Carbon and nitrogen isotope ratios (δ
13C and δ
15N) were determined in the zooxanthellae, host tissue, and whole symbiotic association of the symbiotic temperate coral Cladocora caespitosa, as well ...as in the different components of the coral’s potential food sources (plankton, particulate organic matter in seawater and in the sediment). Data were collected both in winter and summer at three different locations, to assess the extent of auto- and heterotrophy in this species and get a better understanding of the functioning of temperate symbioses. There was a marked seasonal difference in the signature of the zooxanthellae and host tissue, highlighting two clear feeding patterns. In summer, δ
13C signatures of the coral host and the zooxanthellae were similar (−17‰) and very different from the signature of the food sources (from −21‰ to −25‰), suggesting that corals were relying on autotrophy for the acquisition of carbon. δ
15N values also suggested that nitrogen was not acquired through feeding. Conversely, in winter, the δ
13C signature of the host decreased by ca. −23‰ to −28‰, and was more comparable to the signature of the external food sources (between −24‰ and −25‰), suggesting a substantial reliance of C. caespitosa on external food sources during this season. There was also a 3‰ enrichment between the δ
15N signatures of the food (4–5‰) and the signature of the symbiotic association (7–8‰), suggesting that nitrogen was also acquired through feeding. Overall, these results give evidence that C. caespitosa and temperate corals in general derive a large fraction of their energy from heterotrophic feeding in winter.
A rapid temperature increase in the 1980-90s has been accompanied by dramatic and unprecedented changes in the biota and communities of the Ligurian Sea. This review uses existing historical series ...(a few of which have been purposely updated) to assess extent and consequences of such changes. A number of warm-water species, previously absent or occasional in the comparatively cold Ligurian Sea, has recently established thanks to warmer winters. Occurrence among them of invasive alien species is causing concern because of their capacity of outcompeting autochthonous species. Summer heatwaves, on the other hand, caused mass mortalities in marine organisms, some of which found refuge at depth. New marine diseases appeared, as well as other dysfunctions such as the formation of mucilage aggregates that suffocated and entangled benthic organisms. Human pressures have combined with climate change to cause phase shifts (i.e., abrupt variations in species composition and community structure) in different habitats, such as the pelagic environment, seagrass meadows, rocky reefs, and marine caves. These phase shifts implied biotic homogenization, reduction of diversity, and dominance by invasive aliens, and may be detrimental to the resilience of Ligurian Sea ecosystems. Another phase of rapid warming has possibly started in the 2010s and there are clues pointing to a further series of biological changes, but data are too scarce to date for proper assessment. Only well addressed long-term studies will help understanding the future dynamics of Ligurian Sea ecosystems and their possibilities of recovery.
Ecological studies about marine benthic communities received a major leap from the application of a variety of non-destructive sampling and mapping techniques based on underwater image and video ...recording. The well-established scientific diving practice consists in the acquisition of single path or ‘round-trip’ over elongated transects, with the imaging device oriented in a nadir looking direction. As it may be expected, the application of automatic image processing procedures to data not specifically acquired for 3D modelling can be risky, especially if proper tools for assessing the quality of the produced results are not employed. This paper, born from an international cooperation, focuses on this topic, which is of great interest for ecological and monitoring benthic studies in Antarctica. Several video footages recorded from different scientific teams in different years are processed with an automatic photogrammetric procedure and salient statistical features are reported to critically analyse the derived results. As expected, the inclusion of oblique images from additional lateral strips may improve the expected accuracy in the object space, without altering too much the current video recording practices.
Recent investigations have shown the temperate scleractinian coral
Cladocora caespitosa
to be a new potential climate archive for the Mediterranean Sea. Whilst earlier studies have demonstrated a ...seasonal variation in growth rates, they were unable to distinguish which environmental parameter (light, temperature, or food) was influencing growth. In this study, the effect of these three factors on the coral physiology and calcification rate was characterized to aid the correct interpretation of skeletal trace element variations. Two temperatures (13 and 23°C), irradiances (50 and 120 μmol m
−2
s
−1
), and feeding regimes (unfed and fed with nauplii of
Artemia salina
) were tested under controlled laboratory conditions on the growth, zooxanthellae density, chlorophyll (chl) content, and asexual reproduction (budding) of
C. caespitosa
during a 7-week factorial experiment. Unlike irradiance, which had no effect, high temperature and food supply increased the growth rates of
C. caespitosa
. The effect of feeding was however higher for corals maintained at low temperature, suggesting that heterotrophy is especially important during the cold season, and that temperature is the predominant factor affecting the coral’s growth. At low temperature, fed samples had higher zooxanthellae density and chl content, possibly for maximizing photosynthetic efficiency. Sexual reproduction investment of
C. caespitosa
was higher during favourable conditions characterised by high temperatures and zooplankton availability.
We investigated the conservation status and ecosystem substitution in six
Posidonia oceanica (L.) Delile meadows in 2002 along 300
km of the Ligurian coast (NW Mediterranean Sea). We studied the ...meadows by scuba transects and we compared the meadows state of health through
in situ shoot density counts and computing the Conservation Index (CI), the latter measuring the proportional amount of dead matte relative to live
P. oceanica. Both measures evidenced a generalised state of regression for most of the six meadows. We also reported the occurrence, within the meadows, of the other common Mediterranean seagrass
Cymodocea nodosa, the Mediterranean green alga
Caulerpa prolifera, and the invasive green algae
Caulerpa taxifolia and
Caulerpa racemosa. We measured the replacement of
P. oceanica by these species using the Substitution Index (SI), related to the proportional cover of each substitutes. These were ranked in order of their colonisation potential with respect to
P. oceanica. We identified and measured a community “phase shift” occurring within the Mediterranean seagrass meadows using a combined index, the Phase-Shift Index (PSI). The analysis of the three environmental indices (CI, SI and PSI) at regional scale allowed to introduce three “regional” ordinal scales to classify the conservation status, the degree of substitution and the level of phase shift in
P. oceanica meadows.
We assessed the in situ daily primary production, photosynthetic efficiency, and xanthophyll cycling of a temperate coral, Cladocora caespitosa, during the summer using an in situ incubation chamber ...equipped with temperature, oxygen, light, salinity, and pH sensors. During sunny days, photosynthetic carbon (C) production rates of C. caespitosa can be as high as those measured for tropical corals and rapidly follow changes in natural irradiance (from 200 to 1000 μmol photons m−2 s−1 within 2 h). As a consequence, daily production rates varied by a factor of 2 (from 150 and 260 μg C cm−2 d−1) depending on the irradiance received. Under high irradiance levels, corals can suffer from photoinhibition (light-induced reduction in the photosynthetic capacity), especially temperate species, which do not experience high irradiance levels most of the year. However, in C. caespitosa, photoinhibition at irradiances higher than 1000 μmol photons m−2 s−1 was reduced as a result of the involvement of the xanthophyll cycle, with a degree comparable to those measured for tropical species (de-epoxidation ratio of 0.12), that allowed C. caespitosa to maintain high production rates and a maximal autotrophic carbon acquisition during sunny days. However, as soon as irradiance conditions decreased below 200 μmol photons m−2 s−1 because of cloudy weather, autotrophically acquired carbon could not sustain respiratory needs, indicating that C. caespitosa has to rely on other sources, such as heterotrophy, to meet its energetic needs.
Time series on the leaf biometry and rhizome production of the endemic Mediterranean seagrass Posidonia oceanica (L.) Delile were investigated in a meadow of the Ligurian Sea (NW Mediterranean) in ...order to assess changes in the plant growth during a massive flowering event occurred in 2003, in coincidence with the warmest summer temperatures recorded in the last centuries. P. oceanica exhibited the highest values of leaf surface area during the flowering year and the highest values of rhizome production in the previous year. The years immediately following the flowering event were characterized by a decrease in both parameters. Comparison of the years of massive flowering events reported in the literature at the whole Mediterranean-wide spatial scale with the historical series (spanning the last 50 years) of the air temperature and of the sunspot number suggested that intense solar activity, and not warmer temperature per se, was likely to be the main trigger of massive flowering events in Posidonia oceanica.
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.
The conservation of the coastal marine environment requires the possession of information that enables the global quality of the environment to be evaluated reliably and relatively quickly. The use ...of biological indicators is often an appropriate method. Seagrasses in general, and
Posidonia oceanica meadows in particular, are considered to be appropriate for biomonitoring because of their wide distribution, reasonable size, sedentary habit, easy collection and abundance and sensitivity to modifications of littoral zone. Reasoned management, on the scale of the whole Mediterranean basin, requires standardized methods of study, to be applied by both researchers and administrators, enabling comparable results to be obtained. This paper synthesises the existing methods applied to monitor
P. oceanica meadows, identifies the most suitable techniques and suggests future research directions. From the results of a questionnaire, distributed to all the identified laboratories working on this topic, a list of the most commonly used descriptors was drawn up, together with the related research techniques (e.g. standardization, interest and limits, valuation of the results). It seems that the techniques used to study meadows are rather similar, but rarely identical, even though the various teams often refer to previously published works. This paper shows the interest of a practical guide that describes, in a standardized way, the most useful techniques enabling
P. oceanica meadows to be used as an environmental descriptor. Indeed, it constitutes the first stage in the process.
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