Moonshine worms (Diopatra aciculata: Onuphidae, Annelida) in the Knysna Estuary, South Africa; taxonomy and distribution

Abstract

Moonshine worms are a popular bait species used for fishing. The taxon was not detected during surveys of the macrobenthos conducted in Knysna in the 1940s and 1990s, and was first reported as a harvested bait species in the mid-2000s, suggesting that it appeared for the first time in the estuary in the last three decades. A previous molecular analysis identified the worms as Diopatra aciculata, a species first described from Australia. This study provides an updated detailed morphological description of D. aciculata in South Africa to facilitate future identifications and also investigates the species' distribution and population size in the Knysna Estuary. Specimens were examined by scanning electron, stereo- and compound microscopes. Diopatra aciculata has tubes that protrude from the sediment in sandy areas, often decorated with algae and shell fragments; a large body size, up to 600 mm long and 11.5 mm wide. It has 10–18 rings on ceratophores; 5–10 teeth on pectinate chaetae; uni- and bidentate pseudo-compound falcigers and dorsal cirri approximately as long as branchiae. Diopatra aciculata was detected up to 12 km from the mouth of the Knysna Estuary with densities measured at 18 sampled sites. Statistical analysis retrieved high and low density groups that were significantly different from one another (Kruskal-Wallis H(14, 800) = 376.55; P = 0.01), but distribution of high density sites was patchy. We estimate that the population comprises 20–24 million individuals. Given the size of individual worms and the population estimate, this species can be expected to have significant ecological impacts in the estuary.

The Current State of Eunicida (Annelida) Systematics and Biodiversity

“…Regional onuphid faunas were described from Central America and adjacent waters of the East Pacific and West Atlantic [94,189,[449][450][451][452], Antarctic and Subantarctic Seas [13,448]; Japan [453][454][455][456], Australia [53,413,416,417,430,[457][458][459], South and West Africa [46,216,[460][461][462]; South America [43,463,464] and the eastern Atlantic including Norway [343], southern Europe, the Mediterranean [440,[465][466][467][468] and the Macaronesian region [469]. Large parts of the world's onuphid fauna remain poorly studied; for example, from the Indian Ocean and southeastern Asia as well as from most of the deep-sea habitats.…”

“…Both species are broadcast spawners with larvae capable of spending some time in the water column. Thus, potential transport with ballast waters of via aquaculture could result in their recent spread due to human activities [46]. Another example of a species with a wide geographical range, but possibly not due to human mediation, is Nothria conchylega, a species commonly found in shelf and upper slope areas in the Arctic Ocean, the North Atlantic and the North Pacific [447].…”

“…Large-bodied onuphids are widely used as bait and thus harvested by professional and recreational fishermen from the intertidal zone habitats in Australia (Australonuphis spp. and Hirsutonuphis spp., [53]), South Africa (D. aciculata, [46]), the Mediterranean and Portuguese coasts (D. neapolitana, [54,56,484]). One species, D. aciculata, is commercially produced in aquaculture in New South Wales, Australia and sold as food in the conditioning of prawn broodstock and as dry bait for recreational fishing [59].…”

“…All families have records of widely distributed species, which deserve further investigation. Most widespread species studied in detail ended up as more than one species [43][44][45] or exotic species dispersed by human mediated transport [46,47]. However, some species appear to have naturally widespread distributions [48,49] despite the poor natural dispersal capability attributed to eunicidan species.…”

A new record of a cryptogenic Dipolydora species (Annelida: Spionidae) in South Africa

“…However, it is likely that the number of non-indigenous polychaete species identified in the region is underestimated, as evidenced by recent studies (e.g. Williams et al ., 2017; Malan et al ., 2020; van Rensburg et al ., 2020). Polychaetous annelids are frequent members of the non-indigenous marine fauna across the globe, likely due to factors that make them prone to introductions (Çinar, 2013), as well as biological mechanisms that enhance invasion success (Papacostas et al ., 2017).…”