No abstract

Azorean rocky shores are mainly characterized by patchy algae-based communities with variable associated macrofauna. Characterization studies should therefore include quantitative information for both algae and macroinvertebrates. Unlike for the algae, minimal sampling areas are undefined for macroinvertebrates in the Azores. The present study defines the minimal area to be used for the assessment of the abundance of conspicuous benthic macroinvertebrate abundance. This study proposes methodologies to be used for a selected group of invertebrates when simultaneously undertaking quantifications of macroalgae.

Sampling benthic communities usually requires intensive field and lab work which is generally performed by skilled staff. In algal dominated communities, like those on the shores of the Azores, biotope characterization studies focused on the more conspicuous algae categories, thus reducing the skills required for species identification. The present study compares in situ quadrat quantifications done by a skilled reader, with computer based quadrat quantifications using digital photographic records of the same areas read in situ, accomplished by skilled and nonskilled readers. The study was conducted inter-and subtidally at various shore heights/depths. Quantification of algal coverage, both in situ and computer based, used the point to point method with quadrats of 0.25 m · 0.25 m for the intertidal, and 0.50 m · 0.50 m for the subtidal surveys, both subdivided into 36 intersection points. Significant differences were found between in situ readings and computer based readings of photographic records conducted both by experienced and inexperienced readers. Biotopes identified using in situ data and image based data differ both for the subtidal and intertidal.

At 23 sites selected randomly around the island of Sã o Miguel (Azores), video records were made at the depths of 5, 10, 15, 20, 25, and 30 m where a rocky substratum was present. Semiquantitative abundance data of the most common benthic organisms (algae and fixed/sedentary macroinvertebrates) were recorded in the vicinity of each depth reference point. Qualitative samples of the more conspicuous organisms were taken for confirmation of identification in the laboratory. At each site, substratum type, geographical orientation, and depth level were recorded. Multivariate analysis (nonmetric multidimensional scaling; analysis of similarity [Anosim] tests; similarity percentages [Simper] analysis) on the collected data enabled patterns of community distribution to be identified, as well as their relationship to abiotic factors. Since depth was found to be the sole determining factor for communities, it was the only one considered in the subtidal biotope survey protocol proposed here. ADDITIONAL INDEX WORDS:Methodologies, rocky shores, quantification, image.