No. 30. Marine Nearshore

David H. Johnson

Geographic Setting. This habitat reflects marine water areas (high tide line to depth of 66 ft [20 m]) along shorelines not significantly affected by freshwater inputs (i.e., excludes Bays and Estuaries). This includes all marine shorelines of Puget Sound, Hood Canal, San Juan Islands, Strait of Georgia, Strait of Juan de Fuca, and along the outer coastlines of Washington and Oregon. In Washington, there are 3,100 miles (4,990 km) of this nearshore habitat ⁸⁵ (H. D. Berry, Department of Natural Resources, Aquatic Resources Division, Olympia, pers. comm.); in Oregon, there are 377 miles (607 km) of this nearshore habitat (C. Barrett, Northwest Habitat Institute, Corvallis, Oregon, pers. comm.). For mapping and classification purposes, this habitat does not extend into, or overlap with, shallow or intertidal areas found within Bays and Estuaries.

Physical Setting. The outer coastline of Washington and Oregon can be characterized as a series of sandy beaches interspersed with rocky headlands. This coastline is oriented in a north-south direction and is subjected to long-fetch, high-energy waves. Nearshore areas within Puget Sound, Hood Canal, and elsewhere landward from the Straight of Juan de Fuca, are more protected. With the exception of the far-reaching Columbia River plume ¹⁹⁴, the effects of coastal streams are generally local and seasonal ¹⁷⁰.

Landscape Setting. This habitat is adjacent to the Marine Shelf, Inland Marine Deeper Waters, Bays and Estuaries, and a number of terrestrial-based habitats (e.g., Coastal Dunes and Beaches, Westside Lowland Conifer-Hardwood Forest, and Urban). It occurs in a mosaic with Coastal Headlands and Islets.

Structure. Fresh waters drain from lands surrounding these inland marine waters to create estuarine environments nearshore ¹³³ (see Bays and Estuaries habitat). Nearshore subtidal habitats are diversified by degree of wave and current action, availability of sunlight, and presence of vegetation. Submerged unvegetated habitats cover a greater area than do vegetated nearshore habitats, such as salt marshes and eelgrass beds. Various combinations of water depth, character of substrates, and exposure to tidal action create a wide range of benthic habitats. Sand, cobble, boulders, and hardpan are commonly found in areas of moderate to strong currents, whereas silt and clay settle out in protected inlets and bays ^{67, 145}.

Composition. This habitat supports marine organisms capable of withstanding short-term exposure to air. Bottom substrates in exposed areas are generally rock or sand, but can include cobble or gravel. The subtidal photic zone includes the region from mean low low water (MLLW or the 0 ft depth) to about -50 ft (-15 m) where water is deep enough to prevent sufficient light penetration to the marine floor for primary productivity of kelp and other marine plants. The rocky-bottom intertidal habitats support kelps (Laminaria spp., Lessoniopsis spp., Hedophyllum sessile), brown rockweed (Pelvetiopsis limitata), red algae (Iridaea spp.), and surfgrass (Phyllospadix scouleri) as well as an abundance and variety of sessile benthic invertebrate. The larger kelps, such as Macrocystis integrifolia and Nereocystis leutkeana, are found in the rocky-bottom subtidal areas. Because of constant wave action, the sandy-bottom areas of the intertidal and subtidal zones support few or no plants. The moderate to low energy intertidal and subtidal areas where sand, mud, and gravel accumulate support eelgrass (Zostera marina and Z. japonica), and the red alga (Gracilaria pacifica).

Other Classifications and Key References. Dethier ⁶⁸ provided a detailed classification scheme for the estuary, intertidal, and shallow subtidal areas of Washington. The Cowardin et al. ⁵³ classification scheme has several limitations with regards to adopting it for marine and estuarine systems. Levings and Thom ¹⁴³ described 9 categories of nearshore habitat in Puget Sound and Georgia Basin.

Natural Disturbance Regimes. This habitat is strongly influenced by tidal rhythms, wave action, storm events, light penetration, and bottom substrate. Because of these factors, this habitat is characterized by a high degree of patchiness; this patchiness leads to differences in its faunal makeup and use. Herbivory by marine invertebrates also causes significant disturbance in plant communities, as evidenced by the direct control of kelp beds by urchin populations.

Succession and Stand Dynamics. The primary natural processes that shape the nearshore habitats include tides, erosion, accretion, and storm events. The rocky surf zone of the outer coast of the Olympic Peninsula includes some of the most complex and diverse shores in the United States ⁶⁷. Here, high wave energy provides space for habitation for species as materials are eroded away, and by increasing the capacity of algae to acquire nutrients and use sunlight. Examples of succession can be found on rocky intertidal shores where wave energy periodically disturbs established communities, or in kelp forests where herbivory or the scouring action of swift tidal currents removes vegetation.

Effects of Management and Anthropogenic Impacts. This habitat reflects the interface between land and sea, and is the site of intense commercial and navigational activities, such as seaports, marinas, ferry docks, and log booms. A significant concern identified by Broadhurst ³⁵ is the site-by-site consideration of projects with no ability to account for and assess the cumulative environmental effects of various development activities (from small residential projects to large commercial and industrial development projects). Without the ability to measure or understand cumulative effects, managers are permitting individual activities that may result in dramatic resource losses over time. Making high-quality nearshore vegetation and shoreline characteristics inventory mapping available to land-use planners, natural resource scientists, and the public will increase opportunities to protect this habitat.

Status and Trends. Shoreline modification such as bulkheading, filling, and dredging can lead to direct habitat loss. Indirectly, it can lead to changes in the sediment and wave energy on a beach and in adjacent subtidal areas. One third of Puget Sound’s shorelines, approximately 800 miles (1,287 km), has been modified ^{180, 190, 191}. The Central Puget Sound region, with high human population levels, shows the highest level of modification overall (52%) ¹⁸⁰. In Washington there are 26 species of kelp, more than any other area worldwide ⁷⁷. Data on floating kelp along the Strait of Juan de Fuca suggest that while kelp areas are dynamic, the overall extent of kelp has remained stable during 1993-1997 ¹⁸⁰.