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The presence of spiny butterfly rays, Gymnura altavela, in waters less than 20 m deep off the Canary Islands shows marked seasonality, with relatively high abundances in the summer and autumn. Large aggregations of sometimes hundreds of individuals, primarily females, appear in specific shallow areas of the archipelago and seem to be associated with the seasonal variation in water temperature. This seasonal pattern of presence or absence in shallow areas suggests that spiny butterfly rays migrate into deeper waters or other unknown areas during the rest of the year. G. altavela shows sexual dimorphism; in our study, females were larger and more abundant than males, with a sex ratio of 1:18.9. The species’ estimated asymptotic length, L∞, was 183.75 cm and thus close to the common length reported for the species (200 cm). The von Bertalanffy growth constant (k) oscillated between 0.210 and 0.310 year−1, as similarly described for the species in the Western North Atlantic off the U.S. coast. From June to November, the seawater temperature oscillated between 19 and 24 °C, and massive aggregations of females occurred at 22–24 °C and in a few specific sandy beaches on the islands. Spiny butterfly rays, mostly females, show a preference for aggregating in shallow waters during summertime, probably conditionate to mating or breeding behaviour.

Fish aggregating devices (FADs) are used worldwide to attract fish. Previous studies revealed that FADs affect the distribution and dispersal patterns of juvenile fish species during their life stage under floating objects. In this study, we hypothesised that a system of FADs arranged along an inshore–offshore gradient could favour the approach of young fish associated with FADs towards coastal habitats, using individual FADs as stepping stones. Our findings suggest that FAD systems might exert two different effects on juvenile fish distribution: (a) offshore FADs tend to retain associated fish for longer periods of time compared with coastal FADs, (b) coastal FADs favour the transition of fishes from the pelagic to the benthic domain. Furthermore, in order to obtain more information on the dynamic and movement patterns of the young-of-the-year (YOY) Seriola dumerili and Caranx crysos associated with FADs, tagging experiments and underwater visual censuses were conducted. The two juvenile species tagged and released under FADs placed at different distances from the coast showed different movement patterns. S. dumerili exhibited low FAD fidelity and large movements, while C. crysos showed high fidelity to the site. The results of the two research approaches confirm that FADs affect the dispersal of species toward the coast and their correct use could help to improve the sustainable management of these coastal fish resources.

The genus Smeagol consists of five named species of air-breathing marine slugs (restricted to southern Australia and New Zealand) and three undescribed taxa from southern Japan. Only one species, S. hilaris, is known to be from New South Wales (NSW), and it previously had a known distribution limited to one site, Merry Beach on the south coast. This diminutive invertebrate is classified as critically endangered in NSW due to its extremely restricted distribution and concern about its historically declining numbers. Accordingly, the aims of this study were to survey the known population of S. hilaris at Merry Beach and to explore other potentially suitable sites, using a visual census method, to determine if further populations or species exist in NSW. The resulting quantitative surveys of the known population and a new population at Storm Bay, Kiama, NSW, are reported here. DNA barcoding of a ~650 bp segment of the mitochondrial cytochrome c oxidase I (COI) gene for several individuals from each population confirmed the conspecificity among the two populations. The population at Merry Beach was found to remain viable, while the discovery of the new population of S. hilaris represents a doubling of the known global populations of this species. Details of the highly-specialised niche habitat occupied by Smeagol in New South Wales and recommendations for ongoing management are documented.

In this study, loggerhead sea turtle Caretta caretta (Linnaeus 1758) was observed for the first time around the shipwreck of coast guard boat in Ördek Yalağı located at Gökceada Island, North Aegean Sea. The shipwreck is at a depth of 24.8 m. The loggerhead sea turtle Caretta caretta was recorded exactly on the ground and 2 m away from the ship on the shore side of the ship. In this study, Caretta caretta was recorded for the first time in this water depth and around a shipwreck that was used as an artificial reef for Turkish waters.

Although more than 600 marine caves have been recorded so far along the Greek coasts of the Aegean Sea (Eastern Mediterranean), only a few have been systematically studied for their biodiversity. In this study, the benthic communities of six marine caves within a Protected Area of South-Eastern Aegean were studied for the first time, both qualitatively and quantitatively. The association of different geomorphological and topographical factors of the caves with the benthic community structure was investigated. A total of 120 photographic quadrats covering the entrance and semi-dark cave zones were analysed, with regard to coverage and taxon abundance, while motile taxa were qualitatively recorded by visual census. The ecological quality status of the caves was also assessed under an ecosystem-based approach. In total, 81 sessile and 45 motile taxa were recorded, including 12 protected and 10 non-indigenous species. Multivariate community analysis demonstrated that the geomorphological and topographical variables of the caves are significantly associated with the observed biotic patterns. The ecological quality of the caves was assessed as poor or moderate according to the CavEBQI index, highlighting the necessity for systematic monitoring. This study paves the way for similar studies in marine cave habitats aiming at the development of management and conservation actions.

We determined the composition of ichthyofauna of the bays of Huatulco National Park using the the visual census technique for 351 ten-meter-long transects between January 2009 and December 2010. Eighty-nine species belonging to 69 genera and 42 families were identified. The most frequently represented families, according to numbers of species, were Pomacentridae, Labridae and Carangidae, and the most numerous genera were Haemulon, Halichoeres and Scarus. Acanthurus triostegus, Bothus constellathus, Chaetodipterus zonatus, Hemicaranx leucurus, Microlepidotus brevipinnis and Xenichthys xanti were recently recorded for the first time in the study area. The presence of Chaenomugil proboscideus, Narcine entemedor and Pseudobatos leucorhynchus in the Huatulco Bays is confirmed. The fish community in the Huatulco Bays was most similar to those in Panama and Costa Rica. Data published through GBIF (doi:10.15470/eb4hrm).

Coastal fishes are not only valuable elements of marine biodiversity, but they also play an important ecological role in the functioning of coastal ecosystems: food resource, transfer of nutrients, predators. Therefore, data on the compositions of fish assemblages are of great importance. The objectives of the present study were to (i) define the faunistic characteristics of a typical fish community on the Mediterranean coast; (ii) investigate spatiotemporal changes in fish assemblages. Based on a set of indices (Fast protocol) and a long-term data set (6 years, 612 visual counts, 154 h of diving), changes in coastal fish communities were analyzed. Our results indicated that there was a significant shift in fish community structure, with a general decline of the calculated indices. In our study, part of the observed variability in fish assemblage structure could be due to different factors as site location and sampled year. The changes in the fish assemblages associated with inter-annual fluctuations observed in this study also provide important insights into how fish communities may change under environmental and anthropogenic influences.

Coralligenous habitat is considered as one of the most important special habitat types in the Mediterranean; however, due to its inaccessibility, little is known about it, although it is considered as one of the Mediterranean’s richest habitats in terms of species. Due to a low number of studies, it was presumed that the richness of coralligenous fish assemblages is underestimated using traditional visual census methods which are not applicable to the deep, steep, and vertical slopes of coralligenous cliffs and do not capture exhaustively cryptobenthic species commonly found in this habitat. This paper aims at producing a more complete assessment of fish assemblages on a coralligenous cliff by combining different methods, particularly the deep vertical transect visual census and square with anesthetics method. A total of 76 fish species were recorded on a single coralligenous cliff, supporting the opinion that coralligenous cliffs are important Mediterranean biodiversity hotspots. The analysis of species traits between species recorded by the different methods showed how complementary they are to better describe species compositions. Hence, the result of this study demonstrates that the combined use of methods is essential for a more exhaustive description of the whole fish community structure and for accurate estimates of the abundance and diversity patterns, particularly in complex habitats such as coralligenous cliffs.

Data on the distribution and ecology of cryptobenthic fish of marine caves in the Mediterranean Sea are extremely scarce but necessary for scientists and marine managers alike in order to understand these fish’s ecological role and assess their conservation status. Broadscale surveys by implementing underwater visual census and photographic sampling in marine caves of the northeastern Mediterranean Sea, within different expeditions during the last 5 years, brought to light new records of eight rarely reported cryptobenthic fish species. To a smaller extent, complementary citizen science data from diving professionals of Crete were used to fill distribution gaps. A total of 36 new records (66 individuals) from 18 marine caves and caverns of the Aegean and northeastern Levantine Seas were assembled, belonging to the gobies Corcyrogobius liechtensteini, Didogobius splechtnai, Gammogobius steinitzi, and Thorogobius ephippiatus, the blenny Microlipophrys nigriceps, the tripterygiid Tripterygion melanurum, the speleophilic bythitid Grammonus ater, and the gobiesocid Lepadogaster cf. lepadogaster. The above species have been rarely reported from the Eastern Mediterranean Sea, with D. splechtnai and G. steinitzi being recorded for the first and second time from Greek waters, respectively, while L. cf. lepadogaster constitutes the second record of a clingfish species in a marine cave of the Aegean Sea. Interesting behavioral and ecological habits were also noted for some species, based on in situ observations and photographic evidence. Our study contributes to filling gaps in the knowledge of cave fish diversity and demonstrates that cryptobenthic mobile species in understudied cryptic habitats are more common than previously thought in the Mediterranean Sea.

Four visual censuses targeting Octopus vulgaris living in dens on sandy bottoms were carried out from June to October 2013 in the National Park of the Atlantic Galician Islands (NW Spain). Censuses were undertaken by scuba diving between 5 and 21 m depth in daytime. The total area swept was 13.75 ha. There were no significant differences between octopus presence in dens during open and closed fishing seasons. Depth had a significant negative relationship with occupancy. The average number of dens per 1000 m2 was 3.84±0.84 in June and 3.89 in October. The area per den was 260 m2. Den number estimations varied between 1586 and 2057. The largest number of dens (76.5%) was found between 5 and 10 m depth. Den distribution was clumped. No significant differences were found between octopus size classes (small, medium and large) and den diameter. Associate dens were observed. There were no significant differences in den diameter and shell types found around the middens. Many dens could be “permanent”. Drilling bivalve shell behaviour is discussed. The surveyed area had around 1100 individuals, mainly small specimens. No significant differences were found between octopus size and depth. Substrate, den type and food abundance and availability (especially razors Ensis arcuatus) seem to be the main factors influencing dens and octopus density and distribution. Den availability does not appear to be a limiting factor in this case. Temperature, den availability, predators and fishing pressure influencing density and distribution are discussed. Rodas inlet may be a preferential habitat for O. vulgaris individuals ranging from 200 to 2000 g, but especially small specimens ( ≤ 1000 g).

From April to June Atlantic bluefin tuna, Thunnus thynnus, migrate along the western Sardinian coastline in a southward direction, where they are intercepted by the trap fishery. Fishermen claim that Mistral episodes facilitate the entry of tuna schools towards the traps, thus increasing capture rates. To test the fishermen’s hypothesis we conducted underwater visual counts of tuna in the trap chambers and analysed these data under the effect of wind. The results indicate a “stair-step” pattern in the abundance of tuna, demonstrating that major increases in abundance are associated with the Mistral. The second analytical approach involved a longer time scale to test whether higher Mistral occurrences corresponded to periods when higher captures were recorded. Using a linear regression model we found a significant correlation (p < 0.01) between catches and the wind speed class ≤ 15 knots. We hypothesize that the wind-driven current may produce favourable conditions for tuna migration and could play a significant role in enabling fish to save energy. It was also noted that the wind speed class > 15 knots seemed to have a negative effect on captures. This pattern may be caused by wind-induced advection of coastal waters generating a physical boundary that may have had a deterrent effect on tuna schools.

Monitoring strategies which adequately represent the entire community associated with artificial structures will enable more informed decisions regarding the broader effects of artificial structures and their role in the management of fisheries resources. Despite the widespread application of a range of in situ visual monitoring methodologies used in the assessment of artificial structures, the relative biases associated with each method have not been critically examined and remain poorly understood. Estimates of fish abundance on six estuarine artificial reefs carried out by divers using underwater visual census techniques (UVC) were compared with estimates of relative abundance determined by baited remote underwater video (BRUV). It was found that when combined, both methods provided a more comprehensive description of the species associated with estuarine artificial reefs. However, the difference in the number of species detected and the frequency of detection varied between methods. Results indicated that the differences in rates of detection between UVC and BRUV methodologies were primarily related to the ecological niche and behaviour of the species in question. UVC provided better estimates of the rare or cryptic reef associated species. BRUV sampled a smaller proportion of species overall but did identify key recreational species such as Acanthopagrus australis, Pagrus auratus and Rhabdosargus sarba with increased frequency. Correlation of abundance indices for species classified as "permanent" identified interspecific interactions that may act as a source of bias associated with BRUV observations.O monitoramento biológico da comunidade associada a substratos artificiais permite a tomada de decisões corretas em relação ao uso e o papel dos novos habitats no manejo de recursos pesqueiros. Apesar da enorme aplicação das técnicas de censo visual no estudo da ictiofauna em recifes artificiais, os erros relativos de cada metodologia ainda não foram analisados. Estimativas de abundância de peixes obtidas através de censos visuais subaquáticos (CVS) em seis recifes artificias assentados em ambientes estuarinos, foram comparadas com a abundância relativa estimada através de técnicas de monitoramento remoto com vídeo subaquático (MRVS) e isca para atração dos animais. Os resultados combinados de ambas as técnicas descreveram melhor as espécies associadas aos recifes artificiais de regiões estuarinas. Entretanto, a diferença no número de espécies identificadas e a freqüência de detecção entre ambas as técnicas foram devidas principalmente aos nichos ocupados e ao comportamento específico de cada espécie. A técnica de CVS estimou melhores as espécies raras e crípticas associadas aos recifes. A técnica de MRVS estimou uma proporção menor de espécies, mas foi capaz de identificar mais frequentemente e com mais precisão as espécies recreacionais tais como Acanthopagrus australis, Pagrus auratus e Rhabdosargus sarba. Índices de correlação de abundância de espécies "permanentes" revelaram interações específicas que podem representar uma fonte de erro associada às observações com vídeo remoto.

In the present study the fish assemblages in the rocky-bottom habitat of the Sierra Helada Natural Park (Alicante, Spain) were recorded to provide data for future evaluation of any changes induced by long-term management. Visual censuses were carried out along strip transects by Scuba diving on rocky bottoms at depths between 1 and 32 m. In the seven localities sampled, 44 species were recorded. Number of species, abundance, biomass and size structure values recorded did not show differences between high and low protection areas. Species composition was similar to other marine protected areas of the western-Mediterranean. The main differences found between localities can be attributed to the high heterogeneity and complexity of the habitat at smaller spatial scales.

This study compared tidepool fish assemblages within and among habitats at Iparana and Pecém beaches, State of Ceará, Northeast Brazil, using visual census techniques. A total of 8,914 fishes, representing 25 families and 43 species were recorded. The most abundant taxon was Sparisoma spp, followed by Haemulon parra (Desmarest, 1823), Acanthurus chirurgus (Bloch, 1787) and Abudefduf saxatilis (Linnaeus, 1758). Haemulidae was the most abundant family in number of individuals, followed by Scaridae, Acanthuridae and Pomacentridae. Within- and between- site differences in species assemblages probably reflected environmental discontinuities and more localized features, such as pool isolation episodes, or environmental complexity, both acting isolated or interactively. The locality of Iparana was probably subjected to a greater fishing pressure and tourism than Pecém, a potential cause for the observed lowest fish abundance and biodiversity. We conclude that tidepool ichthyofauna may be quite variable between and within reef sites. Thus, observations taken from or damages caused on one area may not be generalized to or mitigated by the protection of adjacent sites.Este estudo comparou assembléias de peixe em poças de maré dentro e entre hábitats nas praias de Iparana e Pecém, estado do Ceará, nordeste do Brasil, usando técnicas de censo visual. Um total de 8.914 peixes, representando 25 famílias e 43 espécies foi registrado. Sparisoma spp. formaram o taxon mais abundante, seguido por Haemulon parra (Desmarest, 1823), Acanthurus chirurgus (Bloch, 1787) e Abudefduf saxatilis (Linnaeus, 1758). Haemulidae foi a família mais abundante em número de indivíduos, seguida por Scaridae, Acanthuridae e Pomacentridae. Diferenças encontradas nas assembléias de espécies provavelmente refletiram descontinuidades ambientais e aspectos mais localizados, como a ocorrência de isolamento das poças, ou complexidade ambiental atuando de forma isolada ou interativamente. A localidade de Iparana provavelmente foi submetida a uma maior pressão de pesca e turismo que Pecém, uma causa potencial para a menor abundância e biodiversidade de peixes observada. Concluímos que a ictiofauna de poça de maré pode ser variável dentro dos recifes e entre localidades diferentes. Assim, observações tomadas ou os danos causados em uma dada área não podem ser generalizados ou mitigados para a proteção de locais adjacentes.

This study presents data on the reproduction of Abudefduf saxatilis, a rocky shore inhabitant at the northern coast of São Paulo State. A total of 73 individuals were collected using hooks and baits. They were measured, weighed and dissected, sex and maturation stage were analysed, first macroscopically, then part of the material was taken for microscopical confirmation. Visual censuses were also done for underwater observation of egg's presence. Results showed equivalence of males and females in the population, first maturation occurring between 101 and 115mm of total length, spawning period occurs from November to February for Abudefduf saxatilis and October to January for Stegastes variabilis. Reproductive period for A. saxatilis was positively related to air temperature and thermic amplitude, but the environmental clue most likely to influence this rhythm is photoperiod. Transects with visual census of males guarding eggs were also a reliable tool for finding reproductive period in these demersal, egg-guarder species.Esse estudo apresenta dados sobre a reprodução de Abudefduf saxatilis, uma espécie habitante de costões rochosos no litoral norte do estado de São Paulo. Os peixes foram coletados com anzol e isca num total de 73 indivíduos, foram medidos, pesados, dissecados, seu sexo e maturidade gonadal foram analisados, primeiro macroscopicamente, depois parte desse material foi levado para confirmação microscópica. Censos visuais também foram feitos para observar a presença de ovos. Os resultados apontam para uma equivalência entre o número de machos e fêmeas na população, a primeira maturação ocorre entre 101 e 115 mm de comprimento total, a desova ocorre entre os meses de novembro a fevereiro em Abudefduf saxatilis e outubro a janeiro em Stegastes variabilis. O período reprodutivo de A. saxatilis está positivamente relacionado à temperatura do ar e amplitude térmica, mas o indicador ambiental mais provável de influenciar o ritmo reprodutivo é o fotoperíodo. Os censos visuais feitos com a transecção mostraram-se uma ferramenta confiável para encontrar o período de desova nessas espécies demersais que guardam seus ovos.

The extensive Brazilian coast comprises diverse reef fish communities. Here, we report a pioneer study on the reef fish community composition of the Cagarras Archipelago. This rocky reef system consists of a small group of coastal islands 5 km south off Ipanema Beach, Rio de Janeiro city, Brazil. A relatively diverse and disturbed fish community (99 species from 39 families) was found in this archipelago. Two different visual census techniques were utilized and a large difference was observed in the number of species compared to other Brazilian reef sites. Trophic structure and biogeographical affinities are discussed. The absence of some reef fish species, mainly top predators, suggests severe environmental impact in this area and exhorts the Brazilian authorities to create a marine protected area. Results obtained in this study will serve to future environmental studies in Cagarras.A extensa costa brasileira abriga uma grande diversidade de peixes recifais. Este trabalho é um estudo pioneiro no que diz respeito à composição de espécies de peixes recifais do Arquipélago das Cagarras. Este sistema recifal é formado por um grupo de ilhas costeiras, distantes 5 km ao sul da Praia de Ipanema no estado do Rio de Janeiro, Brasil. Uma comunidade relativamente diversa e impactada, com 99 espécies pertencentes a 39 famílias de peixes recifais, foi encontrada. A utilização de duas técnicas de censo visual mostrou uma grande diferença nos dados obtidos, quando comparados a outras regiões recifais brasileiras. São discutidos dados da estrutura trófica e a distribuição biogeográfica da ictiofauna da região. A ausência de algumas espécies, principalmente grandes predadores, sugere que a região está sofrendo grande impacto ambiental, e torna urgente a criação de uma área de proteção marinha pelas autoridades Brasileiras. Os resultados obtidos poderão servir como base para futuros estudos ambientais nas Cagarras.

The coast of the state of Santa Catarina only has non-biogenic reefs, i.e. rocky and artificial reefs, and is considered the geographic south limit for many reef fish species. At present the diversity of organisms associated with reef environments is threatened. This study aimed to record the number of families and species of reef fish fauna of the north coast of the state of Santa Catarina. The data were collected through underwater visual census performed on Graças archipelago (26°12'S /48º29'W), Tamboretes archipelago (26°22'S/48°31'W) and Barra do Sul islands (26°27'S/48º35'W). A total of 166 species was observed (6 elasmobranchii and 160 actinopterygii) belonging to 66 families. The families with more species richness were Carangidae (16), Epinephelidae (9), Blenidae (8), Serranidae (7), Haemulidae (6), Sparidae (6) Tetraodontidae (6), Labridae-Scarini (5), Labrisomidae (5) Pomacentridae (5), Lutjanidae (5) and Muraenidae (5). This study add to the current published list, new 115 species, including new occurrences (e.g. Chromis limbata), and some endemic (e.g. Sparisoma amplum), exotic (e.g. Omobranchus punctatus), endangered (e.g. Hippocampus erectus) and overexploited (e.g. Lutjanus analis) species. Twenty one species are present in the IUCN’s list, twelve in the IBAMA’s list and four in the local list. All elasmobranchii recorded here are considered threatened species, like the brazilian guitarfish (Rhinobatos horkelii), which appears in three red lists, and it is considered critically endangered. All species of Epinephelidae are mentioned in the list of risk categories of the IUCN and five are cited as overexploited or threatened with overexploitation by IBAMA. Among Epinephelidae, the goliath grouper (Epinephelus itajara), is present in all red lists and has specific protection rules in Brazil. The gathered information will allow to take appropriate conservation measures, such as the establishment of marine protected areas, monitoring of fishing practices, assessment of the tourism impact and to control harbor activities.

The northern coast of Rio de Janeiro State lacks natural consolidate substrates, making it a proper environment to the development of researches using artificial structures. After studies about the type of substrate, concrete seems to be the most appropriate for studying fouling community development. This research was carried out to investigate the functional role of biofouling in the development of the ichthyic community in the north of Rio de Janeiro State. Percentage data of the epibenthic organisms' coverage and samples of the fish community with gillnet and visual census showed that biofouling in artificial reefs might have more than one functional role, acting as a facilitator in the recruitment of fish species and as a link in the trophic marine chain. Through the increase of localized structural complexity provided by the reef itself and by the fouling organisms which act as "engineering species", additional protection options are offered to the ichthyic community, especially recruits. Also, the epibiont biomass represents an important link in the food web, acting either as a direct source or in the transference of energy to higher trophic levels. Through the relationship between the ichthyic and fouling communities we concluded that the functional role of the latter in artificial reef habitats could be characterized mainly as shelter and feeding grounds for few fish species.O litoral norte do Estado do Rio de Janeiro possui uma escassez de substrato consolidado natural tornando o ambiente propício para o desenvolvimento de pesquisas com estruturas artificiais. Após estudos conclusivos sobre o tipo de substrato, o concreto parece ser o mais apropriado para o desenvolvimento da comunidade incrustante. Novas pesquisas foram realizadas para investigar o papel funcional da bioincrustação no desenvolvimento da comunidade íctica no norte do Estado do Rio de Janeiro. Dados de porcentagem de cobertura dos organismos epibênticos e amostragens da comunidade nectônica com rede de espera e censo visual, evidenciaram que a bioincrustação em recifes artificiais pode assumir mais de um papel funcional, como facilitadora no recrutamento de espécies de peixes e como elo na cadeia trófica marinha. Através do incremento da complexidade estrutural fornecida pelo próprio recife e pelos organismos incrustantes que atuam como "espécies engenheiras", opções adicionais de proteção são oferecidas para a comunidade íctica, principalmente recrutas. Além disso, a biomassa epibionte representa um importante elo na cadeia alimentar, atuando como fonte direta de alimento e/ou transferência de energia para níveis tróficos superiores. Através da relação entre as comunidades íctica e incrustante, conclui-se que o papel funcional desta última em habitats recifais artificiais caracteriza-se principalmente como abrigo e para algumas espécies também como alimentação.

Until now the distribution and abundance of Octopus vulgaris had been investigated in the main fishing areas of the species only by fishing surveys. The catching efficiency of fishing gear is variable and depends on several aspects of the animal´s behaviour and life history as well as on the type of the gear and the environmental characteristics of the area surveyed. A good alternative for studying the abundance of octopus is by visual census. The population density of O. vulgaris was measured by visual census with scuba diving. The survey was conducted in coastal areas of Greece and on soft sediment. O. vulgaris density ranged from 0 to 6.88 individuals/1000 m2 and the mean density values of this study were much higher than those mentioned in other papers. Octopus density was significantly associated with season. Densities of octopuses lower than 500 g were higher in coarse sediments than in finer ones. The density of large octopuses (> 500 g) increased with depth. Octopuses larger than 200 g tended to dwell deeper during the period of intense thermocline than during the no-thermocline period.

To avoid predation, octopuses select and actively modify shelters (also called dens) in the substratum, where they remain most of the time, especially during daylight hours. The main questions that this study deals with are: Is den availability a significant constraint for the distribution of Octopus vulgaris on soft sediment? What kind of dens does O. vulgaris use on soft sediment and what factors affect the selection of one type instead of another? With population density measurements by SCUBA diving and enrichment experiments with artificial dens, we concluded that the availability of solid materials necessary for den construction is a limiting factor for the distribution of O. vulgaris on soft sediment. O. vulgaris used four different types of den on soft sediment: well (a vertical hole in the sediment), rock/stone (the octopus uses a rock or a large stone to dig a cavity under it), shell (an empty shell is used), human origin (a solid material of human origin is used). The relative proportion of the four types of den in the areas studied was: 38.7% human origin, 29.7% well, 21.5% rock/stone, 2.9% shell. Also, 7.3% of the octopuses were found outside their den. The main types of den were found in different relative proportions in relation to the depth, the distance from shore, the octopus size and the granulometry of the sediment.

Fish assemblages associated with 16 marine caves were investigated along the coasts of Spain, France and Italy. Sampling was done in caves that encompassed blind caves (one entrance) and caves with several openings, remarkably variable in morphology, overall extension, presence/absence of ceiling, and characteristics of the bottom. On the whole, 33 fish species were recorded. The distribution patterns of fish assemblages (both in terms of density and biomass) showed a significant variability at the regional (hundreds of kms) and local scale (kms/hundreds of meters), which confirms the great heterogeneity of the cave-associated communities. In terms of occurrence, only the cardinal fish Apogon imberbis and the gobid Corcyrogobius liechtensteini were found in all 16 caves, followed by Scorpaena notata and Serranus cabrilla (n = 15) and Diplodus vulgaris and Didogobius splechtnai (n = 11). A significant number of species were occasionally found, like Sarpa salpa and Diplodus annularis. They usually occur outside caves and could be considered as “sporadic cave visitors”. The high densities of A. imberbis and its frequency of occurrence shows that this species is by far the most represented fish within caves in the western Mediterranean. In spite of the conspicuous variation from cave to cave (from 10 to 70% of the whole fish biomass), a general pattern emerges showing that A. imberbis accounts for a significant proportion of the fish biomass. Average density and biomass of A. imberbis are significantly variable at regional scale (hundreds of kms), but not at local scale (kms/hundred meters). A similar pattern could be explained by multiple processes acting concurrently. Although further studies are needed (e.g. to prove nychthemeral movements inside–outside caves for feeding), this study shows that, based on its density and biomass, A. imberbis has the potential to fulfill a crucial trophic role within Mediterranean marine caves as a vector of organic matter.

Fish assemblages associated with extractive platforms were surveyed, for the first time, using traditional fishing surveys (bottom gill net) and an underwater visual census (UVC) technique in order to test the effectiveness and to identify strengths and weaknesses of both methods. The study was carried out during three seasons at two offshore gas platforms (Eleonora and Squalo C) located in the central Adriatic Sea. Both methods recorded a similar number of fish species although with only eight species in common, thus supplying complementary information and a good estimate of the total fish species richness (39) associated with these gas platforms. The use of innovative techniques, such as UVC, to explore the inner part of the platforms, allowed the censusing of several cryptobenthic species, mostly Blennidae (8 species), never recorded during previous studies. Even if both methods were able to detect temporal variability, only the UVC technique was able to highlight spatial changes between platforms, demonstrating their high efficiency regarding the quality of the scientific information supplied. The innovative method of studying biodiversity presented in this study appears to be highly reproducible and suitable for monitoring fish diversity in artificial and very complex habitats like gas platforms.

This study investigated the composition and spatial distribution of the sublittoral decapods on the reefs of Porto de Galinhas Beach, southern coast of Pernambuco, Brazil, through the Underwater Visual Census technique. Data were collected monthly, at night during full-moon tides in low tide periods from June 2004 to May 2005, using SCUBA diving and a visual census with a fixed belt transect (20 m long). Three sampling areas were defined: Confined Waters (low hydrodynamics) with shallow sites (up to 2.5 m deep); Semi-open Water (3 to 6 m deep), influenced by waves and tidal currents (moderate hydrodynamics); and Open Water (7 to 10 m deep), in the breaker zone (high hydrodynamics). A total of 6,287 individuals of 34 species belonging to the infraorders Brachyura (19 species), Achelata and Anomura (5 species each), Caridea (3 species), and Stenopodidea and Astacidea (1 species each) were collected. Two decapod assemblages were distinguished: in a habitat with low hydrodynamics and shallow (Confined) water; and in a habitat with moderate to high hydrodynamics and depths of 3 to 10 m (Semi-open and Open water). At the sites with high hydrodynamics, i.e., the Open-water Area in the breaker zone, decapod diversity was significantly lower than in the other, protected areas on the reef bench. These results suggest that the distribution of subtidal decapods on coastal reefs is influenced by depth and exposure to water stress caused by waves and currents (hydrodynamics). The visual census technique with SCUBA proved to be suitable for ecological studies on subtidal decapods.