The composition, diversity, and distribution of marine plants and animals reflects the integrated effects of coastline tectonics and geomorphology; degree of exposure to or protection from wave and surf action; extent of tidal amplitude and exposure; speed and direction of currents; local and regional drainage patterns and associated sediment load discharges; topography and sedimentary character of the bottom; shore dynamics such as erosion and transport of sediments and sedimentary characteristics; and freezing and ice conditions.

Neritic habitats encompass all open, near shore waters of the outer coast and contiguous continental shelf. Plankton populations include both animals and plants (zooplankton and phytoplankton). These pelagic organisms (existing at or near the surface of open water) are diverse and abundant and support many higher life forms (Figure 138). The great numbers of seals, walruses, and flocks of birds were recorded by Captain Cook during his exploration of 1788 in the northern Gulf of Alaska. Still most conspicuous to modern seafarers are the size and diversity of flocks of sea birds inhabiting or migrating along the near shore waters of the coast.

More than 100 sea bird colonies lie along the coast of Southcentral Alaska. One colony in the Semidi Islands, Aghiyuk Island, contains more than 1,000,000 birds, while several others contain more than 100,000.

Various marine mammals—seals, sea lions, baleen and toothed whales, and porpoises—also ply the near shore waters in large numbers.

Fish are varied and abundant, as evidenced by active fishing by U.S. and foreign fishermen for halibut, Pacific pollock, Pacific ocean perch which is common to the glacially gouged submarine valleys of the continental shelf and associated submarine canyons, black cod, Pacific cod, turbot, and various other types of groundfish in the continental shelf area. The Yakutat, and Eastern Spit halibut spawning grounds are some of the best known and most important in the northern Pacific. The continental shelf margin between Kodiak and Ocean Cape supports large concentrations of halibut that are transported westward by the prevailing currents.

Scattered investigations and other evidence indicate rich and varied neritic populations and a diversity of communities of benthic (bottom) invertebrates. The richness of the king crab fishery, especially off Kodiak Island, exemplifies the suitability of the shelf environment for invertebrate populations.

The weathervane scallop, another benthic form, is actively fished at several beds along the continental shelf, especially off Kodiak. Various demersal (near bottom dwelling) species of pandalid shrimps are also fished along the central and outer shelf in this area.

The abundance of larger animals in the neritic environment reflects the rich availability of dissolved nutrients, such as phosphates and nitrates, in the offshore water. These nutrients make up a broth which supports rich seasonal crops of unicellular microscopic plants (phytoplankton) providing the primary forage food for zooplankton grazers, such as copepods. Grazers are preyed upon by larger, carnivorous zooplankton, which in turn are preyed upon by still larger, free-swimming forms (nekton).

Since aboriginal times the neritic environment of Alaska's Southcentral Region has provided man with abundant and varied economic and recreational benefits.

In summer nonbreeding shorebirds and gulls are present in large numbers in tidal areas. Immature and nonbreeding gulls are particularly abundant wherever natural and man-made food sources are present. Large concentrations of gulls are attracted to wastes produced by fish processing plants and approximately 10,000 frequent the New England Fish Company's Orca plant at Cordova during June, July, and August. This unnatural abundance of food attracts not only nonbreeding birds, but also breeding birds from as far as the Copper River delta, 50 kilometers away. Black-bellied plovers and several species of sandpipers feed in numbers on the mud flats and sand beaches of the Copper River delta throughout the summer.

Fall migration through the Region is more diffuse than in spring and, therefore, less conspicuous than spring migration. Nonetheless, large numbers of birds pass through during their annual southward movements. Fall migration occurs over an extended period from July through November, and the birds move in small flocks and loose aggregations.

Along the north Gulf coast, migrating birds are restricted to a narrow belt of habitat in fall as well as spring.

During the 1963 fall migration, sandhill cranes passing southeastward between the Copper River delta and Yakutat exceeded 500,000 birds in a five-day period (daylight hours only) in late September.

In late summer and fall, gulls, eagles, and fish-eating ducks gather at the many salmon streams and intertidal spawning locations. There are several hundred short, intertidal spawning streams along the Gulf coast, all with their attendant bird assemblages feeding on dying and dead salmon. Silver salmon spawn the latest, sometimes well into the winter, and may be an important source of food for eagles at times. In September and October more than 10,000 bald eagles may concentrate along the north Gulf coast, excluding Prince William Sound.

The unprotected open coast, subject to the full force of the swells generated by North Pacific weather systems, extends from Cape Spencer to Cape Hinchinbrook. In the Southcentral Region the open coast includes the waters of Icy Bay, the Yakataga coast, the Bering Glacier forelands, and the Copper River delta complex.

Marine flora and fauna of the Southcentral Region are poorly surveyed and the coverage of what is known is far from uniform. However, because of species and general overlap along the North Pacific coast from California to Alaska, a number of references, such as Ricketts et al. (1968), can serve as useful guides to the study and understanding of the Southcentral coastline.

A dominant feature of the unprotected open coast is the east-to-west circulation (Figure 121) and wave-induced sediment transport along the shoreline which gives a westerly skew to the mouths of many streams discharging into the ocean between Icy Bay and the Bering River.

Dense bird populations, with their related activities and migrations, are prominent feature of the coastal area between Yakutat and the western edge of the Copper River delta. Here food is abundant as a result of interactions between longshore currents, tidal action, upwelling, and freshwater outflows. In the Copper River delta, plankton, small aquatic life, and floating seaweed are found in bands as much as several miles long.

The protected open coast encompasses rugged, dissected, mostly rocky coastline on Montague and Kodiak Islands, and the Kenai and Alaska Peninsulas. The prevalence of a rocky substrate, large tidal ranges, and substantial wave action favors the growth of luxuriant, attached algae forming belts that harbor rich and diverse animal communities. The intertidal and subtidal algal forest is one of the best defined and most obvious ecosystems of the coastline.

Sea birds are the most conspicuous dwellers of the area. The Barren Islands, southwest of the tip of the Kenai Peninsula, contain more than 200,000 kittiwakes and murres. Additionally, the island group is inhabited by large populations of sea otters, sea lions, and harbor seals.

Ecological studies of the protected open coast are scant, except for those by Nybakken (1969) on intertidal zonations at Three Saint's Bay, Kodiak Island. These studies, conducted before the 1964 Alaskan earthquake, provided the only baseline reference for the determination of ecological impacts on shoreline communities. The 10+ meter uplift of Montague Island caused by that earthquake spurred investigations of the marine fauna and flora of the area (National Academy of Sciences 1972).

The protected fjord coast encompasses the waters of Prince William Sound, which supports one of the major salmon fisheries of the northern Gulf of Alaska. More than 300 streams empty into Prince William Sound and provide spawning grounds for salmon, mainly pinks and chums (Figure 137c). Sport fishing for salmon in Valdez Arm takes place from June to September. Prince William Sound is also a major herring spawning area and a productive fishery for tanner and Dungeness crabs.

The Sound supports a rich, diverse, indigenous avian population varying in composition with the seasons and is an important migration route for birds of the Pacific Flyway (King and Lensink 1971).

The Cook Inlet estuarine embayment complex encompasses all waters north of the Barren Islands. The distribution of plants and animals in the area reflects the complex interactions of tidal mixing of fresh and salt waters; large tidal amplitudes that result in extensive tidal flats; large loads of suspended glacial sediments; the scouring actions of strong tidal currents; and ice during the winter months.

The waters of Cook Inlet can be subdivided into two major regions. Each lies roughly along either side of a line drawn between Cape Douglas and the city of Kenai. The eastern side includes Kachemak Bay and is under the influence of saltier, relatively clear, inflowing coastal waters. The western side is dominated by the sediment-laden, brackish outflow.

Baseline information on intertidal organisms of Cook Inlet is scant. Perhaps the most reliable indicator of the extent of intertidal biota is the abundance of razor clams collected from the lower Inlet for food by the local people.

While little information is available on benthic communities, the presence and abundance of king, tanner, and Dungeness crabs in the Kachemak Bay-southern Cook Inlet area suggests a diverse and healthy environment (Evans et al. 1972). Food for these crabs includes marine worms, molluscs, brittle stars, small crustaceans, some fish, and other assorted invertebrates.

Pandalid shrimp feed at the bottom on marine worms, small crustaceans, and fresh organic detritus, all abundant in lower Cook Inlet. Herring spawn in abundance along the shores of Kamishak and Kachemak Bays, and eulachon smelts run in upper Inlet streams.

All five species of Pacific salmon inhabit and migrate into streams and lakes surrounding the Inlet (Figure 137b). Exploratory deep water trawls also reveal the presence of 25 species of fin fishes. Butter sole, yellowfin sole, turbot, and Pacific pollock are the most abundant.

Lower Cook Inlet is the habitat of several species of marine mammals. Sea otters inhabit the west side of the Inlet from Shakun Rock to Chinitna Point, mainly concentrating on Augustine Island and Cape Douglas. Harbor seals are found throughout Kachemak Bay and along the west side of the Inlet up to the Susitna River. Primarily, sea lions concentrate on the Barren Islands just south of Cook Inlet. Beluga whales swim up Cook Inlet as far as the Susitna River and Ship Creek. Killer whales and harbor and Dall porpoises are commonly observed in the lower Inlet.

The coastal tidelands, saltmarshes, and wet shorelands consist of the tidal areas between low and high tides. In this Region they include tidal sloughs and river mouths, narrow coastal outwashes exposed by the retreating ice fields along the Yakataga-Controller Bay forelands, the coastal portion of the braided deltaic outwashes of the Copper and Susitna Rivers, and the numerous deltaic deposits of the many small streams draining the rugged, dissected, seaward faces of the coastal mountains.

In the north Gulf region, the tidal area is the habitat most heavily used year-round by birds. Rocky shores are characteristic of the western half of the north Gulf coast, gravel and sand beaches, the eastern half. Miles of mud flats are exposed at low tide on the Copper and Bering River deltas. Approximately 90 species of birds utilize the tidal area as a feeding or resting place. Resident and migrant waterfowl, shorebirds, and gulls gather at times in spectacular numbers within this area. Eagles, hawks, ravens, crows, magpies, and jays are regular foragers. Several species of small passerines, most notably water pipits and song sparrows, regularly utilize the exposed, upper intertidal zone as a feeding area.

In spring tremendous concentrations of migrating waterfowl and shorebirds utilize the tidal area. Densities of more than 100,000 shorebirds per square kilometer were recorded on the Copper River delta in early May 1964. Between 25 April and 15 May the more than 520 square kilometers of tidal flats on this delta host more than 20 million shorebirds and waterfowl. A large percentage of Alaska's shorebird population, including western sandpipers, knots, dunlins, short- and long-billed dowitchers, and least sandpipers, must pass through this area during spring migration. During the same period, rocky tidal areas of Montague Island host near similar numbers of ruddy and black turnstones, surfbirds, whimbrels, wandering tattlers, and American golden and black-bellied plovers.

On 27 April 1971 a waterfowl migration route just north of Straw Point and entering Prince William Sound from the north Gulf coast and Copper River delta was utilized by an hourly average of approximately 5,500 pintails and 500 whistling swans. This flight path is heavily used by migrating waterfowl in later April and early May and again in September and early October.

In summer gulls, alcids, and kittiwakes are among the most abundant breeding birds on sea cliffs and islands. One concentration has been estimated to exceed 1,000,000 birds. Tufted puffins, common murres, and glaucous-winged gulls may occur at near similar numbers. Several large colonies of fork-tailed petrels, pelagic cormorants, and Arctic terns are also found in the western Gulf of Alaska.

Several species of noncolonial nesters, such as pigeon guillemots, commontly nest along the rocky shorelines. Kittlitz's murrelets usually nest in the mountains.

Associated with several of the sea bird colonies are breeding peregrine falcons. Four nest sites are presently known and there is evidence of four more in the Region.

The Copper River delta is an important breeding ground for trumpeter swans. In a late summer survey in 1968, Hansen et al. (1971) reported 1,022 trumpeter swans just inland from Yakataga to Cordova.

In winter resident bald eagles, ravens, crows, and gulls utilize the tidal area as a primary feeding site. Rock sandpipers, dunlins, surfbirds, black turnstones, and black oyster-catchers are frequently observed along rocky shores.

Many land birds and mammals are forced to forage in the tidal area during winters with heavy snowfall. On Montague, Hinchinbrook, and Afognak Islands, storms often drive Sitka black-tailed deer to the beaches to obtain food. During severe winters, bald eagles, ravens, magpies, and gulls congregate on these same beaches to feed on the deer that often die there.

All birds, even those most highly pelagic, move to land at some time to nest. The many nesting habitats on the north Gulf coast are used by a wide variety of breeding birds. Colonial nesters are found on islands and sea cliffs, mostly in the western portion of the Gulf. Many waterfowl, shorebirds, gulls, and terns nest on the higher beaches and brackish water flats of the Copper River delta. Nearly the entire North American population of at least 35,000 dusky Canada geese breed here at densities exceeding 40 nests per square kilometer in prime habitat.

Tidelands and beaches are most important in winter when snow further inland is deep and salmon are gone from the streams. At this time intertidal zone invertebrates and carrion cast up by the sea provide food for almost every active animal. Coyotes, foxes, wolves, and most members of the weasel family patrol the beaches extensively. Many resident birds forage there. Even goats and moose will take advantage of strips of beach vegetation freed from snow by high tides.

The lower segments of streams and their associated pond complexes are prime habitat for the spawning and rearing of coho, pink, and chum salmon. During spawning migrations substantial populations of black and brown-grizzly bears prey heavily on these fish as do mink, otters, and eagles. Foxes, coyotes, ravens, and a host of other scavengers profit from the leavings. After spawning, the salmon die, their carcasses adding nutrients to the water and soil of adjacent areas. Partly because of this enrichment, ponds, sloughs, and marshes are lush and provide important wildlife habitat. Moose, bear, beaver, and waterfowl (including trumpeter swans and dusky Canada geese) are abundant in such places, notably along the lower Copper, Martin, and Bering Rivers.

The freshwater environment consists of wetlands, marshlands, bogs, streams, and lakes. The animal associations reflect the integrated effects of hydrological regimes, topography, topographic gradients, sediment loads, composition and density of riparian-aquatic vegetation, and water. Large areas, such as the Kenai-Susitna lowlands, Nelchina plateau, and Copper River delta lowlands contain extensive marshlands as well as lakes supporting various and abundant bird, mammal, and fish populations.

This glacial outwash plain is the largest flatland lake area on the coast and includes 5,700 square kilometers of habitat. Lying in a rain shadow basin surrounded by high mountains, the area's vegetation is transitional between true rain forest and the dry, boreal forest of the Interior. Trumpeter swans are conspicuous breeding waterfowl in the Kenai lowlands and Susitna Valley. Few geese nest here, and ducks are in lower numbers than in Interior habitat.

All species of salmon spawn in various streams and lakes in this area. Steelheads run in Anchor River, Deep Creek, Ninilchik River, and Stariski Creek, and Dolly Varden are widely distributed throughout the system.

This area, formed by glacial outwash and by delta deposits of the Copper River, has poor drainage, resulting in extensive grass-sedge marshes that provide good waterfowl habitat. This land was elevated six to eight ft. (two to three m.) during the 1964 earthquake, and extensive areas are now above tide level. The enormous glaciers are rapidly retreating, also creating new habitat. The extension of habitat is most beneficial to trumpeter swans, which reach their greatest density here, and occupy all suitable lakes. The entire world population of dusky Canada geese nest here, as well as numerous ducks. In spite of the unique nesting populations, this area is probably most important as a staging and feeding area for waterfowl and other marsh birds bound to and from subarctic and arctic nesting areas immediately to the north (Figure 137c).

Moose, beavers, otters, minks, muskrats, and bears are common inhabitants of the stream-marshlands complex of the area (Figures 135c and 136c).

The Nelchina wetlands are located in an intermountain basin at the headwaters of the Susitna, Copper, and Gulkana Rivers. Elevations throughout the area exceed 600 meters and, as a result, the climate is generally cooler and the ice-free period shorter than in other interior regions. Vegetative growth is primarily sparse forest and alpine tundra. Lakes are less productive of waterfowl than those in river valleys at lower elevations. Scaup, green-winged teal, widgeon, and mallard are principal ducks. An important population of trumpeter swans also nests here.

This system includes some of the most valuable fish producing waters of the area, and there is considerable variation in the characteristics of streams. The Gulkana River is one of the most important fish streams of the Copper River system. Some 100,000 sockeye and 20,000 chinook salmon and some steelhead annually migrate up this stream to traditional spawning areas. The stream also contains abundant populations of rainbow trout and grayling. Fish Creek, a tributary of the Gulkana, provides access for a spawning run of sockeye salmon to Fish Lakes (Figure 137c).

Paxson and Summit Lakes, located in the alpine country of the Alaska Range, are large, clear and deep and support good populations of grayling and lake trout, some whitefish, burbot, and rainbow trout. Both are important rearing areas for sockeye salmon hatched in the upper Gulkana River and Fish Lakes.

Other major tributaries of the Copper River include the Tazlina, Klutina, and Tonsina Rivers. These sizeable streams characteristically have a milky color due to glacial runoff, yet they support sizeable runs of sockeye, chinook, and coho salmon and some steelhead. Resident fish include Dolly Varden, burbot, and lake trout. The Tiekel River has a resident population of Dolly Varden throughout and supports some coho salmon. The Little Tonsina River, an exceptionally clear stream, supports a resident population of Dolly Varden and grayling and runs of chinook and coho salmon.

This system on southwestern Kodiak Island was considered one of the most productive sockeye salmon areas in the North Pacific at the turn of the century. Present productivity of salmon is much lower with a variety of possible explanations for this decline (Rounsefell 1958). Karluk Lake is the major lotic habitat in this system. In addition to sockeye salmon, the other four species of salmon, steelhead-rainbow trout, and Dolly Varden also inhabit this river system.

On the south side of the Alaska Peninsula, the Chignik River is also known for its large stocks of sockeye salmon. Two separate populations exist, divided between those spawning in the Chignik Lake vicinity and another segment spawning in Black Lake and its immediate drainage system (Dahlberg 1968). All five species of salmon, steelhead-rainbow trout, and Dolly Varden are common in this drainage.

Some of the major animal species which occur in the freshwater and marine environments: