Marcia Abreu de Oliveira Figueiredo

Settlement and survival of epiphytes on two intertidal crustose coralline alga

Abstract The effects of the microtopography of the surface and the antifouling ability of crustose coralline alga on the recruitment of epiphytes were tested under different shading conditions. In experiments set up on the south coast of Isle of Man, British Isles, during autumn and winter, epiphyte settlement and survival on Phymatolithon lenormandii (Aresch) Adey and P. purpureum (P. & H. Crouan) Woelkerling and Irvine were compared on epoxy replicas as well as dead and living crusts. Differences in the density of epiphyte germlings between replicas of the surface of two crust species were due to their surface textures. The rough-surfaced P. lenormandii had a higher density of epiphytes, probably because it provides a better refuge for Ulva and Enteromorpha spp. zoospores than for Fucus zygotes, which are larger and thus less protected by crust protuberances on wave washed shores. On the shore, shading with neutral roofs was less effective than canopy algae in cutting out light and suppressing Fucus germlings. Living crusts strongly retarded epiphyte recruitment, but this was dependent on light levels on the shore. The factors influencing this process need to be identified, because mechanical and chemical mechanisms cannot yet be distinguished.

Biotic interactions in the colonization of crustose coralline algae by epiphytes

Abstract Experiments were carried out on the southern coast of the Isle of Man, British Isles, in summer 1990. Canopy removal and grazer exclusion treatments were applied to experimental areas on the mid-shore where two crustose coralline algae were growing together: Phymatolithon lenormandii (Aresch.) Adey and P. purpureum (P. and H. Crouan) Woelkerling and Irvine. Samples were taken to verify changes in the biomass of epiphytes on crusts over time, in the presence and absence of canopy and grazers. Two sets of experiments were run in the same area, one using pieces of crust on plates which allowed the standardization of the microhabitat and surface features of crusts, and another with crusts growing naturally on rocks. Epiphytes were largely absent from crusts beneath the Fucus canopy in both sets of experiments, and were reduced by grazing limpets Patella vulgata L. The rough micro-surface texture of Phymatolithon lenormandii enhanced Enteromorpha but not Fucus biomass, while the smooth microscale but protuberant macroscale topography of P. purpureum provided epiphytes with a refuge from grazing. The substratum type did not affect epiphyte loads as much as the presence of an overlying canopy or, to a lesser extent, grazing limpets, but in the absence of these factors significant differences in epiphyte biomass between crusts were found. These are attributable to features of the crusts and various possibilities are discussed.

Experimental Effects of Sediment Burial and Light Attenuation on Two Coralline Algae of a Deep Water Rhodolith Bed in Rio de Janeiro, Brazil

Abstract A dense rhodolith bed on deep-water soft bottoms in the Peregrino oil field in Campos Basin, Brazil was recently described. This critical habitat is increasingly subjected to disturbances that promote massive sediment dislodgment. This study aimed to test the combined effects of sediment burial and light attenuation on two main rhodolith-forming coralline algae. Experiments were conducted using the dominant algae Mesophyllum engelhartii and Lithothamnion sp. Color changes were measured as a response to burial with a thin layer of fine and coarse sediments compared to uncovered samples at two natural light levels. A mesocosm system exposed species to combined treatments of light and burial by sediments that mimic drill cuttings. M. engelhartii bleached after 75 days and Lithothamnion sp. earlier than that, at 41 days, when buried by fine sediments. Sediments had a strong negative effect on the photosynthesis of coralline algae species within two weeks. Low light levels are not a problem for these deep-water coralline species, but fine sediments have a negative effect after a relatively short time. Lithothamnion was more sensitive than M. engelhartii in terms of color changes but less sensitive in terms of their fluorescence responses to burial.

DISTRIBUIÇÃO DAS ALGAS CALCÁRIAS INCRUSTANTES (CORALLINALES, RHODOPHYTA) EM DIFERENTES HABITATS NA PRAIA DO FORNO, ARMAÇÃO DOS BÚZIOS, RIO DE JANEIRO

(Distribution of the crustose coralline algae (Corallinales, Rhodophyta) in different habitats at Praia do Forno, Armacao dos Buzios, Rio de Janeiro) The crustose coralline algae occupy several different habitats in the rocky shores. In this study morphological characteristics of these algae were related to the influence of environmental factors. The algae collection was done at Praia do Forno (RJ) using 10 m transects lines with 30 random points to quantify coralline algae. The morphological aspects were observed by a stereomicroscope and anatomic sections were prepared to identify the groups/taxons. Six morphological groups were identified being four more abundant. Hydrolithon samoense (Foslie) D. Keats & Y. Chamberlain dominated on the littoral (53%) and sublittoral zones together with the chlorophyte Codium spongiosum Harvey and on barren rocks, exposed to wave action and high density of herbivorous sea-urchins (57-87%). Spongites sp was abundant on nearby rocky crevices on the littoral zone (39-40%). Lithophyllum sp. dominated from littoral (44%) to sublitoral zones together with Codium (43-74%) and Sargassum (74-93%). There was inconspicuous seasonal variation on the distribution of H. samoense and Lithophyllum sp. Protuberant thalli of Lithophyllum dominated in places under high sedimentation while flat thalli of H. samoense and Spongites dominated in areas with high herbivory. The distribution of form-functional groups in different habitats agrees with patterns associated with biotic and abiotic disturbances, expected for rocky shore communities.

The effect of sediment mimicking drill cuttings on deep water rhodoliths in a flow-through system: Experimental work and modeling

The impact of sediment coverage on two rhodolith-forming calcareous algae species collected at 100m water depth off the coast of Brazil was studied in an experimental flow-through system. Natural sediment mimicking drill cuttings with respect to size distribution was used. Sediment coverage and photosynthetic efficiency (maximum quantum yield of charge separation in photosystem II, ϕPSIImax) were measured as functions of light intensity, flow rate and added amount of sediment once a week for nine weeks. Statistical experimental design and multivariate data analysis provided statistically significant regression models which subsequently were used to establish exposure-response relationship for photosynthetic efficiency as function of sediment coverage. For example, at 70% sediment coverage the photosynthetic efficiency was reduced 50% after 1-2weeks of exposure, most likely due to reduced gas exchange. The exposure-response relationship can be used to establish threshold levels and impact categories for environmental monitoring.

Long- and short-term effects of smothering and burial by drill cuttings on calcareous algae in a static-renewal test

Discharge of drill cuttings into the ocean during drilling of offshore oil wells can impact benthic communities through an increase in the concentrations of suspended particles in the water column and sedimentation of particles on the seafloor around the drilling installation. The present study assessed effects of water-based drill cuttings, barite, bentonite, and natural sediments on shallow- and deep-water calcareous algae in short-term (30 d) and long-term (90 d) experiments, using 2 species from Peregrinos oil field at Campos Basin, Brazil: Mesophyllum engelhartii and Lithothamnion sp. The results were compared with the shallow-water species Lithothamnion crispatum. Smothering and burial exposures were simulated. Oxygen production and fluorescence readings were recorded. Although less productive, M. engelhartii was as sensitive to stress as Lithothamnion sp. Mesophyllum engelhartii was sensitive to smothering by drill cuttings, barite, and bentonite after 60 d of exposure and was similarly affected by natural sediments after 90 d. These results indicate that smothering by sediments caused physical effects that might be attributable to partial light attenuation and partial restriction on gas exchange but did not kill the calcareous algae in the long term. However, 1-mo burial by either natural sediments or drill cuttings was sufficient after 60 d for both species to reduce oxygen production, and the algae were completely dead under both sources of sediments.

Computational Visual Stress Level Analysis of Calcareous Algae Exposed to Sedimentation.

This paper presents a machine learning based approach for analyses of photos collected from laboratory experiments conducted to assess the potential impact of water-based drill cuttings on deep-water rhodolith-forming calcareous algae. This pilot study uses imaging technology to quantify and monitor the stress levels of the calcareous algae Mesophyllum engelhartii (Foslie) Adey caused by various degrees of light exposure, flow intensity and amount of sediment. A machine learning based algorithm was applied to assess the temporal variation of the calcareous algae size (∼ mass) and color automatically. Measured size and color were correlated to the photosynthetic efficiency (maximum quantum yield of charge separation in photosystem II, ΦPSIImax) and degree of sediment coverage using multivariate regression. The multivariate regression showed correlations between time and calcareous algae sizes, as well as correlations between fluorescence and calcareous algae colors.

Assessing the potential impact of water-based drill cuttings on deep-water calcareous red algae using species specific impact categories and measured oceanographic and discharge data.

The potential impact of drill cuttings on the two deep water calcareous red algae Mesophyllum engelhartii and Lithothamnion sp. from the Peregrino oil field was assessed. Dispersion modelling of drill cuttings was performed for a two year period using measured oceanographic and discharge data with 24 h resolution. The model was also used to assess the impact on the two algae species using four species specific impact categories: No, minor, medium and severe impact. The corresponding intervals for photosynthetic efficiency (ΦPSIImax) and sediment coverage were obtained from exposure-response relationship for photosynthetic efficiency as function of sediment coverage for the two algae species. The temporal resolution enabled more accurate model predictions as short-term changes in discharges and environmental conditions could be detected. The assessment shows that there is a patchy risk for severe impact on the calcareous algae stretching across the transitional zone and into the calcareous algae bed at Peregrino.