The following is a short summary of the habitat type and how to create/enhance it to a "good" condition. For an informed position, please refer to official up-to-date EUNIS documentation or the UK Government's Condition Assessment Sheet.
Sediment shores characterised by beds of adult mussels Mytilus edulis occur principally on mid and lower eulittoral mixed substrata (mainly cobbles and pebbles on muddy sediments) in a wide range of exposure conditions. In high densities the mussels bind the substratum and provide a habitat for many infaunal and epifaunal species. This biotope is also found in lower shore tide-swept areas, such as in the tidal narrows of Scottish sealochs. A fauna of dense juvenile mussels may be found in sheltered firths, attached to algae on shores of pebbles, gravel, sand, mud and shell debris with a strandline of fucoid algae.
High densities of juvenile mussels attached to seaweed have been recorded from sheltered shores of the Dornoch Firth and Moray Firth. Adult mussel beds can be found below a band of ephemeral green seaweeds (EUNIS A2.821) on more exposed, predominantly rocky shores. On sheltered, predominantly rocky shores either a Fucus vesiculosus dominated biotope or a biotope dominated by the wrack Ascophyllum nodosum (EUNIS A1.3132; A1.3142) can be found above, or the barnacle dominated biotope (AEUNIS 1.1133).
The temporal stability of mussel beds can vary a lot. Some beds are permanent, maintained by recruitment of spat in amongst adults. Other beds are ephemeral, an example of which are beds ocurring at South America Skear where large amounts of spat settle intermittently on a cobble basement. The mussels rapidly build up mud, and are unable to remain attached to the stable cobbles. They are then liable to be washed away during gales. A second example of ephemeral mussel dominated biotopes occurs when mussel spat ("mussel crumble") settles on the superficial shell of cockle beds, such as is known to occur in the Burry Inlet.
This aligns with the description provided by EUNIS A2.7 (and see A2.72 especially)
How to Create / Enhance to a "Good" condition
There are a set of criteria that are used to judge the condition of this habitat. These are listed below.
| Indicator | Good (3 points) | Moderate (2 points) | Poor (1 point) |
A | Coastal processes | Coastal processes are functioning naturally. No evidence of human physical modifications which are impacting the habitat. | Artificial structures present, for example groynes, that are impeding the natural movement of sediments or water, affecting up to 25% of the habitat. | Artificial structures present, for example groynes, that are impeding the natural movement of sediments or water, affecting more than 25% of the habitat. |
B | Presence and abundance of invasive non-native species | Not more than one invasive non-native species is ‘Occasional’ on the SACFOR scale or is occupying more than 1% of the habitat. No high-risk species indicative of suboptimal condition present, see Footnote 1 for details. | No invasive non-native species are present above ‘Frequent’ on the SACFOR scale or they occupy between 1-10% of the habitat. No high-risk species indicative of suboptimal condition present, see Footnote 1 for details. | One or more invasive non-native species are present at an ‘Abundant’ level on the SACFOR scale; they occupy more than 10% of the habitat; or a high-risk species indicative of suboptimal condition is present – GB Non-native Species Secretariat should be notified, see Footnote 1 for details. |
C | Water Quality | No visual evidence of pollution. There are no nuisance algal growths that are likely to be attributable to nutrient enrichment. Consider seasonality of survey timing2. | Visual evidence of low to moderate levels of pollution. Elevated algal growth with increases in cover that may indicate nutrient enrichment. Consider seasonality of survey timing2. | Visual evidence of high algal growth that is indicative of nutrient enrichment. Signs of eutrophication that would impede bird feeding. Consider seasonality of survey timing2. |
D | Non-natural structures and direct human impacts | No evidence of impacts from direct human activities, or they occupy <1% of the habitat area (for example, pontoons, moorings, boats, crab tiles, bait digging or anchoring scars). | Evidence of impacts from direct human activities occupies 1-10% of the habitat area (for example, pontoons, moorings, boats, crab tiles, bait digging or anchoring scars). | Evidence of impacts from direct human activities occupies >10% of the habitat area (for example, pontoons, moorings, boats, crab tiles, bait digging or anchoring scars). |
E | Litter (when examining a beach strandline / mean high water line or intertidal rocky shore) | Following the Marine Conservation Society (MCS) beach litter survey method, the number of items of litter does not exceed 0.0036 m−1 min−1 person−1, equivalent to up to 20 items per person per 100 m per hour. See Footnote 3 for details. | Following the MCS beach litter survey method, the number of items of litter does not exceed 0.0078 m−1 min−1 person−1, equivalent to between 21 and 47 items of litter per per person per 100 m per hour. See Footnote 3 for details. | Following the MCS beach litter survey method, the number of items of litter exceeds 0.0078 m−1 min−1 person−1, equivalent to more than 47 items of litter per person per 100 m per hour. See Footnote 3 for details. |
Condition Assessment Result |
TOTAL SCORE 12-15 (75-100%) = GOOD CONDITION |
TOTAL SCORE 8-11 (50-75%) = MODERATE CONDITION |
TOTAL SCORE 5-7 (0-50%) = POOR CONDITION |