The seafloor is a very suitable indicator of stresses on the marine environment and can act as an early warning system. These stresses can originate from natural and/or anthropogenic sources. The condition of the seafloor (physical, chemical and biological) has been shown to modify in response to external influences. For example, organic matter falling to the seafloor may increase oxygen demand in the vicinity and stress and/or kill organisms located therein. Surveys using a variety of tools have been used to assess natural conditions prior to development or to assess the conservation status of an area. The Marine Environment and Food Safety Services Benthic Monitoring Unit is responsible for the review and assessment of existing and proposed activities that may have an influence on the marine environment.
Activities Requiring Benthic Monitoring
Dumping at Sea
Activities such as maintenance dredging of shipping ports and navigation channels that remove large amounts of sedimentary material from one marine area generally are discarded in other marine areas, if an alternative use cannot be found. The spoil area will require an extensive benthic survey to determine a baseline set of data that can be referred to in subsequent monitoring programs. The disposal of fish waste and other organic material is another issue that typically requires a survey of the benthic environment in order to assess the impact of the activity.
Point Source Discharge
Marine areas influenced by point source effluent (i.e., sewage outfalls) require pre/post benthic surveys to assess the impact of the organic and nutrient input on the environment.
Finfish Aquaculture
Finfish farming (salmon and trout) are carried out along the Western seaboard of Ireland. These activities result in inputs to the marine environment in the form of wasted feed and faecal material. This organic rain falls to the seafloor and can result in stress on benthic environment. As a result, aquaculturists monitor the benthic environment with a view to minimising the impact.
Benthic Monitoring Protocols
In May 2000, the Department of Marine and Natural Resources implemented a series of Protocols to monitor fish farming activities in Ireland. An annual benthic monitoring survey forms a part of these protocols. In the event of a breach of the allowable impact levels, suitable management modifications are implemented to reduce the impact and allow a suitable degree of recovery of the benthic environment.
Benthic Monitoring Tools
There are a number of tools utilised to monitor the benthic environment. These range from observational (qualitative) surveys carried out by divers or Remotely Operated Vehicles (ROVs) to more quantitative surveys carried out using a variety of grabs and cores or some in-situ sediment profiling equipment (Sediment Profiling Imagery - SPI) whose images can be interrogated using a variety of investigative software.
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