The understorey of gorgonian forests in mesophotic temperate reefs

Abstract

1. In the Mediterranean Sea, dense populations of the gorgonian Paramuricea clavata shape marine animal forests, characterizing the seascapes of coralligenous habitats.Despite concerns for its health, with several anthropogenic threats and recent mass mortality events, mainly triggered by thermal anomalies, the understorey of its forests and the ecological processes that they promote are still little known. Here, the abundance and composition of epibenthic assemblages inside and outside P. clavata forests were investigated across the central and western Mediterranean Sea, by applying a multifactorial sampling design.2. In spite of the large variability in the structures of epibenthic assemblages at local and regional scales, the gorgonian understoreys share some common features, such as higher abundances of calcareous builder organisms and reduced invasion by the non-indigenous alga Caulerpa cylindracea, compared with the adjacent unforested rocky bottoms. Paramuricea clavata showed non-linear density-dependent relationships with algal turfs and non-encrusting algae belonging to the genus Peyssonnelia. Moreover, by entrapping benthic mucilaginous aggregates with their branches, these gorgonians risk topical necrotic lesions, but may reduce the suffocation risks for understorey organisms. 3. Overall, P. clavata forests may enhance bioconstruction processes and increase resistance and resilience of the benthic assemblages in the Mediterranean coralligenous habitats. This species and its forests, together with their understoreys, should be considered as essential elements of the ecology of the Mediterranean Sea, and therefore worthy of specific and effective protection measures. 4. Conservation strategies should reduce the risk of mechanical damage by regulating fishing activities, anchorages, and scuba diving where gorgonian forests are present. Moreover, when evident alterations are documented, restoration actions should be implemented to recover the integrity of gorgonian forests.

The importance of coastal gorgonians in the blue carbon budget

“…The contribution of other organisms, whose recruitment is favoured by the presence of gorgonians forests (e.g. sponges, bryozoans, scleractinians and especially coralline algae 69,70 ), and that constitute pre-coralligenous and coralligenous communities should also be considered, in order to calculate more accurately the importance of these ecosystems as C sinks. Further studies will allow this first calculation to be refined evaluating also the C loss determined by the turnover (e.g.…”

Distribution and phenotypic variability of the Mediterranean gorgonian Paramuricea macrospina (Cnidaria: Octocorallia)

“…The importance of gorgonians as an "animal forest" in the Mediterranean Sea has been documented (Cerrano et al 2000) and is currently receiving attention (Ponti et al 2016;Valisano et al 2016;Gori et al 2017) due to their structural and functional role. They increase the three-dimensional complexity of the habitat, modifying local environmental parameters such as water movement and sedimentation processes (Valisano et al 2016), creating new ecological niches and therefore affecting the diversity of associated species (Linares et al 2005;Ponti et al 2014Ponti et al , 2018Gori et al 2017). Gorgonians can build wide facies, sometimes monospecific assemblages, as reported for P. macrospina in the Marmara Sea and Menorca Channel (Topçu & Öztürk 2015;Grinyó et al 2016).…”

“…In the Mediterranean Sea, only two species are known, Paramuricea clavata (Risso, 1826) and the endemic Paramuricea macrospina (Koch, 1882). While the interest in P. clavata as an ecosystem engineer is rapidly growing (Ponti et al 2014(Ponti et al , 2016(Ponti et al , 2018Valisano et al 2016), especially after its severe involvement in widespread and frequent massive mortality events in shallow waters (Cerrano et al 2000;Calvisi et al 2003;Linares et al 2005;Garrabou et al 2009;Huete-Stauffer et al 2011;Vezzulli et al 2013), only little, scattered information, mostly in the form of records, is available for P. macrospina (Aguilar et al 2015;Grinyó et al 2017). The importance of gorgonians as an "animal forest" in the Mediterranean Sea has been documented (Cerrano et al 2000) and is currently receiving attention (Ponti et al 2016;Valisano et al 2016;Gori et al 2017) due to their structural and functional role.…”

Updating the current knowledge on the relationships between Haplosyllis chamaeleon Laubier, 1960 (Annelida, Syllidae) and Paramuricea clavata (Risso, 1826) (Cnidaria, Plexauridae) in the Mediterranean Sea

“…A particular type of bioconstructions are the submarine animal forests formed by gorgonians (Cerrano et al 2010). Their three-dimensional structures may affect edaphic conditions (Valisano et al 2016;Ponti et al 2018) and enhance local biodiversity, especially in Mediterranean coralligenous habitats (Ponti et al 2014(Ponti et al , 2016(Ponti et al , 2018. Anthozoans, including sea-fans, often host organisms seeking for shelter (Molodtsova et al 2016), food and/or reproductive success (Goh et al 1999).…”