68 research outputs found
Fish assemblages cope with ocean acidification in a shallow volcanic CO2 vent benefiting from an adjacent recovery area
Shallow CO2 vents are used to test ecological hypotheses about the effects of ocean acidification (OA). Here, we studied fish assemblages associated with Cymodocea nodosa meadows exposed to high pCO2/low pH conditions at a natural CO2 vent in the Mediterranean Sea. Using underwater visual census, we assessed fish community structure and biodiversity in a low pH site (close to the CO2 vent), a close control site and a far control site, hypothesising a decline in biodiversity and a homogenization of fish assemblages under OA conditions. Our findings revealed that fish diversity did not show a unique spatial pattern, or even significant relationships with pH, but correlated with seagrass leaf canopy. Among-site similarity was found in the abundance of juveniles, contrary to the expected impacts of OA on early life stages. However, pH seems an important driver in structuring fish assemblage in the low pH site, despite its high similarity with the close control site. This unexpected pattern may represent a combined response of fish mobility, enhanced food resources in the acidified site, and a ‘recovery area’ effect of the adjacent control site
Coralline barrens and benthic mega-invertebrates: An intimate connection
: Despite considerable progress in understanding the transition from algal forests to coralline barrens, knowledge of coralline barren ecosystems in terms of community composition and functioning is still sparse and important gaps remain to be filled. Using a barren/forest patch system, we tested the hypothesis that the presence of coralline barren enhances the abundance and diversity of benthic mega-invertebrates. We also analysed trophic functional diversity through isotopic analyses of δ13C and δ15N. The distribution of benthic mega-invertebrates biomass differed markedly between coralline barren and algal forest, being more abundant and diverse in the barren state. Isotopic diversity metrics of the benthic mega-invertebrates assemblage indicated comparable trophic structure between the two states, although higher isotopic uniqueness in coralline barren was determined by sea urchins, especially A. lixula, and carnivorous starfish. We showed that in a patchy coralline barren/algal forest system, a more diversified benthic mega-invertebrates assemblage in the barren caused limited trophodynamic changes. This was possibly determined by the behaviour of some trophic groups such as filter feeders, deposit feeders and omnivores. Finally, our results evidence the close association between coralline barrens and benthic mega-invertebrates, contradicting the common view of coralline barrens as depauperate habitats with low diversity and productivity
Hiding behaviour of Oxynoe olivacea (Mollusca: Opisthobranchia: Sacoglossa) in the invasive seaweed Caulerpa taxifolia
The occurrence of the invasive seaweed Caulerpa taxifolia in the Straits of Messina (Italy) provides an excellent opportunity to examine the spatial and temporal patterns of abundance of the endemic Mediterranean sacoglossan Oxynoe olivacea. Densities of this species were recorded in March, June and October 2000 on three different habitats: the underside of boulders (UNB), the upper side of boulders (UPB), and the surface of concrete blocks (CB). Results showed that in March, O. olivacea was consistently more abundant on UNB whereas in June it was present exclusively on CB. The density of O. olivacea was similar in the three habitats in October. The hiding behaviour of O. olivacea and its seeming disappearance in March did not coincide with a decline of abundance of phylloids of C. taxifolia. The results represent an important basis for further studies devoted to the investigation of abundance of these marine invertebrates, which has been traditionally thought of as unpredictable
Functional traits of two co-occurring sea urchins across a barren/forest patch system
Temperate rocky reefs may occur in two alternative states (coralline barrens and erect algal forests), whose
formation and maintenance are often determined by sea urchin grazing. The two sea urchin species
Paracentrotus lividus and Arbacia lixula are considered to play a similar ecological role despite their differing
morphological traits and diets. The patchy mosaic areas of Ustica Island, Italy, offer an ideal environment in
which to study differences in the performance of P. lividus and A. lixula in barren versus forest states. Results
show that the two sea urchin species differ in diet, trophic position, grazing adaptation, movement ability and
fitness in both barren and forest patches. We confirmed herbivory in P. lividus and omnivory with a strong
tendency to carnivory in A. lixula. When the sea urchin escape response to a predator was triggered, P. lividus
responded faster in barren and forest patches. Forest patch restricted movement, especially in A. lixula (velocity
in barren ≈10-fold greater than in forest). A large Aristotle's lantern, indicative of durophagy, confirmed
adaptation of A. lixula to barren state
Multiple Processes Regulate Long-Term Population Dynamics of Sea Urchins on Mediterranean Rocky Reefs
We annually monitored the abundance and size structure of herbivorous sea urchin populations (Paracentrotus lividus and Arbacia lixula) inside and outside a marine reserve in the Northwestern Mediterranean on two distinct habitats (boulders and vertical walls) over a period of 20 years, with the aim of analyzing changes at different temporal scales in relation to biotic and abiotic drivers. P. lividus exhibited significant variability in density over time on boulder bottoms but not on vertical walls, and temporal trends were not significantly different between the protection levels. Differences in densities were caused primarily by variance in recruitment, which was less pronounced inside the MPA and was correlated with adult density, indicating density-dependent recruitment under high predation pressure, as well as some positive feedback mechanisms that may facilitate higher urchin abundances despite higher predator abundance. Populations within the reserve were less variable in abundance and did not exhibit the hyper-abundances observed outside the reserve, suggesting that predation effects maybe more subtle than simply lowering the numbers of urchins in reserves. A. lixula densities were an order of magnitude lower than P. lividus densities and varied within sites and over time on boulder bottoms but did not differ between protection levels. In December 2008, an exceptionally violent storm reduced sea urchin densities drastically (by 50% to 80%) on boulder substrates, resulting in the lowest values observed over the entire study period, which remained at that level for at least two years (up to the present). Our results also showed great variability in the biological and physical processes acting at different temporal scales. This study highlights the need for appropriate temporal scales for studies to fully understand ecosystem functioning, the concepts of which are fundamental to successful conservation and management
Dati preliminari sul movimento di Paracentrotus lividus ed Arbacia lixula sul barren habitat
NEW RECORD OF CAULERPA TAXIFOLIA (CAULERPALES, ULVOPHYCEAE) IN THE SOUTH-WESTERN SICILIAN WATERS (ITALY)
Preliminary data on movement of sea-urchins Paracentrotus lividus and Arbacia lixula in two habitats with different structural complexity.
Hiding behaviour of <em>Oxynoe olivacea</em> (Mollusca: Opisthobranchia: Sacoglossa) in the invasive seaweed <em>Caulerpa taxifolia</em>
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