sailmarshes
the upper fringe of soft sediment shores is often dominated by salt marsh vegetation comprising woody perennials,succulent annuals and grasses. Saltmarshes are usually associated with temperate climates but occur throughout the world, from sub-polar regions to the tropics. On tropical shores, sailmarshes are often associated whit mangroves, occupying the upper and lower intertidal zone respectively. Species composition is determined to a large extent by salinity. For example, in low salinity or brackish waters found in the upper reaches of estuaries, marsh vegetation gives way to reed beds. Plant detritus carried away from marshes also contributes to food webs in estuaries and near shore waters. Many saltmarshes have been attributed special conservation status under the Ramsar Convention on Wetland of International Importance, due to their importance as habitats for birds, especially migratory species.
The impact of an oil spill on saltmarshes depends on the time of year relative to periods of plant growth. Temperate or cold region marshes are dormant during winter months, while in the Mediterranean growth is slow during high summer temperatures. A single event is unlikely to cause more than temporary effects but longer term damage, possibly over several years, can be inflicted by repeated, chronic oiling or by aggressive clean-up activity, such as trampling, the use of heavy equipment or removal of contaminated substrate. Cleaning of a saltmarsh is difficult without risking additional damage and so it is frequently recommended to leave marshes to clean naturally. However, if burning or cutting vegetation has died back. In general, as long as the roots or bulbs of the plants are not hermed by serious oiling or excessive compaction during the clean –up, seasonal re-growth may be expected to follow.
Mangroves
Mangroves are salt-tolerant trees and shrubs growing at the margins of sheltered tropical and sub-tropical waters. Mangroves stands provide a valuable habitatfor crabs, oysters and other invertebrates as well as important nursery areas for fish and shrimp. Inaddition, thus reducing erosion of coastlines and minimizing deposition of terrestrial sediments on adjacent seagrass bads and coral reefs.
Their location means that mangroves are highly vulnerable to oil spills. MangrovesAre also considered to be extremely sensitive to contamination by oil, dependent to a large extent on the substrate in which the mangroves are growing. Mangroves typically grow in dense muddy anaerobic sediments and rely on oxygen supplied through small pores (lenticels) on aerial roots (Figure 9). Heavy oil inundation of the root systems may block this oxygen suooly ansd may cause the mangroves to die. However, in open aerated sediments, which allow relatively free seawater exchang, the root systems draw oxygen from seawater and so have a higher tolerance to smothering by oil. In the second mechanism, the toxic components of oil, notably in light refined products, interfere whit the plants, systems for maintaining the salt balance, thereby affecting their ability to tolerate salt water. Experience has indicated that loss of mangroves due to heavy oil smothering appears to be less likely than mortality due to inundation with lighter products, including some cleaning agents, which can result localized loos of tree cover.
Organisms living within the mangrove ecosystem cam be impacted both by direct effects of the oil and also the longer term loss of habitat. Natural recovery of the complex mangrove ecosystem can take a long time and reinstatement measures may have real potential to accelerate the recovery process in such habitats.