Halosere

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In river estuaries, large amounts of silt are deposited by the ebbing tides and inflowing rivers.

The earliest plant colonizers are algae and eel grass which can tolerate submergence by the tide for most of the 12-hour cycle and which trap mud, causing it to accumulate. Two other colonisers are "salicornia" and "spartina" which are halophytes -i.e. plants that can tolerate saline conditions. They grow on the inter-tidal mudflats with a maximum of 4 hours' and exposure to air every 12 hours.

"Spartina" has long roots enabling it to trap more mud than the initial conlonizing plants and "salicornia", and so on. In most places this becomes dominant vegetation. The initial tidal flats receive new sediments daily, are waterlogged to the exclusion of oxygen, and have a high pH value.

The sward zone, in contrast, is inhabited by plants that can only tolerate a maximum of 4 hours submergence everyday (24 hours). The dominant species here are sea lavender and other numerous types of grasses.