Shallow-buried Pleistocene Madrepora-dominated coral mounds on a muddy continental slope, Tuscan Archipelago, NE Tyrrhenian Sea

Subfossil azoxanthellate deep-sea coral mounds occur at 355–410 m on the continental slope of the NE Tyrrhenian Sea between Gorgona and Capraia islands, Tuscan Archipelago. These low-relief patch reefs are at present buried by a thin muddy drape. Their age is latest Pleistocene. The colonial scleractinian Madrepora oculata is the major frame builder, in association with the solitary coral Desmophyllum dianthus and the colonial coral Lophelia pertusa. These NE Tyrrhenian Madrepora-dominated coral mounds represent one of the few known Mediterranean examples of deep-coral colonization of a muddy, low-gradient continental slope.     

First geo-marine survey of living cold-water Lophelia reefs in the Ionian Sea (Mediterranean basin)

Abstract Prosperous deep coral mounds including living colonies of Lophelia pertusa together with Madrepora oculata and Desmophyllum dianthus (= D. cristagalli) have been discovered in 2000, by fishery operations on the eastern side of the Ionian Sea. The living coral mounds are located between ca. 300 and 1,100 m on a gently dipping shelf off Apulia at Santa Maria di Leuca (SML), and characterized by a complex seabed topography. Side scan sonar, shallow high-resolution seismics and sampling indicate that these Lophelia-bearing coral mounds colonize quasi-indurate (firmground) Pleistocene sediment. At places live corals were found on Pleistocene coral-hardgrounds. The fauna associated with these Ionian modern coral mounds is less diversified than modern Eastern Atlantic counterparts. The core of living coral mounds colonies is at present located in 500–700 m and is tentatively suggested that their survival is mostly controlled by oceanographic factors. The SML coral banks represent so far a unique example of living Lophelia-bearing coral mounds in the Mediterranean basin.This revised version was published online in January 2005 with corrections to the author name and figure captions 4 and 5.     

Fossil analogues of present-day Cladocora caespitosa coral banks: Sedimentary setting, dwelling community, and taphonomy (Late Pliocene, W Mediterranean)

 Cladocora caespitosa is a common zooxanthellate, ahermatypic, constructional scleractinian coral in shallow waters of the present-day Mediterranean. Extensive coral banks in Upper Pliocene shallow marine deposits of the Almería-Níjar Basin (SE Spain) contain the same species. These banks occur on debris-flow conglomerates deposited in a fan delta, or on bioclastic accumulations interpreted as storm deposits. Direct relationships of coral beds with coastal facies indicate that C. caespitosa colonized shallow settings near the paleocoast, probably not deeper than 20–30 m. Low turbulence allowed corals to colonize substrates, which remained stable for long periods. Activity of organisms in the coral community, storms, and detritic discharges from the fan delta were the most significant mechanisms disturbing the coral development. The hard substrata provided by coral banks promoted colonization by cemented and epibyssate organisms. Coral banks marked maximum flooding surfaces at the end of transgressive systems tracks. They were suddenly buried by sediment input into the basin. Taphonomic signatures measured on components of the coral bank communities indicate a low turbulence environment, probably a bay. The low hydraulic energy further inhibited post-burial reworking, thus promoting the in situ preservation of a great part of the organisms inhabiting the bioconstructions. Accepted: 2 December 1997     

Desmophyllum dianthus (Esper, 1794) in the Scleractinian Phylogeny and Its Intraspecific Diversity

The cosmopolitan solitary deep-water scleractinian coral Desmophyllum dianthus (Esper, 1794) was selected as a representative model species of the polyphyletic Caryophylliidae family to (1) examine phylogenetic relationships with respect to the principal Scleractinia taxa, (2) check population structure, (3) test the widespread connectivity hypothesis and (4) assess the utility of different nuclear and mitochondrial markers currently in use. To carry out these goals, DNA sequence data from nuclear (ITS and 28S) and mitochondrial (16S and COI) markers were analyzed for several coral species and for Mediterranean populations of D. dianthus. Three phylogenetic methodologies (ML, MP and BI), based on data from the four molecular markers, all supported D. dianthus as clearly belonging to the “robust” clade, in which the species Lophelia pertusa and D. dianthus not only grouped together, but also shared haplotypes for some DNA markers. Molecular results also showed shared haplotypes among D. dianthus populations distributed in regions separated by several thousands of kilometers and by clear geographic barriers. These results could reflect limited molecular and morphological taxonomic resolution rather than real widespread connectivity. Additional studies are needed in order to find molecular markers and morphological features able to disentangle the complex phylogenetic relationship in the Order Scleractinia and to differentiate isolated populations, thus avoiding the homoplasy found in some morphological characters that are still considered in the literature.     

Solenosmilia variabilis-bearing cold-water coral mounds off Brazil

Coral Reefs - Cold-water corals (CWC), dominantly Desmophyllum pertusum (previously Lophelia pertusa), and their mounds have been in the focus of marine research during the last two decades;...     

Regional genetic differentiation among populations of Cladocora caespitosa in the Western Mediterranean

Cladocora caespitosa is the only reef-forming zooxanthellate scleractinian in the Mediterranean Sea. This endemic coral has suffered severe mortality events at different Mediterranean sites owing to anomalous summer heat waves related to global climate change. In this study, we assessed genetic structure and gene flow among four populations of this species in the Western Mediterranean Sea: Cape Palos (SE Spain), Cala Galdana (Balearic Islands), Columbretes Islands, and L’Ametlla (NE Spain). The results obtained from Bayesian approaches, F _ST statistics, and Bayesian analysis of migration rates suggest certain levels of genetic differentiation driven by high levels of self-recruitment, a fact that is supported by egg-retention mechanisms. Conversely, genetic connectivity among distant populations, even if generally low, seems to be related to sporadic dispersal events through regional surface currents linked to the spawning period that occurs at the end of summer-beginning of autumn. These features, together with a certain isolation of the Columbretes Islands, could explain the regional genetic differentiation found among populations. These results help to better understand population structure and connectivity of the species and will serve as an approach for further studies on different aspects of the biology and ecology of C. caespitosa.     

The impact of seawater temperature on coral growth parameters of the colonial coral Cladocora caespitosa (Anthozoa, Scleractinia) in the eastern Adriatic Sea

The scleractinian coral Cladocora caespitosa deserves a special place among the major carbonate bioconstructors of the Mediterranean Sea. Annual coral skeleton growth, coral calcification, and skeleton density of the colonial coral C. caespitosa taken from 25 locations in the eastern Adriatic Sea were analyzed and compared with annual sea surface temperatures (SST). The growth rates of the coral C. caespitosa from the 25 stations in the Adriatic Sea ranged from 1.92 to 4.19?mm per year, with higher growth rates of the investigated corallites in the southern part of the Adriatic Sea. These growth rates are similar to those measured in other areas of the Mediterranean Sea. The correlation between coral growth and sea temperatures in the Adriatic Sea is seen as follows: An X-radiograph analysis of coral growth in C. caespitosa colonies that are over 60?years old showed that higher growth rates of this coral coincided with a warmer period in the Mediterranean Sea. A positive significant correlation exists between corallite growth rates and SST and coral calcification and SST. A negative correlation exists between coral density and SST. Coral growth rates also showed a correlation with higher eutrophication caused by nearby fish farms, along with a greater depth of the investigated colonies and high bottom currents.     

Pleistocene to Recent scleractinian deep-water corals and coral facies in the Eastern Mediterranean

Recent investigations of the Eastern Mediterranean Sea carried out during the GECO cruise with RV Urania provided a substantial number of new cold-water coral (CWC) records, including branching and solitary scleractinian species. These new sites are located along steep escarpments and on topographic highs along the margins of Crete, Karpathos, and Rhodes. The majority of the corals represent fossil occurrences, predominantly Late Pleistocene assemblages. Our research documents that the Eastern Mediterranean Basin has been colonized by CWC at favorable times during the Last Glacial, in particular during the Younger Dryas. Schizocyathus fissilis is reported for the first time for the Mediterranean, while the finding of Ceratotrochus magnaghii represents the first record for the Eastern Mediterranean. Various coral facies occur on the southerly island slopes of Crete, Karpathos, and Rhodes, including hardgrounds and loose skeletal sediments. Hardgrounds occur on steep topographies between ca. 500 and 1,700 m, and can conveniently be subdivided as (1) Neopycnodonte-Desmophyllum framestone, (2) Desmophyllum-Caryophyllia framestone, (3) Madrepora-Lophelia rudstone, (4) Pelagic mudstone and wackestone, and (5) Siliciclastic-carbonate conglomerate and breccia. Unconsolidated skeletal sediments containing corals mainly occur on gentler topographic situations between ca. 140 and 600 m and can be subdivided as: (A) Lophelia-Madrepora rubble, (B) Dendrophyllia rubble, (C) Stenocyathus rubble, (D) Caryophyllia calveri rubble, and (E) fine-grained sediment with octocoral axes. Many of these facies types are also present in the western part of the Mediterranean and have fossil representatives from the Pleistocene to the Recent. Radiocarbon dating (AMS-¹⁴C) reveals Younger Dryas ages between 12.4 and 12.0 ka cal BP for Lophelia pertusa and Madrepora oculata. Desmophyllum dianthus occurs during the Last Glacial Maximum (21.8 ka cal BP) and the Younger Dryas (11.7 ka cal BP), as well as during the Late Holocene and subrecent times (4.4?C0.6 ka cal BP). Caryophyllia sarsiae occurs during the Late Glacial (15.5 ka cal BP), while Caryophyllia calveri occurs during the Early Preboreal (10.8 ka cal BP). The ages for the framework-constructing corals L. pertusa and M. oculata are coherent with their temporal predominance during the Younger Dryas in other parts of the Mediterranean.     

Effects of temperature, light and heterotrophy on the growth rate and budding of the temperate coral Cladocora caespitosa

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.     

Vibrio communities in scleractinian corals differ according to health status and geographic location in the Mediterranean Sea

The increase in seawater temperature associated with global warming is a significant threat to coral health and is linked to increasing mass mortality events and Vibrio-related coral diseases. In the Mediterranean Sea, the endemic Cladocora caespitosa and the invasive species Oculina patagonica are the main scleractinian corals affected by mass mortalities. In this study, culturable Vibrio spp. assemblages associated with healthy and unhealthy colonies of these two shallow coral species were characterized to assess the presence of Vibrio pathogens in tissue necrosis. Vibrio communities associated with O. patagonica and C. caespitosa showed geographical differences, although these became more homogeneous in unhealthy specimens of both species. Furthermore, the number of recovered Vibrio specimens was more than five times higher in unhealthy than in healthy corals. Within these culturable vibrios, the known pathogens Vibrio mediterranei and Vibrio coralliilyticus were present in unhealthy colonies of both coral species in the two localities, suggesting that they could play a role in the health status of C. caespitosa and thus act as generalist pathogens in Mediterranean corals. Nonetheless, a clonal type of V. coralliilyticus detected in C. caespitosa was not associated with disease signs, suggesting that this species could encompass assemblages with different levels of virulence.     

High thermal tolerance of two Mediterranean cold-water coral species maintained in aquaria

In the Mediterranean deep-sea, scleractinian cold-water corals (CWC) are observed to survive at the uppermost end of their presumed thermal distribution range (4–13 °C). Here, we show that 2 common CWC species (i.e. Dendrophyllia cornigera and Desmophyllum dianthus) maintained in aquaria can indeed tolerate considerably elevated seawater temperatures (17.5 ± 0.1 °C), while growing at similar (D. dianthus) or significantly higher (D. cornigera) rates than conspecifics cultured in parallel for 87 days at ambient Mediterranean deep-sea temperature (12.5 ± 0.1 °C). Neither differences in coral appearance nor mortality were evident for both species at either temperature. D. dianthus grew significantly faster (0.23 ± 0.08 % day^?1) than D. cornigera (0.05 ± 0.01 % day^?1) under ambient thermal conditions. Growth of D. cornigera increased significantly (0.14 ± 0.07 % day^?1) at elevated temperature, while Desmophyllum dianthus growth showed no significant difference under both conditions. These findings suggest that D. dianthus and D. cornigera may be capable of surviving in warmer environments than previously reported, and thus challenge temperature as the paramount limiting environmental factor for the occurrence of some CWC species.     

The ecology of the Mediterranean stony coral Cladocora caespitosa (Linnaeus, 1767) in the Gulf of Trieste (northern Adriatic Sea): a 30-year long story

Cladocora caespitosa is an endemic coral of the Mediterranean Sea and an important carbonate bioconstructor that adds 3D complexity to the habitat, thus increasing marine biodiversity. Despite its important role in the ecosystem, the real status of the population along most of the Mediterranean coastline is still poorly investigated and very little is known about the resilience of the species. Using non-destructive visual surveys, colonies of C. caespitosa were investigated by SCUBA diving in 2013 and 2015 at seven sites of the northern Adriatic Sea (southern part of the Gulf of Trieste). Data about colony size, index of sphericity and corallite diameter were collected. Almost all biometrical parameters differed significantly among sampling sites, showing low occurrence of the larger size classes compared to the abundance of small-sized colonies. This pattern of distribution is typical of long-lived organisms. The positively skewed colony size distribution could be due to both a high mortality rate of small colonies unable to reach larger size classes, and to a high fragmentation rate of colonies, related to a strong hydrodynamic forces. The northern Adriatic population of C. caespitosa has previously been investigated by Schiller, who reported size and abundance data of colonies from one site, at a depth range of 2–5?m. We compared these data with our findings from the same sampling site, adding new information about the ecology of C. caespitosa. After a 30-year period, the comparison shows a change in the size distribution of colonies, with a decrease of the small class and an increase of the medium class of colonies. In view of these conclusions, further assessments are required in order to evaluate the trend of the northernmost C. caespitosa population in the Mediterranean Sea.     

Hidden impacts of ocean acidification to live and dead coral framework

Cold-water corals, such as Lophelia pertusa, are key habitat-forming organisms found throughout the world''s oceans to 3000 m deep. The complex three-dimensional framework made by these vulnerable marine ecosystems support high biodiversity and commercially important species. Given their importance, a key question is how both the living and the dead framework will fare under projected climate change. Here, we demonstrate that over 12 months L. pertusa can physiologically acclimate to increased CO₂, showing sustained net calcification. However, their new skeletal structure changes and exhibits decreased crystallographic and molecular-scale bonding organization. Although physiological acclimatization was evident, we also demonstrate that there is a negative correlation between increasing CO₂ levels and breaking strength of exposed framework (approx. 20–30% weaker after 12 months), meaning the exposed bases of reefs will be less effective ‘load-bearers’, and will become more susceptible to bioerosion and mechanical damage by 2100.     

Discordant coral–symbiont structuring: factors shaping geographical variation of Symbiodinium communities in a facultative zooxanthellate coral genus,Oculina

Understanding the factors that help shape the association between corals and their algal symbionts, zooxanthellae (Symbiodinium), is necessary to better understand the functional diversity and acclimatization potential of the coral host. However, most studies focus on tropical zooxanthellate corals and their obligate algal symbionts, thus limiting our full comprehension of coral–algal symbiont associations. Here, we examine algal associations in a facultative zooxanthellate coral. We survey the Symbiodinium communities associated with Oculina corals in the western North Atlantic and the Mediterranean using one clade-level marker (psbA coding region) and three fine-scale markers (cp23S–rDNA, b7sym15 flanking region, and b2sym17). We ask whether Oculina spp. harbor geographically different Symbiodinium communities across their geographic range and, if so, whether the host’s genetics or habitat differences are correlated with this geographical variation. We found that Oculina corals harbor different Symbiodinium communities across their geographical range. Of the habitat differences (including chlorophyll a concentration and depth), sea surface temperature is better correlated with this geographical variation than the host’s genetics, a pattern most evident in the Mediterranean. Our results suggest that although facultative zooxanthellate corals may be less dependent on their algal partners compared to obligate zooxanthellate corals, the Symbiodinium communities that they harbor may nevertheless reflect acclimatization to environmental variation among habitats.

     

The Biology of Lophelia pertusa (Linnaeus 1758) and Other Deep-Water Reef-Forming Corals and Impacts from Human Activities.

Over the last twenty years, human exploitation has begun to have an impact in the deep sea, especially in the upper bathyal zone. This has mainly taken the form of deep-sea fishing but more recently oil exploration has extended beyond the continental shelf. Deep-water coral reefs occur in the upper bathyal zone throughout the world. These structures, however, are poorly studied with respect to their occurrence, biology and the diversity of the communities associated with them. In the North-East Atlantic the coral Lophelia pertusa has frequently been recorded. The present review examines the current knowledge on L. pertusa and discusses similarities between its biology and that of other deep-water, reef-forming, corals. It is concluded that L. pertusa is a reef-forming coral that has a highly diverse associated fauna. Associated diversity is compared with that of tropical shallow-water reefs. Such a highly diverse fauna may be shared with other deep-water, reef-forming, corals though as yet many of these are poorly studied. The main potential threats to L. pertusa in the North-East Atlantic are considered to be natural phenomena, such as slope failures and changes in ocean circulation and anthropogenic impacts such as deep-sea fishing and oil exploration. The existing and potential impacts of these activities on L. pertusa are discussed. Deep-sea fishing is also known to have had a significant impact on deep-water reefs in other parts of the world.     

A new laboratory method for monitoring deep-water coral polyp behaviour

Deep-water corals are found along the oceanic margins world-wide and in the north east Atlantic the most abundant species is Lophelia pertusa (L.). There is now growing evidence that deep-water reefs formed by such species are coming under increasing pressures from resource exploitation, principally deep-sea trawling and hydrocarbon exploration. Here a novel and unobtrusive method of recording deep-water coral behaviour in the laboratory is described using time-lapse video to record silhouettes of the polyps under infrared illumination. The polyps of L. pertusa behaved asynchronously and did not show any clear diurnal patterns over a three-day observation period. Conceptually, sessile benthic suspension feeders appear to be vulnerable to smothering by sediments disturbed by bottom trawls or sub-seabed drilling. This method allows deep-water coral polyp behaviour to be continuously monitored in the laboratory and, therefore, the responses of coral polyps to environmental perturbations such as sedimentation can be recorded. Further work is necessary to resolve the sensitivity of deep-water corals to short-term environmental change and the combined approach of in situ monitoring and subsequent laboratory experimentation has great potential to address these issues.     

Inferred calcification rate of a Mediterranean azooxanthellate coral is uncoupled with sea surface temperature along an 8° latitudinal gradient

Introduction

Correlations between sea surface temperature (SST) and growth parameters of the solitary azooxanthellate Dendrophylliid Leptopsammia pruvoti were assessed along an 8° latitudinal gradient on western Italian coasts (Mediterranean Sea), to check for possible negative effects of increasing temperature as the ones reported for a closely related, sympatric but zooxanthellate species.

Results

Calcification rate was correlated with skeletal density but not with linear extension rate, indicating that calcium carbonate deposition was preferentially allocated to keep a constant skeletal density. Unlike most studies on both temperate and tropical zooxanthellate corals, where calcification rate is strongly related to environmental parameters such as SST, in the present study calcification rate was not correlated with SST.

Conclusions

The lower sensitivity of L. pruvoti to SST with respect to other sympatric zooxanthellate corals, such as Balanophyllia europaea, may rely on the absence of a temperature induced inhibition of photosynthesis, and thus the absence of an inhibition of the calcification process. This study is the first field investigation of the relationship between SST and the three growth parameters of an azooxanthellate coral. Increasing research effort on determining the effects of temperature on biological traits of the poorly studied azooxanthellate scleractinians may help to predict the possible species assemblage shifts that are likely to occur in the immediate future as a consequence of global climatic change.

     

First Evidence of an Important Organic Matter Trophic Pathway between Temperate Corals and Pelagic Microbial Communities

Mucus, i.e., particulate and dissolved organic matter (POM, DOM) released by corals, acts as an important energy carrier in tropical ecosystems, but little is known on its ecological role in temperate environments. This study assessed POM and DOM production by the temperate coral Cladocora caespitosa under different environmental conditions. The subsequent enzymatic degradation, growth of prokaryotes and virus-like particles (VLPs) as well as changes in the structure of the prokaryotic communities were also monitored. C. caespitosa produced an important quantity of mucus, which varied according to the environmental conditions (from 37.8 to 67.75 nmol carbon h^-1 cm^-2), but remained higher or comparable to productions observed in tropical corals. It has an important nutritional value, as highlighted by the high content in dissolved nitrogen (50% to 90% of the organic matter released). Organic matter was rapidly degraded by prokaryotes’ enzymatic activities, and due to its nitrogen content, aminopeptidase activity was 500 fold higher than the α-glucosidase activity. Prokaryotes, as well as VLPs, presented a rapid growth in the mucus, with prokaryote production rates as high as 0.31 μg h^-1 L^-1. Changes in bacterial and archaeal communities were observed in the ageing mucus and between mucus and the water column, suggesting a clear impact of mucus on microorganism diversity. Overall, our results show that the organic matter released by temperate corals, such as C. caespitosa, which can form reef structures in the Mediterranean Sea, stimulates microbial activity and thereby functions as a significant carbon and nitrogen supplier to the microbial loop.     

Characterization of 10 microsatellite loci for the deep‐sea coral Lophelia pertusa (Linnaeus 1758)

The scleractinian coral, Lophelia pertusa, is distributed globally on continental slopes, mid‐oceanic ridges and in fjords. This species forms cold‐water reefs, which are associated with a diverse animal community. These communities are poorly understood but are currently under threat from human activities. Molecular markers are required to assess the spatial genetic population structure of this key species for management and conservation purposes. Ten polymorphic microsatellite loci were isolated for Lophelia pertusa using an enriched partial library technique. Nine loci showed significant differences from Hardy–Weinberg expected genotype frequencies, eight of which showed heterozygote deficiencies.     

Spawning of the colonial coral <Emphasis Type="Italic">Cladocora caespitosa</Emphasis> (Anthozoa,Scleractinia) in the Southern Adriatic Sea

Data on sexual reproduction of scleractinian coral species living in temperate zones, particularly in the Mediterranean Sea, are quite scarce. This paper describes sexual reproduction of the colonial coral Cladocora caespitosa from Veliko jezero (Mljet Island) in the Adriatic Sea. Spawned orange eggs and white sperm bundles were observed on the coral bank of C. caespitosa two nights before the full moon (20 June 2005) coinciding with increasing water temperature and correlated with the lunar cycle. Spawning was observed during five nights, involving about 30% of the colonies from the coral bank. Different colonies on the bank released only one type of gamete during the reproductive period. The diameter of the sperm bundles ranged from 100 to 200 μm (average 163 μm; SD = 47.08), while the female gametes diameter ranged from 300 to 500 μm (average 416 μm; SD = 73.12).