Atlantic lower circalittoral mud

This habitat is present across the region in deep basins as well as deep sheltered inlets. There are well known extensive and well-developed deep water mud basins in the North East Atlantic in the Kattegat, the Grand Vasiere off Gascony, France and to the west of Ireland. This habitat is also present in deep, sheltered inlets such as some of the Scottish sea lochs. Some declines in habitat quantity (as a result of shifts to different sediment composition) have been recorded and there are many well documented examples of decline in quality.
Most sedimentary benthic systems of the continental shelf of Europe have been modified by fishing activity in the last 100 years, particularly by mobile demersal gears, and this remains a significant pressure. Disturbance of the substratum due to intensive fishing activities using bottom trawls or dredges can damage or modify infaunal communities, with burrowing echinoderms and bivalves being particularly vulnerable.research suggests that some gears may also be modifying the biogeochemistry of the sediments by affecting organic matter remineralization and nutrient cycling through sediment resuspension and burial of organic matter to depth. Analysis by ICES (for the period 2009-2012) shows considerable overlap of this habitat with fishing intensity by gears which are known to have damaging effects on the epifauna and shallow infauna. More recent data for a single year (2013/2014) have revealed that more than 95% of modelled area of deep circalittoral mud across in the North Sea and Celtic Sea is considered to have been subject to fishing pressure by EU trawlers (bottom otter, beam and mid-water trawls) and that more than 80% of the deep circalittoral mud habitat across the North East Atlantic shelf area has been subject to abrasion disturbance. There are also regional studies, such as in the Kattegat, which show a similar pattern of overlap of this habitat type with the use of bottom gears that are known to alter the quality and take place at a frequency which maintains a disturbed condition. Much the same footprint of activity is likely each year and as this type of fishing pressure has been ongoing for many decades, there has most likely been a cumulative impact on habitat quality. Signficant effects have been observed in response to long-term chronic disturbance from otter trawling, for example, with negative effects on benthic infauna abundance, biomass and species richness with clear changes in community composition that may have far-reaching implications for the integrity of marine food webs.
Expert opinion is that there has been a very substantial reduction in quality of this habitat, most likely an intermediate decline affecting more than 80% of its extent although it is clear that in some locations there has also been a severe decline. The severity will depend on factors such as the intensity and frequency of disturbance. This habitat has therefore been assessed as Endangered for both the EU 28 and EU 28+ because of both past and likely continuing declines in quality.

• Urbanisation, residential and commercial development
• Discharges
• Biological resource use other than agriculture & forestry
• Fishing and harvesting aquatic resources
• Professional active fishing
• Benthic or demersal trawling
• Demersal seining
• Benthic dredging
• Pollution
• Nutrient enrichment (N, P, organic matter)
• Natural System modifications
• Human induced changes in hydraulic conditions
• Modification of hydrographic functioning, general

Timescale between incidents of damaging activity, the type of damaging activity and the predominant species, influences recovery. Studies have shown that recovery times following dredging were significantly shorter for short-lived species (<1 – 3 years), free-living and tube-dwelling species and for scavenging or opportunistic species, than for medium-lived species (3 – 10 years), burrow-dwelling species and suspension feeders. Free living species are also likely to recolonise areas more quicky that those that grow attached to the substratum and have an erect or stalked body form such as seapens. Recovery times of communities in deep circalittoral mud habitats following oxygen depletion and pollution has been investigated in several studies of the Gullmarsfjord, Sweden where they reported to be between 2-8 years.
Differences in the recoverability of different species groups following fishing may result in changes in community composition and ecosystem functioning over the long term.