Diadema africanum ? Rodríguez et al. 2013

Diadema africanum ? Rodríguez et al., 2013

Diadema africanum Rodriguez et al. 2013 — $ Minderlein & Wirtz 2014: 2, fig. 2.

Type locality: Tenerife, Canary Islands.

See: Rodrigues et al. (2013).

Occurrence: East Atlantic, from Senegal to Gulf of Guinea (Koehler 1914b, Rodrigues et al. 2013) and also in the Azores (Minderlein & Wirtz 2014), Madeira (Alves et al. 2001), Selvagens (Pérez-Ruzafa et al. 2002), Canaries (Hernández et al. 2013), Cape Verde (Pérez-Ruzafa et al. 2002) and S„o Tomé (Koehler 1914b).

Depth: strictly a littoral form (Alves et al. 2001; Hernández et al. 2013); AZO: 8 m (Minderlein & Wirtz 2014).

Habitat: hard substrates (Alves et al. 2001; Hernández et al. 2013).

Larval stage: probably planktotrophic (inferred from the genus; see Emlet 1995).

Remarks: the inclusion of the Azores in the geographical distribution of Diadema antillarum by Mortensen (1940a) at the time appears to be a product of a misprint since no specimen belonging to this species was reported from the archipelago (see below remarks under Centrostephanus longispinus). Recently, however, Minderlein & Wirtz (2014) have identified Diadema africanum in Santa Maria Island, making the Azores the northernmost limit for this species. Nevertheless, considering its known gregarious behaviour and conspicuous presence on shallow rocky shores throughout this species distribution (Alves et al. 2001; Schultz 2006; Hernández et al. 2008), it is hard to believe that D. africanum could represent a case of an overlooked shallow–water element of the Azores in over 150 years of echinoderm studies in the area. In the future, it will be interesting to understand if the specimen found in the southernmost island of the Azores represent a solitary vagrant or a recent established population, as a result of a recent range expansion of this tropical East Atlantic form to the northern waters of the Azores. Minderlein & Wirtz (2014) remarked that since its collection in 2010 no other sightings have been reported, indicating that the presence of this species in the archipelago could be a direct result of the global warming, as occasional propagules find the increasingly warmer waters in the Azores suitable for establishment. Its rare occurrence could be the result of lag times between the initial invasion event(s) to population outbreaks, which are a common phenomenon in the invasion process of many marine species. For example, after its initial discovery more than a decade ago, the alien invasive Diadema setosum still is exceptionally rare in the Mediterranean (Bronstein et al. 2017).