Marine Biology

Estuarine Vegetation

The macroflora of estuaries is also limited. Most of the permanently submerged portions of estuaries consist of mud substrates unsuitable for macroalgel attachment. In addition, the highly turbid water restricts light penetration to a narrow upper layer. As a result, the deeper layers of the estuary are often barren of plant life. The upper layers of waters and the intertidal zone have a limited number of plants. In the lower reaches of the estuary there may be beds of sea grasses ( zostera, Thalastia, Cymodocea) . On and below  mean low water. These beds are considered as subtidal communities

The intertidal mud flats are inhabited by a limited number of green algel species. Common genera include Ulva, Enteromorpha, Chactomorpha and Cladophora . These are often seasonly abundant, disappearing during certain times of the year.

Estuarine mudflats have abundant diatom flora. The benthic diatoms are more abundant in estuaries than their planktonic relatives. Many are motile and undergo a rhythmic migratory pattern, moving upto the surface or down into the mud depending on the illumination. Estuarine muds also provide a suitable habitat for filamentous blue-green algae of several types. These algae may form mats upto 1cm thick on the mud surface and on the bases of various emergent vascular plants.

The highly turbid water in estuaries means that the dominant vegetation in terms of biomass is emergent plants. These are generally long-lived flowering plants in the upper intertidal and form the characteristic salt marsh communities that fringe estuaries throughout the temperate zones of the world. The dominant genera include Spartina and Salicornia. In the tropics, another community, the mangrove forest, is found.

A final component is the bacteria. Both the water and mud of the estuaries are rich in bacteria because of the abundance of organic matter to decompose. Estuarine waters are known to contain hundreds of times more bacteria than seawater, and the upper layers of mud contain more than a thousand times more bacteria than the overlying water. Densities of bacteria in estuarine muds of 100-400 million per gram have been reported.