Loading...
39 results
Search Results
Now showing 1 - 10 of 39
- Characterization of the coccolithophore community off Cabo Verde archipelago, including the Senghor Seamount (Eastern North Atlantic)Publication . Narciso, Áurea; Javidpour, Jamileh; Chi, Xupeng; Cachão, Mário; Kaufmann, ManfredA systematic investigation of the extant coccolithophore community around Cabo Verde archipelago was per formed during the cruise MSM49 of RV Maria S. Merian, which took place in the late fall of 2015. The description of the spatial and vertical distributions of coccolithophores was based on a survey performed to the north, east and south of Cabo Verde archipelago, between the surface and 150 m water depth. The total cell densities ob tained for the studied region were relatively low, reaching to a maximum of 30 × 103 cell L− 1 in the upper 50 m over the southeastern slope of the Senghor seamount. Emiliania huxleyi and Gephyrocapsa oceanica were the dominant species, followed by Florisphaera profunda. The coccolithophore distribution off Cabo Verde was essentially explained by relatively warm and nutrient-depleted waters in the region during the surveyed interval, in result of the weaker NE trade winds and the northward migration of the Intertropical Convergence Zone. In these conditions, a notable zonation of coccolithophores along depth was depicted, in consequence of the inferred general well-stratified water column. Four typical depth-related groups were identified: (i) a Shallow oligotrophic (10–30 m), represented by Discosphaera tubifera and Umbellosphaera spp.; (ii) an Intermediate (40–50 m), formed by the three placolith-bearing species E. huxleyi, G. ericsonii and G. oceanica, and by Algir osphaera robusta, Helicosphaera spp., Michaelsarsia spp., Syracosphaera spp. and Umbilicosphaera spp.; (iii) a Deep (60–75 m) with F. profunda, Ophiaster spp., Oolithotus spp. and Reticulofenestra sessilis as typical members; (iv) and The Deepest (>80 m), composed by Gladiolithus flabellatus and Syracosphaera lamina. In addition, high abun dances of G. oceanica related with the Eddy station were attributed to the transport and thriving of the coastal coccolithophore community, dominated by this species, from the African coast towards Cabo Verde.
- Sea urchin Diadema africanum mass mortality in the subtropical eastern Atlantic: role of waterborne bacteria in a warming oceanPublication . Clemente, S.; Lorenzo-Morales, J.; Mendoza, J. C.; López, C.; Sangil, C.; Alves, F.; Kaufmann, M.; Hernández, J. C.A widespread mass mortality event of the sea urchin Diadema africanum was detected in the subtropical eastern Atlantic, extending from Madeira to the Canary Islands, covering a straight line distance of >400 km. This is the first disease related die-off of a diadematid documented in the eastern Atlantic Ocean. Diseased individuals showed deterioration of the epidermis and water-vascular system, resulting in epidermal necrosis and release of spines. Despite some spatial heterogeneity in disease incidence at the study sites, there was a 65% overall reduction in urchin abundance after the mortality event compared to numbers pre-mortality. However, the reduction in urchin numbers did not compromise the species’ reproductive success; the settlement peak following the mortality event was of a similar magnitude to that in prior years. Bacterial isolation and cul ture techniques, and subsequent laboratory in fection experiments, strongly suggested that Vibrio alginolyticus was involved in the disease. We hypo thesize that the mass mortality event devel oped due to anomalously high seawater tempera tures recorded in the 2 studied archipelagos and that warmer temperatures enabled infection of D. africa - num by waterborne pathogenic bacteria. Fluctua tions in urchin populations are key in de termining the structure and functioning of benthic ecosystems: under the current seawater warming scenario, dis ease may result in more frequent phase shifts, aiding the persistence of macroalgae.
- Influence of disturbance and nutrient enrichment on early successional fouling communities in an oligotrophic marine systemPublication . Canning-Clode, João; Kaufmann, Manfred; Molis, Markus; Wahl, Martin; Lenz, MarkDisturbance and productivity are often cited as the main factors determining temporal and spatial patterns in species distribution and the diversity of com munities. A field experiment was conducted to test the role of these factors in the structuring of early successional fouling communities in a nutrient limited system at the south coast of Madeira Island. Macro-benthic sessile communi ties, established on artificial settlement substrata, were manipulated and sur veyed over a 9-week period. We applied mechanical disturbances of four different frequencies crossed with three levels of inorganic nutrient enrichment. Fertilization enhanced community diversity by favouring the establishment and growth of macroalgae. Disturbance reduced diversity by eliminating species – but only at the highest nutrient level. This is explained by a multiple-stressor model; species most sensitive to nutrient deficiency (only present in the highest enrichment treatment) were simultaneously the most sensitive to disturbance.
- A non-native macroalga is less attractive for herbivores but more susceptible to light limitation and grazing stress than a comparable native speciesPublication . Ramalhosa, Patrício; Debus, Sarah-Lena; Kaufmann, Manfred; Lenz, MarkIt has been suggested that non-native species are more tolerant towards abiotic stress than ecologically compara‑ ble native species. Furthermore, non-native marine macroalgae should be under lower grazing pressure than native seaweeds, because they left their co-evolved enemies behind. As a consequence, they generally need to allocate less energy to defences and can invest more into compensating the negative effects of abiotic stress or, assuming that grazing pressure is low but not zero, to defensive reactions following grazer attack. This, in turn, should make them more stress tolerant and less susceptible to herbivory. However, empirical evidence for both concepts is still scarce and very little is known about whether enemy release is commonly associated with an enhanced tolerance towards abiotic or biotic stress. We therefore ran an experimental study that (a) assessed attractiveness for grazers, (b) verified whether short-term low-light stress impairs growth and (c) investigated whether light limitation and previous grazing interactively affect the consumption of two macroalgae from Madeira Island, the native brown alga Stypopodium zonale and the non-native red alga Grateloupia imbricata by the sea urchin Paracentrotus lividus. To come to ecologi‑ cally meaningful low-light stress levels, pilot studies were performed in order to determine the light compensation point of photosynthesis for each algal species and then we established six light regimes around this point by reduc‑ ing the amount of incoming light. Simultaneously, we let one sea urchin graze on each algal individual to stimulate a chemical defence in the seaweeds if present. In parallel to this, we kept the same number of algal replicates in the absence of sea urchins. After 21 days, we compared algal growth in the absence of grazers as well as the attractive‑ ness of previously grazed and non-grazed algal material for P. lividus across all light regimes. Algal attractiveness was assessed in no-choice feeding assays. The observation that the non-native alga was less consumed by the grazer than the native species generally confirms the concept of enemy release. However, light limitation reduced growth in the non-native but not in the native seaweed, while previous grazing reduced consumption of the native but enhanced it in case of the non-native alga. These findings do not corroborate the assumption that enemy release can, through the re-allocation of energy, enhance tolerance to abiotic (light limitation) or biotic (grazing) stressors in non-native marine macroalgae.
- From a basic microalga and an Acetic Acid Bacterium cellulose producer to a living symbiotic biofilmPublication . Nóbrega, Vítor; Faria, Marisa; Quintana, Antera; Kaufmann, Manfred; Ferreira, Artur; Cordeiro, Nereida Maria AbanoBacterial cellulose (BC) has recently been the subject of a considerable amount of research, not only for its environmentally friendly biosynthesis, but also for its high potential in areas such as biomedicine or biomaterials. A symbiotic relationship between a photosynthetic microalga, Chlamydomonas debaryana, and a cellulose producer bacterium, Komagataeibacter saccharivorans, was established in order to obtain a viable and active biofilm. The effect of the growth media composition ratio on the produced living material was investigated, as well as the microalgae biomass quantity, temperature, and incubation time. The optimal temperature for higher symbiotic biofilm production was 30 °C with an incubation period of 14 days. The high microalgae presence, 0.75% w/v, and 60:40 HS:BG-11 medium (v/v) induced a biofilm microalgae incorporation rate of 85%. The obtained results report, for the first time, a successful symbiotic interaction developed in situ between an alkaline photosynthetic microalga and an acetic acid bacterium. These results are promising and open a new window to BC living biofilm applications in medical fields that have not yet been explored.
- Deriving phytoplankton size classes from satellite data: validation along a trophic gradient in the eastern Atlantic OceanPublication . Brotas, Vanda; Brewin, Robert J.W.; Sá, Carolina; Brito, Ana C.; Silva, Alexandra; Mendes, Carlos Rafael; Diniz, Tânia; Kaufmann, Manfred; Tarran, Glen; Groom, Steve B.; Platt, Trevor; Sathyendranath, ShubhaIn recent years, the global distribution of phytoplankton functional types (PFT) and phytoplankton size classes (PSC) has been determined by remote sensing. Many of these methods rely on interpretation of phytoplankton size or type from pigment data, but independent validation has been difficult due to lack of appropriate in situ data on cell size. This work uses in situ data (photosynthetic pigments concentration and cell abundances) from the north-east Atlantic, along a trophic gradient, sampled from 2005 to 2010, as well as Atlantic Meridional Transect (AMT) data for the same region, to test a previously developed conceptual model, which calculates the fractional contributions of pico-, nano- and micro-plankton to total phytoplankton chlorophyll biomass (Brewin et al., 2010). The application of the model proved to be successful, as shown by low mean absolute error between data and model fit. However, regional values obtained for the model parameters had some effect on the relative distribution of size classes as a function of chlorophyll-a, compared with the results according to the original model. The regional parameterisation yielded a dominance of micro-plankton contribution for chlorophyll-a concentrations greater than 0.5 mg m−3 , rather than from 1.3 mg m−3 in the original model. Intracellular chlorophyll-a (Chla) per cell, for each size class, was computed from the cell enumeration results (microscope counts and flow cytometry) and the chlorophyll-a concentration for that size class given by the model. The median intracellular chlorophyll-a values computed were 0.004, 0.224 and 26.78 pg Chla cell−1 for pico-, nano-, and micro-plankton respectively. This is generally consistent with the literature, thereby providing an indirect validation of the method based on pigments to assign size classes. Using a satellite-derived composite image of chlorophyll-a for the study area, a map of cell abundance was generated based on the computed intracellular chlorophyll-a for each size-class, thus extending the remote-sensing method for mapping size classes of phytoplankton from chlorophyll-a concentration to mapping cell numbers in each class. The map reveals the ubiquitous presence of pico-plankton, and shows that all size classes are more abundant in more productive areas.
- Challenges for sustainable monitoring and evaluation of the EU Marine Strategy Framework Directive in the Atlantic offshore waters: the iFADO projectPublication . Campuzano, F.; García, M.; Dabrowski, T.; Groom, S.; Ruiz-Villarreal, M.; Brotas, V.; Kaufmann, M.; Hartman, S.; Oliveira, P.; Martins, A.; Juliano, M.; Vieira, F.; Lux, M.; Barreda, C.; Rebour, X.; Simão, A.P.; Neves, R.The European Atlantic Area in situ characterization/monitoring is challenging due to the high costs involved (24% of total EU waters for 12% of total population). The implementation of the EU Marine Strategy Framework Directive (MSFD) is complex if the objective is to extend periodic monitoring programs to offshore waters. Remote sensing and modelling have been recognised by the Copernicus Marine Service as suitable methodologies to characterise the global ocean both for nowcast and forecast. iFADO (Innovation in the Framework of the Atlantic Deep Ocean, 2017-2021) is an Interreg Atlantic Area project which main objective is to integrate technologies, including remote sensing, numerical modelling and in situ monitoring, to ease management decisions from MSFD competent authorities. The iFADO project builds on the most recent technologies for data gathering and processing, suited for providing sustainable services to blue economy agents by fostering the regional quadruple helix cooperation (public sector, university/research centres, enterprise and citizens).
- Local–regional richness relationship in fouling assemblages – effects of successionPublication . Canning-Clode, João; Bellou, Nikoleta; Kaufmann, Manfred J.; Wahl, MartinThe number of species in a local habitat depends on local and regional processes. One common approach to explore ecological saturation of local richness has been to plot local versus regional richness. We expand this approach by incorporating two dimensions of diversity – taxonomic and functional – and different successional ages of marine fouling communities. In four different biogeographic regions (Mediterranean Sea, NE Atlantic, Western Baltic Sea and North Sea) 60 experimental units made from artificial substratum were deployed for colonization. Local richness was assessed as the average number of species and functional groups (FG) per unit area while regional richness was estimated as the estimated (Jack 2) asymptote of the accumulation curves for species or FG in local panel communities. Our findings indicate that the nature of the relationship between local and regional diversity is sensitive to successional stage and the dimension of diversity considered. However, as a general pattern, for taxonomic and functional richness, the slope of the local–regional relationship increased in the course of succession. We discuss how this pattern could have been produced by a combination of low number of recruiting species and incomplete competitive exclusion as is typical for early succession.
- Population structure of short-finned pilot whales in the oceanic archipelago of Madeira based on photo-identification and genetic analyses: implications for conservationPublication . Alves, Filipe; Quérouil, Sophie; Dinis, Ana; Nicolau, Cátia; Ribeiro, Cláudia; Freitas, Luís; Kaufmann, Manfred; Fortuna, Caterina1. Pilot whales Globicephala spp. are known to display a hierarchical social pattern, but longitudinal data to infer population structure of short-finned pilot whales Globicephala macrorhynchus are rare. 2. Using data collected between 2003-2011 in the oceanic archipelago of Madeira, the grouping structure of short-finned pilot whales was studied using photo-identification methods and mtDNA sequences and microsatellite markers to test the hypotheses that (1) there is at least one pelagic and one or more island-associated communities, and (2) groups are made of related individuals, with a matrilineal social structure. 3. Pilot whales demonstrated a large degree of variability in site fidelity, including residents (up to 14-year interval), regular visitors and transients. The social and temporal analyses revealed a well-differentiated society with long-lasting relationships (of years). The genetic analyses suggested that individuals of the three residency patterns may not be genetically isolated, and that small groups are made up of related individuals, suggesting some degree of social philopatry, while large groups are probably temporary associations of smaller groups. 4. It is proposed that the pilot whales encountered in Madeira belong to a single population encompassing several clans, possibly three clans of island-associated whales and others of transients, each containing two to three matrilineal pods, each with a mean of 15 individuals (SD=9, range: 4-29). We suggest that the clans interact for mating purposes when they meet. 5. For management decisions, it is considered that the island-associated whales should not be regarded as demographically independent populations, but instead as stable social entities to be included in governmental management plans and requiring periodic evaluation of their status. The high proportion of marked individuals and low rate of mark change encourages further research in this species.
- Bottlenose dolphin Tursiops truncatus group dynamics, site fidelity, residency and movement patterns in the Madeira Archipelago (North-East Atlantic)Publication . Dinis, A.; Alves, F.; Nicolau, C.; Ribeiro, C.; Kaufmann, M.; Cañadas, A.; Freitas, LThe bottlenose dolphin Tursiops truncatus is one of the most frequently sighted cetacean species in the Madeira Archipelago (North-East Atlantic); however, little is known about its population ecology in these waters. Photo-identification undertaken during systematic, non-systematic and opportunistic surveys conducted between 2001 and 2012 was used to assess group dynamics, site fidelity, residency and movement patterns of bottlenose dolphins in the archipelago. Three different patterns of residency were assigned, based on individual sighting histories. Group size ranged between 2 and 90 individuals (median 12), with no significant monthly difference in group size. All resident dolphins formed a core, complex network with migrant and transient dolphins. In contrast, satellite clusters were formed exclusively by transient individuals. The lagged identification rate (LIR) model indicated that a dolphin remained in the area for an average of 90 days, whereas the average time an individual spent outside the study area was approximately 313 days. The Madeira Archipelago appears to be only a section of a much larger home range for this population, with the dolphins exhibiting three different patterns of occurrence that associate with each other. The information gained about this poorly studied population contributes to the overall knowledge of bottlenose dolphins in insular oceanic habitats.