Ericaria zosteroides (C. Agardh) Molinari et Guiry

Ericaria zosteroides (C. Agardh) Molinari et Guiry

(Figure S7).

Morphological description of specimens: thalli are not caespitose, with a short single axis, which branches out in height or extension (Figure S7A). The holdfast is formed by simple or branched haptera. Apex is smooth and not prominent. Primary branches are cylindrical near the base and flattened in the distal portion. Higher order branches are ribbon-shaped, with an alternate–distichous branching and a faint midrib, and are provided with flattened spines (Figure S7B). Tophules are ovoid and smooth and located on the basal part of the thallus (Figure S7C). Receptacles were not observed.

Habitat: Ericaria zosteroides was found along the southern and north-western coasts of the island (corresponding to Zone B) from 20 to 42 m forming abundant patches.

Remarks: This species has shown a stable trend over time in the E-MPA, as was recorded in all previous records (Catra et al. 2006; Giaccone 1970; Giaccone and Sortino 1974).

Gongolaria montagnei var. compressa (Ercegovi Ć) Verlaque, Blanfuné, Boudouresque et Thibaut (Figure S8).

Morphological description of specimens: thalli are not caespitose attached to the substratum by a discoid holdfast (Figure S8A). The axis is short and can be simple or ramified. Apex is smooth, and not prominent (Figure S8B). Primary branches are cylindrical near the base and flattened in the distal portion. Higher order branches are flattened with an alternate arrangement and a central midrib. They can often carry spinose appendages. Tophules are located near the base of the axis and are oblong and spinose. Receptacles were not observed.

Habitat: Gongolaria montagnei var. compressa was found along the eastern side of the island (in Zone C) and along the southern side (in Zone B), from 23.3 to 35.7 m deep generally with scattered individuals or more rarely forming abundant patches as at Secca del Cammello (SC).

Remarks: this species was not previously reported in the E-MPA.

Gongolaria sauvageauana (Hamel) Molinari et Guiry

(Figure S9).

Morphological description of specimens: thalli are not caespitose, (Figure S9A), attached to the substratum by a discoid holdfast. Axis can be simple or branched and is spinose and very prominent in relation to the insertion of the primary branches (Figure S9B). Primary branches are cylindrical and slender. Higher order branches are cylindrical and carry delicate and divaricate spinose appendages (Figure S9B). Receptacles are cylindrical, diffuse, with a few spinose appendages.

Habitat: Gongolaria sauvageauana was found along all sides of the island, except the eastern coast, from 6.9 to 39.4 m deep, with scattered individuals, except in the site of Punta Cretazzo ( CRE) where it formed abundant patches.

Remarks: this species was previously reported by Giaccone and Sortino (1974), but it was not subsequently found by Catra et al. (2006). It is likely that this species has recently found better conditions to thrive and recover after a period of regression.

Sargassum acinarium (Linnaeus) Setchell ( Figure 6A View Figure 6 ).

Morphological description of specimens: thalli are not caespitose with a single axis attached to the substratum by a discoid holdfast. Axis is cylindrical, rough and knotty. Primary branches are cylindrical and have narrow foliaceous branches ( Figure 6A View Figure 6 ). These have a central midrib, denticulate margin and acute apex. Aerocysts are located on the upper portion of the thallus ( Figure 6A View Figure 6 ). They are spherical and are sited on a small cylindrical pedicel. Receptacles were cylindrical, slender and simple or bifurcated and borne at the base of a pedicel at the axil of the foliaceous branches.

Habitat: Sargassum acinarium was found on the north-eastern side (in Zone C) at 30.6 m forming abundant patches, and on the south-western side (Zone B) at 15.4 m deep with scattered individuals.

Remarks: Sargassum acinarium was previously reported by Giaccone and Sortino (1974) and was no longer observed. The finding of the species in only two sites on the island of Marettimo might suggest that this species has suffered a severe regression over the years and has been confined to only a few areas. Therefore, this species should be given more attention in the future.

Sargassum cf furcatum Kützing ( Figure 6B and C View Figure 6 ).

Morphological description of specimens: thalli with a creeping habit not caespitose, attached to the substratum by a small discoid holdfast. Axis is knotty and short and divides into open and spaced branches, usually arranged in a fan shape ( Figure 6B View Figure 6 ). Apex is smooth and slightly prominent. Primary and secondary branches are knotty and have foliose lanceolate or lobate branches with a central midrib, wavy margins, and an acute apex ( Figure 6B View Figure 6 ). The foliose branches are dichotomously divided from one to four times and the midrib follows these bifurcations ( Figure 6C View Figure 6 ). Aerocysts and receptacles were not observed during this study.

Habitat: Sargassum cf furcatum was found along the southern (Zone B) and north-eastern (Zone C) coasts, with scattered individuals, from 13.1 to 21.3 m deep.

Remarks: This species has never been reported before from the island. The identification at the species level was not certain because we did not find fertile specimens during this study. However, along the Ionian coast of Sicily, this species is usually fertile from June to August ( Marletta et al. 2024). This could depend on the fact that the seawater temperature in June in the sites where the phenology of this species was studied is around 22–26 °C ( Marletta et al. 2024), while in Marettimo it was around 17–22 °C in the same period. This is most likely due to the upwelling currents affecting the south and western parts of Sicily (Béranger et al. 2004). The finding of this species in Marettimo could further prove the expanding trend of S. furcatum in the Central Mediterranean.

Sargassum vulgare C. Agardh nom. illeg. ( Figure 6D and E View Figure 6 ).

Morphological description of specimens: thalli are not caespitose, attached to the substratum by a discoid holdfast. The axis is knotty and can be simple or branched.

Apex is smooth and not prominent. Primary branches are cylindrical and knotty and have secondary branches with alternate-distichous branching. Foliose branches are lanceolate, with an evident midrib, toothed or with wavy margins and acute apex ( Figure 6D View Figure 6 ). Areocysts are spherical, with a short cylindrical pedicel, and are located at the axil of the foliose branches ( Figure 6D View Figure 6 ). Receptacles are cylindrical or slightly flattened, warty, simple, or branched, and are borne on a short sterile pedicel ( Figure 6E View Figure 6 ).

Habitat: Sargassum vulgare was found along all sides of the island (except the eastern coast, Zone C) from 0.5 to 25.5 m deep, with scattered individuals or forming dense patches.

Remarks: This species has shown a stable trend on the island over the years, as it was reported by Giaccone (1970), Giaccone and Sortino (1974), and Catra et al. (2006).