1,721,052 research outputs found
Devil’s Tongue Weed (Grateloupia turuturu Yamada) in northern Portugal: passenger or driver of change in native biodiversity?
No full textUnderstanding the mechanisms underlying biological invasions is essential to separate their actual ecological effects from those of other human disturbances. This study examined experimentally whether the non-native red seaweed Grateloupia turuturu is an opportunistic species taking advantage of degraded local conditions (passenger model), or the primary driver of changes in the structure of benthic assemblages (driver model). In a first experiment, traits of G. turuturu likely associated to its invasion success were compared between unmanipulated controls and treatments subjected to the removal of canopy-forming macroalgae to test for the passenger model. In a second experiment, rock pool assemblages where G. turuturu was selectively removed were compared with initially similar control (unmanipulated) assemblages to test for the driver model. Over a period of four months, G. turuturu showed larger cover, higher number of individuals and longer fronds in the canopy-removed compared to the control pools, while no significant differences were detected between assemblages where G. turuturu was continuously removed and those where invasion was allowed to occur. Present findings suggest that G. turuturu would rely on disturbances removing potential native competitors to spread into the recipient habitat, rather than being the main driver of ecological alterations
Light pollution enhances temporal variability of photosynthetic activity in mature and developing biofilm
No full textArtificial light at night (ALAN) has been recently recognized as a threat for aquatic systems, but a comprehensive knowledge of its effects is still lacking. A fundamental question is whether and how ALAN might affect temporal variability of communities, thus undermining the stability of mature assemblages or influencing the colonization process. Here we investigated the role of ALAN on temporal variability of total biomass and maximum photosynthetic efficiency of marine autotrophic biofilms colonizing Mediterranean high-shore rock surfaces while controlling for density of their main grazers. Results showed stability in total biomass, but an increase in maximum photosynthetic efficiency from unlit to lit conditions, which suggested a temporal change in composition and/or abundance of different taxa within mature assemblages. The effect was weaker during the colonization process; in this case, density of grazers acted in the opposite direction of ALAN. We suggest that the addition of light at times when it would not be naturally present may affect the temporal variability of a variety of functioning in aquatic systems, depending on species-specific sensitivities to ALAN within microbial assemblages and/or indirect effects mediated by their consumers. We highlight to further investigate the role of this emergent topic in aquatic ecology
Effects of mean intensity and temporal variability of disturbance on the invasion of Caulerpa racemosa var. cylindracea (Caulerpales) in rock pools
No full textSpatial variation of reef fishes and the relative influence of biotic and abiotic habitat traits
Full text linkPatterns of distribution of reef fishes were examined across three spatial scales and related to habitat traits along
25 km of the northern Portuguese coast. Response variables included the multivariate assemblage structure, the total
number of taxa and individuals, and the abundance of single groups categorized according to their preference for
the benthic, proximo-benthic or pelagic environment, feeding and reproductive behaviour. Habitat traits included
topographic elements (small and large ‘drops’ like cracks and crevices) and the extent of dominant morpho-functional
types of macroalgae (kelp, large foliose, small erect, turf-forming filamentous, and encrusting). All fish responses were
characterized by the largest variance at the smallest scale (among transects tens m apart), followed by that among
reefs (hundreds m to 1 km apart) and almost null variance among sites (some km apart). Small and large ‘drops’ of
the substratum explained, respectively, considerable variation of assemblage structure and the total abundance of
individuals, while the extent of bare rock influenced the richness of taxa and that of benthic fishes, fishes feeding on
sessile invertebrates and fishes laying benthic eggs or having nesting behaviour. Combinations of abiotic and biotic
structural attributes of reefs influenced proximo-benthic fishes, the predators of mobile animals and fishes releasing
pelagic eggs. The here reported associations between patterns of distribution of reef fishes and habitat traits have
implications for the design of future protection schemes suitable to guarantee the conservation of reef fish communities
and of the processes responsible for their variation. Within the SLOSS (single-large vs. several-small) debate in the
design of marine reserves, for example, effective protection to the studied reef fishes would be provided by a set of
small reserves, rather than a single large which might be appropriate for fishes having wider home ranges
Patterns of benthic assemblages invaded and non-invaded by Grateloupia turuturu across rocky intertidal habitats
No full textIntertidal benthic assemblages invaded and non-invaded by the introduced Asian red alga Grateloupia turuturu were compared at a rocky shore along the NW coast of Portugal. The structure of whole assemblages, the total richness of taxa and the abundance of individual taxa were examined as response variables in two different habitats (rock pools and emergent rock), two shore levels (low and mid intertidal) and two dates of sampling (June 2013 and June 2014).
Invaded and non-invaded assemblages differed consistently across habitats and shore levels. Such differences were driven by 13 (with the green alga genus Ulva, the red alga Chondrus crispus and the mussel Mytilus galloprovincialis driving the total dissimilarity) out of the total 37 taxa identified. Individual taxa revealed idiosyncratic patterns, in several cases (C. crispus, M. galloprovincialis, articulated coralline algae of the genus Corallina and the crustose sporophyte of the red alga Mastocarpus stellatus) there were differences in the abundance of a taxon between invaded and non-invaded assemblages varying with levels of some other experimental factors. The total number of taxa was higher in invaded compared to non-invaded assemblages for each combination of habitat and shore level.
Patterns of invasion by G. turuturu along the Portuguese continental coast were recently described in terms of its temporal and spatial distribution, but never examined in terms of differences between invaded and non-invaded assemblages. Such information is very limited for other geographic areas where this species is recorded out of its native range of distribution. Therefore, the present study provides a new contribution to the understanding of modifications of native assemblages associated with the invasion of G. turuturu, opening avenues of research aimed at specifically examining the factors and processes likely responsible for the invasion dynamics and success of this species
The amphipod assemblages of Sabellaria alveolata reefs from the NW coast of Portugal: An account of the present knowledge, new records, and some biogeographic considerations
Full text linkAmphipod assemblages associated with the biogenic reefs built by the honeycomb worm Sabellaria alveolata were studied at two sites (Praia da Aguda and Belinho) along the northwestern coast of Portugal. A total of 3909 specimens were collected, comprising 14 different amphipod species. A first record from the northeastern Atlantic coast was registered here for the species Caprella santosrosai, which was, up to now, recorded only along the Mediterranean coast of the Iberian Peninsula. A male specimen collected from the Sabellaria-reef located in Belinho allowed an update to the known distribution of C. santosrosai, thus altering its previous status as an endemic Mediterranean species. The most common species collected during the study were Microdeutopus chelifer (n = 1828), Jassa ocia (n = 1426), and Hyale stebbingi (n = 452). Forty-three percent of the total recorded species were encountered in both study sites, whereas the remaining 57 % were restricted to a single site (Belinho). The majority of the collected species (93 %) showed an Atlantic-Mediterranean distribution, confirming the close affinity between eastern Atlantic and Mediterranean amphipod assemblages and the role of the Portuguese coast as a transition zone through which numerous warm-water species, coming from North Africa and the Mediterranean Sea, could enter into the Atlantic and possibly get mixed with species coming from the North Sea and the Arctic, typically having affinity for colder waters
Comparison between epiphyte assemblages of leaves and rhizomes of the seagrass Posidonia oceanica subjected to different levels of anthropogenic eutrophication
No full textThis paper aimed to compare epiphyte assemblages of leaves and rhizomes of Posidonia oceanica exposed to different levels of concentration of nutrients. The same design including a potentially impacted meadow and two reference meadows was used in each of two locations, characterized by the presence of a city or of suspended cages of a fish farm, respectively. This allowed to test for the consistency of responses of epiphytic assemblages to different sources of eutrophication. In both studies, results documented differences in patterns of composition and abundance of epiphytic assemblages on leaves between disturbed and reference meadows, while assemblages on rhizomes did not appear sensitive to this kind of disturbance. Moreover, in potentially impacted meadows, both assemblages showed different patterns of spatial variability compared to reference assemblages. Species composition and abundance of epiphyte assemblages seemed suitable for detecting moderate nutrient increases, even if adequate sampling designs are needed to separate patterns related to the large natural spatial variability of these systems from those related to changes in environmental conditions
Complex positive interactions among rocky shore sessile species
No full textPositive interactions are important drivers of community structure and ecosystem functioning and may involve benefactor and beneficiary species directly in contact with each other, or spatially separated. On a Mediterranean coast, we examined the possible set of interactions linking 3 key taxa: the barnacle Chthamalus stellatus, the annual alga Rissoella verruculosa, which forms a belt at lower shore levels, and epilithic microphytobenthos (EMPB), widely distributed on all substrata across the mid- and high intertidal zones. We predicted that barnacles could stimulate R. verruculosa growth (through nutrient-rich excretions washed from high to low shore) and EMPB biomass and photosynthetic activity (through the same mechanism or by providing favourable habitat among calcareous shells). In turn, R. verruculosa could act as a secondary facilitator for EMPB by buffering physical stress underneath its fronds. We tested this model through an experiment involving the complete removal or killing (without removal) of C. stellatus crossed with the removal of R. verruculosa. We did not find any effect of barnacles on R. verruculosa during the period of development of algal fronds (March, April, May). In summer (July and August, when algal fronds had been lost), EMPB biomass was smaller where barnacles and algae had been removed. These results negate facilitation of R. verruculosa by C. stellatus, but they indicate positive effects of both species on EMPB. Our study provides an example of adjacent facilitation on intertidal rocky shores, likely mediated by physical mechanisms, and suggests that effects on beneficiary species can persist after the loss of the macroscopic form of the benefactor
Human impacts on biogenic habitats: effects of experimental trampling on Sabellaria alveolata reefs
No full textHuman trampling is one of the main anthropogenic threats to coastal communities, especially in rocky intertidal habitats. The adverse effects of human trampling have recently received increasing attention from conservation biologists, especially when concerning species playing key functional roles. These include biogenic reefs providing extremely productive and diverse habitats due to their structural heterogeneity and three-dimensional complexity. The degradation of such habitats could not only adversely affect the whole coastal biota, but it could also have strong socio-economic implications. This study investigated the potential impact of human trampling on biogenic reefs built by the honeycomb worm Sabellaria alveolata in north-western Portugal. Three increasing intensities of human trampling were manipulated to test for their direct effects on S. alveolata bio-constructions and indirect effects on associated benthic infauna. Experimental trampling, even at low intensity, negatively affected reefs by reducing the percentage cover of intact S. alveolata concretions over a period of two months, but it did not alter the structure of whole assemblages compared to the unmanipulated condition. Idiosyncratic responses were shown by the most conspicuous taxa, ranging from no significant effects on S. alveolata and Amphipoda to spatially and temporally variable effects on the Syllidae and Sabellidae polychaetes, the Mytilidae bivalves and the Rissoidae gastropods. When present, however, differences were always in the direction of larger abundances under the highest intensity of trampling than in the less disturbed treatments and the unmanipulated control. This study provides one of the first experimental evidence linking the intensity of human trampling to the physical damage of S. alveolata reefs. Direct implications of present findings as tools to promote a sustainable use of these systems at a local scale and to stimulate protection and management initiatives at other locations are discussed
Functional responses of juvenile kelps, Laminaria ochroleuca and Saccorhiza polyschides, to increasing temperatures
No full textWe tested the ability of juvenile sporophytes of two coexisting kelps native to Portugal, Laminaria ochroleuca and Saccorhiza polyschides, to adjust their photosynthesis and respiration to increasing sea water temperatures. These responses were measured for S. polyschides from both the subtidal and the intertidal habitat, and for L. ochroleuca from the intertidal habitat. L. ochroleuca showed a reduced ability to acclimatize to changing conditions, whereas S. polyschides demonstrated a larger physiological flexibility. These findings are connected with the life-history traits of these species. Additionally, optimum temperatures for the primary production of kelps were assessed, indicating higher values for inter- than subtidal S. polyschides. Significant physiological differences between inter- and subtidal S. polyschides were observed, based on metabolic rates of primary production and dark respiration. This study suggests that, under a warming climate scenario, responses can significantly vary for each species, and that L. ochroleuca is more susceptible to ocean warming than S. polyschides, due to larger acclimatization capacity of the latter
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