, which provides ideal conditions for many plant species. Much of the land in the park is thick with spruce, hemlock, devil’s club, as well as yellow cedar, which plays an important role in maintaining the cycle of nutrients in the forest, provides shade for the ground below, and creates a habitat for organisms such as birds, as well as moose, wolves, and deer.
Moose
Moose are known to live within the forests of Glacier Bay. As a keystone species, moose play an important role in the ecosystem, as they contribute to nutrient cycling and can influence the density and composition of plants they feed upon, such as various willow species. This in turn alters the availability of resources for other animals that also live in the forest, such as birds. Their main predators are wolves and bears.
Wolves
Wolves are a common predator in Glacier Bay, as they are known to prey on deer, moose, mountain goats, birds, salmon, and even sea otters in some areas. The wolves migrate in packs, moving between the tidal areas and the forests, even swimming among nearby islands, to look for food, which results in a diverse diet.
Mountain Goats
The mountain goats in Glacier Bay are found throughout southeast and south-central coastal Alaska. They can be identified by their short horns and all-white coats that are thick, long, and shaggy during the winter. Once summer hits, mountain goats will shed their winter coat, leaving them with one that is softer. Their specially designed hooves allow them to live in somewhat rugged terrain and move among slippery rocks; however, they are also known to live on the coast and in tidal areas. Mountain goats most commonly graze on shrubs and grasses, as well as berries, hemlock, and lichen, depending on the season.
Bears
There are two types of bears that live in Glacier Bay: black bears and brown bears. Bears are an omnivore species, meaning they feed on both plants and animals. They spend 6-8 months of the year feeding on grass, fish, berries, and insects to prepare for hibernation during the winter season. During hibernation, they can sleep for long periods during which their body temperatures and metabolic rates decrease. The black bears live mostly inland in the forests of southeast Alaska. Their claws are fit for digging food and catching small prey, and despite their name, black bear fur can appear dark brown, reddish-brown, or even greyish blue in the case of the glacier bear, which is a color variant of the black bear. Brown bears appear to be more widely spread in Glacier Bay and can often be found on the coast of the southeastern peninsula, flipping over rocks in tidal zones to find small fish and aquatic vertebrates upon which they feed. They often congregate and feed in and around streams where salmon spawn, and like black bears, the color of their fur can vary.
Intertidal and Coastal Zone
One significant tidal area of Glacier Bay is Bartlett Cove, part of the intertidal zone on the coast. Here, the tides are known to fluctuate, causing the animals that live among the rocks to adapt and/or move with the tides as they travel in and out of the Bay in order to avoid getting stuck in the sun and drying out. Among the organisms that live and/or feed in Bartlett Cove’s intertidal zone are algae, kelp, sea urchins, sea stars, barnacles, mussels, sea otters, and shore birds, as well as bears and even mountain goats.
Sea Otters
Sea otters are a keystone species in Glacier Bay, that is, the relative abundance of the species has major effects on the composition of organisms and resources in the ecosystem. For example, the population of sea otters in the North Pacific, particularly Glacier Bay, was essentially absent until 1994. Since then, sea otters have recovered to a population of around 8,000 individuals in Glacier Bay. As a part of current research of sea otter recovery in the area, USGS scientists have been tracking the abundance of crabs, clams, and sea urchins in the area, and are working to predict how increased predation is likely to affect the availability of resources as well as the populations of other predators like octopuses, sea stars, fishes, birds, and other mammals.
Sea Birds
Glacier Bay is also home to many sea birds, including the puffin and a small, reddish-brown and white sea bird known as the Kittlitz’s Murrelet. Kittlitz’s Murrelet has large eyes, which is thought to aid in its ability to locate prey in cloudy water. To catch their prey, these birds dive into the water to catch shallow swimming fish, such as Pacific herring, capelin, and Pacific sandfish, and small crustaceans. These birds are known to spend the summer seasons breeding throughout the coastal marine waters of Alaska, including Glacier Bay, preferring the rocky and treeless mountains.
Currently, USGS scientists are tracking Kittlitz’s Murrelet to better understand their movement patterns, especially as not much is known about their habitat use in the colder months. The tracking also aids in understanding how the birds are using and interacting with their environment, as well as how long they are in a particular area. The animation below depicts the movement of multiple tagged Kittlitz’s Murrelets from May through October in a single year. The map indicates they were spotted all around Alaska’s coast, though they were most notably recorded in the southern part of the state. The map also reveals that Glacier Bay is among the more frequently visited areas.
Crabs
Dungeness crabs are a very common species of crab found in Bartlett Cove, Glacier Bay. They are a big part of Alaska’s fishing industry and are often prey for many sea mammals such as sea otters. The crabs have relatively small legs compared to their broad oval shaped bodies, and are known to eat small invertebrates, worms, and fish. USGS scientists have researched dungeness crab prevalence in Glacier Bay, along with the Pacific halibut, in order to determine how commercial fishing affects their abundance in the National Park. Previous work also includes assessing how sea otter predation affected crab populations in Glacier Bay. The study showed that in areas with more otters, the abundance of dungeness crabs was lower than in other areas with less sea otters.
Ocean
The marine waters of Glacier Bay provide food and habitat for a diversity of sea life. Among the giant floating icebergs live humpback whales, sea otters, orcas, krill, a variety of fish, and even different types of corals.
Humpback Whales
Humpback whales are a migratory species. While they spend the winter season in warm tropic waters, they tend to spend the summer season in cold Alaskan waters, including Glacier Bay, the Bering Sea, Prince William Sound, and the Aleutian Islands. The humpback whales that visit Glacier Bay during the summer migrate throughout the Pacific Ocean during the year, often spending winters in Hawaii, where they mate and give birth. During their time in Alaska, humpback whales feed on krill, masses of tiny shrimp-like crustaceans that get trapped easily in their baleen plate “teeth.” As whales intake a large volume of water in their mouth, the baleen acts as a sieve, filtering out the water while trapping small organisms, such as krill. Another method of feeding used by groups of whales to maximize their catch is called bubble net feeding. As the whales swim in circles below their prey, they release bubbles, which catches the prey in a “net.” The whales then lunge to the surface through the bubble net and feed as a group. However, humpback whales typically travel alone or in relatively small groups.
Deepwater Diversity
Glacier Bay also has a unique underwater ecosystem that displays deepwater emergence. This means the fjord conditions of Glacier Bay allow for benthic organisms typically found in deeper parts of the ocean, such as red tree corals, anemones, and certain fishes, to exist at shallower depths. The USGS defines a fjord as a “glacially eroded or modified U-shaped valley that extends below sea level and connects to the ocean. Filled with seawater, depths may reach more than 1,000 feet below sea level.” In Glacier Bay, underwater features channel cold, nutrient-rich water from the ocean into the fjords, which helps create the conditions needed by the deepwater emergent communities. This exchange also transports important food resources, such as plankton which forms the basis of the food webs throughout Glacier Bay. Additionally, when freshwater from snow and glacial melt enters the Bay, the less-dense freshwater can form a layer on top of the denser salt water. This can block sunlight, making the environment much darker, and more suitable for species that typically prefer the cold, dark waters of the deep-sea.
