The distribution of non-marine animals is more complex than that of plants. Not being rooted in place, animals can roam through various plant communities. Birds and many flying insects are especially mobile, and so are able to overcome most physical barriers. But they are particular about habitat choice, and most are associated with a certain group of plant communities. Animals of this type tend to be more widely distributed, but are found in specific habitats.
The opposite tends to be true for mammals. The largest species often use a variety of habitats from the beach to the alpine. Yet because many mammals lack a dispersal phase in their life history comparable to the mobile seeds or spores of plants or the winged migrations of birds, their large-scale distribution is relatively incomplete.
For instance, of the approximately 48 mammal species living in the interior of British Columbia with ranges bordering on our region, only about 29 have made it across the mountain passes and become established at Haines. Only about 11 of these have made it past the water barriers to Chichagof Island. This excludes the marten, red squirrel, mountain goat, and feral dog, which were introduced by people. The relatively few land-based animals able to colonize the extremities of our region have often attained large numbers. Among these are bears, deer, mink and otter.
Only two fishes with no connection to salt water--round whitefish near Haines and northern pike near Yakutat--have made it to the fringes of this region. The bulk of freshwater fishes are salmon and char, which spend parts of their life cycles in salt water, and so can get past the mountains and marine channels that limit the distribution of strictly freshwater animals. Most of the region's streams, even most of those directly under glacial influence, contain spawning and rearing salmon. Some, such as the Situk and Alsek Rivers, are of world-class importance. These major river systems are in the minority. More salmon transit through the region's marine waters than spawn in the region's streams.
A fortunate combination of characteristics make seas of the Glacier Bay region immensely productive. The waters are warmed and enriched by waters from the adjacent Pacific Ocean, then further fertilized by nutrient runoff from the land. Complicated shoreline and bottom topography combine with exceptionally high tidal energies to produce strong currents that stir nutrients to the surface. Two other factors are necessary to translate nutrients into productivity--enough light for plant plankton to photosynthesize rapidly, and enough water column stability to allow these tiny organisms to stay in the zone of light near the surface. All these factors come together in spring and early summer.
Then, for a few weeks, the concentrations of plant plankton reach astronomical proportions. Many animal plankton (e.g., krill, copepods) and bottom-dwelling invertebrates (e.g., starfish, sea urchins, worms, and clams) time their reproduction to coincide with this brief time of plenty. Vast shoals of small fishes such as herring, capelin and sand lance in turn feed upon this animal plankton. Salmon, sea lions, porpoises, cormorants, and murrelets forage on the fishes, while humpback whales come from Hawaii and Baja California to harvest small fish and the plankton by the ton.
Seaweed and salt-marsh vegetation also begins to grow in early spring. They support an abundance of grazers, from deer and geese (at low tide) to snails (at high). When this vegetation decomposes, it produces detritus for bottom-dwellers like worms and sand fleas.
Summer in the upper waters is a brief but exuberant season. Hordes of migrants arrive to join the winter holdouts in harvesting the bounty. Most marine birds and mammals raise their young and then put on fat while the good times last. Fishes exhibit a variety of reproductive strategies. Herring and cod release eggs that hatch into larvae which fend for themselves in the rich plankton soup. Skates produce large yolk-rich eggs produced from stored energy from the previous season. Ling cod males utilize stored energy reserves to defend their brood of eggs from predation.
As the snows and gales of winter come, and the sun moves ever lower in the sky, much of the marine world goes "on hold". Many species leave for the south or the warmer temperatures of the open sea. Most of the rest curtail their activity. Salmon eggs rest in creek gravels. Herring and rockfish school in a rocky deep to await the coming of spring when the drama will be replayed.
But the marine ecosystem does not grind to a halt over winter. A portion of the living matter from upper waters makes its way to the bottom in the form of detritus, where it is eaten by filter feeders such as barnacles, anemones and clams. What they miss is incorporated into bottom sediments to be eaten through the year by tiny crustaceans and worms. These in turn feed flounders, crabs, cod and diving birds such as scoters. Seals, sea otters and flounders provide the next link in this benthic food chain, which fluctuates much less through the seasons than that of the open waters, and thus becomes disproportionately important during winter.
Marine productivity comes ashore in numerous ways. Salmon carry it to the far corners of the region when they spawn. The young of some species remain in ponds and streams, where they are important food for mergansers and kingfishers. Eagles, otters and mink hunt at sea and carry their catch to land.
Most important, shores provide hundreds of miles of interface between land and sea. They provide thoroughfares and den sites; carcasses wash up on them; and they grow lush intertidal communities that are dry land when the tide is out. A large array of predators and scavengers from bears to shrews and ravens patrol the beaches, eating flotsam and some of the intertidal invertebrates. Herbivores like deer, moose, mountain goat, porcupine and voles graze on plants of the upper intertidal zone or eat kelp for salt.
Did You Know?
Crescent Gunnels are often found in seaweed-filled tidepools where they hide under rocks encrusted with barnacles and other growth. Due to their elongated shape they are often mistaken for eels.