Martina Canessa

Early life stages play a key role in structuring marine benthic communities, yet the mechanisms controlling recruitment in confined habitats remain poorly understood. In particular, the...

Alcyonium coralloides has traditionally been classified as an opportunistic epibiont of exposed gorgonian skeletons. However, the ecological nature of its interaction remains poorly understood. Using Marine Strategy Framework Directive (MSFD) monitoring data (2015–2025) across 310 ROV transects (30–100 m depth) along the Ligurian coast (NW Mediterranean Sea) and long-term photographic series of infested colonies from the Tavolara–Punta Coda Cavallo MPA (Sardinia, NW Mediterranean Sea), we investigated its distribution and host associations in the NW Mediterranean. A. coralloides occurred in ~50% of the surveyed gorgonian forests, significantly increasing with host density. Infestation rates were markedly higher on Eunicella cavolini (10.1 ± 4.2%) than on Paramuricea clavata, E. verrucosa, and Leptogorgia sarmentosa (1.5–1.9%). While host necrosis facilitates initial settlement, time-series data revealed rapid overgrowth rates (30–55 cm yr⁻¹) along host branches. Direct contact zones between the coenenchimes of the epibiont and that of the host exhibited portions of denuded host skeletons, hypertrophic tissue borders, and reduced host polyp expansion adjacent to the advancing parasitic margin. These results indicate that the ecological interaction extends beyond simple opportunistic epibiosis. We propose that A. coralloides represents an intermediate stage along a continuum between epibiosis and active spatial competition, shaping community dynamics within Mediterranean animal forests.

Cladocora caespitosa is an endemic hermatypic scleractinian in the Mediterranean Sea, currently threatened by both environmental and anthropogenic pressures, whereas Oculina patagonica is a cryptogenic hermatypic scleractinian that is expanding across the basin. This study provides the first assessment of co-occurring natural populations of these shallow-water taxa, examining their population structures, habitat preferences, and responses to environmental stressors based on SCUBA surveys conducted in the summers and autumns of 2022 and 2023. Both species were dominated by medium- to large-sized colonies, indicating relatively stable population structures, with C. caespitosa exhibiting significantly higher densities than O. patagonica. Both scleractinians showed a preference for sub-vertical and vertical rocky substrates, although O. patagonica appeared more tolerant of horizontal surfaces. Disease events were more frequent and severe in C. caespitosa, particularly affecting larger colonies during autumn 2022, whereas O. patagonica showed lower incidence and greater resilience overall. Temporal comparisons suggest that O. patagonica may act as a strong competitor to C. caespitosa; however, both species demonstrate a considerable capacity for recovery, likely due to adaptation to high-stress environments. These findings highlight key differences in ecological strategies and vulnerability to environmental stressors, emphasizing the need for targeted conservation approaches to preserve Mediterranean shallow-water coral communities under accelerating climate change.

Savalia savaglia is one of the few zoantharians capable to grow with a parasitic habitus, infesting damaged gorgonians, such as Eunicella spp., Paramuricea sp., Leptogorgia spp., and antipatharians. It causes tissue necrosis in its hosts and progressively overgrows their skeleton with its own coenenchyme. While previous studies have mainly focused on its distribution, biology, ecology, and conservation, little information is available about its growth patterns and ecological interaction with other benthic organisms. A photographic monitoring of the same S. savaglia specimen over time (2018 and 2025) was carried out within the C zone of the Tavolara—Punta Coda Cavallo Marine Protected Area (NE Sardinia, Tyrrhenian Sea). The image analysis revealed a progressively overgrown of this colony by the encrusting orange sponge Crambe crambe observed. After seven years, the covered portion increased of about 185 cm2 y ^-1 . The case here described represents the first documented instance of S. savaglia losing a competitive interaction with another benthic organism, indicating that the latter is not always a winner. Probably, the sponge’s aptitude to spatial competition and environmental tolerance facilitates its expansion at the expense of S. savaglia, particularly when the latter’s colony integrity is already compromised or exhibits reduced resilience to disturbance.

The gold coral Savalia savaglia parasitizes gorgonians in coralligenous habitats, causing tissue necrosis in its hosts and overgrowing their skeletons with its coenenchyme. While previous studies have mainly focused on its distribution, biology, ecology, and conservation, limited information is available about its skeletal architecture and growth patterns. Photographic observations of the same specimens over time revealed that S. savaglia grows rapidly during early colonization, slowing once the host is completely overgrown. In the Tavolara Channel (NE Tyrrhenian Sea), large, old dead specimens—radiocarbon-dated to approximately 800 years—resulted from the coalescence of several colonies, highlighting their evolution over a long timescale. Colonies merge when trunks or apical branches come into contact, forming polygonal meshes. Scanning Electron Microscopy (SEM) analysis revealed a laminar skeletal structure covered with small blunt spines, resembling those observed in antipatharians. These spines cement adjacent layers, increasing the skeleton’s resistance to currents and affecting its susceptibility to mechanical damage. These findings support early descriptions by H. Lacaze-Duthiers in the 18th century. Chemical analysis revealed the presence of 7% chitin in the skeleton, along with a high protein content.