Lorenzo Bramanti

The role of light in mediating the effects of ocean acidification on coral calcification

SUMMARY We tested the effect of light and PCO2 on the calcification and survival of Pocillopora damicornis recruits settled from larvae released in southern Taiwan. In March 2011, recruits were incubated at 31, 41, 70, 122 and 226 μmol photons m−2 s−1 under ambient (493 μatm) and high PCO2 (878 μatm). After 5 days, calcification was measured gravimetrically and survivorship estimated as the number of living recruits. Calcification was affected by the interaction of PCO2 with light, and at 493 μatm PCO2 the response to light intensity resembled a positive parabola. At 878 μatm PCO2, the effect of light on calcification differed from that observed at 493 μatm PCO2, with the result that there were large differences in calcification between 493 μatm and 878 μatm PCO2 at intermediate light intensities (ca. 70 μmol photons m−2 s−1), but similar rates of calcification at the highest and lowest light intensities. Survivorship was affected by light and PCO2, and was highest at 122 μmol photons m−2 s−1 in both PCO2 treatments, but was unrelated to calcification. In June 2012 the experiment was repeated, and again the results suggested that exposure to high PCO2 decreased calcification of P. damicornis recruits at intermediate light intensities, but not at lower or higher intensities. Together, our findings demonstrate that the effect of PCO2 on coral recruits can be light dependent, with inhibitory effects of high PCO2 on calcification at intermediate light intensities that disappear at both higher and lower light intensities.

Impact of ocean acidification and warming on the Mediterranean mussel (Mytilus galloprovincialis)

In order to assess the effects of ocean acidification and warming on the Mediterranean mussel (Mytilus galloprovincialis), specimens were reared in aquarium tanks and exposed to elevated conditions of temperature (+3 °C) and acidity (-0.3 pH units) for a period of 10 months. The whole system comprised a factorial experimental design with 4 treatments (3 aquaria per treatment): control, lowered pH, elevated temperature and lowered pH/elevated temperature. Mortality was estimated on a weekly basis and every 2 months, various biometrical parameters and physiological processes were measured: somatic and shell growth, metabolic rates and body fluid acid-base parameters. Mussels were highly sensitive to warming, with 100 % mortality observed under elevated temperature at the end of our experiment in October. Mortality rates increased drastically in summer, when water temperature exceeded 25 °C. In contrast, our results suggest that survival of this species will not be affected by a pH decrease of ~0.3 in the Mediterranean Sea. Somatic and shell growth did not appear very sensitive to ocean acidification and warming during most of the experiment, but were reduced, after summer, in the lowered pH treatment. This was consistent with measured shell net dissolution and observed loss of periostracum, as well as uncompensated extracellular acidosis in the lowered pH treatment indicating a progressive insufficiency in acid-base regulation capacity. However, based on the present dataset, we cannot elucidate if these decreases in growth and regulation capacities after summer are a consequence of lower pH levels during that period or a consequence of a combined effect of acidification and warming. To summarize, while ocean acidification will potentially contribute to lower growth rates, especially in summer when mussels are exposed to sub-optimal conditions, ocean warming will likely pose more serious threats to Mediterranean mussels in this region in the coming decades.

Settlement and early survival of red coral on artificial substrates in different geographic areas : some clues for demography and restoration

The red coral Corallium rubrum (L 1758) is a long-lived, slow-growing gorgonian, endemic to Mediterranean rocky bottoms. Because of its high economic value, red coral has long been harvested, and most populations have been depleted. In the present study, 54 marble tiles were placed in June 2003 within red coral populations over 3 different geographic areas (Calafuria-Livorno and Elba MPA in Italy and Medes Islets MPA, in Spain), on vertical cliffs between 25 and 35 m. In each area 2 different sites were randomly selected. Tiles were subsequently sampled photographically. Between July and August 2003 red coral recruits settled on tiles in all the geographic areas and sites, exhibiting wide variability in their density. On the basis of a 2-factors nested ANOVA a significant variability between different sites at a few hundred metres distance occurred, indicating high variations in the recruitment process within the same red coral population. Mortality, measured in June 2004, widely varied between different geographic areas.

Settlement and recruitment: The first stages in the life cycle of two epibenthic suspension feeders (Corallium rubrum and Anomia ephippium)

Abstract Studies on the population dynamics of the Mediterranean octocoral Corallium rubrum may prove extremely important for the conservation and management of this overexploited species. This study provides a detailed analysis of the settlement and recruitment processes in a red coral coastal population of the Eastern Ligurian Sea. Marble tiles, placed at two different depths (25 m and 35 m) were sampled photographically each month over two years, and the resulting densities of settlers were compared with those measured on the natural substrate. Red coral planulae successfully colonized tiles from August to September, showing a time‐limited recruitment. Contrary to red coral, Anomia ephippium, a bivalve that frequently colonizes tiles, exhibited a ‘pulsing’ recruitment throughout the year. Red coral settler density varied significantly between the different depths and times, while no statistical difference was found between artificial and natural substrates. As the tiles were permanent, they enabled us to follow the history of individuals and cohorts from settlement to their second year of life. Several mortality events affected settlers at both depths contemporaneously. In November 1999, the mass mortality that occurred in Ligurian shores also affected red coral settlers. These findings provide basic knowledge on the early phases of the red coral life cycle.

Habitat constraints and self-thinning shape Mediterranean red coral deep population structure: implications for conservation practice.

The Mediterranean red coral, Corallium rubrum, is one of the most precious corals worldwide. Below 50 m depth, C. rubrum populations are generally characterised by large and sparse colonies, whereas shallow populations (above 50 m depth) show high densities of small colonies. We show here instead that populations dwelling between 80 and 170 m depth exhibited a continuous range of population density (from 2 to 75 colonies per 0.25 m2), with less than 1% of variance explained by water depth. An inverse relationship between maximum population density and mean colony height was found, suggesting that self-thinning processes may shape population structure. Moreover, demographically young populations composed of small and dense colonies dominated along rocky vertical walls, whereas mature populations characterised by large and sparsely distributed colonies were found only in horizontal beds not covered by sediment. We hypothesise that, in the long term, shallow protected populations should resemble to present deep populations, with sparsely distributed large colonies. Since the density of red coral colonies can decay as a result of self-thinning mechanisms, we advise that future protection strategies should be based also on a measure of red coral spatial coverage instead of population density.

Limited Genetic Connectivity between Gorgonian Morphotypes along a Depth Gradient.

Gorgonian species show a high morphological variability in relation to the environment in which they live. In coastal areas, parameters such as temperature, light, currents, and food availability vary significantly with depth, potentially affecting morphology of the colonies and the structure of the populations, as well as their connectivity patterns. In tropical seas, the existence of connectivity between shallow and deep populations supported the hypothesis that the deep coral reefs could potentially act as (reproductive) refugia fostering re-colonization of shallow areas after mortality events. Moreover, this hypothesis is not so clear accepted in temperate seas. Eunicella singularis is one of the most common gorgonian species in Northwestern Mediterranean Sea, playing an important role as ecosystem engineer by providing biomass and complexity to the coralligenous habitats. It has a wide bathymetric distribution ranging from about 10 m to 100 m. Two depth-related morphotypes have been identified, differing in colony morphology, sclerite size and shape, and occurrence of symbiotic algae, but not in mitochondrial DNA haplotypes. In the present study the genetic structure of E. singularis populations along a horizontal and bathymetric gradient was assessed using microsatellites and ITS1 sequences. Restricted gene flow was found at 30–40 m depth between the two Eunicella morphotypes. Conversely, no genetic structuring has been found among shallow water populations within a spatial scale of ten kilometers. The break in gene flow between shallow and deep populations contributes to explain the morphological variability observed at different depths. Moreover, the limited vertical connectivity hinted that the refugia hypothesis does not apply to E. singularis. Re-colonization of shallow water populations, occasionally affected by mass mortality events, should then be mainly fueled by larvae from other shallow water populations.

Variation in lipid and free fatty acid content during spawning in two temperate octocorals with different reproductive strategies: surface versus internal brooder

AbstractThis study investigates the energetic investment during spawning of two Mediterranean gorgonians characterized by different reproductive strategies: Corallium rubrum (internal brooder) and Paramuricea clavata (surface brooder). Sexual products (number of oocytes and spermatic sacs) were quantified, and biochemical characteristics (lipid content and free fatty acid content and composition) were determined to investigate the parental energetic investment and demand in reproduction. Results suggested that the majority of the energetic cost was due to reproductive activity (i.e., gametogenesis and spawning). The two species exhibited different life history strategies, with P. clavata investing more energy in reproduction than C. rubrum. However, P. clavata is reproductively more sensitive to inter-annual changes in environmental conditions.

Applying cathodically polarised substrata to the restoration of a high value coral

Larval settlement of the high value red coral, Corallium rubrum, was studied on three different CaCO3 substrata, viz. lithogenic (marble), electro-accreted calcium carbonate in the presence and in the absence of cathodic polarisation. The last two substrata consisted of stainless steel plates galvanically coupled with Zn anodes. The electrochemical characterization of the settlement device was studied in order to investigate correlations between cathodic parameters (polarisation potential, current density, calcareous deposit composition) and larval settlement. The results obtained in the natural habitat (at 35 m depth) showed that settlement was five times lower on the electro-accreted aragonite in the presence of low cathodic current densities (i ≤ 1 μA cm−2) compared to both marble tiles and electro-accreted aragonite in the absence of polarisation. These last two substrata showed similar settlement values. The implications of these findings on restoration strategies for C. rubrum are discussed.

Spearfishing modulates flight initiation distance of fishes: the effects of protection, individual size, and bearing a speargun

Valerio Sbragaglia*, Lorenzo Morroni Lorenzo Bramanti, Boris Weitzmann, Robert Arlinghaus, and Ernesto Azzurro Department of Biology and Ecology of Fishes, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany Institute for Environmental Protection and Research (ISPRA), Via del Cedro 38, 57122 Livorno, Italy Department of Life and Environmental Sciences, Polytechnic University of Marche, Via Brecce Bianche, 60131 Ancona, Italy Sorbonne Universitè, CNRS, Laboratoire d’Ecogéochimie des Environnements Benthiques (LECOB), Observatoire Oceanologique Banyuls sur mer. 1 Avenue Pierre Fabre, 66650 Banyuls sur mer, France Parc Natural del Montgrı́, les Illes Medes i el Baix Ter, L’Estartit, Catalunya, Spain Division of Integrative Fisheries Management, Department of Crop and Animal Sciences, Faculty of Life Sciences, Humboldt-Universität zu Berlin, Invalidenstrasse 42, 10115 Berlin, Germany Stazione Zoologica Anton Dohrn (SZN), Villa Comunale 80121 Napoli, Italy *Corresponding author: tel: þ39 0650074030; fax: þ39 0586896248; e-mail: valeriosbra@gmail.com. Equally contributed to this study.

Spearfishing promotes a timidity syndrome and increases the safe operating distances in fish

In a landscape of fear, humans are altering key behaviors expressed by wild-living animals, including those related to foraging, reproduction and survival. When exposed to potentially lethal human actions, such as hunting or fishing, fish and wildlife is expected to behaviorally respond by becoming more timid, but proving such responses underwater in the wild has been challenging. Using a rich dataset collected in situ, we provide evidence of spearfishing-induced behavioral effects in five coastal fish species using the flight initiation distance (FID) as a proxy of predator avoidance and boldness. We document that spearfishing promotes a timidity syndrome (i.e., an increase of the average timidity of harvested populations) and that the wariness of prey’s wariness is influenced by individual size, level of protection offered through marine protected areas and the ability to recognize the risk posed by underwater human predators. In particular, we show that changes in the appearance of the observer (spearfisher vs. snorkeler) modulate the risk perception among the exploited species, and these differences are more evident outside marine protected areas where spearfishing is allowed. We also detected a positive correlation between FID and fish size, with larger specimens (that are more likely targets of spearfishers) revealing larger FID. The behavioral effects were most clearly expressed in the most heavily exploited species and declined towards the less desired and less targeted ones, which may be a result of learning mechanisms and plasticity and/or fisheries-induced evolution of timidity. Our study reveals a trade-off where intensive spearfishing negatively affects future spearfishing success through behavior-based alteration of catchability. Either rotating harvest or implementation of mosaics of protected and exploited areas might be needed to manage spearfishing-induced timidity in exploited stocks.