**3. Results**

#### *3.1. Distribution and Occurrence*

The population of *Eunicella verrucosa* of Tavolara MPA is composed of light pinkishcolonies settled on granitic outcrops arising from the detritic bottom and surroundings in the centre of the Tavolara Channel (Figure 1). These outcrops (Figure 2A–C) were characterised by a high level of sedimentation, scarce development of the crustose coralline algae and by the widespread presence of the brown algae *Carpomitra costata*, and to a lesser extent, *Ericaria zosteroides*. The animal community was mainly composed of large, erect sponges, particularly *Axinella* spp. and several species of Keratosa (*Dysidea* spp., *Sarcotragus foetidus*, *Spongia lamella* and *S. officinalis*) (Figure 2D–E). Together with *E. verrucosa*, *Paramuricea clavata* was also relatively abundant.

Colonies (Figure 2F–H) were recorded in 34 of the 77 investigated sites, in an area of approximately 30 ha (Table 1, Figure 1). All the colonies (100) were found between a depth of 35 and 59 m; about one-third of the colonies were settled near the areas where the detritic sediment borders the rocks, whereas the remaining specimens were mainly observed on the sloping flanks of the outcrops and less frequently on their top.

Generally, the colonies were isolated or spread, without the formation of a true forest (sensu Chimienti [28]). The highest number of colonies were found at sites N159 (12 colonies) and N27 (14 colonies), exactly in the middle of the channel (Figure 1).

The colony size of the 100 recorded specimens ranged from 10 to 66.3 cm in height, with the size class 30–40 cm being dominant. Size–frequency distribution was simmetric and leptokurtic (Figure 3A). The fan surface measured for 63 colonies ranged from 27 to 2350 cm<sup>2</sup> and was linearly related to height (*n* = 63; r = 0.73; *p* < 0.001) (Figure 3B).

According to the equation proposed by [39], the age estimation ranges were from 3 to 130 years, with a distribution showing a mode in the 30–50-year-old class, showing a highly skewed and leptokurtic distribution, with a long tail toward large age classes (Figure 3C).

#### *3.2. Epibiosis and Damages*

A total of 55% of the observed colonies did not show epibionts or direct damages, whereas the remaining was affected at different levels and in different portions of the colony (base, fan surface, apexes) (Table 2, Figure 4A); no relationship between damages and colony height was observed (on average, healthy colonies were 33.99 ± 1.74 cm height, whereas damaged ones measured 37.22 ± 1.93 cm). Damaged specimens were randomly located across the investigated sites.

**Figure 3.** Morphometric description of *Eunicella verrucosa* colonies at the Tavolara MPA. (**A**) size– frequency distribution of the colony heights; (**B**) correlation between height and fan area; (**C**) age– frequency distribution, inferred from height of colonies according to [39].

Only one colony was observed as dead, at site N25 (Figure 5A). Seven colonies showed parts of branches deprived of coenenchyme with an exposed naked skeleton without epibiosis (Figure 5B). In total, 43 colonies hosted epibionts; 29% of these were covered for less than 25% of the total surface, 8% were affected between 25–50%, 4% showed 50–75% of the surface covered and 3% for more than 75% (Figure 4A). Two colonies were recorded entangled by an abandoned nylon line (N151-2 and N159-7) (Figure 5C) and one colony was enveloped by plastic debris (N27-12). This colony was also found spawning on 10 November 2019 (Figure 5D).

In total, 18 species/OTUs were found associated with the colonies (Figure 4B). The most common taxon was the parasitic octocoral *Alcyonium coralloides*, recorded on 39.5% of the damaged colonies (Figure 5E). Overall, branched bryozoans were settled on 67% of the suffering colonies: the most common one was *Turbicellepora avicularis*, present on 37.2% of the colonies (Figure 5F), followed by *Adeonella calveti* and *Pentapora fascialis* (32.6 and 14%, respectively) (Figure 5G). Sponges, particularly *Crella elegans* (25.6%) (Figure 5G), were responsible for the epibiosis on 30% of the colonies. The serpulids of the *Salmacina/Filograna* complex (Figure 5H) and the bivalve *Pteria hirundo* (Figure 5I) were found on 11.6% and 5% of the colonies, respectively.

Three predators, the nudibranch *Duvaucelia odhneri*, the ovulid *Simnia spelta* and the decapod *Balssia gasti* were observed (Figure 6A–C). The most represented was *D. odhneri*, recorded on eleven colonies, in four cases together with their eggs (Figure 6A,A'). Three specimens of *S. spelta* were recorded on two colonies (Figure 6B). One colony (N182-1) hosted ten specimens of *B. gasti* (Figure 6C,C'). Moreover, two specimens of the decapod *Periclimenes scriptus* were recorded on two colonies at site N27 (Figure 6D). Five colonies hosted the large acrophilic ophiuroid, *Astrospartus mediterraneus* (Figure 6E).

**Figure 4.** Health state of the studied *Eunicella verrucosa* population. (**A**) percentage of healthy and damaged colonies, according to the percentage of affected surface. White bars, percentage of colonies characterized by naked skeleton; grey bars, percentage of surface covered by epibionts. (**B**) percentage of colonies hosting associated species/OTUs.

**Figure 5.** Examples of mechanical damages and epibiosis affecting *E. verrucosa*. (**A**) dead colony (white arrow); (**B**) a colony with a huge portion deprived by coenenchyme; (**C**) colonies entangled with an abandoned line and plastic debris (**D**) Red circle refers to spawning polyps; (**E**–**H**) main epibionts affecting *E. verrucosa*: the parasitic octocoral *Alcyonium coralloides* (**E**) the bryozoans *Turbicellepora avicualaris*, (**F**) *Adeonella calveti*, with the sponge *Crella elegans*, (**G**) the *Salmacina*/*Filograna* complex (**H**) and (**I**) the bivalve *Pteria hirundo*.

**Figure 6.** Associated vagile fauna with *Eunicella verrucosa*. The three predators, the nudibranch *Duvaucelia odhneri* (red circles) (**A**) together with its eggs (white circles) and damaged zones (blue arrows), (**A'**) the ovulid *Simnia spelta* (red arrow), (**B**) and the decapod *Balssia gasti*, (**C**,**C'**) the decapod *Periclimenes scriptus,* (**D**) the large acrophilic ophiuroid and (**E**) *Astrospartus mediterraneous*.
