Estuaries

Large shallow inlets and bays

The biotope complexes covered by this report fall within the Annex I habitats defined under the European Directive. This Appendix gives the definitions of those habitats.

Biotope Complex: Intertidal Mudflats and Sandflats - ‘Mudflats and sandflats not covered by seawater at low tide’

In the context of the Habitats Directive Annex I (code 14) classification, this biotope complex is included in the habitat defined as ‘Mudflats and sandflats not covered by seawater at low tide’ - sands and muds of the coasts, their connected seas and associated lagoons, not covered by sea water at low tide, devoid of vascular plants, usually coated by blue/green algae and diatoms.

Biotope Complex: Subtidal Mobile Sandbanks - ‘Sandbanks which are slightly covered by sea water all the time’

In the context of the Habitats Directive Annex I (code 11.25) classification, this biotope complex will be included in the broad category habitat of ‘Sandbanks which are slightly covered by sea water all the time’ - sublittoral sandbanks, permanently submerged, with water depth seldom more than 20m below Chart Datum and including non-vegetated sandbanks or sandbanks with vegetation belonging to the Zosteretum marinae and Cymodeceion nodosae.

The EU Manual definition of estuaries is that they are the downstream part of a river valley, subject to the tide and extending from the limit of brackish waters. River estuaries are coastal inlets where, unlike ‘large shallow inlets and bays’ there is generally a substantial freshwater influence. The mixing of freshwater and sea water and the reduced current flows in the shelter of the estuary lead to deposition of fine sediments, often forming extensive intertidal sand and mud flats. Where the tidal currents are faster than flood tides, most sediments deposit to form a delta at the mouth of the estuary

These are indicated by the EU Manual definition as large indentations of the coast where, in contrast to estuaries, the influence of freshwater is generally limited. These shallow indentations are generally sheltered from wave action and contain a great diversity of sediments and substrata with a well developed zonation of benthic communities. These communities generally have a high biodiversity. The limit of shallow water is sometimes defined by the distribution of the Zosteretea and Potametea associations. Several physiographic types may be included under this category providing that the water is shallow over a major part of the area: embayments, fjords, rias and voes

References