What are salt marshes?
Salt marshes lie at the edge of land and sea, on wave-protected coasts. They are dominated by low-lying, salt-tolerant vegetation and are laced with networks of tidal channels and pools. Salt marshes are communities of emergent herbs, grasses, or low shrubs, rooted in soils and alternately flooded and drained by tidal action.
Where are salt marshes found around Victoria?
As in many places throughout the world, many salt marshes that previously existed in the main urban harbours of Victoria have been filled in and replaced with agricultural land or urban development. For example, a salt marsh existed in the vicinity of the Empress Hotel, at the mouth of a creek that flowed from a wetland near present day Cook and Moss streets. Another salt marsh was located near where Point Hope Shipyards is today. Long-time locals may recall other salt marshes that have been lost.
Despite the loss of these historic salt marshes, some still remain and continue to provide valuable wildlife habitat. A small salt marsh lies at the mouth of Colwood Creek in Esquimalt Lagoon, and a narrow salt marsh fringe borders the western shore of the lagoon itself. A salt marsh also exists at the mouth of Millstream Creek, in Esquimalt Harbour. In the Gorge Waterway and Portage Inlet, some small, patchy salt marsh fringe still exists. New developments and restoration projects provide excellent opportunities to restore some of the previously existing salt marsh.
How do salt marshes form?
The extent and composition of salt marshes vary in different parts of the world. Whereas the Atlantic coast of North America is dominated by large deltas and salt marshes, the Pacific coast is much more rugged and has fewer and smaller salt marshes. Nevertheless, the structure and controlling factors of salt marshes in general are similar.
Salt marshes form along shallow-sloped coasts where there is a source of sediment that is transported to the ocean by streams or rivers, or deposited along the shore by wave action and currents. Marsh grasses initially colonize the sediment, by sending out underground stems called rhizomes. The roots, stems and leaves of the grass dissipate the energy of waves and cause more sediment to accumulate.
Eventually, dead plant mass and sediment build up, and the marsh grows vertically. It then becomes cut with channels and tidal creeks, from the flows of both fresh and salt water. As the structure of the marsh changes, different plants colonize the sediment, depending on their tolerance to salt and flooding, and their ability to compete with other species.
Mature salt marshes have high marsh and low marsh. High marsh is flooded only by the highest high tides, whereas the low marsh is flooded daily with the tides, and is dominated by salt-tolerant species.
What lives in salt marshes?
Salt marshes are highly productive environments. Abundant herbs, grasses and low shrubs dominate the view, while birds, crabs, snails and fish take shelter among the plants and in shallow water. Many species have evolved special traits to tolerate salt water, and the constantly changing conditions (wet/dry, freshwater/salt water, warm/cold).
In the low marsh, closest to the ocean, Lyngby’s sedge (Carex lyngbyi
) is one of the most common colonizers of mud flats, and provides food for geese and trumpeter swans. Sea arrow-grass (Triglochin maritimum
) and pickleweed (also called sea asparagus; Salicornia virginica
) are also common. Slightly higher grows seashore saltgrass (Distichlis spicata
). In the upper marsh, beyond the influence of salt water, cattails (Typha latifolia
) and bulrush (Scirpus maritimus
) are common.
Although few animals live exclusively in salt marshes, many feed or breed there. Some animals that can be seen in salt marshes include:
- Invertebrates such as insects, worms, crustaceans (e.g. crabs, amphipods and shrimp) and molluscs (e.g. snails, mussels).
- Birds such as Great Blue Herons, Brant Geese, Canada Geese, Mallards, Greater Yellowlegs, sandpipers, kingfishers, mergansers, Green-winged Teals, Gadwalls, plovers, snipe, Bald Eagles, Ospreys, hawks and owls.
- Mammals such as shrews, mice, voles, raccoons and river otters.
- Many types of fish shelter, rear and breed among the tidal channels of salt marshes, and in the deeper water of estuaries. Some of these include herring, salmon, cutthroat trout, stickleback, sole, flounder and surf perch.
Why are salt marshes important?
- Salt marshes provide important feeding and breeding grounds for many bird species, and act as nurseries for fish such as Pacific salmon and Cutthroat trout. They therefore contribute significantly to the overall function of the marine environment, and host many commercially important species for at least part of their life cycle.
- The plant material from salt marshes is broken down by microorganisms and exported offshore by tidal currents. This material is subsequently ingested by free-floating plankton, forming the basis of many marine food chains.
- Salt marshes help to filter and store pollutants that flow through streams from urban sources.
- Vegetation in salt marshes helps to anchor sediment and soil along the shoreline. This helps prevent stream flow, rainwater and waves from scouring away the land. This natural barrier also helps to dissipate the energy of large waves that can otherwise inflict serious damage on human life and property.
- The abundant wildlife in salt marshes provides valuable recreation, tourism, education and research opportunities for people.
What threatens salt marshes?
Although salt marshes are highly valuable and productive ecosystems, they are also vulnerable to damage. They are often located in areas that are highly desirable for agriculture, shipping, industry and urban development. By far the greatest threat to salt marshes is the practice of filling them in, for construction related to these activities. In many cases the process was begun by diking and draining the salt marsh for agriculture. Since 1800, 70% of Pacific salt marshes in Canada have been drained or lost to other functions. Other threats to salt marshes include:
- The spread of invasive species such as reed canary grass, which can crowd out native species and reduce the habitat value of the marsh
- Runoff of pollution such as heavy metals, oils and gas, particularly from impervious surfaces in urban areas
- Agricultural contamination, such as pesticides and fertilizers
- Pollution from boats
- Trampling of vegetation by people and animals
Another concern is the threat of sea level rise due to global warming. If this occurs too quickly, the salt marsh may not be able to adapt by migrating inland. Furthermore, landward migration is often constrained by agricultural, residential or urban development, a situation known as “salt marsh squeeze”. On one hand salt marshes help to protect inland property from the damage of storm surges, which are predicted to become more frequent with climate change in our region. On the other hand, their ability to perform this service is seriously hampered by coastal development. Restoration of salt marshes may therefore become even more important in the near future.
How can I help protect salt marshes?
For more information on protecting salt marshes, please visit our How Can I Help
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