Coastal alteration

Increases in agricultural and sewage discharges

Fishing for ecological critical species

Leisure activities

The addition of breakwaters, promenades and sea defences to EU coasts is becoming commonplace. These constructions inevitably result in changes in the depositional and erosional patterns of the local coastal area. These changes may be gradual and continuous or may be catastrophic (storm related) but intermittent. Gradual but continuous changes are the norm on mobile depositional shorelines such as much of the east coast of England. Where an area of shore is protected with solid defences, erosional scouring increases adjacent to the ends of the protected area. If constructions result in the formation of tide driven or wind and wave driven eddies, the scouring may take place at a considerable distance from the structure. Previous comments on the effects of sediment loading and turbidity apply to coastal alterations.

No case studies are known.

Eutrophication, the increase in the levels of macronutrients (particularly nitrogen and phosphorus), is due in European coastal waters principally to the use of artificial fertilisers and also to the discharge of untreated sewage or sewage with only primary treatment. It can result in the excessive growth of ephemeral species of macroalgae (commonly refered to as green tides where the effects are visible on the shore). Eutrophication also causes increased turbidity of the coastal water due to more prolific growth of phytoplankton. Both these effects could result in damage to maerl biotopes. Heavy overgrowth of epiphytic algae would reduce light levels available to the maerl, presumably reducing growth rates, as would increased turbidity from planktonic blooms. In addition, the macroalgal overgrowths and phytoplankton might compete with the maerl for selected nutrients.

There are reports that the effects of deep ploughing, field boundary removal, irrigation and the canalising of rivers is resulting in the increased silt loading of river-waters disgorged into the sea. The activities of the US Army Corps of Engineers on the major river systems of the USA are now recognised to be deleterious to the riverine ecosystems themselves but more recently are suspected to be causing increased sediment deposition in coastal areas (Tibbetts, 1997).

Hily et al. (1992) reported for Brittany that increased terrigenous material in river effluents, as a result of unspecified changes in agricultural activities, is responsible for the increase in turbidity in the rade de Brest. Where high turbidity and eutrophication occurred, these prevented the establishment of many algal species, causing the ubiquitous ones to dominate (Ulva sp., Ceramium rubrum).

Grall & Glémarec (1997) investigated the effects of eutrophication in the rade de Brest, by comparing impacted and control sites. Overall, there was an increase in algal cover, shown as greatly increased biomass at the impacted site. Species richness of animals in most of the trophic groups (e.g. carnivores, detritivores and scavengers) was slightly reduced, although diversity of surface deposit feeders was enhanced. The numbers of individuals per sample was slightly increased for the most abundant trophic group, detritivores.

The harvesting of one or more species from a biotope may result in an ecological imbalance within the maerl bed. If this is not ameliorated by the influx of replacement individuals of the harvested species, then long-term shifts in the composition of the biotope may occur. Information available on the relationships between species in maerl biotopes suggests some possible effects of predator removal.

In the rade de Brest, the presence of the echinoderm Sphaerechinus granularis at local densities of 2 or 3 m^-2 can affect algal cover over small spatial and temporal scales (Hily et al., 1992). Predation by decapods and Asterias rubens maintained the densities of most molluscan and echinoderm herbivores below the presumed capacity of the environment, and at normal herbivore densities, the growth of algae restricted the ability of the herbivores to eat the young plants. It could be postulated that removal of selected decapod species would enable the development of a larger herbivore population, grazing out the algal species stabilising the surface of the maerl bed.

Leisure activities, particularly marine ones, are part of an important growth industry at present. Several activities connected with yachting, e.g. anchoring either by temporary anchors or by permanent moorings, can damage maerl. In the Fal, the action of the mooring chain as vessels swing in the tide has been observed to crush maerl and other organisms. It is likely, however, that yachtsmen would be open to suggestions of less damaging types of moorings.

Sensitivity of maerl biotopes has been categorised by OSPAR (IMPACT, 1998) under the headings "habitat sensitivity" (scale of increasing sensitivity from 0 to 5) and "recovery potential" (scale of decreasing recoverability from 0 to 5).

In terms of habitat sensitivity, maerl biotopes are classed for different types of impacts as:

2. Force of impact would have to be >crushing or prolonged/concentration high and long-term/variation from normal would be required to cause habitat and/or community to be lost.

Impact types: Temperature change, sewage discharge, deoxygenation from aquaculture, predator removal.

3. Considerable force/concentration/variation from normal or prolonged or several events required to cause habitat and/or community to be lost.

Impact types: Scallop dredging, sediment loading, channel dredging.

4 . Minor impact/concentration/variation from normal in a prolonged or multiple event would cause habitat and/or community to be lost.

Impact type: Maerl extraction.

Recovery potential in relation to a single event causing mortality has been classed as

4. Poor, partial recovery likely within 10 years, full recovery like to take up to 25 years.