BIOLUMINESCENCE IN OCTOCORALS (Table 1).--- For the sake of the following discussion, the various groups of octocorals are defined here as follows. Stoloniferous octocorals have separate polyps connected at their bases by membranous or ribbon-like stolons. Soft corals have polyps embedded in a common coenenchyme and are attached to hard substrata by basal holdfasts, they have no axial development, and only free sclerites comprise the skeletal elements. Gorgonians, like the soft corals, have polyps embedded in a common coenenchyme and are attached to the substratum by basal holdfasts, but unlike soft corals, in addition to free sclerites, have some form of internal axial development composed of calcium carbonate, gorgonin, or a combination of the two. Sea pens or pennatulaceans have the coral colony divided into a proximal muscular peduncle that is anchored in soft substrata, and a distal rachis that contains several kinds of polyps. They may or may not have a calcareous axial skeleton.

Williams (1999: 23, 49-50) provides a historical review and comprehensive bibliography pertaining to pennatulacean bioluminescence. The scientific literature regarding bioluminescence in octocorals is relatively rich, extending back to the sixteenth century with the works of Gesner, Boussuet, Imperato, Rondelet, and others. Important modern contributions include: Panceri (1871,

1872a, b); Parker (1920); Harvey (1940, 1952); Nicol (1958); Titschak (1965, 1966); Morin (1976); Muzik (1978); and Herring (1991). Harvey (1952: 168) states, "…but among the Alcyonaria are to be found some of the most brilliant and striking luminous animals. Of the three groups of Alcyonaria, the Alcyonacea, the Gorgonacea, and the Pennatulacea, only luminescence of the Pennatulacea has been carefully studied." Pertaining to alcyonaceans, only a few species in the gorgonian family Isididae have until now been the only taxa known to luminesce. Mangold's (1910) record of Leuckart's luminescent Alcyonium is considered by Harvey (1952: 169-170) to be "very dubious". No subsequent records of bioluminescence in the genus Alcyonium, or any other soft coral taxon for that matter, are known in the previous literature.

The only records of bioluminescent soft corals are represented by new data presented here of Eleutherobia grayi from the Solomon Islands, as well as observations made on two other species of Eleutherobia (Eleutherobia spp. indet.). One of these is found on vertical surfaces at 12 meters depth in southern Luzon, Philippines (pers. observ., and pers. comm. T.M. Gosliner), and Saipan (pers. comm. J. Starmer), and the other has been collected from Palau (pers. comm. J. Starmer). These observations presented here are the first records of bioluminescent soft corals (outside of the dubious record of Leuckart's Alcyonium).

The phenomenon of bioluminescence in the Pennatulacea, although commonly encountered in bathymetrically diverse habitats and supported by a relatively rich literature, is by no means universal, as some taxa are definitely not luminescent. For example, Herring (1978: 204) states that some species of Virgularia have been shown to be non-luminous.

Bioluminescence has thus far been recorded in only 53% of the pennatulacean families (8 of 15), 40% of the genera (13 of 32), and 10% of the estimated number of valid species (19 of 186). If the total number of described species in the literature are taken into account, then the latter percentage drops to approximately 4% (or 19 of 436). These estimates represent minimum values, but could be much higher, and are based on numbers of taxa in Williams (1995: 93) and table 1 of the present paper.

It is surprising that after nearly 450 years of published observations resulting in more than eighty published accounts of pennatulacean bioluminescence, a mere nineteen species (or approximately 10% of the valid species) have been recorded. This number seems especially low considering the introduction of modern technological means to make observations - such as SCUBA, remote operational vehicles (ROV's), and manned deep-sea submersibles. Only a few sea pens are diurnal and/or zooxanthellate, and are not known to bioluminesce. The majority of shallow water species (at least in the Indo-Pacific) are nocturnal and azooxanthellate (Williams, pers. observ.). One South African species, Actinoptilum molle, appears to be active both during the day and night, and is at the same time azooxanthellate and bioluminescent (Williams, 1990: 63). In addition, a remarkable diversity of deep-water taxa are known (Williams, 1993: 733-734; 1997: 499, 503), which live in perpetual darkness. It is therefore assumed that the actual number of bioluminescent sea pens could be much higher than is presently documented.

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