Browsing by Author "van Rensburg, Hendré"
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- ItemTaxonomy and distribution of moonshine worms (Diopatra sp.) in Knysna estuary(2019-12) van Rensburg, Hendré; Simon, Carol A.; Matthee, Conrad A.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Polychaetes as fish bait have become increasingly popular in the Knysna Estuary over the last decade. The presence of an unknown polychaete, Diopatra sp. was first reported in the Knysna Estuary ten years ago, when it was harvested as fish bait in small quantities by local fishermen who called it the moonshine worm. Since this very conspicuous species was not detected by intensive biodiversity sampling in the estuary in the 1950s and 1990s, it should thus be considered new to the estuary. A preliminary morphological investigation showed that Diopatra sp. may be Diopatra neapolitana (Delle Chiaje, 1841). However, D. neapolitana is a pseudo-cosmopolitan species with local distribution restricted to Durban and Port Elizabeth. As several cosmopolitan species have recently been described as cryptic endemic species, it is likely that Diopatra sp. in the Knysna Estuary may also represent an undescribed cryptic endemic species. The aims of this study were firstly to identify Diopatra sp. using molecular and morphological techniques and secondly to determine the density and distribution of the species throughout the estuary and estimate population size and baiting pressure (the percentage of worms recently removed from an area due to baiting) for conservation management. Bayesian and maximum likelihood analysis of COI and 16S markers indicated that the species in South Africa is Diopatra aciculata (Knox & Cameron, 1971) from Australia. Although sequence divergence between D. aciculata and D. neapolitana is lower than among other species in the genus, it was still an order of magnitude greater than the intra-specific sequence diversity of either of these species. The separation of these species is confirmed by species delimitation analysis. Molecular similarity between D. aciculata and D. neapolitana is reflected by morphological similarity, and the two species have so many features in common that it is very difficult to tell them apart. The morphology of D. aciculata from South Africa closely matched descriptions from Australia. The confirmation of the moonshine worms as an alien rather than an undescribed indigenous species increases the need for understanding population densities as management focus has shifted from conservation to mitigation or extirpation. During November and December 2017, density of D. aciculata was determined at 18 sites in the Knysna Estuary; 13 in the intertidal zone and 5 in the subtidal zone. Five sites also fell within the invertebrate reserve where baiting is prohibited. Diopatra aciculata was present throughout the estuary up to where freshwater conditions dominated. Distribution was patchy, with median densities ranging from 0 ± 0.03 to 8 ± 1.03 worms.m-2 (median ± standard error) and a maximum of 58 worms.m-2. Despite overall low mean density 3.54 worms.m-2, the estimated population size occupying the total potential habitable area of 6,487,600m2 exceeds 22 million worms. Bait collecting by fishermen is unlikely to be effective for large scale removal as baiting pressure was very low (5.48% maximum). Urgent research is needed to determine the impact of this species in the estuary as the Knysna Estuary is one of the most important estuaries in South Africa and alien ecosystem engineers such as Diopatra can have profound physical and biological impacts on their surroundings.