Bedrock outcrops
Biotope description :
Specific biotope is variable depending on physical setting with respect to hydrodynamic regime, water depth and light attenuation. High biodiversity is typical except where outcrops are adjacent to highly mobile coarse sediment in a high energy environment resulting in scour reducing diversity. A wide range of flora and attached epifauna may be found (e.g. algae, hydroids, bryozoans, sponges, ascidians, anemones, molluscs, barnacles & keel worms) with increased diversity often observed on sloping or highly fractured surfaces. Encrusting, massive or erect forms of faunal taxa may dominate depending upon the physical environment. Lithology and any sediment veneers also determine species composition and dominance; where the rock is sedimentary boring species may increase in dominance (e.g. boring sponges & anemones) ; where sediment veneers are sufficiently thick burrowing megafauna may be supported. The attached fauna/flora also provide habitat for other taxa including nudibranchs, chitons, gastropods, amphipods, pycnogonids, isopods and some decapods etc. Bedrock outcrops are notable refuges and nursery habitat for many fish species, decapods and octopus.
Biotope description :
Specific biotope is variable depending on physical setting with respect to hydrodynamic regime, water depth and light attenuation. High biodiversity is typical except where outcrops are adjacent to highly mobile coarse sediment in a high energy environment resulting in scour reducing diversity. A wide range of flora and attached epifauna may be found (e.g. algae, hydroids, bryozoans, sponges, ascidians, anemones, molluscs, barnacles & keel worms) with increased diversity often observed on sloping or highly fractured surfaces. Encrusting, massive or erect forms of faunal taxa may dominate depending upon the physical environment. Lithology and any sediment veneers also determine species composition and dominance; where the rock is sedimentary boring species may increase in dominance (e.g. boring sponges & anemones) ; where sediment veneers are sufficiently thick burrowing megafauna may be supported. The attached fauna/flora also provide habitat for other taxa including nudibranchs, chitons, gastropods, amphipods, pycnogonids, isopods and some decapods etc. Bedrock outcrops are notable refuges and nursery habitat for many fish species, decapods and octopus.
Key-words :
reef, biodiversity, rock, Intrusion, Lithology
Habitat description :
Stable bedrock exposed from surrounding sediment. Bedrock may be high to low relief with scarps and ridges, and potentially bedding and structural planes may be apparent. Bedrock may be fissured; where such fissures are large enough these may be partially infilled with sediment, cobbles or boulders. Exposed bedrock may be covered by a thin sediment veneer in lower-energy environments. Bedrock is commonly exposed in moderate to high energy environments but may also be found to a lesser extent in low energy settings. Bedrock outcrops do not include man-made structures, although the term ‘reef’ includes bedrock outcrops, boulder reefs and man-made seabed structures.
Habitat description :
Stable bedrock exposed from surrounding sediment. Bedrock may be high to low relief with scarps and ridges, and potentially bedding and structural planes may be apparent. Bedrock may be fissured; where such fissures are large enough these may be partially infilled with sediment, cobbles or boulders. Exposed bedrock may be covered by a thin sediment veneer in lower-energy environments. Bedrock is commonly exposed in moderate to high energy environments but may also be found to a lesser extent in low energy settings. Bedrock outcrops do not include man-made structures, although the term ‘reef’ includes bedrock outcrops, boulder reefs and man-made seabed structures.
Place : Coastal area of Trégor-Goëlo (France)
Mesh regional Sea : Western Channel
Comments : REBENT 10 cruise (Ifremer/DYNECO)
Mesh regional Sea : Western Channel
Comments : REBENT 10 cruise (Ifremer/DYNECO)
Lat :
48.919900
48.919900
Lon :
-2.946200
-2.946200
Description :
Substrates - Rocky bottoms
Comments :
Outcroppings of the bedrock, located less than seven kilometres to the North-North-East from Bréhat island. According to the initial geological studies done by coring in the sector (Lefort, 1970 and 1975), the rocky substrate corresponds to an acid volcanic formation (ignimbritic rhyolites), from the Cambrian (547 Ma: Auvray, 1979) or Cadomian (622 Ma: Egal et al., 1996). Thanks to the acoustic imaging, it can be seen that these materials are highly resistant to erosion. Their rugged relief shows numerous suborthogonal joints. This acoustic facies shows that the bottoms are chaotic and entirely similar to the northern part of the Héaux foreshore on Bréhat island.
Technique(s) :
Backscatter images
- Type
sidescan
- Make & Model
Edgetech – DF 1000
- Operating frequency (kHz)
105
- Total swathe width (m)
107
- Approximate water depth (m)
39
- Gray level (positive or negative image)
negative image
Substrates - Rocky bottoms
Comments :
Outcroppings of the bedrock, located less than seven kilometres to the North-North-East from Bréhat island. According to the initial geological studies done by coring in the sector (Lefort, 1970 and 1975), the rocky substrate corresponds to an acid volcanic formation (ignimbritic rhyolites), from the Cambrian (547 Ma: Auvray, 1979) or Cadomian (622 Ma: Egal et al., 1996). Thanks to the acoustic imaging, it can be seen that these materials are highly resistant to erosion. Their rugged relief shows numerous suborthogonal joints. This acoustic facies shows that the bottoms are chaotic and entirely similar to the northern part of the Héaux foreshore on Bréhat island.
Technique(s) :
Backscatter images
- Type
sidescan
- Make & Model
Edgetech – DF 1000
- Operating frequency (kHz)
105
- Total swathe width (m)
107
- Approximate water depth (m)
39
- Gray level (positive or negative image)
negative image
Date : 04/04/2006
Date accuracy : Day
From : Ehrhold A. - Ifremer/DYNECO-EB
Contact email : Axel.Ehrhold@ifremer.fr
Data owner : Ifremer, Rebent project
Date accuracy : Day
From : Ehrhold A. - Ifremer/DYNECO-EB
Contact email : Axel.Ehrhold@ifremer.fr
Data owner : Ifremer, Rebent project
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