2010-11 Coastal and Marine Environmental Research. St Mawes maerl and Zostera bed video transects.

notPlanned

"Video transect survey of Maerl and Zostera beds at the mouth of the Percuil River for the St Mawes Harbour Conservation Trust. Collected to continue the baseline data on maerl and sea grass beds in this area and to promote awareness and interest in life underwater in St Mawes harbour. The scheme for scoring the flora and fauna shown in photo-quadrats was similar to that for scoring physical substratum materials. Three types of biological variables were scored: (i) individual species; (ii) groups of closely-related species that were hard to distinguish; and (iii) groups of similarly-looking, but not closely related-species. In all, there were 74 different biological variables. Broadly speaking these were all species or groups that were common and/or conspicuous in photo-quadrats. Because of the large number of biological variables, it was not possible to assess relative abundance in every case. Assessments of relative abundance were reserved for two key variables only: (i) seagrass (Zostera marina); and (ii) living maerl (Lithothamnion corallioides and/or Phymatolithon calcareum). All other biological variables were scored simply as either present (= 1), or absent (= 0). Given the large number of photo-quadrats showing seagrass, it was decided to only distinguish between sparse versus dense seagrass, with sparse being defined as less than 10 leaves per photo-quadrat. Hence, the scoring scheme for seagrass was 0 = absent; 1 = 10 leaves (sparseand 2 = 10 leaves (dense Where live maerl was present, three categories of abundance were recognized: 1 = 20% cover (sparse2 = 20-80% cover (intermediateand 3 = 80% cover (denseThe ecological significance of the 20% cover or sparse category is that at densities lower than this, maerl nodules tend to occur as dispersed individual nodules, rather than interlocked aggregations that could be regarded as parts of a true maerl bed."