Diana Boaventura

Analysis of competitive interactions between the limpets Patella depressa Pennant and Patella vulgata L. on the northern coast of Portugal

Inter- and intraspecific competitive interactions among the species Patella depressa Pennant and P vulgata L. were analysed on the northern coast of Portugal, where both species co-occur in similar proportions. Increased (x 2, x 4), normal and decreased (x 1/2 intraspecific only) densities of limpets were used to test the effects of competition on the growth and mortality of the limpets, and competitive interactions between the different species. Fenced plots of 25 x 25 cm enclosing marked limpets at various densities were set up at a mid tidal level on the shore. Twelve treatments with three replicates of different combinations of densities and species were established. Mortality was recorded every 15 days and length was measured monthly during the 5 months of the experiment. At the end of the experiment, limpets were collected for biometry, sex determination and gonad staging. Both species of grazing molluscs showed increased mortality and reduced size and weight in increased density treatments. Limpets in decreased density treatments showed lower mortality and higher size. There were no significant differences between the effect of P. vulgata on R depressa and the effect of P. depressa on P. vulgata on mortality and length. There were, however, decreases in weight due to intraspecific effects for both species. For P. vulgata, interspecific effects were much less than intraspecific effects and for P. depressa, the interspecific effects depended on density. The analysis of the gonad stage at the end of the experiment showed that the lower stages of development were most prevalent at increased densities and the occurrence of neuter individuals only in increased densities single species plots corroborated the evidence of a stronger intraspecific interaction. The availability of food was indirectly assessed by determination of chlorophyll concentration with spectrophotometric analysis of rock chips. Microalgal food assessment in this experiment, however, did not show any clear trends. The results were compared with previous studies of competition in grazing molluscs and discussed in relation to the limits of distribution of P vulgata on the Portuguese coast.

The effects of grazing on the distribution and composition of low-shore algal communities on the central coast of Portugal and on the southern coast of Britain

A red algal turf is often found just below the barnacle/limpet zone of many European shores, especially on steep shores of moderate exposure. The hypothesis that grazing by limpets determines the upper limit of distribution of this red algal turf was tested on moderately exposed shores in Portugal and Britain. We also aimed to assess whether the grazing effect is modified at various spatial scales. Grazers were excluded by fences, with half-fenced and unfenced controls. Exclusion plots were rapidly colonised by green ephemeral algae in the months immediately after the beginning of the experiment (summer); these algae were later replaced by perennial algae. The percentage cover of turf-forming macroalgae showed a significant increase at both locations. The upper limit of distribution extended more than 50 cm on most of the shores studied. In contrast, control and half-fenced plots remained devoid of algae. After 2 years, ungrazed plots were mainly colonised by a red algal turf (e.g. Caulacanthus ustulatus, Gelidium spp., Laurencia pinnatifida) in Portugal, while canopy cover (Fucus serratus and Himanthalia elongata) dominated in Britain in marked contrast to the grazed plots. Physical factors acting at both local and geographical scales may explain these differences. However, although physical factors probably have an important influence on the identity, size and abundance of sublittoral fringe macroalgae, grazers play a major role in directly setting their upper limits. The effect of grazing by limpets was not consistent for all of the morphological algal groups and spatial scales considered in the present study. The effect of grazing on the cover of turf algae varied between Portugal and Britain (location scale), while effects on ephemeral and canopy algal cover varied at the shore scale within location.

Gonad development and fatty acid composition of Patella depressa Pennant (Gastropoda : Prosobranchia) populations with different patterns of spatial distribution, in exposed and sheltered sites

The present study examines the effect of shore exposure on the feeding performance (assessed by fatty acid analyses of the whole body) and gonad condition (stage of development and gonad somatic index, GSI) of Patella depressa populations. Male and female limpets were collected at exposed and sheltered sites, during winter and summer. The population at the exposed site was at a more advanced stage of gonad development, with a higher dispersion of gonad stages, both in winter and summer. Additionally, limpets from the exposed site, particularly the males, presented a higher GSI than the corresponding stage in the sheltered site. The quantitatively most important fatty acids were the saturated fatty acids (SFA) 16:0, 14:0, and 18:0, the monounsaturated fatty acids (MUFA) 18:1(n-7), 18:1(n-9), 16:1(n-7) and 20:1(n-9) and the polyunsaturated fatty acids (PUFA) 20:5(n-3) and 20:4(n-6). Females had a significantly higher fatty acid methyl esters (FAME) content (in summer and winter) and higher amounts of SFA and MUFA (in summer), which points to a higher degree of storage of neutral lipids in this sex. Male and female limpets at the exposed site had a significantly higher FAME, SFA, MUFA, PUFA and highly unsaturated fatty acids (HUFA) content than the corresponding sex in the sheltered site in summer. In addition, an inversion in the eicosapentaenoic acid (EPA)/arachidonic acid (ARA) and (n-3)/(n-6) ratios was observed in the sheltered site, as a result of the significantly higher levels of ARA and (n-6) fatty acids and lower amounts of EPA and (n-3) fatty acids found in the sheltered limpets. A high variability among patches in the fatty acid composition in the exposed site was found in winter, possibly related to the aggregation of limpets at this time. The differences found between limpets from the exposed and sheltered sites suggest qualitative and quantitative differences in their diets. Additionally, the results show that the spatial aggregation strategy adopted by limpets in sites of great wave and wind exposure does not affect their feeding and reproductive success, at least in the site examined here. In fact, more developed gonads, a higher GSI and an elevated FAME content was found in the exposed population. Possible factors are suggested and discussed to explain these observations.

Spatial and temporal variation of the fatty acid composition of Patella spp. (Gastropoda: Prosobranchia) soft bodies and gonads

This study evaluated the effects of season and spatial distribution on the fatty acid composition of Patella depressa gonads and Patella spp. soft body tissue. The results show that the quantitatively most important fatty acids were the saturated fatty acids (SFA) 16:0, 14:0 and 18:0; the monounsaturated fatty acids (MUFA) 18:1(n-7), 18:1(n-9), 16:1(n-7) and 20:1(n-9) and the polyunsaturated fatty acids (PUFA) eicosapentaenoic acid (EPA 20:5(n-3)), and arachidonic acid (ARA 20:4(n-6)). P. depressa and P. ulyssiponensis soft body fatty acid profiles revealed significant differences between sexes; males showed significantly higher percentages of PUFA, highly unsaturated fatty acids (HUFA), (n-3) fatty acids and ARA, while in females significantly higher proportions of MUFA were found. Analysis of variance on the fatty acid composition of P. depressa gonads revealed significant differences between sexes, which were more marked than when the whole body was analysed. Males showed a significantly higher percentage of PUFA, HUFA, fatty acids from the (n-3) and (n-6) series, ARA and EPA, while females were seen to have higher proportions of SFA, MUFA and total fatty acid methyl esters (FAME). Some variability was seen to occur due to shore location and seasons, but these effects were not so obvious.

Trophic structure of macrobenthic communities on the Portuguese coast. A review of lagoonal, estuarine and rocky littoral habitats

Abstract This work is based on a compilation and treatment of data obtained on several studies regarding the macrobenthos trophic structure, carried out in different habitats of the Portuguese coast: a lagoon, rocky subtidal shores and estuarine eelgrass beds. Macrobenthic organisms were assigned to four distinct trophic groups (filter feeders, detritivores, herbivores and carnivores). Detritivores were the dominant trophic group in soft-bottom communities. Filter feeders dominated in subtidal rocky shores while eelgrass communities were equally represented by detritivores and herbivores. Current intensity and sediment deposition are discussed as factors affecting the observed distribution. Nevertheless, different sampling methods used in these studies and the lack of information on feeding habits of some species can also influence the results obtained.

Macrobenthic Colonisation of Artificial Reefs on the Southern Coast of Portugal (Ancão, Algarve)

Artificial reef systems play an important role in the increase of natural production of biological marine resources and they have been deployed worldwide. In Portugal, seven artificial systems have been deployed along the southern coast of the Algarve. Research to date has focussed mainly on fish populations, particularly those of economical importance. The present work aims to study the macrobenthic communities of the artificial reef structures, as these will enhance the food resources and shelter, making the reefs more attractive to fish. In particular, we experimentally analysed the sequence of colonisation of macrobenthic communities of the Ancao artificial reef system, which was deployed in the summer of 2002. The study of the colonisation of benthic communities was done using samples of concrete cubic units (15 × 15 cm) that were suspended at the reef modules at a depth of 20 m, at the time of the reef immersion. Four replicate samples were collected by SCUBA diving from two groups of the Ancao reef every three months from the starting date. Sampling was done using essentially non-destructive methods to assess the percentage cover of macrobenthic organisms in both vertical and horizontal surfaces. The percentage cover of the taxonomic groups was compared within the different surfaces of the samples and between the two reef groups. The bottom surface of cubic samples had a significantly higher colonisation related to the dominance of barnacle cover, probably due to lower sedimentation levels. Samples from both reef groups showed a similar pattern of colonisation. Barnacles, bryozoans and serpulids dominated the samples three months immediately after the beginning of the experiment. Other invertebrates groups, such as Porifera, Hydrozoa, Anthozoa, other sessile Polychaeta, Decapoda, Gastropoda and Bivalvia, were more abundant after six months of colonisation.

Effect of depth and reef structure on early macrobenthic communities of the Algarve artificial reefs (southern Portugal)

This study was carried out on the “Faro/Ancao” artificial reef (AR), located off Faro, deployed in May 2003. We aimed to characterise early macrobenthic community colonisation of two concrete AR groups located at different depths (16 m and 20 m depth) and to test the effect of reef structure on these communities. The non-colonial organisms were counted; barnacles and colonial species were quantified using biomass. Multivariate analyses indicated that early macrobenthic communities (6 months of immersion) were affected by depth, and that barnacles and colonial species were also affected by reef structure. Univariate analyses showed that the biomass of barnacles and colonial species was significantly different among reefs and layers of modules. Both AR groups were characterised by the species Balanus amphitrite, Gregariella subclavata, Musculus cf. subpictus, Paleanotus cf. bellis and Syllidia armata. Jassa marmorata and Bugula neritina were characteristic species at 16 m depth, particularly on the AR Upper layer of modules, whereas Anomia ephippium was particularly common at 20 m, especially on the Lower layer of modules.

Is surface orientation a determinant for colonisation patterns of vagile and sessile macrobenthos on artificial reefs

In order to examine how substratum colonisation can affect community structure, a 1-year study was conducted at the Faro/Ancão artificial reef (Algarve, Portugal). In the study of hard substratum communities, motile species are usually neglected and only the conspicuous species are taken into account. Therefore, the development of vagile and sessile components of the epibiotic community were analysed separately. Differences between assemblages on horizontal surfaces, but not on vertical surfaces, were detected. Multivariate analysis detected differences in macrobenthic community structure either considering sessile or motile components. However, significant differences were only detected for vagile fauna. Moreover, this study suggests that for hard substratum communities, analysis of the vagile fauna is important and should be taken into account in the functioning of the artificial raft.

Predation: a regulating force of intertidal assemblages on the central Portuguese coast?

Predation has long been recognized as an important biological force driving community patterns in intertidal rocky shores throughout the world. Little is known, however, about the role of predation by mobile marine predators in shaping intertidal prey populations in Portuguese rocky shores. The abundance and population structure of crabs were assessed during nocturnal low-tides on two rocky shores to characterize potential predator species. To assess the effect of predation on intertidal species including limpets, barnacles and mussels, predator exclusion experiments using full cage, partial cage and no cage treatments, were set up for two months on two shores on the central Portuguese coast. Pachygrapsus marmoratus (Fabricius) and Eriphia verrucosa (Forsskal) were the most abundant crabs. Results from predator exclusion experiments suggested that predators do not exert a significant control on abundance of limpets, mussels or barnacles on the midshore during the experimental period. Despite the fact that these crabs are known to feed on the analysed prey, several factors may account for the observed absence of impact on prey abundance and these are discussed.

Promoting Science Outdoor Activities for Elementary School Children: Contributions from a research laboratory

The purposes of the study were to analyse the promotion of scientific literacy through practical research activities and to identify childrens conceptions about scientists and how they do science. Elementary school children were engaged in two scientific experiments in a marine biology research laboratory. A total of 136 students answered a questionnaire about their previous habits towards science and carried out the following actions: (1) a guided visit to the laboratory, (2) a brief presentation of the research theme, (3) the development of two experiments, and (4) a questionnaire about the experiments and science conceptions. The research methods included observation, document analysis, and content analysis of the answers to the questionnaires. Additionally, each visit was video recorded in order to design learning materials. The results revealed that most of the pupils were able to follow every stage of experimentation. However, some of them misinterpreted results and conclusions. One implication of the study is that this type of outdoor activity is extremely important to promote meaningful science learning in children, but more care should be taken in practical science activities so that children can overcome some common difficulties when performing scientific inquiry.