Live to Die Another Day: Regeneration in Diopatra aciculata Knox and Cameron, 1971 (Annelida: Onuphidae) Collected as Bait in Knysna Estuary, South Africa

SIMPLE SUMMARY: The estuarine moonshine worm, Diopatra aciculata, is used extensively as bait in the Knysna Estuary in South Africa. During collection, the worm frequently breaks into multiple pieces. If discarded or unused pieces can regenerate to form separate individuals, the population may be maintained, or even increase, despite harvesting. This study investigated bait collecting habits of local fishermen and the natural incidence of regeneration in D. aciculata. Fishermen usually removed only part of the worm, leaving its tail in the tube and more than half the fishermen return up to 50% of bait collected to the estuary. Naturally occurring D. aciculata can regenerate missing anterior and posterior chaetigers, but only if amputation occurs before the 17th or after the 21st segment. Most unused fragments are probably too small to recover from damage inflicted during bait collection, so regeneration is unlikely to cause population expansion despite harvesting. However, some fishermen do move bait from the estuary. Range expansion can therefore occur if large fragments discarded at fishing sites in other estuaries do regenerate, forming new populations. ABSTRACT: Regeneration is critical for survivorship after injury, sublethal predation, and asexual reproduction; it allows individuals to recover, potentially enabling populations of bait species to overcome the effects of bait collection through incidental asexual reproduction. Opportunities for regeneration are created when worms break during collection (which happens more often than not) and are thrown back into the estuary. Additionally, the trade and movement of bait could result in the range expansion of invasive species. This study investigated bait collection habits of local fishermen and the in situ incidence of regeneration in the estuarine moonshine worm, Diopatra aciculata. The evidence shows that this species is capable of anterior and posterior regeneration. The disproportionately small percentage of worms that seem to be recovering from the degree of damage that may be inflicted during bait collection suggests that regeneration may not help worms to withstand the effects of bait collection. However, the continuous movement and discarding of even small numbers of bait in other estuaries can lead to range expansion through incremental build-up, forming new populations, if these fragments are large enough to regenerate.