What’s the key for success? Translocation, growth and thermal stress mitigation in the Mediterranean coral Cladocora caespitosa (Linnaeus, 1767)

Abstract

Marine heat waves (MHWs) are affecting corals populations, advocating their inclusion in restoration actions since conservation measures may be not sufficient. Cladocora caespitosa is a Mediterranean reef-building, long-living species, with low recruitment rate and high juvenile mortality, leading to the need for its inclusion in international and European legislations. The aim of this study, conducted in the southern Tyrrhenian Sea, was to test the translocation of several C. caespitosa colonies thriving on an artificial substrate intended for demolition, applying transplantation techniques. Thirty-four colonies were transplanted in May 2018, and monitored over 4 years, to check for their persistence and health status. The shaded position of the recipient site resulted adequate, considering that colony survival rates were as high as 82.4%, 70.6% and 55.9% in October 2018, January 2020 and October 2022, respectively. Colonies presented signs of suffering only after the high temperatures occurred during summer 2022, with a decreasing rate of -2.5 ± 0.4 corallite/month. To better interpret the documented survival rates, 40 fragments of C. caespitosa were reared in aquaria to test temperature and light effects on growth rates and resistance to thermal stress, simulating a MHW and exacerbating the dim-light natural conditions of the recipient site, exposing half of the fragments to complete darkness. Only bigger fragments produced new corallites, with a rate of 1.3 ± 0.3 corallites/month, like the natural growth rate obtained in the field before the thermal anomaly, highlighting the suitability of ex-situ rearing as a potential tool to supply restoration project. After 5-days at 28.5°C, all fragments survived, despite showing tissue retraction, shorter tentacles, lower responsiveness, and zooxanthellae density variation. Overall, our results highlighted a promising plasticity of C. caespitosa in the field, representing a good candidate for restoration purposes. In aquaria this adaptive potential has been tested on a single genotype and more tests are needed to assess the intraspecific variability of these responses. A first insight into the species-based siting selection was provided to ensure the success of a restoration action. Our results point out the importance of knowing life history traits and ecological optima to design proper management and restoration measures.

Potentialities of the combined use of underwater fluorescence imagery and photogrammetry for the detection of fine-scale changes in marine bioconstructors

“…Photogrammetry and fluorescence imagery data capturing, image enhancement, and strategies for multi-temporal analyses were performed on live colonies of Cladocora caespitosa as a model. This endemic zooxanthellate coral is the most important reef-building species in the Mediterranean (Roveta et al, 2023), and it is included in the Red List of the International Union for the Conservation of Nature (IUCN) as an endangered species (Kersting et al, 2023; https://www.iucnredlist.org/species/133142/ 165739749). Coral fragments were retrieved at San Vito Lo Capo (38°10′N,12°45′E,Trapani,Italy) in September 2021 at 15 m depth, among those naturally detached from the substrate after sea storms.…”

“…First, coral morphology was described based on planar (2D) underwater photos next to a ruler, using an underwater digital camera (Olympus Tough TG-6) (see for example Roveta et al, 2023). The positioning of the corals and the ruler on the same plane requires special attention, to reduce perspective distortions caused by different distances between the two objects and the camera lens.…”

Coastal Biodiversity Assessment Aided by Citizen Science Volunteers: A Look at the Italian Central Adriatic

“…CR, critically endangered; EN, endangered; VU, vulnerable; NT, near threatened; LC, least concern; NE, not evaluated. The Mediterranean Pillow Coral (Cladocora caespitosa Linnaeus, 1767) is an endangered long-lived reef-building species indigenous to the Mediterranean Sea, where it forms scattered colonies, beds, or vast banks [76,77]. Cladocora caespitosa is declining in the Adriatic Sea due to its great sensitivity to pollution [78], invasive algae [79], eutrophication [80], trawling, dredging [81], and climate change.…”

“…Cladocora caespitosa was discovered in the setting of infra-littoral algal biocenosis, providing additional evidence of the presence of the Habitat of European Concern 1170 "Reefs" on several coastal tracts where the habitat had not previously been documented. Moreover, the WCC's new knowledge may enable future scientific campaigns to adequately record and map the Reef EU habitat, updating its distribution range in the Central Adriatic area and extending the execution of necessary conservation actions [77].…”