Aspects of the biology of deep-sea anthozoa

Bronsdon, Sarah Kirstin (1997) Aspects of the biology of deep-sea anthozoa. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This thesis considers aspects of the life history and reproduction of deep-sea members of two anthozoan orders from the northeast Atlantic. Shallow water representatives of the hexacorals and the octocorals have been extensively studied; many investigations have been directed at their reproductive mode and its influence on population genetics. Much of the currently accepted theory concerning reproductive strategies in the marine environment is derived from investigations of anthozoan species. In the remote bathyal and abyssal environments of the deep-sea, however, what little is known of anthozoan biology is largely restricted to taxonomy and distribution.

Two epizoic actinian species from the northeast Atlantic provide the main focus in this thesis. The first species, Amphianthus inornata, is epizoic on a bathyal gorgonian (Acanella arbuscula) and the second, Kadosactis commensalis, is epizoic on a holothurian which is characteristic of abyssal depths in the northeast Atlantic (Paroriza prouhoi). The octocorals considered in this thesis are species of the pennatulacean genus Umbellula. This pandemic genus is found in soft sediments at bathyal to abyssal depths. It occurs at low population densities, and is rarely captured. The taxonomy of this genus, of which there is currently no consensus, is reviewed. The most numerous species identified from the samples is Umbellula lindahli.

For the actinian species studied, theories developed from the examination of preserved material led to genetic investigations using enzyme electrophoresis. Genetic evidence suggests that Amphianthus inornata proliferates by asexual means. This is the first known case of asexual reproduction in a deep-sea actinian. Sexual reproduction in this species appears to be seasonal and may be related to the seasonal flux of phytodetritus known to occur in the northeast Atlantic. Information from wet weights, and histological evidence, suggest that Kadosactis commensalis is a protandrous hermaphrodite. Genetic data provided no evidence for asexual proliferation in this species, but it implies a degree of inbreeding in the population. There is no evidence to suppose that this species reproduces on a seasonal basis.

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