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- Changes in benthic community structure due to clam dredging on the Algarve coast and the importance of seasonal analysisPublication . Alves, Filipe; Chícharo, Luís; Nogueira, António; Regala, J.Patterns in community structure of meiofauna and macrofauna in relation to Portuguese clam dredging were compared during a 2-y-period o¡ Lagos and Vilamoura, south Portugal. SCUBA divers randomly sampled corer and quadrat samples before and immediately after simulating commercial dredge ¢shery. Univariate measures (abundance, number of taxa, evenness, diversity and biomass) and multivariate analyses (Cluster, MDS and SIMPER) revealed changes in the meio- and macro-benthic community structure caused by dredge disturbance (short-term e¡ects), with a general decrease in all measures.Macrofauna were found to be more sensitive to dredge disturbance, and aggressive predatory behaviour was observed after disturbance in the continuously dredged area. Nevertheless, higher signi¢cant natural changes were found between seasonal periods, indicating that dredging may only cause a small-scale and short-term impact.
- Grazing by Diadema antillarum (Philippi) upon algal communities on rocky substratesPublication . Alves, Filipe; Chícharo, Luís; Serrão, Ester; Abreu, A. D.Grazing by Diadema antillarum sea urchins is well documented for coral reefs, although information is scarce for the eastern part of the Atlantic Ocean, where rocky substrate dominates the sea bottom. This study analysed grazing activity by D. antillarum upon the algal communities living on rock substrates, and its possible impact on the subtidal communities. Controlled feeding experiments using exclusion cages were performed between May and September 1998 at Madeira Island (NE Atlantic). Three experimental treatments were used: (1) closed cages to exclude sea urchins, (2) open cage controls, and (3) uncaged controls (nine replicates in each treatment). After four months, in September 1998, the percentage algal cover was quantified. One-way analysis of variance followed by Post Hoc Tukey (HSD) tests showed significant differences between algal abundance in the presence (uncaged and open cage controls) or absence (closed cages) of sea urchins. In the areas where D. antillarum was excluded (closed cages), algal abundance increased by about 10% in the four-month period. Diadema antillarum thus effectively reduces algal abundance, and this may have important consequences in determining the algal community structure of rocky substrate.
- Reburial time and indirect mortality of Spisula solida clams caused by dredgingPublication . Chícharo, Luís; Chicharo, Maria Alexandra Teodosio; Gaspar, M.; Regala, J.; Alves, FilipeClam-dredging results in the exposure of Spisula solida individuals not caught by the dredge. Subsequent survival depends on clam damage, reburial time, and the time needed by predators to reach the impacted area.We analyse these variables and discuss the importance of predation on exposed S. solida caused by dredge fishing. Sampling was performed in July 2000 off the southern coast of Portugal, at Vilamoura, a traditional S. solida sandy fishing ground.We compared the time needed for S. solida individuals to rebury themselves, relative to the abundance of potential predators. Bivalves collected by divers were placed on the seabed, and the times required for reburial were measured. These were compared with the times needed for reburial of the clams exposed by dredge impact. At each of three dredge tracks, we analysed the number of predators that entered three equal quadrats (0.0250 m2) per minute. These results were compared with a non-affected control area. Impact caused by the fishing dredge significantly increases the number of exposed S. solida clams ðp < 0:05Þ and the abundance of potential predatory species ðp < 0:05Þ. The brittle star Ophiura texturata was the most abundant and first species to reach the dredge track (less than 3 min after dredge impact). Other species reaching the dredge track were Pomatochistus spp. (6 min after impact), Diogenes pugilator, and Nassarius reticulatus (both 9 min after impact). Although predators reached the impacted area while S. solida bivalves were still exposed, our results suggest that predation on the non-buried clams in the dredge track is not a major factor for subsequent indirect mortality of S. solida.
- Adenylic-derived indices and reburying time as indicators of the effects of dredging-induced stress on the clam Spisula solidaPublication . Teodosio, Maria; Araújo Amaral, Ana Margarida; Condinho, S.; Alves, Filipe; Regala, J.; Gaspar, M.; Chícharo, LuísLittle attention has been given to the behavioural and physiological effects of dredging on clams. The response of the clam Spisula solida under stress imposed by dredging activity is analysed in terms of reburial time and two acute indices: AEC (adenylic energetic charge) and ATP per milligram dry weight. Stress on undersized (<25 mm) S. solida, due to habitat disturbance by dredging itself and subsequent aerial exposure was measured with in situ studies during September 1999 at Vilamoura, a bivalve sandy ground, off the southern coast of Portugal. The study showed significant increases in reburial time and a decrease in adenylic-derived indices of stressed bivalves compared with in situ control bivalves monitored by SCUBA divers. It was concluded that the stress caused by dredging affects the behavioural and physiological responses of S. solida. Moreover, the reburial time is an easy and valuable indicator of stress levels in the studied clam.
- Diel variation of the RNA/DNA ratios in Crassostrea angulata (Lamarck) and Ruditapes decussatus (Linnaeus 1758) (Mollusca : Bivalvia)Publication . Chícharo, Luís; Chícharo, Maria Alexandra; Alves, Filipe; Araújo Amaral, Ana Margarida; Pereira, A.; Regala, J.The aim of the present study was to quantify differences in RNA:DNA ratios between male and female fish Pomatoschistus microps, crustaceans Crangon crangon, and bivalves Ruditapes decussatus. RNA:DNA ratios were greater in females than in males, especially because of a greater RNA content per unit dry weight in females. Sexual dimorphism in addition to physiological and behavioural differences between males and females may account for these results. RNA:DNA ratios of adult marine organisms should be interpreted with caution, because the effect of sex on nucleic acid concentrations may bias results if the sex ratio in the sample from which results were derived is not representative of the population.
- Algal cover and sea urchin spatial distribution at Madeira Island (NE Atlantic)Publication . Alves, Filipe; Chícharo, Luís; Serrão, Ester; Abreu, A. D.This study describes sea urchin spatial distribution in relation to environmental factors, and the relationship between Diadema antillarum density and algal abundance. Twenty-three transects around Madeira Island were surveyed by scuba divers, and sea urchin density and algal cover were determined in situ. Sampling sites along these transects were characterised in terms of distance from the tide line, water depth, substratum type, bottom declivity and water turbulence. Diadema antillarum was the dominant sea urchin species. Paracentrotus lividus and Arbacia lixula occurred at shallower depths (2-6 m), contrasting with the distribution of Sphaerechinus granularis, which occurs among D. antillarum (4-20 m). Surveys found two alternative types of communities on rocky shores: 1) a community with high algal cover and low numbers of sea urchins, along the north and south-west coasts and; 2) a community with little algal cover and high densities of sea urchins, along the south-east coast. Macroalgal cover and D. antillarum densities were inversely correlated (adjusted R2=75.6%; n = 429; p< 0.05). The results showed that water turbulence was the most important factor limiting the distribution of D. antillarum on rocky substrates. We propose a multiple non-linear regression model (using backward stepwise analysis) to explain D. antillarum abundance on the rocky shores: D. antillarum/m2 (??)= 0.121 - 0.209 distance from shore (in m) (??) + 2.052 water depth (in m) (??) - 1.778 water turbulence level (??) - 0.007 water turbulence level4 (??); where ?? indicates data are square-root transformed (adjusted R2 = 60.99%; n = 454; p< 0.05).
- Ecological characterization of dredged and non-dredged bivalve fishing areas off south PortugalPublication . Chícharo, Luís; Chicharo, Maria Alexandra; Gaspar, M.; Alves, Filipe; Regala, J.Macro and meiobenthic communities of two fishing areas (Vilamoura and Lagos) in the western part of south Portugal (Algarve coast) were analysed. Both locations had been under severe dredge-fishing impact until four years previously. Vilamoura has since continued to be dredged, while fishing activity in Lagos was stopped in 1995 as a response to overfishing. For each location, three replicate areas were analysed at depths of 7–9 m. In each of these areas, 18 quadrats for macrofauna and 12 cores for meiofauna were randomly sampled by SCUBA divers during September 1999. The Shannon–Weiner diversity index was higher for meiofauna in the fished area, whereas macrofauna diversity was higher in the recently non-fished area. Bray–Curtis dissimilarity between the two areas was 87·82%. Major differences were found between Ampeliscidea, Amphiura mediterranea, Spisula solida, Haustoriidae, Nemertinea and Diogenes pugilator populations at the two sites. There was higher abundance but lower biomass of potential macrofaunal scavengers in the fished area, and carnivore biomass was also higher in this area. Deposit-feeders dominated meiofauna abundance in both study areas. The community structure of the continuously fished area was dominated by small, opportunistic, short-lived species while the community structure of the recently non-fished area was dominated by more fragile and long-living sessile organisms.
- Macrofauna spatial differences within clam dredge-tracks and their implications for short-term fishing effect studiesPublication . Chícharo, Luís; Regala, J.; Gaspar, M.; Alves, Filipe; Chicharo, Maria Alexandra TeodosioIn situ observations of clam dredging showed that the effects of the dredge on the benthic macrofauna may not be constant during a tow. A sand buffer forms in front of the gear approximately 10m after the beginning of a tow, and this pushes the sediment partially aside.In this study, we analyse differences in abundance, the number of taxa present, diversity, and evenness within sections of dredge-tracks in a disturbed, fished area and a non-fished area along the southern coast of Portugal. These areas were sampled by divers before and after dredge-fishing activity. At each site, three dredge-tracks were produced. These tracks were divided in three longitudinal sections 1start, middle and end) and two transverse sections 1track and edge). Six quadrats were used to sample macrofauna in each section of every track and edge. Our results show differences exist in macro- faunal distribution and abundance across sections of a dredge-track. These differences should be considered in any assessment of the short-term ecological impact of dredges on benthic macrofauna
- Ecophysiological traits of highly mobile large marine predators inferred from nucleic acid derived indicesPublication . Alves, Filipe; Dromby, Morgane; Baptista, Vânia; Ferreira, R.; Correia, A. M.; Weyn, M.; Valente, R.; Froufe, E.; Rosso, M.; Sousa-Pinto, I.; Dinis, A.; Dias, E.; Teodosio, M ANucleic acid-derived indices such as RNA/DNA ratios have been successfully applied as ecophysiological indicators to assess growth, nutritional condition and health status in marine organisms given that they provide a measure of tissue protein reserves, which is known to vary depending on changes in the environment. Yet, the use of these biochemical indices on highly mobile large predators is scarce. In this study, we tested the applicability of using nucleic acids to provide insights on the ecophysiological traits of two marine mammal species (common bottlenose dolphins and short-finned pilot whales) and explored potential related factors (species, sex, season, and residency pattern), using skin tissue (obtained from biopsy darts) of apparently healthy and adult free-ranging animals. Significantly higher RNA/DNA ratios were obtained for bottlenose dolphins (p < 0.001), and for visitor pilot whales when compared with resident pilot whales (p = 0.001). No significant changes were found between the sexes. Based on the percentile approach, the samples contain individuals in a general good condition (as the 10th percentile is not closer to the mean than the 75th percentile), suggesting that the studied region of Macaronesia may be considered an adequate habitat. The combination of this effective tool with genetic sexing and photographic-identification provided an overall picture of ecosystem health, and although with some limitations and still being a first approach, it has the applicability to be used in other top predators and ecosystems.
- Grazing by Diadema antillarum (Philippi) upon algal communities on rocky substratesPublication . Alves, Filipe; Chícharo, Luís; Serrão, Ester; Abreu, A. D.Grazing by Diadema antillarum sea urchins is well documented for coral reefs, although information is scarce for the eastern part of the Atlantic Ocean, where rocky substrate dominates the sea bottom. This study analysed grazing activity by D. antillarum upon the algal communities living on rock substrates, and its possible impact on the subtidal communities. Controlled feeding experiments using exclusion cages were performed between May and September 1998 at Madeira Island (NE Atlantic). Three experimental treatments were used: (1) closed cages to exclude sea urchins, (2) open cage controls, and (3) uncaged controls (nine replicates in each treatment). After four months, in September 1998, the percentage algal cover was quantified. One-way analysis of variance followed by Post Hoc Tukey (HSD) tests showed significant differences between algal abundance in the presence (uncaged and open cage controls) or absence (closed cages) of sea urchins. In the areas where D. antillarum was excluded (closed cages), algal abundance increased by about 10% in the four-month period. Diadema antillarum thus effectively reduces algal abundance, and this may have important consequences in determining the algal community structure of rocky substrate.