Salcombe-Kingsbridge estuary
The Salcombe-Kingsbridge Estuary, located in the South Hams district of Devon, England, is a unique coastal biome characterized as a ria—a partially submerged river valley shaped by rising sea levels. It stretches approximately 5 miles inland, with a shoreline of 30 miles and an area of 1,665 acres, encompassing diverse ecosystems formed by extensive intertidal sandflats and mudflats. The estuary is primarily marine, receiving limited freshwater from small streams, and experiences significant tidal influences with a range of up to 15 feet. This estuary is notable for its biodiversity, housing rare species such as the spiny seahorse and the fan mussel, as well as various migratory wading birds and larger marine animals like dolphins and seals.
Human activity has long utilized this sheltered harbor for fishing, shipbuilding, and trade, with historical significance dating back to the 16th century. However, recent environmental challenges include the introduction of invasive species, which have disrupted local habitats and impacted fisheries. Climate change poses additional risks, raising concerns about coastal erosion and habitat degradation. Efforts are ongoing, led by local partnerships, to manage and sustain the ecological health of the Salcombe-Kingsbridge Estuary, ensuring its preservation for future generations while balancing human interests and environmental integrity.
Subject Terms
Salcombe-Kingsbridge estuary
Category: Marine and Oceanic Biomes.
Geographic Location: Europe.
Summary: This unusual estuary in southwestern Britain has diverse flora and invertebrate fauna, but must contend with invasive species.
The Salcombe-Kingsbridge estuary is in the South Hams district of the county of Devon in England. Salcombe and Kingsbridge are small towns lying near the mouth and head of the estuary. An estuary, the coastal part of a river valley that is influenced by the tide as it approaches the sea, typically extends from the upper limit of brackish water to the increasingly saline marine conditions of the open sea. The Salcombe-Kingsbridge is no different in this regard.
Hydrology
Sediment washed down by the river and an environment sheltered from wave action have led to the development here of extensive intertidal sandflats, mudflats, and sediment-filled subtidal channels. These wetlands at the margins of the land and the sea form a link between marine subtidal, marine intertidal, freshwater, and terrestrial ecosystems.
The Salcombe-Kingsbridge Estuary biome is a specific type of estuary called a ria. The word ria (from the Galician language of northwestern Spain) refers to an unglaciated river valley partially flooded by rising sea levels. As typical of rias, this estuary has a treelike form, with an irregular coastline and numerous side channels. Also typical of rias is the absence of a large river. The Salcombe-Kingsbridge Estuary instead is fed by a few small streams that rise from nearby springs. Consequently, the estuary is primarily a marine system, with limited freshwater inflow, and it covers a large area relative to the size of the feeder streams.
This estuary is macrotidal, with a tidal range of 15 feet (5 meters). The tidal influence runs 5 miles (8 kilometers) inland to Kingsbridge. The shoreline is 30 miles (49 kilometers) long, and the estuary covers an area of 1,665 acres (674 hectares), with an intertidal area of 1,102 acres (446 hectares).
The estuary has been designated as being within the South Devon Area of Outstanding Natural Beauty; it also forms part of the South Devon Heritage Coast. It supports some rare habitats and species, leading to its designation as a site of special scientific interest and a local nature reserve.
The lower estuary consists of rocky shoreline and sandy bays, and is partially cut off from the open sea by a sandbar. The bar is exposed during low spring tides; when strong southerly winds blow, entrance to the estuary is more difficult regardless of tides.
Biodiversity
In the lower estuary, the seabed consists of sand and mud, supporting numerous species of burrowing fauna, and colonized by important seagrass beds and especially eelgrass (Zostera marina) beds. Eelgrass, also called seawrack, is unusual because it is a flowering plant that lives in fully marine conditions. The good water quality and the eelgrass beds in the Salcombe-Kingsbridge Estuary provide a home for one of Britain’s rarities: the spiny seahorse (Hippocampus histrix). Eelgrass also helps stabilize loose estuarine sediment and provides an important nursery habitat for juvenile fish.
In the upper estuary, large areas of intertidal mudflats are exposed at low tide. These flats contain abundant tube-living and burrowing worms, bivalves, anemones, snails, and small crustaceans. These in turn provide important food sources for wading birds and fish within the estuary.
The estuary also provides conditions suitable for the fan mussel (Atrina fragilis). This mussel is large, often growing to more than 16 inches (400 millimeters). It is a long-lived, bivalve mollusk, and occurs sparsely in a few locations around Britain. It is one of the United Kingdom’s rarest and most threatened species. Four types have been found in the Salcombe-Kingsbridge estuary, one of which is particularly unusual because it lives intertidally rather than subtidally.
Numerous species of resident waders and wildfowl feed, nest, and overwinter in the sheltered waters of the creeks, and seabirds forage on the outer shores of the estuary or dive for fish beyond the sandbar. Migrant waders also feed on marine invertebrates from the mudflats before or during their long journeys. Larger animals including otters, dolphins, seals, and basking sharks also come into the estuary to feed.
The estuary is now home to several invasive species, including a seaweed commonly known as japweed (Sargassum muticum) and the gastropod known as slipper limpet (Crepidula fornicata). The numbers of slipper limpets, a kind of marine snail, have increased drastically over recent years. They can occur in vast numbers, often completely smothering the seabed. They are a serious pest of oyster beds and have detrimental effects on scallop fisheries in the estuary. Most scallops here now have slipper limpets on their shells, which may affect their ability to move and their vulnerability to predation. This development also has commercial implications. Scallops covered with slipper limpets require more time for sorting and cleaning, and are less acceptable at market. The buildup of pseudofeces from the slipper limpets is also changing the chemical and nutrient nature of the seabed, with potential effects on biodiversity.
Effects of Human Activity
The naturally sheltered harbor formed by the estuary means that the waterway has been used and valued by people for hundreds of years. There are records from the 16th century of seine fishers and herring fishers based at Salcombe. The estuary then developed as a successful center for shipbuilding, and as a port for fishing and trade. During the 1800s, Salcombe was a major center for the fruit trade, with oranges, lemons, and pineapples shipped here from the Mediterranean, the Azores, and the Caribbean. The estuary is still used as a minor fishing port, primarily for shellfish such as the scallops and edible crabs (Cancer pagurus).
In 1987, the Batson Creek channel in the estuary was dredged to improve access for local fishing boats. A total approaching 21,000 cubic feet (16,000 cubic meters) of mud was excavated and subsequently dumped on the seabed, smothering the biodiverse habitats on the underwater cliff and boulder slope off Scoble Point. Despite strong tidal currents, the dredge spoil did not get washed away. Between 1999 and 2002, a project to create an artificial reef on top of the dredge spoil was completed. Hundreds of large granite blocks were dropped from a barge. Recruitment of marine life to the artificial reef occurred rapidly. Within days, the blocks were covered by sea firs (hydroids), and after several years, the blocks were so covered with life that they were scarcely visible and now form a good replacement for the original habitat.
Climate change may impact the area by creating rising sea levels, which in turn could foster greater coastal erosion. The big question is whether to prepare for such an event by creating bulwarks against erosion and rising sea levels, or to allow nature to change the face of the ria, as it has over the eons. In the mid-2010s, the partnership that manages the South Devon Area of Outstanding Natural Beauty (AONB), a region that includes the Salcombe-Kingsbridge estuary as well as the Yealm, Erme, Avon, and Dart estuaries, unveiled a proposal to highlight the positives of the region, identify problematic issues, and seek solutions to the problems. Known as the South Devon AONB Estuaries Management Plan, the effort began in 2016 and was set to continue until 2024.
Bibliography
Born, Anne. The History of Kingsbridge and Salcombe. Fremont, CA: Orchard Publications, 2002.
South Devon Area of Outstanding Natural Beauty (AONB). “The Salcombe and Kingsbridge Estuary.” 2010. http://www.southdevonaonb.org.uk/downloads.asp?PageId=294.
“South Devon Estuaries Environmental Management Plan.” South Devon Area of Outstanding Natural Beauty (AONB), www.southdevonaonb.org.uk/wp-content/uploads/2020/01/SDEMP‗Text‗version-1.pdf. Accessed 1 Sept. 2022.
Waterhouse, Gordon. The Wildlife of the Salcombe and Kingsbridge Estuary. Fremont, CA: Orchard Publications, 1999.