Medes Islands Research Articles

When resilience is not enough: 2022 extreme marine heatwave threatens climatic refugia for a habitat-forming Mediterranean octocoral.

Climate change is impacting ecosystems worldwide, and the Mediterranean Sea is no exception. Extreme climatic events, such as marine heat waves (MHWs), are increasing in frequency, extent and intensity during the last decades, which has been associated with an increase in mass mortality events for multiple species. Coralligenous assemblages, where the octocoral Paramuricea clavata lives, are strongly affected by MHWs. The Medes Islands Marine Reserve (NW Mediterranean) was considered a climate refugia for P. clavata, as their populations were showing some resilience to these changing conditions. In this study, we assessed the impacts of the MHWs that occurred between 2016 and 2022 in seven shallow populations of the octocoral P. clavata from a Mediterranean Marine Protected Area. The years that the mortality rates increased significantly were associated with the ones with strong MHWs, 2022 being the one with higher mortalities. In 2022, with 50 MHW days, the proportion of total affected colonies was almost 70%, with a proportion of the injured surface of almost 40%, reaching levels never attained in our study site since the monitoring was started. We also found spatial variability between the monitored populations. Whereas few of them showed low levels of mortality, others lost around 75% of their biomass. The significant impacts documented here raise concerns about the future of shallow P. clavata populations across the Mediterranean, suggesting that the resilience of this species may not be maintained to sustain these populations face the ongoing warming trends.

Marine protected areas in a changing ocean: Adaptive management can mitigate the synergistic effects of local and climate change impacts

During the last two decades, several Marine Heatwaves (MHWs) have affected coralligenous assemblages in the Mediterranean Sea, causing catastrophic mass mortalities of several habitat-forming species such as gorgonians, corals, and sponges. Even though Marine Protected Areas (MPAs) are contributing to effectively protect marine ecosystems, the impacts associated to extreme climatic events within MPAs are jeopardizing their protective role. Therefore, minimizing local stressors within MPAs is crucial to minimize interactive effects with global, more difficult to manage, stressors. To address this, we assessed to what extent the regulation of diving frequentation can support more effective protection to climate change, focusing on the case study of the Medes Islands, which has recently suffered the impacts of different global stressors and is one of the most visited MPAs in the Mediterranean Sea. We combined 6 years of demographic data of the red gorgonian Paramuricea clavata with population modelling tools, to explore the long-term viability of this species to different managing schemes and mass mortality events scenarios. Overall, our results show that climate-adaptive management of the recreational diving activity under climate change can enhance the long-term viability of this key Mediterranean habitat-forming octocoral, which is otherwise predicted to go locally extinct at shallow depths (<25 m) within the next 20 years. This study provides one of the few attempts to quantify to what extent an adaptive management scheme may help delay climate change impacts in a Marine Protected Area.

The Moral and Ethical Baseline of Marine Socio-Ecological Values: the Case of Recreational and Artisanal Fishing in NW Mediterranean Coastal Waters (Catalonia, Spain)

Scant attention has been paid to values not expressed in monetary terms, due in part to the difficulty of assessing them. Moreover, the notion and understanding of “value” differs depending on the discipline and academic approaches. This ethnographic study focused on three marine spaces from the Catalonia region in Spain (Natural Park of Cap de Creus, Medes Islands protected area, and Natura 2000 Network area) addresses the competing values of maritime activities, small-scale fishing and recreational fishing, that make value judgements based on moral and ethical standards with which to legitimize activities and use of marine resources. The results highlight the co-existing market and non-market values involved in carrying out these activities, and the need to identify values as drivers of socioecological systems in order to evaluate sustainability. Through the lens of social theory mainly stemming from social anthropology, the study discusses on the moral and ethical issues at play.

Distribution and ten-year temporal trends (2009–2018) of perfluoroalkyl substances in gull eggs from Spanish breeding colonies

Gull eggs are excellent bioindicators of environmental pollution as reflect the contamination levels of coastal areas, especially of persistent and bioacumulative compounds such as perfluoroalkyl substances (PFAS). This study aims to evaluate the geographical distribution and 10-year temporal trends (2009–2018) of 17 PFAS in eggs of two gull species (Larus michahellis and Larus audouinii) from 5 main Spanish colonies. ∑PFAS ranged from 13.7 ± 5.9 to 164 ± 17 ng g−1 wet weight and higher concentrations were observed in L. audouinii than in L. michahellis. Perfluorooctane sulfonate (PFOS) was the predominant compound in all samples, followed by perfluoroundecanoic acid (PFUnA) and perfluorotridecanoic acid (PFTriDA). Perfluorododecanoic acid (PFDoA), perfluorodecanoic acid (PFDA) and perfluorooctanoic acid (PFNA) were also found in all studied areas but at lower concentrations, while perfluorooctanoic acid (PFOA) was only detected in the Medes Islands. Principal Component Analysis revealed the co-occurrence of the 6 detected PFAS, and differentiated samples from Ebro Delta and Medes Islands, both located in the North-Eastern Mediterranean Sea, with high contribution of all PFAS, from Chafarinas and Atlantic Islands with lower concentration levels and variability. Also, different patterns were observed among colonies, suggesting the fish-based diet plays an important role in PFAS bioaccumulation. In all colonies, except for the Medes Islands, ∑PFAS decreased through the 10-year study period, with PFOS, PFUnA, and PFTriDA showing a significant concentration reduction in a colony-specific manner. This study demonstrates the usefulness and importance of continuous systematic long-term monitoring to determine the geographical distribution and temporal variations of PFAS in marine protected areas using gull eggs as bioindicators of environmental pollution.

Ecological traits, genetic diversity and regional distribution of the macroalga Treptacantha elegans along the Catalan coast (NW Mediterranean Sea)

The widespread decline of canopy-forming macroalgal assemblages has been documented in many regions during the last decades. This pattern is often followed by the replacement of structurally complex algal canopies by more simplified habitats (e.g., turfs or sea urchin barren grounds). Against all odds, the fucoid Treptacantha elegans, a large Mediterranean brown macroalga, broadened its depth range to deeper and exposed environments and displayed an unexpected range expansion along the northern coast of Catalonia over the last two decades. Here, we reconstruct the spread of T. elegans in time and space and unravel ecological and demographic traits such as population dynamics and genetic patterns to provide a comprehensive and integrated view of the current status and geographical expansion for this species. Fast-growing dynamics, early fertile maturity, and high turnover rate are the main competitive advantages that allow the exposed populations of T. elegans to colonize available substrata and maintain dense and patchy populations. We also provided evidence that the deeper and exposed populations of T. elegans constitute a single group across the Catalan coast, with little genetic differentiation among populations. This seems to support the hypothesis of a unique source of spread in the last decades from the Medes Islands No-Take Zone towards both southern and northern waters.

Conservation of Native Wild Ivory-White Olives from the MEDES Islands Natural Reserve to Maintain Virgin Olive Oil Diversity.

Food diversity, and in particular genetic diversity, is being lost at an alarming rate. Protection of natural areas is crucial to safeguard the world’s threatened species. The Medes Islands (MI), located in the northwest Mediterranean Sea, are a protected natural reserve. Wild olive trees also known as oleasters make up part of the vegetation of the Meda Gran island. Among them, in 2012, a wild albino ivory-white olive tree with fruit was identified. Fruits were collected from this tree and their seeds were first sown in a greenhouse and then planted in an orchard for purposes of ex situ preservation. Seven out of the 78 seedling trees obtained (12%) produced ivory-white fruits. In autumn 2018, fruits from these trees were sampled. Although the fruits had low oil content, virgin olive oil with unique sensory, physicochemical, and stability characteristics was produced. With respect to the polyphenols content, oleacein was the main compound identified (373.29 ± 72.02 mg/kg) and the oleocanthal was the second most abundant phenolic compound (204.84 ± 52.58 mg/kg). Regarding pigments, samples were characterized by an intense yellow color, with 12.5 ± 4.6 mg/kg of chlorophyll and 9.2 ± 3.3 mg/kg of carotenoids. Finally, oleic acid was the main fatty acid identified. This study explored the resources of the natural habitat of the MI as a means of enrichment of olive oil diversity and authenticity of this traditional Mediterranean food

Habitat changes over 45 years on the small Mediterranean archipelago of the Medes Islands (Catalonia, NE Spain)

The small islands in the Mediterranean basin play an important role in its diversity because they have very unique natural habitats. They are very vulnerable to the direct and indirect effects of human activity, which severely impact ecosystems. Our study analysed the dynamics of the vegetation over recent years on one small island in an attempt to understand how the vegetation is changing and whether this is impacting the habitat diversity. The study was conducted on the Meda Gran, the largest island in the Medes Islands archipelago, which is located to the northeast of the Iberian Peninsula. A diachronic analysis was performed using the current vegetation cartography and a map published in 1984. Two dynamics were identified: the ruderalization caused by the overpopulated seagull colony and the natural succession of the vegetation. These processes have led to a loss of habitats on the island, such as the Astragalus tragacantha habitat, or on the contrary, the growth of populations of invasive species such as Opuntia ficus-indica. These patterns highlight the vulnerability of these small islands and the need for effective management to conserve these protected natural areas and their habitats.

The effects of marine protected areas on ecosystem recovery and fisheries using a comparative modelling approach

Abstract The overexploitation of many marine resources and ecosystems calls for the development and implementation of measures to support their recovery and conservation. The potential contributions to support fisheries and ecosystem recovery were assessed at the local level of the three multiple‐use marine protected areas (MPAs) of Cerbère‐Banyuls, Medes Islands, and Cap de Creus, located in the north‐western Mediterranean Sea. For each MPA, a food‐web model accounting for each protection level (PL) was developed: the fully protected area (FPA), the partially protected area (PPA) and the unprotected area (UPA) surrounding the MPA. Using the resulting nine food‐web models, the ecosystem structure and functioning of each PL were compared and characterized, differences and similarities within and among the three MPAs were assessed, and ecosystem response to full protection was evaluated for the three MPAs. Differences in terms of ecosystem structure and functioning were found among PLs. Overall, FPAs presented the most positive effect of protection in terms of ecosystem structure and functioning, followed by PPAs. However, the effects of protection on neighbouring UPAs were hardly noticeable. Similarities between Cerbère‐Banyuls and Medes Islands MPAs were observed, while Cap de Creus MPA showed the least benefits from protection overall. These results are likely to be due to similarities in the configuration of the protected areas, the levels of enforcement and compliance, and the impact of recreational and small‐scale fisheries allowed in the PPAs and UPAs. This study illustrates that well‐enforced Mediterranean MPAs, even when small, can yield local positive impacts on the structure and functioning of marine ecosystems that can contribute to support local fisheries.

Multi-zone marine protected areas: Assessment of ecosystem and fisheries benefits using multiple ecosystem models

The current alarming state of many coastal ecosystems and fisheries calls for the development of tools to support recovery of exploited stocks, ensure their sustainable exploitation and protect marine ecosystems. Multi-zone Marine Protected Areas (MPAs) are often advocated to reconcile conservation and fisheries benefits. However, while there is a consensus about the ecological benefits whether such types of MPAs can really provide both benefits is still uncertain. Here, we analysed three existing Northwestern Mediterranean multi-zone MPAs (Cerbère-Banyuls, Cap de Creus and Medes Islands) using a comparative temporal ecosystem modelling approach to assess their effectiveness over time in recovering marine resources and ecosystem in the area. Our results showed differences in the ecological effectiveness of the three MPAs, potentially driven by MPA design, management and implementation features. Temporal increases of benefits were small, whenever detected, and showed slight recoveries of some target species and ecological indicators, mostly in Cerbère-Banyuls and Medes Islands MPAs. Our results confirm the benefits of protection to coastal marine resources and ecosystems when MPAs are enforced but highlight the current limitations of the three MPAs due to their small size and the significant impacts of small-scale and recreational fisheries. This study illustrates the capability to evaluate protection effects of small multi-zone MPAs with an ecosystem modelling perspective and represents the baseline to develop future scenarios of alternative management options to foster ecosystem recovery and resource rebuilding in the studied MPAs.

Comparison of diver operated stereo-video and visual census to assess targeted fish species in Mediterranean marine protected areas

Underwater visual census (UVC) is currently the primary tool used to survey shallow water fish assemblages in the Mediterranean Sea. However, the rapid development of digital technologies, such as underwater video cameras and photogrammetric techniques, are providing new sampling opportunities in marine ecosystems. In this study we compare two non-destructive sampling methods, UVC and diver operated stereo-video systems (stereo-DOVs), to characterize assemblages of targeted fish species. Surveys were undertaken in three zones with different levels of protection from fishing (MR, marine reserve; PP, partially protected reserve; NP, non-protected area) in the Montgrí, Medes Islands and Baix Ter Natural Park (NW Mediterranean Sea). There were no statistically significant differences between stereo-DOVs and UVC surveys in terms of species richness, relative abundance and biomass of targeted fish species across the three protection levels. Both methodologies found statistically significant differences between areas closed to fishing (MR) and areas where fishing is regulated (PP) or allowed (NP), whereby higher fish biomass, density, species richness and larger sizes were found in MR surveys. Length estimates of fish were comparable between methods albeit with some species-specific differences in the size-distribution, and a tendency for UVC to overestimate the size of larger fishes. Our results suggest that stereo-DOVs provide an equivalent and complementary technique to UVC to survey assemblages of targeted fish species. In addition to structural data (e.g., biomass, abundance, and length) recorded by UVC, stereo-DOVs provide a permanent visual record of a fish community and enable additional factors such as fish behaviour, precise distance and length, and benthic composition to be quantified. Stereo-DOVs may, therefore, facilitate the continuity and expansion of long-term monitoring programs of fish assemblages in the Mediterranean Sea.

Effects of Age and Culling on Movements and Dispersal Rates of Yellow-Legged Gulls (Larus michahellis) from a Western Mediterranean Colony

This study reports the effects of age and culling of breeding adults on movements and dispersal rates of Yellow-legged Gulls (Larus michahellis) from a western Mediterranean colony (the Medes Islands) based on recaptures and resightings of birds banded as chicks. Juveniles (1-year-old birds) were most frequently located in the French coast of Biscay and in the Western North Mediterranean. Older gulls became concentrated near the colony and its surroundings (core area), with 3rd year sub-adults and adults accounting for more than 70% and 90% of resightings in this area, respectively. Culling of breeding adults increased the dispersal rate of juveniles (pre-cull: 62.6% ± 6.0 SD; post-cull: 71.2% ± 6.4 SD) and mean distance of resightings of juveniles (pre-cull: 250.5 km ± 267.6 SD; post-cull: 367.6 km ± 300.1 SD), and favored displacement of juveniles to the French Atlantic coast. Culling also increased the dispersal rate of adults (pre-cull: 31.7% ± 16.6 SD; post-cull: 38.8% ± 16.3 SD) and mean distance of adult resightings (pre-cull: 27.4 km ± 108.7 SD; post-cull: 35.7 km ± 113.0 SD). This could be attributed to an increase in the number of gulls recruited to other colonies near the Medes Islands after culls. Culling performed in the Medes Islands colony seems to have effects at metapopulation level, conditioning the dynamics and management of other colonies.

Parasite communities of the white seabream Diplodus sargus sargus in the marine protected area of Medes Islands, north-west Mediterranean Sea.

Marine protected areas are considered a useful tool to preserve and recover the biodiversity of ecosystems. It is suggested that fisheries not only affect populations of target and bycatch species but also their parasite communities. Parasites can indicate fishery effects on host species and also on the whole local community, but the effects of fisheries and protection measures on parasite communities are relatively unknown. This study analyses parasite communities of the white seabream Diplodus sargus sargus in order to assess potential effects exerted by protection measures within and by fisheries outside a reserve in the western Mediterranean Sea. This small scale analysis offered the opportunity to study different degrees of fishery effects on parasite infracommunities, without considering climatic effects as an additional factor. Parasite infracommunities of fishes from the no-take zone (NTZ) differed in their composition and structure compared with areas completely or partially open to fisheries. The detected spatial differences in the infracommunities derived from generalist parasites and varied slightly between transmission strategies. Monoxenous parasites were richer and more diverse in both fished areas, but more abundant in the no-take, whereas richness and abundance of heteroxenous parasites were higher for the NTZ. In addition to host body size as one factor explaining these spatial variations, differences within parasite infracommunities between the areas may also be linked to increased host densities and habitat quality since the implementation of the NTZ and its protection measures.

Motivation and attachment to a diving destination: The case of Medes Islands (Catalonia, Spain)

Motivations and place attachment constructs have been previously used as antecedents of behavioral intentions regarding a destination. Nevertheless, previous studies investigating behavioral intention models have paid little attention to the influence of motivations on place attachment and the influence of place attachment on behavioral intentions within the same structural model. This article develops an integrated model to investigate these relationships. Data were collected from recreational scuba divers in Catalonia, Spain. The results suggest that personal escape and personal seeking are the main motivations, and these factors influence place dependence and place identity. Other findings indicate that place dependence influences behavioral intentions more than place identity. In addition, the level of involvement in the activity moderates the links between constructs in some of the relationships.

Thermal stratification drives movement of a coastal apex predator

A characterization of the thermal ecology of fishes is needed to better understand changes in ecosystems and species distributions arising from global warming. The movement of wild animals during changing environmental conditions provides essential information to help predict the future thermal response of large marine predators. We used acoustic telemetry to monitor the vertical movement activity of the common dentex (Dentex dentex), a Mediterranean coastal predator, in relation to the oscillations of the seasonal thermocline during two summer periods in the Medes Islands marine reserve (NW Mediterranean Sea). During the summer stratification period, the common dentex presented a clear preference for the warm suprathermoclinal layer, and adjusted their vertical movements following the depth changes of the thermocline. The same preference was also observed during the night, when fish were less active. Due to this behaviour, we hypothesize that inter-annual thermal oscillations and the predicted lengthening of summer conditions will have a significant positive impact on the metabolic efficiency, activity levels, and population dynamics of this species, particularly in its northern limit of distribution. These changes in the dynamics of an ecosystem’s keystone predator might cascade down to lower trophic levels, potentially re-defining the coastal fish communities of the future.

The Cost of Mediterranean Sea Warming and Acidification: A Choice Experiment Among Scuba Divers at Medes Islands, Spain

A choice experiment is undertaken to elicit preferences of scuba divers in the Marine Protected Area of Medes Islands (Spain). This is the first non-market valuation study of a typical Mediterranean habitat, the Coralligenous, which is characterized by high biodiversity, geomorphologic complexity and iconic species like gorgonians. This habitat is not only very attractive for scuba diving, but is also threatened by climate change and ocean acidification, which is our motivation for undertaking this valuation study. Choice attributes include the number of divers on a diving trip, underwater landscape, presence of jellyfish species, expected state of gorgonians, and price of a dive. Results of multinomial and random parameter logit models indicate a decrease in the attractiveness of Coralligenous areas for scuba diving as a result of both environmental pressures. Estimates of welfare values show that the local extinction of gorgonians had the highest negative effect on utility equivalent to a cost of €60 per dive, followed by abundance of stinging jellyfish with a cost of €26 per dive. Choice probabilities for the selection of different dive experiences indicate the highest rejection rates for the combined sea warming and acidification scenarios.

Circulation of a Meaban-Like Virus in Yellow-Legged Gulls and Seabird Ticks in the Western Mediterranean Basin

In recent years, a number of zoonotic flaviviruses have emerged worldwide, and wild birds serve as their major reservoirs. Epidemiological surveys of bird populations at various geographical scales can clarify key aspects of the eco-epidemiology of these viruses. In this study, we aimed at exploring the presence of flaviviruses in the western Mediterranean by sampling breeding populations of the yellow-legged gull (Larus michahellis), a widely distributed, anthropophilic, and abundant seabird species. For 3 years, we sampled eggs from 19 breeding colonies in Spain, France, Algeria, and Tunisia. First, ELISAs were used to determine if the eggs contained antibodies against flaviviruses. Second, neutralization assays were used to identify the specific flaviviruses present. Finally, for colonies in which ELISA-positive eggs had been found, chick serum samples and potential vectors, culicid mosquitoes and soft ticks (Ornithodoros maritimus), were collected and analyzed using serology and PCR, respectively. The prevalence of flavivirus-specific antibodies in eggs was highly spatially heterogeneous. In northeastern Spain, on the Medes Islands and in the nearby village of L'Escala, 56% of eggs had antibodies against the flavivirus envelope protein, but were negative for neutralizing antibodies against three common flaviviruses: West Nile, Usutu, and tick-borne encephalitis viruses. Furthermore, little evidence of past flavivirus exposure was obtained for the other colonies. A subset of the Ornithodoros ticks from Medes screened for flaviviral RNA tested positive for a virus whose NS5 gene was 95% similar to that of Meaban virus, a flavivirus previously isolated from ticks of Larus argentatus in western France. All ELISA-positive samples subsequently tested positive for Meaban virus neutralizing antibodies. This study shows that gulls in the western Mediterranean Basin are exposed to a tick-borne Meaban-like virus, which underscores the need of exploring the spatial and temporal distribution of this flavivirus as well as its potential pathogenicity for animals and humans.

Long-Term Recovery Patterns and Limited Spillover of Large Predatory Fish in a Mediterranean MPA

Based on 19 y of visual census data from the Medes Islands MPA (NW Mediterranean), this study analyzes the carrying capacity (K) and population recovery time of six species of fish strongly affected by harvesting pressure along the Mediterranean coast. Three of these species (Epinephelus marginatus, Diplodus cervinus and Dicentrachus labrax) have practically reached carrying capacity in the Medes Islands MPA, while others are still approaching population stabilization (Sciaena umbra) or are still increasing in biomass (Dentex dentex). The one exception to these trends is S. aurata, which tended to decrease inside the MPA, probably due to fishing just outside its borders. These results confirm that fish populations may require decadal time scales to recover from exploitation, both in terms of total abundance (21 to 29 y to exceed 95% K) as well as total biomass (25 to 35 y), and that rates of recovery differ between species (13 to 31 y). The recovery and saturation observed within the no-take zone contrasts with results obtained in the partially protected buffer area and the peripheral area open for fishing, which show much lower biomass values. In general, the spillover from the MPA is very moderate, and its effects extend only to the partially protected area.

Sexual reproductive cycle of the epibiotic soft coral Alcyonium coralloides (Octocorallia, Alcyonacea)

Alcyonium coralloides is an epibiotic soft coral overgrowing living colonies of Medi- terranean gorgonians. The main features of the sexual reproductive cycle of this soft coral species are described and quantified for the first time, in a population found at 18 to 22 m depth off the Medes Islands (NW Mediterranean). A. coralloides is a gonochoric internal brooder. The sexual cycle showed a single reproductive event per year. Gametogenesis took 5 to 6 mo, which is the shortest known gametogenesis in littoral octocorals (especially for oogenesis). The maximum mean ± SD diameter was 365 ± 86 µm for spermatic cysts and 632 ± 125 µm for mature oocytes. Sperm was released in spring (late May). Average male and female fecundity in this last phase of the cycle was 15 ± 9 spermatic cysts and 7 ± 4 oocytes per polyp, respectively. Larvae of about 1000 µm in length were observed in the gastrovascular cavities of female colonies in May, before they were released in June. We suggest that the remarkable short gametogenesis and timing shown by A. coralloides is an adaptation to optimize the colonization of its host (in this case the gorgonian octocoral Paramuricea clavata). We conclude that A. coralloides larvae could be ready to settle in early summer when the host P. clavata is probably more vulnerable as a result of its own reproductive cycle coming to an end.

Effects of thermal stress on early developmental stages of a gorgonian coral

Ongoing sea temperature increase threatens reefs worldwide. In this study we experimentally examined for the first time the response of the early life stages of a long-lived structural gorgonian, the Mediterranean species Paramuricea clavata (Risso 1826), to the highest summer temperature recorded so far in the study area (25°C; the Medes Islands, Northwestern Mediterranean). This temperature also simulates the end-of-century predicted warming (+3°C) over the temperature maxima recorded during the species' reproductive period. The results showed a severe negative impact of constant thermal stress on the viability of P. clavata embryos and larvae, resulting in reduced survivorship, completely abnormal embryonic development and impaired metamorphosis. The deteriorating effect was rapid for embryos (after 7 h), whereas the impact on larvae became evident after 10 d of stress. Larval modifications started 7 d earlier under elevated temperature conditions, but the appearance of spherical, aberrant shapes prevented an assessment of whether metamorphosis was initiated but abnormal, or deterred altogether. The apparent higher sensitivity of embryos suggests that thermal stress during embryonic develop- ment may be the most critical factor for the viability of P. clavata larvae. In the context of an ongo- ing warming trend, the reduced viability of early life stages would jeopardize the persistence of P. clavata, which relies on successful recruitment for replenishment of its populations. Further research into the effects of thermal stress on the reproduction of structural invertebrate species and the viability of their early life stages will improve our understanding of the long-term conse- quences of environmental global change in marine benthic communities.

Seasonal cycle of sexual reproduction of the Mediterranean soft coral Alcyonium acaule (Anthozoa, Octocorallia)

Alcyonium acaule (Cnidaria, Octocorallia) is a common, hard-bottom soft coral in the northwestern Mediterranean Sea. This study describes sexual reproduction and the gamete development cycle of this soft coral. A population at 15–18 m depth in the Marine Protected Area of the Medes Islands (42o02′55″ N, 3o13′30″ E) was sampled from July 1994–August 1995. A. acaule is gonochoristic and a surface brooder, spawning once a year in early summer. The mean diameter of ripe spermatic sacs was 400 ± 91 (SD) μm, and the mean diameter of mature oocytes was 473 ± 37 (SD) μm. There were 30 spermatic sacs polyp−1 in males and 14 oocytes polyp−1 in females. Different phases of gametogenesis in female and male colonies were examined separately with respect to seasonal changes in bottom temperature and solar irradiance. The data suggest that the relatively constant temperatures in January–April are probably not related to oocyte maturation, but that rising temperatures in May could affect sperm maturation. Rapidly increasing solar irradiance in March may be the trigger for vitellogenesis and oocyte maturation, although the mechanism for this in anthozoans is not understood.