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Correlations between solar radiation, sea surface temperature (SST), biometry, and population density were assessed along a wide latitudinal gradient in the non-zooxanthellate solitary coral Caryophyllia inornata. Biometric parameters were more strongly correlated with temperature than with solar radiation as in previous studies on Mediterranean solitary corals. With increasing SST, populations were characterized by bigger polyps, and consequently by a higher percent area coverage and mass per square meter. Population abundance was not correlated with SST, similarly to the non-zooxanthellate solitary Leptopsammia pruvoti. Instead, the population density of the zooxanthellate solitary Balanophyllia europaea decreases with increasing SST. When extrapolating the relationships between biological parameters of the three species and SST, according to the projected seawater temperature increase, a higher tolerance to temperature for non-zooxanthellate species seems to be confirmed

Massive, long-lived deep-sea red tree corals (Primnoa pacifica) form a solid, layered axis comprised of calcite and gorgonin skeleton. They are abundant on the outer continental shelf and upper slope of the Northeast Pacific, providing habitat for fish and invertebrates. Yet, their large size and arborescent morphology makes them susceptible to disturbance from fishing activities. A better understanding of their growth patterns will facilitate in-situ estimates of population age structure and biomass. Here, we evaluated relationships between ages, growth rates, gross morphological characteristics, and banding patterns in 11 colonies collected from depths of ~141–335 m off the Alaskan coast. These corals ranged in age from 12 to 80 years old. They grew faster radially (0.33–0.74 mm year-1) and axially (2.41–6.39 cm year-1) than in previously measured older colonies, suggesting that growth in P. pacifica declines slowly with age, and that basal diameter and axial height eventually plateau. However, since coral morphology correlated with age in younger colonies (< century), we developed an in-situ age estimation technique for corals from the Northeast Pacific Ocean providing a non-invasive method for evaluating coral age without removing colonies from the population. Furthermore, we determined that annual bands provided the most accurate means for determining coral age in live-collected corals, relative to radiometric dating. Taken together, this work provides insight into P. pacifica growth patterns to inform coastal managers about the demographics of this ecologically important species. With this new ability to estimate the age of red tree corals in-situ, we can readily determine the age-class structure and consequently, the maturity status of thickets, using non-invasive video survey techniques when coupled with mensuration systems such as lasers or stereo-cameras. Enhanced surveys could identify which populations are most vulnerable to disturbance from human activities, and which should be highlighted for protection.

The coral Astroides calycularis (Scleractinia: Dendrophylliidae) is endemic to the Mediterranean Sea (Terrón‐Sigler et al. 2016), where it can be reef forming (Musco et al. 2017: Fig. 1). In shallow water, it may cover up to 90% of rocky substrate from the surface down to 15 m depth where it is found in caves and on vertical walls. Astroides calycularis colonies frequently occur in dense aggregations (Goffredo et al. 2011), possibly favored by limited dispersion ability of both sexual (Goffredo et al. 2010) and asexual propagules (Serrano et al. 2017). High water movement promotes massive colony shapes with closely connected polyps usually forming continuous orange surfaces, leaving little space for the settlement of other benthic organisms (Casado‐Amezua et al. 2013). Astroides calycularis is “polystomatous,” forming small colonies composed of polyps connected to each other as a single organism bearing several mouths. Colony morphology is also strongly controlled by food availability (Goffredo et al. 2011). Polyps are typically 4–5 mm in length but larger polyps can grow up to 8 mm long. Like other azooxanthellate corals, A. calycularis is an obligate suspension feeder (Cebrian and Ballesteros 2004) and it is assumed to feed primarily on zooplankton transported by water movement, although the identity of its most preferred prey is unknown.

Shallow-water corals of the Mediterranean Sea are facing a dramatic increase in water temperature due to climate change, predicted to increase the frequency of bleaching and mass mortality events. However, supposedly not all corals are affected equally, as they show differences in stress susceptibility, as suggested by physiological outputs of corals along temperature gradients and under controlled conditions in terms of reproduction, demography, growth, calcification, and photosynthetic efficiency. In this study, gene expression and induction of a 70-kDa heat shock protein (HSP70) was analyzed in five common shallow-water hard corals in the Mediterranean Sea, namely Astroides calycularis, Balanophyllia europaea, Caryophyllia inornata, Cladocora caespitosa, and Leptopsammia pruvoti. The main aim was to assess the contribution of this evolutionary conserved cytoprotective mechanism to the physiological plasticity of these species that possess different growth modes (solitary vs colonial) and trophic strategies (zooxanthellate vs azooxanthellate). Using quantitative real-time PCR, in situ hsp70 baseline levels and expression profiles after a heat-shock exposure were assessed.Levels of hsp70 and heat stress induction were higher in zooxanthellate than in azooxanthellate species, and different heat stress transcriptional profiles were observed between colonial and solitary zooxanthellate corals. On the whole, the hsp70 transcriptional response to heat stress aligns with stress susceptibility of the species and suggests a contribution of trophic strategy and morphology in shaping coral resilience to stress. Understanding these molecular processes may contribute to assess the potential effects and relative resilience of Mediterranean corals under climate change. published

The intra-skeletal fatty acid concentration and composition of four Mediterranean coral species, namely Cladocora caespitosa, Balanophyllia europaea, Astroides calycularis and Leptopsammia pruvoti, were examined in young and old individuals living in three different locations of the Mediterranean Sea. These species are characterized by diverse levels of organization (solitary or colonial) and trophic strategies (symbiotic or non-symbiotic). Fatty acids have manifold fundamental roles comprehensive of membrane structure fluidity, cell signaling and energy storage. For all species, except for B. europaea, the intra-skeletal fatty acid concentration was significantly higher in young individuals than in old ones. Moreover, fatty acid concentration was higher in colonial corals than in solitary ones and in the symbiotic corals compared to non-symbiotic ones. Analysis by gas chromatography-mass spectrometry (GC-MS) revealed that palmitic acid (16:0) was the most abundant fatty acid, followed by stearic (18:0) in order of concentration. Oleic acid (18:1) was detected as the third main component only in skeletons from symbiotic corals. These results suggest that, in the limits of the studied species, intra-skeletal fatty acid composition and concentration may be used for specific cases as a proxy of level of organization and trophic strategy, and eventually coral age.

Ocean acidification is predicted to impact ecosystems reliant on calcifying organisms, potentially reducing the socioeconomic benefits these habitats provide. Here we investigate the acclimation potential of stony corals living along a pH gradient caused by a Mediterranean CO2 vent that serves as a natural long-term experimental setting. We show that in response to reduced skeletal mineralization at lower pH, corals increase their skeletal macroporosity (features >10 μm) in order to maintain constant linear extension rate, an important criterion for reproductive output. At the nanoscale, the coral skeleton's structural features are not altered. However, higher skeletal porosity, and reduced bulk density and stiffness may contribute to reduce population density and increase damage susceptibility under low pH conditions. Based on these observations, the almost universally employed measure of coral biomineralization, the rate of linear extension, might not be a reliable metric for assessing coral health and resilience in a warming and acidifying ocean., Global warming and ocean acidification impact coral ecosystems. Here, the authors show higher skeletal porosity and reduced bulk density at lower pH in corals living along a natural pH gradient in the Mediterranean, which may contribute to reduce population density and increase damage susceptibility.