No. 29. Inland Marine Deeper Water

Landscape Setting. This habitat is commonly adjacent to Bays and Estuaries, Coastal Headland and Islets, and Marine Nearshore habitats and merges with the Marine Shelf habitat in the Strait of Juan de Fuca. Inland marine waters are used extensively for navigation, commercial transport of goods, recreation, tourism, and fishery operations.

Structure. A diversity of underwater structures are created as swift tidal currents circulate waters of the Pacific Ocean through the reaches of Straight of Georgia, Puget Sound, Hood Canal and the Straight of Juan de Fuca. Aspects of geology are particularly important in understanding the structure and dynamics of this habitat. Glacial ice initially excavated several long, narrow valleys that today form Lake Washington, Lake Sammamish, Hood Canal, and the major basins of Puget Sound. The arrangement of the present shorelines was established 13,000 years ago when glacial ice retreated from the Puget Lowland ⁷⁶. Organics, silt, and sand are the primary substrate components of this habitat and vary in specific composition and distribution with fluctuating physical factors ¹²⁰. Through deposition of sediments, major river deltas have advanced substantial distances into the deep basins of Puget Sound ⁷⁶.

Composition. Marine waters dominate fresh water influences in areas away from riverine discharges or from the shoreline. Because of the water depths involved, sunlight is diffused, and few if any, plants attached to the benthic substrates are capable of growing.

Other Classifications and Key References. Cowardin et al. ⁵³ included this region in the Columbia Province and described a hierarchical classification for wetlands and deepwater habitats in the U.S. Dethier ⁶⁸ described a classification for marine and estuarine habitat types in Washington State. Habitat types were defined by depth, substratum type, energy level, and a few modifiers. Harper et al. ¹⁰⁶ described a shore-zone mapping system for use in sensitivity mapping and shoreline countermeasures. Proctor et al. ¹⁷⁶ described an ecological characterization of the Pacific Northwest Coastal Region, including physical and chemical environments as well as socioeconomic aspects of watershed units and of the region. Schoch and Dethier ¹⁸⁹ provided high-resolution data on the physical features and associated biota of Puget Sound’s shorelines using the SCALE model (Shoreline Classification and Landscape Extrapolation).

Natural Disturbance Regime. Seasonal and larger, periodically occurring disturbances shape this habitat. Seasonal variation in tidal regimes, precipitation and riverine discharges (winter highs), as well as periodic storm events cause changes in temperature, salinity, energy level, and gradual or sudden erosion and accretion in localized areas.

Successional and Community Dynamics. Diverse plant and invertebrate communities compete for a variety of habitats. Succession occurs in each habitat area as disturbances create temporary vacancies, allowing opportunistic species to become established.

Effects of Management and Anthropogenic Impacts. Land conversion, use, and management have altered significant portions of this habitat. The physical, chemical, and biological condition of some habitats are degraded by both point and nonpoint discharges from municipal and industrial effluents. Functional plant and animal communities are altered by domestic and agricultural runoff of pesticides, herbicides, and fertilizers. Large portions of shoreline have been converted for residential, commercial, and port development, affecting inputs into the adjacent deeper waters. Benthic communities are significantly impacted by maintenance dredging done to support navigation and commerce. The transport of oil and chemical substances creates the potential for harmful spills that can affect these areas for extended periods of time. Passage of vessels from other regions increases the introduction rate of exotic species which, once established, can effectively out-compete native species.

Status and Trends. With the important exceptions of locally increased sedimentation rates and contaminant deposition/retention, the status and trends in the physical and biological aspects of this habitat are poorly known.