Regeneration and reproduction in Sabella pavonina (Savigny): developing a novel method to culture marine ornamental sabellids
Student thesis: Doctoral Thesis
Collection of invertebrates from coral reefs has increased dramatically over the past two decades in response to the growing marine ornamental industry and, currently, more than 500 species (excluding corals) are traded globally. Controversy over the sustainability of the industry has been focused on damaging collection methods and, as a result, aquaculture of ornamental species is deemed the future priority solution in mitigating the effects of wild collection. For this to be realised, an in-depth understanding of the species' reproductive cycle, life history patterns and optimum growth conditions is necessary to overcome the current bottlenecks associated with artificial fertilisation which limit the success of rearing ornamental species in captivity. This research aimed to develop a novel method to culture ornamental sabellids utilising their excellent regenerative capacity in a process similar to coral fragging. Sabella pavonina, a temperate species found in Langstone Harbour, Portsmouth, UK, has been the subject of previous regenerative studies and was used as a model to develop the culture procedure for tropical species. A morphological study using standard scanning electron microscopy provided detailed observations on both anterior and posterior regeneration in sabellids which informed production of morphological keys used to quantify the process of regeneration. In addition, light microscope images were taken at 7 day intervals and processed using image analysis software to record the length of new tissue added to both an anterior and a posterior cut surface. Survivorship was high with :::: 80 % of individuals, which had been cut up to eight times, replacing the lost body part within four weeks. Replacing the missing posterior involved the healing of the cut surface, reconstruction of the pygidium and subsequent segment addition and was characterised by a gradual increase in the length of new tissue. Anterior regeneration was a more complex process following wound healing, involving reconstruction of a new mouth and the emergence of the branchial crown structure. The greatest increase of new tissue added anteriorly was between day 14 and day 21 when the branchial radioles were elongating in a process which exhibited a high degree of between-individual variation. Ornamental sabellids from various tropical locations including, the Batam Islands, Philippines and Kenya, like S. pavonina, were all capable of regenerating anteriorly and posteriorly within a four week period. In contrast to S. pavonina, the regeneration blastema of both the anterior and posterior cut surface of tropical sabellids was concealed by an invagination at the amputation site, and in addition, the process of morphallaxis was not observed. Higher mortality was recorded with the increasing XlI number of cuts made to tropical sabellids maintained in small static beakers of seawater and only 20 % of worms cut into eight pieces surviving the duration of the experiment. However, it is hypothesised that with the use of the biologically filtered culture system, survivorship could be further increased and regeneration rates optimised. Individuals that had regenerated were also capable of reconstructing a new tube within 10 days, replicating the appearance of their original, when maintained in aquaria containing suspended sediment. Trade of ornamental polychaetes in the UK was surveyed for the duration of this three year study through collaboration with Europe's largest wholesaler of marine ornamentals, the Tropical Marine Centre in London, and additionally, through postal and telephone surveys with retailers. The annual trade figures for polychaetes established in this research indicate that data available on the Global Marine Aquarium Database, the only available source of ornamental trade monitoring, is grossly underestimating the trade in polychaetes. While the Global Marine Aquarium Database state that 11,178 polychaetes were imported into the UK over a 10 year period, this study recorded import figures at 11,110 in one year alone. Furthermore, the confusing nature of trade taxonomy is confounded by knowledge gaps in the scientific literature and morphological keys currently available. A trade-off in the resource allocation between regeneration and reproduction has been documented in corals and, therefore, to facilitate the interpretation of regeneration results in the model S. pavonina, an ecological survey of the collection site was carried out. Population density quadrats, sediment cores and monthly reproductive sampling were undertaken for the duration of the research. Highest population densities (up to 30 per m2) were recorded on the low shore section with proximity to EL WST, and on sediment of mixed size. No significant relationship was found between the presence of S. pavonina and the associated macrofaunal community, however, the presence of epibionts on the surfaces of the sabellid tubes suggests they provide a unique form of secondary settlement space. Oogenesis was found to be a long process with oocytes first visible 10 September/October, approximately 9 months prior to spawning. The exact time of spawning was not identified and emphasised the need for further study to confirm the cost of regeneration in the context of reproduction. Ultimately, regeneration has excellent scope as a novel method of culture for ornamental sabellids, however, to fully optimise the technique, further research is vital in order to develop an in-depth knowledge of the species reproductive biology, ecology and biochemical composition.