Taxonomy and distribution of moonshine worms (Diopatra sp.) in Knysna estuary

van Rensburg, Hendré (2019-12)

Thesis (MSc)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Gesegmenteerde wurms as vis lokaas het die afgelope dekade toenemende gewildheid ervaar in die Knysna-riviermonding. Die teenwoordigheid van ‘n onbekende wurm, Diopatra sp. is tien jaar gelede vir die eerste keer in die Knysna-riviermond aangemeld toe dit in klein hoeveelhede as vis lokaas geoes is deur plaaslike vissers wat na die wurms as maanskyn-wurms verwys het. Aangesien hierdie baie opvallende spesie nie deur intensiewe biodiversiteit opname in die riviermonding in die 1950's en 1990's bespeur is nie, moet dit dus as nuut in die riviermonding beskou word. ‘n Voorlopige morfologiese ondersoek het getoon dat Diopatra sp. mag dalk Diopatra neapolitana (Delle Chiaje, 1841) wees. Diopatra neapolitana is egter 'n pseudo-kosmopolitaanse spesie met plaaslike verspreiding beperk tot Durban en Port Elizabeth. Aangesien verskeie kosmopolitiaanse spesies onlangs as kriptiese endemiese spesies beskryf is, is dit waarskynlik dat Diopatra sp. in die Knysna-riviermond ook 'n onbeskryfde kriptiese endemiese spesie verteenwoordig. Die doelstellings van hierdie studie was om eerstens Diopatra sp te identifiseer deur die gebruik van molekulêre en morfologiese tegnieke en tweedens om die digtheid en verspreiding van die spesies regdeur die riviermonding te bepaal asook die bevolkingsgrootte en die lokaasdruk (Hoeveelheid wurms onlangs verwyder in ʼn area weens lokaas oes) vir bewaringsbestuur. Bayesiese en maksimum waarskynlikheid analise van COI en 16S merkers het aangedui dat die Diopatra sp. in Suid-Afrika is Diopatra aciculata (Knox & Cameron, 1971) van Australië. Alhoewel DNS verskille tussen D. aciculata en D. neapolitana laer is as tussen ander spesies in die genus, was dit steeds 'n orde van grootte groter as die intra-spesie DNS diversiteit van albei spesies. Die skeiding van hierdie spesies word bevestig deur spesie-afbakening analise. Molekulêre ooreenkomste tussen D. aciculata en D. neapolitana word weerspieël deur morfologiese ooreenkomste en die twee spesies het soveel kenmerke in gemeen dat dit moeilik is om tussen hulle te onderskei. Die morfologie van D. aciculata uit Suid-Afrika het sterk ooreenkomste met beskrywings van Australië. Die bevestiging van die maanskyn-wurms as uitheems eerder as 'n onbeskryfde inheemse spesie, intensifiseer die behoefte om die digtheid van die bevolking te verstaan, aangesien fokus van bewaring tot versagting of uitwissing verskuif is. Gedurende November en Desember 2017 is digtheid van D. aciculata bepaal op 18 plekke in die Knysna-riviermonding; 13 in die tussengety-sone en 5 in die subgety-sone. Vyf plekke het ook in die ongewerwelde reservaat geval waar die oes van lokaas verbied is. Diopatra aciculata is regdeur die riviermonding aangetref tot aar varswater toestande begin oorheers het. Verspreiding was lappend, met mediaan digthede wat wissel van 0 ± 0.03 tot 8 ± 1.03 wurms.m-2 (mediaan ± standaard fout) en 'n reeks van 58 wurms.m-2. Ten spyte van ‘n algehele lae gemiddelde digtheid van 3.54 wurms.m-2, is die beraamde bevolkingsgrootte in die potensiële woonbare oppervlakte van 6,487,600m2 meer as 22 miljoen wurms. Dit is onwaarskynlik dat lokaas oes deur vissers effektief sal wees vir grootskaalse verwydering, aangesien die lokaasdruk baie laag was (5,48% maksimum). Dringende navorsing is nodig om die impak van hierdie spesie in die riviermonding te bepaal aangesien die Knysna-riviermonding een van die belangrikste riviermondings in Suid-Afrika is en uitheemse ekosisteem-ingenieurs soos Diopatra diepgaande fisiese en biologiese impakte op hul omgewing kan hê.

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