Habitats of the Puget Sound watershed

"Habitat" describes the physical and biological conditions that support a species or species assemblage and refers to conditions that exist at many scales. An oyster shell provides habitat for some algae and invertebrates, whereas cubic miles of sunlit water in Puget Sound comprise the habitat for many planktonic species.

Photo: NOAA.

Habitat creation

Habitats are created and sustained by long-term physical processes such as sedimentation, stream flows, and tidal currents, and can be structured by habitat-forming species such as cedar forests, eelgrass, mussels, and bull kelp that are also integral to the distribution and abundance of other species. Within the terrestrial, freshwater, and marine habitats of the Puget Sound ecosystem, a complex set of physical processes determine the habitat that is present and the groups of species that are thus able to thrive.

Habitat classifications

A number of thorough habitat classifications and typologies have been developed for marine and terrestrial environments in the Puget Sound region. Freshwater and terrestrial habitats have also been described in considerable detail in major species’ recovery plans, including the Puget Sound Salmon Recovery Plan (Shared Strategy, 2005) and the Federal Forest Plan (FEMAT, 1993) and are not presented here in depth. At the regional ecosystem level, a guide for prioritizing habitat conservation efforts has been organized by The Nature Conservancy (Floberg et al. 2004) to assess biological diversity and the availability of related habitats in the Puget Sound/Willamette Valley/Georgia Basin region.

Freshwater and terrestrial habitats

Freshwater and terrestrial habitats of Puget Sound are built around the soils formed by glacial deposits and coniferous lowland forests. Changes in soil, gradient, and related variations in precipitation have given rise to diverse plant and animal communities on land. Before European settlement, lowland forests were dominated by western red cedar, western hemlock, and Douglas fir, with mixed stands of Douglas fir, Garry oak, and Pacific dogwood in drier areas. Today forest plant and animal groups coexist in a mosaic with agricultural and urban lands. Considerable attention has been placed on the need to create or preserve habitat of adequate quality, quantity, and connectivity for species migration and colonization throughout the Pacific Northwest region (Georgia Basin-Puget Sound Ecosystem Indicators, 2002).

Marine and estuarine habitats

The shallow nearshore areas of Puget Sound contain the vegetated habitats where light can penetrate the water, allowing numerous species to thrive. These habitats support eelgrass, seaweeds, and most marine fish and invertebrate populations at some time during their life cycle. As in other estuaries, the interface between terrestrial or freshwater environments and the marine environment is an important transition; actions in the headwaters affect habitats throughout the marine regions of Puget Sound. Additionally, numerous species continually move back and forth between terrestrial and marine environments. Bald eagles, marbled murrelets, and many other bird species utilize marine areas for forage while roosting and nesting on land. Adult bull trout repeatedly transit between freshwater and marine areas; their seaward migration is limited, thus placing great reliance for this species on the Puget Sound nearshore. Several species of salmon migrate and rear in these environments at different life stages. When the narrow fringe of habitat along the Puget Sound shoreline is degraded or destroyed, the support system for numerous plants and animals is disproportionately removed.

In marine systems, the pelagic zone is the part of the open sea or ocean compromising the water column, as opposed to the benthos or bottom. The couplings of pelagic and benthic systems are dynamic processes essential to ecosystem function. Just as gradient, soil, and precipitation contribute to terrestrial and freshwater ecosystems, physical characteristics such as depth, substrate, exposure, salinity, and gradient largely define the plants and animals that can utilize any given area in the marine and estuarine environment.

  • Depth and its correlates (temperature and light) influence the areas that can support primary productivity. In Puget Sound pelagic areas, the euphotic, or lighted, zone extends to about 20m in the relatively clear regions of the northern Puget Sound, and to 10m in the more turbid waters of the South Sound. In shallow nearshore regions, both the water and the substrate can support primary producers. Epibenthic diatoms are found on muddy bottoms; both micro- and macroalgae, such as Fucus sp. or Nereocystis, grow on cobble or rocky substrates.
  • Substrate is another primary contributor to habitat type and is strongly affected by wave and current exposure. Exposed areas do not generally accumulate fine sediments, and thus tend to have clean and mobile sand, or are rocky, either with bedrock or large cobble and boulders. More protected areas accumulate finer sediments, and the most protected areas collect very fine sediment and organic matter, making them muddy or silty.

    Most of the bottom of Puget Sound is comprised of soft sediments, ranging from coarse sands to fine silts and clay. Communities of sediment-dwelling organisms vary according to sediment type, water depth, and geographic location throughout Puget Sound. For example, shallow areas are often dominated by eelgrass, while deeper areas are dominated by sea pens (Ptilosarcus gurneyi) and the rich community of predators they support. Deeper sand or mud may contain geoduck clams and other burrowing organisms. Very deep basins contain unusual heart urchins, sea cucumbers, bivalves, and a variety of bottom-dwelling fishes.

    Rocky shores are composed of bedrock or a mixture of boulder and cobble substrates and tend to occur in areas where sediments do not accumulate. Cobble and mixed-substrate sites have communities of diverse bivalves, gastropods, sea stars, brittle stars, and many other invertebrates. Rocky substrates are more stable than sediment-dominated habitats, and the biological communities that develop on rocky shores reflect this. Often, so-called ‘ecosystem engineers’ such as kelps and mussels are species that themselves influence the physical conditions of local habitats so that they are more hospitable to other species. For example, Fucus (or rockweed) communities on rocky substrates support a rich array of small grazers and their predators. In lower intertidal and shallow subtidal areas, Fucus is replaced by several species of kelp and red algae that support a different and even richer community of grazers and predators.

  • Salinity and the gradient from freshwater to brackish and marine waters affect habitat types and the species that can be supported. Deltas and small estuaries within Puget Sound tend to be characterized by soft sediments as well as gradual salinity change. Rooted vegetation, including marsh grasses such as invasive Spartina and native species such as Salicornia or pickleweed, tend to be more common in deltas than in other areas of Puget Sound.

Variation within the Sound

In the greater Puget Sound these physical characteristics generally occur in a transition from north to south, as the influence of the ocean is moderated. Areas to the north and in the Strait of Juan de Fuca are more exposed and consequently tend to be rockier, less turbid, and more saline. The South Sound tends to be more protected, somewhat shallower, with more sandy and muddy bottoms. Circulation is weaker here, and thus the area is slightly less saline than the more exposed region.

About the Author: 
The development of the Sound Science document has been a collaborative process among scientists from a variety of disciplines and institutions throughout Puget Sound. The content reflects the wealth of knowledge in existing plans, research projects and personal expertise. The open dialogue and vigorous discussion about the interactions between components of the ecosystem, key threats to the system and critical science needs is almost as significant as the findings themselves. This document is the product of over 30 authors and almost 100 reviewers from federal, tribal, state, local, non-governmental, and academic institutions across the Puget Sound region. In total, hundreds of natural and social scientists have contributed either as co-authors, through extensive reviews, or by participating in workshops to debate and improve the information. We believe that the resulting content of the document thus reflects the collective views of the broad community of natural and social scientists familiar with Puget Sound. Key contributing agencies: King County Department of Natural Resources and Parks, National Oceanic and Atmospheric Administration (NOAA), Northwest Indian Fisheries Commission, People for Puget Sound, Puget Sound Action Team, The Nature Conservancy, US Environmental Protection Agency, US Geological Survey, University of Washington, Washington State Department of Ecology, Washington Department of Fish and Wildlife, Washington State Department of Health, Washington State Department of Natural Resources.