Dosima fascicularis Crustacea, Cirripedia

The buoy barnacle, Dosima fascicularis,

is a pedunculate barnacle with a swollen capitulum bearing five large plates (two scuta, two terga and a carina) and a naked stalk. The shell plates are very thin and delicate. The tergum and the scutum are translucent, light bluish-purple in color, with their external surfaces delicately granular (Figure 2a, b, d). All seven specimens were attached to a large float, constructed by the barnacle around the original substratum, a piece of wood (Figure 2 a–c, e). The maximum size recorded for the species in European waters is 37 mm (Minchin 1996) and 49 mm in South African waters (Ryan & Branch 2012). The average size of the specimens from the Algerian basin is relatively larger than that of the individuals from Maltese (Mifsud 2005) and Italian waters (Betti et al. 2017) (Table 1).

Discussion

The pelagic Dosima fascicularis is an abundant species in temperate waters of both northern and southern hemispheres. Weisbord (1979) provided an updated list of the world-wide occurrences of D. fascicularis. The species is common in temperate waters, but is also observed occasionally in higher latitudes and in the tropics. Sciberras & Schembri (2007) commented that, as this species is common in the Atlantic Ocean, it could accidentally enter the Mediterranean Sea through the Straits of Gibraltar. Recent changes in Mediterranean surface water temperatures, related to global warming, are affecting circulation (Theocharis et al. 1999) and may be linked to new ingressions and stranding episodes of floating organisms from the Atlantic Ocean (Betty 2017). The weather on the Algerian coast was unstable throughout April 2018 and Algeria is among the countries at high risk of climate change. (UNU-EHS, 2017).

The seven live specimens reported on herein were collected on the east coast of the Algerian Basin and 1026 km from the Gibraltar Strait, which is the only source of exchange with the Atlantic Ocean. Therefore, we cannot exclude the possibility that the specimens incidentally entered the Mediterranean through the Straits of Gibraltar, in what may be a natural expansion of its range.

Studies of Dosima fascicularis are scarce and mostly based on stranding events that occur under singular oceanographic and climatic conditions that cast pleustonic organisms ashore (Minchin 1996, Liss & Duce 1997). Other authors have linked the distribution of this barnacle to the availability of potential attachment substrate(s) (e.g. Junoy & Junoy 2014). For example, synthetic and non-biodegradable materials provide attractive, alternative substrata for a number of opportunistic colonizers (Gregory 2009). Such durability allows pelagic plastics to remain at sea for long periods, and thus to travel distances of more than 3000 km from their source (Ryan & Moloney 1993). Barnes (2002) estimated that the increase in anthropogenic rubbish in the sea has roughly doubled the propagation of rafting fauna in the subtropics and more than tripled it in high latitudes. Whitehead (2011) also concluded that the increasing abundance of plastic is drastically increasing the opportunities for colonization by goose barnacles.

A continuous monitoring strategy and observation of strandings of pelagic fauna on the Algerian coast particularly, and the Mediterranean Sea more generally, in relation to unusual oceanographic and environmental conditions observed, would provide new insights into their distribution and the main cause of their stranding beyond their usual distributions.