Dusky Gregory

Stegastes nigricans, commonly known as the dusky farmerfish, is a damselfish species residing in tropical coral reefs at depths ranging from one to 12 meters, within latitudes of 30°S to 30°N. It is recognized for cultivating monocultures of algae, particularly cyanophores and rhodophytes.

First described by Gerald R. Allen and Alan R. Emery in 1985, Stegastes nigricans belongs to the genus Stegastes, which derives its name from the Greek word "stegastos," meaning covered. The species name "nigricans" translates from Greek as swarthy or black-skinned. Recent studies classify this species within the monotypic taxon Pomacentrinae, which shares close phylogenetic relations with the subfamilies Amphiprioninae, known for clownfish, and Chrominae, noted for their vibrant coloration.

The dusky farmerfish reaches an average length of nine centimeters, with a maximum length of 14 centimeters. It possesses 12 dorsal spines, 15 to 17 dorsal soft rays, two anal spines, and 12 to 14 anal soft rays. Adult specimens exhibit a generally brown coloration, with darker shades on the dorsal head and nape, tapering to tan on the lower head and breast. Distinctive features include whitish lips, blue suborbital regions, and brown or dusky fins. A well-defined dark spot at the base of the posterior dorsal rays differentiates this species from S. lividus. During courtship or egg protection, males display a broad white bar and a pale blue stripe along the body.

This species is predominantly located along the East African coast, around 🇲🇬 Madagascar, in the British 🌊 Indian Ocean Territory, the southern coast of 🇮🇳 India, Southeast Asia, the northern coast of 🇦🇺 Australia, and in regions across Melanesia, 🇫🇲 Micronesia, and Polynesia, with occasional sightings in the 🌊 Red Sea, 🌊 Persian Gulf, Gulf of California, and the Western coast of Central America. S. nigricans thrives in reef flats and lagoon reefs, frequently amidst staghorn coral, where they feed on algae, gastropods, sponges, and copepods. Their territorial nature is evident as they cultivate and defend their filamentous algae patches, attacking intruders if necessary.

Reproductively, S. nigricans is oviparous, with males forming pair bonds during breeding seasons. Their demersal eggs adhere to substrates, guarded and aerated by males, who are notably aggressive during these periods. The species actively removes competitive algae, nurturing delicate algae varieties despite a lack of cellulases for digestion. This behavior indicates a symbiotic relationship, as the preferred brown carpet algae relies on S. nigricans for growth, enhancing primary productivity in their ecosystem through increased oxygen, nitrogen, and phosphorus concentrations.