Natural England - Estuarine rocky habitats

Estuarine rocky habitats

Estuaries are usually soft, muddy places, so rock and stable boulders in estuaries are rare, and occur mostly in drowned river valleys and fjords. They form a small proportion of estuarine seascapes but are important because they contribute a lot to the richness of life within estuaries. The rich and sheltered waters of estuaries provide nursery grounds for fish, and the rocky areas are an important part of these.

Estuarine rocky habitat © Keith Hiscock

Estuarine rocky habitats © Keith Hiscock

Conditions in estuaries are very different from those on the open coast, where rocky seascapes are usually found. The communities of plants and animals within estuaries are adapted to conditions of low wave energy, strong tides, freshwater inflow from rivers, murky water and choking silt. There can be considerable differences between communities living in rocky environments at the upper ends of estuaries and those towards the mouth, which more closely resemble open coast rocky shores.

Large seaweeds, wracks and kelps, with an understorey of barnacles, seaweed, snails, shrimp-like animals and occasionally sponges and sea squirts, can dominate the shore. Green seaweeds grow in rockpools.

Below the low water mark, the communities are equally variable, with anemones, sponges, sea mats and sea squirts growing on the rock surface.

Threats to estuarine rocky habitats include mobile fishing gear, dredging, coastal protection, pollution and, potentially, climate change and sea level rise.

Brief description of European distribution

Distribution map

Distribution map: (582kb)pdf document

Most estuarine rocky habitats are found in the north and western UK; few examples are found on the predominantly soft shores of eastern England.

Conservation status / need

UKBAP Priority Habitat

Component of the Habitats Directive Annex I habitat: Estuaries

Further information sources

UK Biodiversity Action Plan - Priority Habitat Descriptionsexternal link (PDF) (UKBAP)

Interesting fact

The sugar kelp, which normally has a long wavy, leaf-like frond, adopts a different form in the sheltered environment of estuaries. The frond widens, and can grow to the size of a bath towel.