Mesophotic Coral Ecosystems

In January 2022, I will start my masters thesis on the effect of marine animal forests on the surrounding benthic communities in the beautiful Marine Protected Area of Portofino, Italy. Deep-water coral reefs are largely unexplored and research like the here presented study is urgently needed to understand their functional role and protect these valuable habitats from various anthropogenic impacts. To realise this project, we will collect photographic samples and record environmental data between 30 m and 70 m depth.

Progress on the Project

01/07/2021 - The thesis proposal is written and handed it.

20/09/2021 - My proposal was accepted by my university! The planning of the project can begin .

28/11/2021 - The last exams of my masters program are written and all presentations are held. Next up: preparing the practical part of my upcoming research.

11/12/2021 - Successfully completed the GUE Tech 1 course! Now, I can perform decompression dives with mixed gases. This will be essential for the sampling process of my research.

14/02/2022 - The project officially launched! You can find continuous updates on my Instagram page @rabbitholediving

18/04/2022 - Sampling is completed and the analysis can start. Many weeks of identifying species, and segmenting pictures lay ahead.

30/06/2022 - The analysis is done and the preliminary results have been presented. Now, the writing begins.

07/08/2022 - My thesis project is completed and the dissertation is handed in. Thank you for all the support, it would not have been possible without you! You can find media content of the project on my social media channels included below. Furthermore, I will add a summary here on this page.

The Mesophotic Zone

The tropical mesophotic zone supports a high habitat complexity and diversity (Bridge et al., 2012; Lesser et al., 2009), only a small portion of mesophotic studies were performed in temperate latitudes (Cerrano et al., 2019). No consensus, on the bathymetric limits of the mesophotic zone, has been found. Most often, it has been defined as the area between 40 m and 120 m of depth (Cerrano et al., 2019), but recently the following limitations have been proposed: as upper limit, the depth at which arrives 1 % of the surface irradiance and as lower limit, the deepest depth at which primary producers can be found (Cerrano et al., 2019). Through this definition, the mesophotic zone is placed between the euphotic and the aphotic zone, while also being variable in depth as a result of different levels of transparency of the water column (Cerrano et al., 2019). Through recent developments in scuba diving technologies, namely the use of mixed gases (trimix) and closed-circuit rebreathers, studies and manipulative experiments in this area have been made accessible (Sherman et al., 2013). Nevertheless, deep reef habitats in the Mediterranean Sea (> 30 m) are largely unexplored (Cerrano et al., 2010, 2019). The functional role of mesophotic coral ecosystems (MCE) is not well understood but MCEs are hypothesized to serve as refugium for shallow water species escaping unfavourable conditions, as well as nursery grounds that replenish shallower reefs with larvae (Bongaerts et al., 2010; Lesser et al., 2009; Riegl & Piller, 2003).

Marine animal forests

Dense populations of erect benthic species, such as the gorgonian Paramuricea clavata (Risso, 1826) and the gold coral Savalia savaglia (Bertoloni, 1819), can form marine animal forests. Long-lived species with 3D-structures can be considered ecosystem engineers, since they may alter light intensity, current velocity, and rates of bioaccumulation (Bruno & Kennedy, 2000; Romero et al., 2015). Marine animal forests, like their terrestrial counterparts, are associated with modified microclimates that foster significantly different benthic assemblages than similar habitats without animal forests and promote benthic diversity and ecosystem processes (Cerrano et al., 2010; Ponti et al., 2018). Earlier findings suggest that gorgonian forests promote coralligenous habitats, when no gorgonian forest was present, habitats dominated by algae were more common (Ponti et al., 2018).

Why this study?

The ecologically valuable marine animal forests are facing multiple threats including mechanical damage from lost fishing gears and recreational divers, damage through the aggregation of mucilage, invasive species, increased sedimentation rates, and global climate change (Ponti et al., 2018 and references therein). Marine heatwaves are likely to increase with the ongoing global climate change (Easterling et al., 2000; Lima & Wethey, 2012; Meehl & Tebaldi, 2004). Multiple mass mortality events, linked to high temperatures, have been documented for the north-western Mediterranean Sea in groups such as gorgonians and sponges (Cebrian et al., 2011; Coma et al., 2006; Garrabou et al., 2001; Huete-Stauffer et al., 2011; Linares et al., 2005). The loss of gorgonian forests could lead to major shifts in the associated benthic community and could result in lower diversity, as well as lower resistance and resilience to disturbances (Ponti et al., 2018). Furthermore, the loss of engineering species may facilitate the spread of invasive species (Cebrian et al., 2012; Diez et al., 2012; Linares et al., 2012). In order to understand the functional role of MCEs and protect these valuable habitats, baseline information about their community composition and structure is needed. Thus, the goal of this research is to study differences in benthic communities related to the presence or absence of dense populations of forest-building species at different depths, 30 m, 50 m, and 70 m.

Credit for the beautiful pictures goes to Niccolò Crespi!


Bongaerts, P., Ridgway, T., Sampayo, E. M., & Hoegh-Guldberg, O. (2010). Assessing the “deep reef refugia” hypothesis: focus on Caribbean reefs. Coral Reefs, 29, 309–327.

Bridge, T. C. L., Fabricius, K. E., Bongaerts, P., Wallace, C. C., Muir, P. R., Done, T. J., & Webster, J. M. (2012). Diversity of Scleractinia and Octocorallia in the mesophotic zone of the Great Barrier Reef, Australia. Coral Reefs, 31(1), 179–189.

Bruno, J. F., & Kennedy, C. W. (2000). Patch-size dependent habitat modification and facilitation on New England cobble beaches by Spartina alterniflora. Oecologia, 122, 98–108.

Cebrian, E., Linares, C., Marschal, C., & Garrabou, J. (2012). Exploring the effects of invasive algae on the persistence of gorgonian populations. Biological Invasions, 14, 2647–2656.

Cebrian, E., Uriz, M. J., Garrabou, J., & Ballesteros, E. (2011). Sponge mass mortalities in a warming mediterranean sea: are cyanobacteria-harboring species worse off? PLoS ONE, 6(6), e20211.

Cerrano, C., Bastari, A., Calcinai, B., Di Camillo, C., Pica, D., Puce, S., Valisano, L., & Torsani, F. (2019). Temperate mesophotic ecosystems: gaps and perspectives of an emerging conservation challenge for the Mediterranean Sea. European Zoological Journal, 86(1), 370–388.

Cerrano, C., Danovaro, R., Gambi, C., Pusceddu, A., Riva, A., & Schiaparelli, S. (2010). Gold coral (Savalia savaglia) and gorgonian forests enhance benthic biodiversity and ecosystem functioning in the mesophotic zone. Biodiversity and Conservation, 19, 153–167.

Coma, R., Linares, C., Ribes, M., Diaz, D., Garrabou, J., & Ballesteros, E. (2006). Consequences of a mass mortality in populations of Eunicella singularis (Cnidaria: Octocorallia) in Menorca (NW Mediterranean). Marine Ecology Progress Series, 327, 51–60.

Diez, J. M., D’Antonio, C. M., Dukes, J. S., Grosholz, E. D., Olden, J. D., Sorte, C. J. B., Blumenthal, D. M., Bradley, B. A., Early, R., Ibáñez, I., Jones, S. J., Lawler, J. J., & Miller, L. P. (2012). Will extreme climatic events facilitate biological invasions? Frontiers in Ecology and the Environment, 10(5), 249–257.

Easterling, D. R., Meehl, G. A., Parmesan, C., Changnon, S. A., Karl, T. R., & Mearns, L. O. (2000). Climate extremes: observations, modeling, and impacts. Science, 289, 2068–2074.

Garrabou, J., Perez, T., Sartoretto, S., & Harmelin, J. G. (2001). Mass mortality event in red coral Corallium rubrum populations in the Provence region (France, NW Mediterranean). Marine Ecology Progress Series, 217, 263–272.

Giusti, M., Innocenti, C., & Canese, S. (2014). Predicting suitable habitat for the gold coral Savalia savaglia (Bertoloni, 1819) (Cnidaria, Zoantharia) in the South Tyrrhenian Sea. Continental Shelf Research, 81, 19–28.

Huete-Stauffer, C., Vielmini, I., Palma, M., Navone, A., Panzalis, P., Vezzulli, L., Misic, C., & Cerrano, C. (2011). Paramuricea clavata (Anthozoa, Octocorallia) loss in the Marine Protected Area of Tavolara (Sardinia, Italy) due to a mass mortality event. Marine Ecology, 32(SUPPL. 1), 107–116.

Lesser, M. P., Slattery, M., & Leichter, J. J. (2009). Ecology of mesophotic coral reefs. Journal of Experimental Marine Biology and Ecology, 375, 1–8.

Lima, F. P., & Wethey, D. S. (2012). Three decades of high-resolution coastal sea surface temperatures reveal more than warming. Nature Communications, 3(704).

Linares, C., Cebrian, E., & Coma, R. (2012). Effects of turf algae on recruitment and juvenile survival of gorgonian corals. Marine Ecology Progress Series, 452, 81–88.

Linares, C., Coma, R., Diaz, D., Zabala, M., Hereu, B., & Dantart, L. (2005). Immediate and delayed effects of a mass mortality event on gorgonian population dynamics and benthic community structure in the NW Mediterranean Sea. Marine Ecology Progress Series, 305, 127–137.

Meehl, G. A., & Tebaldi, C. (2004). More intense, more frequent, and longer lasting heat waves in the 21st century. Science, 305, 994–997.

Ponti, M., Turicchia, E., Ferro, F., Cerrano, C., & Abbiati, M. (2018). The understorey of gorgonian forests in mesophotic temperate reefs. Aquatic Conservation: Marine and Freshwater Ecosystems, 28, 1153–1166.

Riegl, B., & Piller, W. E. (2003). Possible refugia for reefs in times of environmental stress. International Journal of Earth Sciences, 92, 520–531.

Romero, G. Q., Gonçalves-Souza, T., Vieira, C., & Koricheva, J. (2015). Ecosystem engineering effects on species diversity across ecosystems: a meta-analysis. Biological Reviews, 90, 877–890.

Sherman, C., Appeldoorn, R., Ballantine, D., Bejarano, I., Carlo, M., Kesling, D., Nemeth, M., Pagan, F., Ruiz, H., Schizas, N., & Weil, E. (2013). Exploring the mesophotic zone: Diving operations and scientific highlights of three research cruises across Purto Rico and US Virgin Island. In M. A. Lang & M. D. J. Sayer (Eds.), Proceedings of the 2013 AAUS/ESDP Curaçao Joint International Scientific Diving Symposium (pp. 297–33). American Academy of Underwater Sciences.