| JNCCMNCR10213502 |
JNCCMNCR10000156 |
1982-83 Bullimore Skomer sublittoral monitoring |
JNCCMNCR10009214 |
1982-08-29 |
1982-08-29 |
D |
North Wall Transect (Skomer Island) |
Point |
51.7415531594542 |
-5.28250943922823 |
WGS84 |
135144 |
Caryophyllia (Caryophyllia) smithii |
FALSE |
C |
|
FALSE |
A moderate, very broken, bedrock slope extends from above chart datum to 7-8m, is continuous either side of the transect and is interrupted by steep sided gullies and large clefts. Between 7-8m and 11-12m is a steeply sloping rock face terminating at a bedrock ridge forming an 8-10m wide platform across which the transect runs. Immediately either side of the ridge are short, steep, boulder slopes extending to 15m. The slope to the west is about 5m broad and terminates in a further steep rock face. Below 13m, the bedrock becomes steeply sloping then vertical or overhanging. These cliff faces extend both east and west of the transect and are broken by deep vertical clefts. At 30m is a steep boulder slope which extends beyond 35m. Silt is found on the boulder slopes and in gullies of a moderate thickness (2-5mm). The following is a brief description of the communities present during, and the most apparent changes since, July 1982. It does not represent a comprehensive species list for the station. The abundance scales and notations of Hiscock (1980) have been employed. All four sites were dominated by a turf of small, erect bryozoans (mainly Crisia spp. and Scrupocellaria spp. but including Bicellariella ciliata and those colonies of Chartella papyracea and Bugula spp. too small to be identified individually) which covered on average half the available space. A well concealed low layer of the calcareous tubeworm Salmacina dysteri and barnacles occurred at all sites and was generally underestimated from the photographs. At the 10m site Cellaria spp. and Nemertesia antennina were common, N. ramosa and Aglaophenia pluma frequent. Caryophyllia smithii was common (in numbers per unit area though with only 1.5% cover, see section 7.3) and Alcyonium digitatum abundant (with 2.5% cover). S. dysteri, in reality common, was estimated as occasional. Lithothamina occurred occasionally but was masked (overhung) by erect animal species which caused underestimation in some sets of photographs. In addition, occurring rarely or occasionally (i.e. one or very few specimens included in the photographs), were several encrusting, boring and erect sponge species (including Cliona celata, Myxilla incrustans, Raspalia hispida, Scypha ciliata), Corynactis viridis, colonial ascidians (mainly Botryllus schlosseri), hydroids and small foliose red algae. The percentage cover of bryozoan turf has remained unaltered though it was somewhat more dense and taller in 1983. There has been an increase in both numbers and colony size of Cellaria spp.. Both species of Nemertesia, frequent or common during August of both years, were heavily grazed and easily overlooked by early autumn. The only noticeable increase of a hydroid species was where one colony of Abietinaria abietina occurred in 1982 there were several in 1983. Bryozoan turf occupied about 45% of the 15m site and Cellaria spp. were common. A. digitatum was abundant, Nemertesia spp. and C. viridis frequent and C. smithii occasional. Encrusting sponges, bryozoans and colonial ascidians occurred as at the 10m site though there were fewer erect sponges. Bugula spp. could be recognised and were densest in cracks and below small overhangs. The S. dysteri/barnacle layer was estimated as occurring frequently. The bryozoan turf and Cellaria spp. were denser and taller at this site also in 1983 and N.antennina more common. Areas of bare rock and calcareous barnacle base which became available for colonisation in late 1982 were occupied by bryozoan turf in mid 1983. Similar areas, mainly of barnacle bases, have become available during October-November 1983. The 20m and 25m sites were of similar general appearance. Whilst there was still an abundance of the bryozoan turf, C. viridis became the dominant feature. The density of C. viridis generally exceeded 50/0.01 metre squared with 20-35% cover (when contracted) and, locally, 100% cover when the individuals were expanded. There are fewer tall organisms at these sites. A. digitatum is common at 20m and Cellaria spp. occasional at both depths. S. dysteri, again underestimated, is counted as 1-2% cover when the bryozoan turf is densest, increasing to 3-4% in autumn. There is a high percentage cover of encrusting organisms comprising mainly B. schlosseri but including the boring stage of C. celata and other encrusting sponges. In common withthe shallower sites, areas of bare rock and barnacle bases became available during the autumn of both seasons. Those areas bared in 1982 were covered with bryozoan turf in 1983. Generally the bryozoan abundance was greater in 1983. The turf was not only denser but other species were recognisable including Bugula plumosa, B. flabellata and C. papyracea. |
