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The gooseneck barnacle Pollicipes pollicipes is a very valuable marine resource on the coasts of Spain and Portugal. To maintain the sustainable exploitation of this species, periodical large-scale population assessments are essential. Because of the heterogeneous distribution of these populations in aggregates, together with the difficulties associated with sampling (i.e., access to rocky reefs, wave exposure, high tides, etc.), there is a lack of studies in this regard. In light of these constraints, the coverage, biomass, and available stock of gooseneck barnacle were first estimated using a novel semiquantitative method along a 215-km long coast at 10 fishing zones and three tidal levels. This study contributed to the first assessment of the distribution variability of gooseneck barnacle in the Cantabria region (N Spain), as the first step toward a long-term monitoring goal. The proposed method is based on a general coverage (GC) estimation, by means of (1) quantitative coverage measurements on quadrats (50 cm350 cm) located along vertical transects covering the intertidal bandwidth and corrected by tidal level bandwidths, (2) semiquantitative coverage estimates in larger areas, including 5 m on either side of the quadrats along the transect. Biomass samples were collected at each sampling point by scraping the 50 cm350 cm quadrat and fresh weight of the samples was measured. This method arrives at the biomass estimates by means of a power regression model for the coverage?biomass relationship. The population distribution pattern along the coast was also explored separately, by commonly used (1) quantitative coverage estimates in quadrats with no bandwidth correction (sample coverage, SC) and (2) semiquantitative estimates, as in the proposed method (transect coverage, TC), both of which included biomass sampling. Biomass and standing stocks values obtained using GC were lower and consumed less sampling time than those obtained by TC, and particularly SC. The results suggest that the proposed method might be suitable for the assessment of P. pollicipes populations in large coastal areas, as it potentially avoids stock overestimation by detecting the spatial distribution heterogeneity and reduces the sampling time. The main Directorate of Fisheries of Cantabria (DFC) funded this work. We wish to thank DFC technicians, fishery guards and shell-fishermen for the specific support during the fieldwork, and the colleagues from DFC, who helped us in the laboratory works.

The assessment of anthropogenic impacts on coastal waters is an important task to accomplish under the European Water Framework Directive (WFD 2000/60/EEC). Macroalgae are one of the biological quality elements that must be considered, but their assessment has been generally limited to intertidal areas due to the difficulties and costs associated with working in subtidal areas. In this work, the suitability of using landscape mosaicing techniques is analyzed for the application of the “Quality of Rocky Bottoms” index (CFR by its Spanish acronym) in subtidal areas. For this purpose, the sensitivity and accuracy of both the indicators that compose the CFR index (characteristic macroalgae coverage, fraction of opportunistics and characteristic macroalgae richness) and the index itself were tested against different sampling surfaces and validated through direct applications of the CFR carried out in situ by scuba divers. The study was carried out at three sites, located on the coast of Cantabria (N. Spain), covering a variety of environmental conditions (depth ranges and anthropogenic pressures). Underwater video transects of 5-20 m length were recorded by scuba divers and processed with specialized software to build continuous image mosaics of the assessment sites. Each mosaic was inserted into a Geographical Information System where all distinguishable macroalgae species were identified and their coverages were estimated. Replicated subsamples of different areas (0.25 m2, 0.5 m2, 1 m2 and 2.5 m2) were tested from each mosaic for the estimation of both the single indicators and the CFR index itself. Main results showed that larger subsample areas produced higher and more accurate CFR values, mainly related to higher richness values and to smaller variability within the replicates. Accordingly, the minimum sample size required to carry out this type of studies was estimated to be of 2.5 m2, showing no significant differences with the total mosaics. At this spatial scale, the assessments of the CFR index using mosaics showed a significant correlation and an excellent agreement with the results obtained in situ. In summary, underwater video mosaicing techniques proved to be a useful tool for the application of the CFR index and could also be of great interest for the study of subtidal environments by allowing visualization of extensive seafloor areas.

En la presente tesis doctoral se desarrollan una serie de procedimientos para evaluar el estado de los diversos componentes bióticos (fitoplancton, macroalgas, invertebrados bentónicos) y abióticos (calidad fisicoquímica de las aguas) del medio marino en relación a la incidencia humana sobre el mismo. El objetivo de dichos procedimientos es dar respuesta a las exigencias establecidas en la Directiva Marco del Agua (Directiva 2000/60/CE) en lo que respecta a la evaluación del estado ecológico de las masas de agua costeras. En este sentido, además de ampliar el conocimiento existente sobre las características fisicoquímicas y biológicas de las masas de agua costeras de Cantabria, constituye una importante aportación tanto desde el punto de vista científico como desde el punto de vista de la gestión. Entre las contribuciones más destacadas de esta tesis cabría mencionar el desarrollo del Índice de Calidad de Fondos Rocosos (CFR) para la valoración de las comunidades de macroalgas costeras., In this PhD. Thesis, several procedures are developed to assess human influence on the status of the marine environment biotic (phytoplankton, macroalgae, benthic invertebrates) and abiotic (physicochemical quality of water) components. The purpose of these approaches is to meet the requirements of the Water Framework Directive (2000/60/EC) regarding the ecological status assessment of coastal water bodies.In this sense, besides increasing the existing knowledge on the physicochemical and biological characteristics of the Cantabrian coastal water bodies, it provides an important contribution both from a scientific and a management point of view. One of the most outstanding contributions of this thesis is the development of the Quality of Rocky Bottoms Index (CFR) for the assessment of coastal macroalgae communities.