Boating and marinas
The boating impacts from propeller scarring and propeller dredging are considered to be one of the most serious threats to Florida's seagrasses meadows. Physical damage from boat groundings and anchor dropping can be severe where anchor damage is proportional to the size of the boat (i.e. weight of the anchor and length of anchor chain) and dependent on the type of community impacted (seagrass, sand, coral etc). Recovery of for example coral damage from boat groundings is slow. During the summer, many pleasure boats sail in Italian waters. Anchoring is usually made possible in a narrow strip, causing particular stress to the communities living in these shallow habitats because of the mechanical action of chains and anchors, dumping of trash, and hydrocarbon spills from recreational vessels. In this case as in many throughout the Mediterranenan where shallow coastal habitats suffer from the same stresses, physical damage from boats could best be avoided though the installation of permanent moorings, designation of anchorages and provision of adequate information on anchoring and mooring.Picture courtesy of NOAA.
Marina construction work is often associated with the deployment of groins, breakwaters and other physical structures which will alter current and water circulation patterns, in turn affecting sediment transport and distribution patterns (erosion and accretion), as well as beach dynamics. For example, a large scale recreational marina was developed in El Alamien, about 94 km west of Alexandria. In order to create a safe water body for bathing activities, three man-made inlets protected by jetties connect the recreational lagoon to the Mediterranean. In order to stabilise the inlets - which are naturally hypersaline - and maintain continued water exchange, five offshore jetties were constructed. All of the described physical structures have created local erosion along the downdrift adjacent beaches threatening a number of condominiums and resort buildings of the town centre. In another example, the building of the Campoloro marina in Corsica in the 1970s, caused erosion of the sandy beach to the north of the marina of as much as 60 m. Areas to the south became silted up by approximately 80 m. These modifications seemed to be directly linked to the current alterations caused by the projection of the port.
Ultimately, the impacts of marinas and small harbours depend on the site location, design and construction of the development. Designing the marina so as to take maximum advantage of the natural attributes of a site can drastically reduce problems resulting from its construction. The main threats to marine and coastal habitats due to marina construction result from the:
- Construction of the marina itself - protect critical habitats, gather information on geomorphology and hydrology of the site so as to minimise impact.
- Dredging - deploy silt curtains and dispose of dredged material appropriately.
- Runoff - sanding, painting and vessel maintenance can cause significant harm as materials such as solvents, thinners, paints, and anti fouling agents compromise water quality, damage marine life - especially benthic communities - and accumulate in marine fauna and bottom sediments. Preference should be given to water-based materials and maintenance activities carried out on shore in designated areas.
- Boat wastes - Waste discharge can lead to increased levels of nutrients in surrounding waters accelerating oxygen depletion through uncontrolled algal blooms. Introduced pathogens can also make marina and surrounding waters unsafe for bathing.