Andrea Peirano

The Introduced Green Alga Caulerpa Taxifolia Continues to Spread in the Mediterranean

The tropical green alga Caulerpa taxifolia in the Mediterranean has spread steadily since its introduction in 1984. At the end of 2000, approximately 131 km2 of benthos had been colonized in 103 independent areas along 191 km of coastline in six countries (Spain, France, Monaco, Italy, Croatia and Tunisia). Large regions neighboring the invaded areas appear favorable to further colonization, and there is thus no reason to believe that spreading will slow down in the years to come.

Tissue necrosis and mortality of the temperate coral Cladocora Caespitosa

Abstract Mass‐mortality events of the temperate coral Cladocora caespitosa were recorded in the Gulf of La Spezia (NW Mediterranean) in the summers of 1997, 1998 and 1999. At the end of the summer 1999, 60% of the colonies found in 1997 were damaged and more than 50% of the damaged colonies were completely dead. Complete death of the largest colonies caused a modal shift of colony size‐frequency distribution towards the smallest size classes. In order to verify experimentally the hypothesis that mass‐mortality was primarily induced by a seawater temperature increase of up to 4 °C for several weeks, as proposed by several Authors, nubbins of the coral were maintained in aquaria at a temperature of 28 °C, i.e., 4 °C higher than the normal maximum summer value. After three weeks of treatment, the nubbins showed a mortality pattern similar to that observed in the field, with the gradual necrosis of tissue to leave only the bare skeleton. Similarly, nubbins long‐term exposed to the summer temperature of 24 °C showed signs of stress. In situ tissue necrosis and loss, first from coenosarcs, then from polyps, started from different parts of the colonies simultaneously. In addition, C. caespitosa did not bleach during the thermal stress, which is different from the heat‐induced mass mortality events in tropical corals.

The Mediterranean coral Cladocora caespitosa: a proxy for past climate fluctuations?

Sclerochronology was applied to recent, Holocene and Pleistocene samples of Cladocora caespitosa. Late Pliocene samples were recrystallised and thus unsuitable for sclerochronology. Quaternary samples showed a clear, alternating banding pattern as in the living coral, confirming a marked seasonality of past climate. The computed mean annual growth rates ranged from 2.1 to 6.9 mm year 1 , with highest growth rates during the warmer phase (isotope stage 5e) of the first climate cycle. It is hypothesised that the largest fossil banks of C. caespitosa grew in a coastal environment with considerable alluvial inputs and warmer temperatures than today. D 2003 Elsevier B.V. All rights reserved.

3-D reconstruction of biological objects using underwater video technique and image processing

This paper describes a 3-D reconstruction method which allows accurate measurements of volume, surface area and other morphometric measurements of three-dimensional biological objects, without removing them from the sea. It represents a novel approach based on multiple views (eight resulted to be sufficient) from underwater video images and a new image processing procedure (MOD3D), whose application has met the basic requirements (i.e. to work on images recorded in turbid waters, with nonuniform lighting, to investigate large areas and in reasonable time, etc.) imposed when operating in the marine environment with simple, easy-to-use and nonprofessional equipment. It is a noninvasive, nondestructive and in the field fast method, thus suitable for sampling also at relevant depth, whose applicability has specifically been set up for a range of growth forms from massive to submassive and irregularly shaped. The accuracy of the method was assessed using models with three levels of 3-D complexity: simple, moderate and complex morphology. A high accuracy of volume measurements made through MOD3D image analysis software was achieved when compared with the laboratory water displacement method, which represents the most accurate method for volume measurement, with an overall mean percent error of about 1.7% (S.D. 2.2%). For all three levels of morphologic complexity, no significant differences (p>0.05) were found. Volume measurements obtained in field based on geometric approximation resulted rough, with significant differences from the MOD3D values (p<0.05). The geometric approximation was lower than MOD3D for simple and moderate morphology, and variable for complex morphology. For all three models, MOD3D values for surface area computation were consistently lower (mean error 13%) than the foil-wrapping values (p<0.05), due to overlap error when foil wrapping. Two applications were made with the bryozoan Pentapora fascialis and the coral Cladocora caespitosa to quantify carbonate standing stock and biomass of these two carbonate framework builders, whose importance has been recently recognised among the temperate sublittoral benthic species. Time required for the 3-D reconstruction method (about 3 h) makes it suitable for routine application particularly for relatively large area investigations, with irregularly shaped objects on rough substrate and several biological objects within the area.

Ecological Change, Sliding Baselines and the Importance of Historical Data: Lessons from Combing Observational and Quantitative Data on a Temperate Reef Over 70 Years

Understanding the effects of environmental change on ecosystems requires the identification of baselines that may act as reference conditions. However, the continuous change of these references challenges our ability to define the true natural status of ecosystems. The so-called sliding baseline syndrome can be overcome through the analysis of quantitative time series, which are, however, extremely rare. Here we show how combining historical quantitative data with descriptive ‘naturalistic’ information arranged in a chronological chain allows highlighting long-term trends and can be used to inform present conservation schemes. We analysed the long-term change of a coralligenous reef, a marine habitat endemic to the Mediterranean Sea. The coralligenous assemblages of Mesco Reef (Ligurian Sea, NW Mediterranean) have been studied, although discontinuously, since 1937 thus making available both detailed descriptive information and scanty quantitative data: while the former was useful to understand the natural history of the ecosystem, the analysis of the latter was of paramount importance to provide a formal measure of change over time. Epibenthic assemblages remained comparatively stable until the 1990s, when species replacement, invasion by alien algae, and biotic homogenisation occurred within few years, leading to a new and completely different ecosystem state. The shift experienced by the coralligenous assemblages of Mesco Reef was probably induced by a combination of seawater warming and local human pressures, the latter mainly resulting in increased water turbidity; in turn, cumulative stress may have favoured the establishment of alien species. This study showed that the combined analysis of quantitative and descriptive historical data represent a precious knowledge to understand ecosystem trends over time and provide help to identify baselines for ecological management.

Biomass, carbonate standing stock and production of the mediterranean coralCladocora caespitosa (L.)

SummaryThe Mediterranean coralCladocora caespitosa often occurs in large beds, i.e. populations of hemispherical clonies with stock densities varying between 1.9 and 4 coloneis ·m−2. Laboratory measurements of volume, skeleton weight, surface and number of corallites per colony, coupled with mean annual growth rates evaluated through sclerochronology, allowed for the estimation of biomass, skeleton bulk density, calcimass (carbonate standing stock) and secondary production (both organic and inorganic) of twoC. caespitosa beds at 4 and 9 m depth. The mean colony biomass varied between 0.73 and 0.99 kg dw ·m−2, corresponding to a calcimass between 2 and 5 kg CaCO3·m−2. Organic secondary production was 215.5–305.4 g dw of polyps ·m−2·y−1, while the potential (mineral) production was 1.1–1.7 kg CaCO3·m−2·y−1, for the year 1996–1997.These values show thatC. caespitosa is one of the major carbonate producers within the Mediterranean and one of the major epibenthic species originating stable carbonate frameworks both in recent and past times.

Lepidochronology and internodal length methods for studying Posidonia oceanica growth: are they compatible?

Two techniques to estimate growth of the Mediterranean seagrass Posidonia oceanica are compared. Leaf scale thickness and internodal length of orthotropic rhizomes were measured on the same rhizomes. Yearly cycles from internodal length measurements were in phase with lepidochronological years only after 3 years of rhizome growth. The start of a lepidochronological year roughly corresponded to the yearly maximum of internodal length measurements. Lepidochronology was a more sensitive method for identifying seasonal and yearly cycles. Both methods proved accurate and in agreement when samples exceeded 20 units (rhizomes). A combination of the two methods may improve dating techniques but the limitations should be taken into account when applied to population analysis and to primary production computations.

Measuring change of Mediterranean coastal biodiversity: diachronic mapping of the meadow of the seagrass Cymodocea nodosa (Ucria) Ascherson in the Gulf of Tigullio (Ligurian Sea, NW Mediterranean)

Monitoring the extension of seagrass meadows over time is of primary importance for the surveillance of marine coastal biodiversity. Here, we analyse the evolution of the meadow of Cymodocea nodosa in the Gulf of Tigullio, a coastal tract of naturalistic interest but subjected to high anthropogenic pressure. Historical maps at a scale 1:25,000 of C. nodosa meadow drawn in 1986, 1991 and 2001 were processed with GIS (Geographical Information System), using overlay vector methods. Diachronic analyses allowed the measurements of temporal changes, in term of percentage gain or loss of meadow extension, through concordance and discordance maps. A general increase in the extension of the meadow from 1986 to 1991 was evidenced, but the disparity of mapping methods (SCUBA diving in 1986, Side Scan Sonar in 1991) in the two surveys imposes caution when interpreting this result. On the other hand, the comparison of 1991 and 2001 maps, both derived from Side Scan Sonar surveys, showed a regression of the meadow of about 60% in the northern area, and modifications in the upper and lower limits of the meadow due to the impact of coastal works. C. nodosa meadow showed the only enlargement in front of the mouth of the Entella River, due to the increase in nutrient contents for rainfall in the period 1988–1994. The overall analysis evidenced a net decrease in seagrass meadow extension, an early warning of risk for marine coastal biodiversity in the Gulf of Tigullio.

Anthozoa from a subtidal hydrothermal area of Milos Island (Aegean Sea), with notes on the construction potential of the scleractinian coral Madracis pharensis

Abstract Eleven species of Anthozoa (two Octocorallia and nine Hexa‐corallia) were found on subtidal (2 to 90 m depth) hard substrata off Palaeochori Bay (SE Milos Island), an area characterised by submarine hydrothermalism. For each species, depth distribution and habitat were recorded. Their ecology at Milos was consistent with previous knowledge in other areas of the Mediterranean Sea. The corallites of Caryophyllia inornata (and perhaps other species) were comparatively small‐sized, thus apparently conforming to the so‐called ‘eastern nanism’ (i.e., high occurrence of dwarf individuals in the Aegean as compared to the western Mediterranean) for many Mediterranean benthic species. Madracis pharensis was very common, especially in sites close to vents, locally covering up to 30% of the primary rock with a calcareous crust. Skeletal bulk density (1.95–2.10 g‐cm‐3) was higher, and porosity (29%) lower, than in typical constructional corals. Layering of distinct generations of colonies suggests the significant accretion of a persistent biogenic substratum. It cannot be excluded that the construction potential of the species is enhanced by the hydrothermal activity: impulses of heat from vents maintain water temperature warmer during winter, and emission of Ca and CO2 may favour the biological deposition of carbonates and/or the activity of symbiotic zooxanthellae.

Seasonal Stability in the Microbiomes of Temperate Gorgonians and the Red Coral Corallium rubrum Across the Mediterranean Sea

Populations of key benthic habitat-forming octocoral species have declined significantly in the Mediterranean Sea due to mass mortality events caused by microbial disease outbreaks linked to high summer seawater temperatures. Recently, we showed that the microbial communities of these octocorals are relatively structured; however, our knowledge on the seasonal dynamics of these microbiomes is still limited. To investigate their seasonal stability, we collected four soft gorgonian species (Eunicella singularis, Eunicella cavolini, Eunicella verrucosa and Leptogorgia sarmentosa) and the precious red coral (Corallium rubrum) from two coastal locations with different terrestrial impact levels in the Mediterranean Sea, and used next-generation amplicon sequencing of the 16S rRNA gene. The microbiomes of all soft gorgonian species were dominated by the same ‘core microbiome’ bacteria belonging to the Endozoicomonas and the Cellvibrionales clade BD1-7, whereas the red coral microbiome was primarily composed of ‘core’ Spirochaetes, Oceanospirillales ME2 and Parcubacteria. The associations with these bacterial taxa were relatively consistent over time at each location for each octocoral species. However, differences in microbiome composition and seasonal dynamics were observed between locations and could primarily be attributed to locally variant bacteria. Overall, our data provide further evidence of the intricate symbiotic relationships that exist between Mediterranean octocorals and their associated microbes, which are ancient and highly conserved over both space and time, and suggest regulation of the microbiome composition by the host, depending on local conditions.