Introduction

Almost all Puget Sound nearshore areas have significantly changed from their historical structures since European settlement in the region, and the vast majority of changes to Puget Sound shorelines have been caused by humans¹. Total shoreline in Puget Sound has decreased by about 15 percent due to simplification² and, not surprisingly, the areas where the most urban development has occurred have become the most impaired¹. Physical changes to nearshore areas include altered river deltas and reduced estuaries, elimination or disconnection of coastal embayments by placement of fill and tidal barriers, altered sediment processes caused by development of beaches and bluffs, and loss of estuarine wetlands³. Human-caused stressors that impact ecosystem processes include tidal barriers, nearshore fill, shoreline armoring, railroads, nearshore roads, marinas, breakwaters and jetties, overwater structures, dams, stream crossings, impervious surfaces, and land cover development³. These changes have caused disruption of ecosystem processes and alteration of habitat that have led to dramatic changes in the Puget Sound ecosystem, and restoration and conservation is urgently needed to restore those processes and systems.

Puget Sound currently has approximately 3,969 kilometers of shoreline and a 36,080 square kilometer drainage area¹. This drainage area can be divided into seven sub-basins, with the largest being Whidbey Sub-Basin (40.7 percent of the total drainage area), and the smallest being North Central Sub-Basin (1.4 percent of the total drainage area; see Figure 1 for a map of Puget Sound and its sub-basins)¹. The South Central Sub-Basin, which contains the cities of Seattle and Tacoma, has been the most extensively developed and urbanized overall, whereas the North Central Sub-basin located north of Everett has remained less disturbed¹.

Figure 1. Map of the Puget Sound region showing sub-basins highlighted in green (adapted from Schlenger et al. 2011).

Many species are found in the Puget Sound nearshore area. At the bottom of the food web are plankton, shellfish, and crustaceans, which support a variety of species at higher trophic levels, including many species of fish, seabird, and marine mammal. Smaller fish such as forage fish provide food for larger predatory fish such as the well-known salmonids. In turn, these fish support marine birds and mammals such as the iconic orca (Orcinus orca), the harbor seal (Phoca vitulina) and the California sea lion (Zalophus californianus). Many bird species are associated with bays, estuaries, and inland marine waters in Washington State, which are areas that are most heavily impacted by shoreline development⁴.

Shoreline development and its impacts on Puget Sound have many components, including development of artificial shoreforms, dredging to create deepwater access to ports, shoreline armoring, removal of shoreline vegetation, increased amounts of impervious surfaces, inputs from septic systems, and disturbance of riparian wildlife². All of these alterations can have adverse impacts on shoreline processes and functions, and they have consequences for wildlife species throughout the ecosystem and food web.

Shoreline Armoring

Shoreline armoring refers to the development of structures that have the objective of preventing erosion caused by waves. It is often used to keep fill material in place, protect roads and railroads located close to the water, and prevent loss of residential and industrial areas. More than 27 percent of Puget Sound’s total shoreline has been armored, varying between 9.8 percent and 62.8 percent in each sub-basin depending on the amount of development¹. The South-Central Puget Sound sub-basin, which contains the cities of Seattle and Tacoma, is the most developed, having nearly 63 percent of its shoreline armored, followed by South Puget Sound sub-basin, which contains the city of Olympia, with 34.5 percent armored shoreline. Whidbey Basin has armoring on 22.5 percent of its shoreline and Hood Canal has armoring on 21.2 percent of its shoreline. The least developed sub-basins are North Central Puget Sound, with only 9.8 percent armored shoreline, San-Juan Islands-Strait of Georgia, with 14 percent armored shoreline, and the Strait of Juan de Fuca with 16.1 percent armored shoreline¹.

Shoreline armoring in Puget Sound has been linked to disruption of natural sediment transport and the support functions for nearshore biota. The impacts of shoreline armoring on coastal sediment transportation processes include reduced supply of sediment, increased rate and volume of sediment transport, and reduced deposition of fine sediment, woody debris, and other organic material². This has resulted in the loss of 42 barrier beaches and appearance of 29 new bluff-backed beaches throughout Puget Sound, suggesting an overall loss of depositional beaches due to disruption caused by shoreline armoring². There also can be changes to patterns of freshwater seepage onto beaches⁵.

The impacts of shoreline armoring can vary based on the type of shoreline that has been altered, the location of armoring on the beach, and the amount of interaction with wave energy². If armoring is located on the upper part of the beach, it prevents sediment from moving from bluffs to the beach⁶. If the armoring is located lower on the beach, it causes increased erosion on the side of the structure facing the water because wave energy is reflected⁷. This results in coarser substrate on the beach, which is detrimental to forage fish spawning³. Armoring on the lower beach also changes the amount and rate of sediment transport^8,9. Beach loss is a major concern associated with armored shorelines and can be caused by the placement of structures and fill themselves, as well as by the effects of sea level rise moving up against an un-moving armored shoreline³.

Altered sediment processes caused by shoreline armoring can degrade habitat for many species. Species that depend on the input of fine sediments, including forage fish, shellfish, eelgrass, and shorebirds, no longer have appropriate habitat^10-12. When the upper beaches are buried due to these sediment processes, spawning habitat for forage fish is lost¹³. Any changes that result in an altered beach profile, with an increased beach slope and a reduction in intertidal area, can also result in reduced forage fish spawning². Shoreline armoring also reduces connectivity along and across the shore, changing migration corridors for juvenile salmon and making them more vulnerable to predation^14,15. Juvenile salmon and other fish species are further impacted by a reduction in shallow water habitat, caused both by fill and by erosion at the toe of the armoring structure³.

Tidal Barriers

Tidal barriers are structures that prevent tidal flow between areas. These barriers are often dikes and levees, but can also include roads or railroads built across wetlands. Dikes are often used to turn river deltas into farmland. Because tidal flow is prevented, water and sediment cannot flow into marshes, and vegetation and geomorphic changes occur^16-20. Without the flooding brought in by tides, areas with organic soils subside and are filled in by sediment, killing estuarine vegetation that no longer has the conditions and water flow that it needs to survive. Tidal channels are removed or reduced, and marsh area is lost. These changes result in reduced resilience against sea level rise, reduced transport of detritus and nutrients into Puget Sound, and loss of habitat for animals that depend on marsh areas³.

Tidal barriers have consequences for an array of wildlife including salmon, shellfish, birds, eelgrass, and kelp. Impacts to these important species also indirectly affect other species throughout the food web. As nutrient transport is impaired, tidal marsh vegetation dies and invertebrates disappear, resulting in a loss of food resources at the bottom of the food web which impacts foraging birds and fish. The impacts on juvenile salmon are especially heavy, as they are no longer able to access estuarine areas for rearing and foraging and the tidal channels they depend on are constrained. If the result is a decline in salmon populations, tidal barriers are also likely to indirectly affect orcas and other top predators, which rely on salmonids as a food source.

Tidal barriers have been constructed along 11 percent of Puget Sound’s shoreline and affect a 206 square kilometer area³. These changes have resulted in a great deal of wetland loss and conversion throughout Puget Sound. The Whidbey sub-basin has had the largest losses, while the southern parts of Puget Sound have been comparatively less impacted³.

Nearshore Fill and the Destruction and Degradation of Embayments and Wetlands

Embayments are small areas that are sheltered from wave action. They usually have some type of a barrier separating them from open water and often support tidal wetlands and tide flats. Types of embayments include barrier estuaries, barrier lagoons, closed lagoons/marshes, and open coastal inlets. When they occur at the mouths of streams and rivers, embayments contribute sediment and large woody debris into the nearshore environment³. Embayments also provide valuable habitat for juvenile salmon^21,22. Young Chinook and chum salmon fry usually rear in and along estuarine embayments²¹. As salmon runs become increasingly threatened, it is important to preserve areas that are important for their growth at all life stages. Because embayments are so sheltered, they can also provide ideal habitat for native shellfish, eelgrass and kelp beds, and shorebirds³.

In Puget Sound, embayments once were found along more than 1,100 kilometers of shoreline, but have seen a 46 percent reduction and are now only found along 600 kilometers³. The number of naturally occurring embayments of each type and amount of loss varies by sub-basin. The South Puget Sound Sub-Basin has always had the most barrier estuary shoreline, and it has retained much of it; in contrast, the North Central Puget Sound Sub-Basin has lost 88 percent of its barrier estuary shoreline³. The San Juan Islands-Strait of Georgia Sub-Basin has always had the most barrier lagoon shorelines, though most areas have seen losses of 50 percent or more³. Closed lagoons/marshes have gone from being the most abundant embayment type to the least abundant throughout Puget Sound³. Open coastal inlets were once the least abundant embayments, but they have become the second most abundant due to significant losses of the other embayment types³.

Embayments have most often been removed by placement of nearshore fill³. Fill has historically been used to create uplands for development and to remove material from areas where deeper water was required for ship traffic. Less than 20 percent of the total nearshore aquatic area in Puget Sound is covered by fill, but it is much more extensive in the South Central sub-basin, which has 100 percent fill in the nearshore aquatic area, and the South Puget Sound, which has 67.8 percent fill in the nearshore aquatic area¹. We can see a prime example of this right here in Olympia, where many of the buildings on the waterfront downtown have been constructed on top of fill material after Budd Inlet was dredged to allow better access by watercraft for shipping²³.

Nearshore fill results in wetland loss, disruption of sediment and woody debris transport, reduction in the amount of water that can flow in and out during tides, impediment of marsh formation, and loss of tidal channels, in addition to creating a barrier between the nearshore marine environment and the upland forest habitats which reduces inputs of nutrients, debris, and organisms³. These changes impact wildlife and ecosystems both directly and indirectly. Species that depend on shallow water and wetland habitats such as salmon and shorebirds lose habitat for foraging and refuge, and beach spawning forage fish lose habitat as beach sediment becomes too coarse due to interruption of sediment flows or beaches are buried under fill²⁴. Coarse sediment is also unsuitable for native shellfish species³. Additionally, riparian vegetation along the shoreline is often removed when an area is filled, which affects water temperature, beach moisture, and input of terrestrial insects, making it detrimental to salmon, forage fish, and shellfish^11,25.

Loss of Tidal Wetlands

Wetlands have been mentioned several times already because they are impacted by many of the previously discussed shoreline modifications, but they deserve additional explanation because they represent an important habitat within the Puget Sound ecosystem. Tidal wetlands are wetland areas that are subject to tidal influence, and they can be categorized based on salinity and location. Tidal freshwater wetlands experience changes in water level corresponding to the tides but have little to no salinity, oligohaline wetlands have low salinity and are often surrounded by scrub-shrub vegetation, estuarine mixing wetlands have more salinity mixing and emergent marshes, and euryhaline unvegetated wetlands are mudflats and tideflats³. Tidal wetlands often form because of sediment deposition in large river deltas. However, river deltas have seen especially large declines and have completely disappeared from the South Central Puget Sound Sub-basin (which contains Seattle and Tacoma) due to transitions to artificial shoreline structures¹. With these declines, most Puget Sound deltas have also seen dramatic losses in the total area of wetlands, especially those of the upper-estuary, fresher type¹.

Tidal wetlands provide habitat for a wide variety of fish, shellfish, bird, and other wildlife species. They are especially important transition, migration, and rearing areas for anadromous species like salmon³. Loss of tidal channels has caused declines in salmon populations in the Skagit River system, which is the largest river system in Puget Sound²². Freshwater seeps that flow into tidal wetlands bring cool water and support species like native shellfish and forage fish³. Shorebirds and herons also rely on tidal wetlands in the Puget Sound, especially during migration and for overwintering¹². In addition to habitat provision, tidal wetlands also provide valuable ecosystem services like nutrient cycling, flood control, water purification, and production of benthic invertebrates and insects to support the base of the food web; for these functions to continue, fresh water input, sediment transport, tidal flow, channel migration, exchange of aquatic organisms, and inputs of detritus must occur³.

During the development of Puget Sound’s major ports and urban centers, wetlands were filled extensively³. Almost all of the previously discussed shoreline modifications result in losses of wetland habitat in addition to their other impacts. Tidal freshwater and oligohaline transition wetlands have seen the largest losses³.

Overwater Structures

A somewhat different type of impact comes from the construction of overwater structures. Overwater structures can include anything that shades nearshore habitats, such as docks, piers, bridges, floating breakwaters, or moored boats³. There are 8,972 separate overwater structures in the nearshore zone of Puget Sound, which would cover an area of 9 square kilometers if they were all placed next to each other³. South Central Puget Sound and South Puget Sound have the highest number and density of structures, with 4 structures per kilometer and 3 structures per kilometer respectively³. South Puget Sound, however, contains smaller structures that are most often associated with development by residential landowners³.

These types of structures alter light, wave energy, sediment, and water conditions. Piling that supports these structures reduces wave energy that reaches the shoreline and causes substrate to be deposited below and in front of the structures, reducing sediment supply to areas further down and impacting organisms at the base of the food web that need fine sediment³. Reduced wave energy does benefit some species, however, as juvenile salmon prefer slower moving water and bivalve shellfish production has been found to increase under docks^26,27. Many species also colonize the hard substrates provided by the supports, including barnacles, mussels, sponges, crabs, macroalgae, and kelp³. Herring sometimes use piles as spawning substrate, but their embryos die if the piles are made of wood that has been treated with creosote²⁸. Contaminants can also leach out of construction materials and degrade water quality, especially in older structures that are made of wood that has been treated with creosote or copper²⁹. Many toxins can be absorbed by species such as shellfish and forage fish at the base of the food web and bioaccumulate as they make their way up to species like marine birds, salmon, and orcas. The shade created by overwater structures also impacts the ecosystem. Species that find their prey visually, such as salmon, forage fish, and Dungeness crab, may have an impaired ability to find food in low light conditions³⁰. The contrast between light and dark areas can also change fish behaviors and movements related to schooling, migration, and feeding, potentially increasing exposure to predators^16,30. Shade also limits plant growth and impacts survival of eelgrass, kelp, and macroalgae under or near overwater structures, creating unvegetated areas that fragment vegetation beds³.

Opportunities for Restoration and Conservation

Several opportunities exist for the restoration of Puget Sound’s nearshore ecosystem. The first is to restore the connectivity and size of formerly large river deltas³. These deltas are important contributors to the overall health of Puget Sound ecosystems, and the nearshore ecosystem processes that they influence could be restored by removing tidal barriers, roads, and railroads and bringing back historical delta areas and tidal wetlands³. Another important restoration effort could be aimed at restoring sediment processes, including input, transport, and accretion of sediment³. Restoring these kinds of sediment movements is crucial to restoring ecosystem processes throughout Puget Sound³. Restoration of embayments in areas where they have been eliminated or reduced could increase distribution, shoreline complexity, and length, in addition to providing important shallow water and tidal wetland habitats³. Finally, enhancing the connectivity and heterogeneity of the landscape along shorelines would help to restore ecosystem processes³. In addition to restoration, the value of conserving what intact areas we have left must also be remembered. It will be important to prevent further degradation of the remaining large river deltas, protect intact beaches that have not yet been armored or otherwise altered, and conserve relatively intact embayment shoreforms³.

Conclusion

Although there are many types of shoreline construction and development that serve different purposes for urban populations, they have many of the same effects on ecosystem processes and wildlife. Shoreline armoring, construction of tidal barriers, nearshore fill, and development of roads all result in disruption of sediment processes, loss of wetlands, simplification of the shoreline, and overall declines in habitat quality. These changes have direct and indirect repercussions throughout the food web and may have contributed to declines in some species. Salmon are particularly hard hit by many of the impacts of shoreline development, which is especially of concern because of the threatened or endangered status of many species. There are opportunities to restore some of these lost functions and habitats, and restoration will likely be a critical part of ensuring the survival of iconic Puget Sound species such as salmon and orcas alongside urban development areas.

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