Introduction
The presence of octocorals is recorded in all the world’s oceans and at all depths. While diversity of the group is highest in the tropical western Pacific, the Atlantic also maintains a rich octocoral species assemblage. Worldwide, there are approximately 340 genera of octocorals from 46 valid families (Bayer 1981a; Williams 1995; Williams 2001-2010). The growing number of new species recorded and revisions within the families makes it difficult to arrive at an exact number of species, but it is estimated at over 3200 worldwide (Bayer 1981a; Williams 1995; Williams 2001-2010; Daly et al. 2007). The Octocorallia has been the subject of many recent molecular phylogenetic studies which may eventually lead to major revisions of the classification as it is currently accepted. C.S. McFadden reviewed these studies and their significance to modern classification in Daly et.al (2007). Using the classification of Bayer (1981a) and Williams (1995), this work discusses 28 species from 11 families known from the South Atlantic Bight (SAB) to a depth of 200 m.
The presence of octocorals in nearly all benthic marine habitats indicates the adaptive nature of this group compared to other taxa within the Cnidaria. Octocorals are very numerous in shallow tropical reef communities and are well-documented in deep benthic communities, where the colonies may provide substrate in habitats with poor complexity. The diversity of the Octocorallia (=Alcyonaria) in the shallow SAB is low in comparison to similarly shallow areas of the Caribbean and tropical western Pacific, however this group can be considered an abundant sessile invertebrate taxon in hard bottom communities and colonies are often associated with numerous commensal organisms.
The paucity of recent, regional taxonomic literature and the problematic identification associated with the Octocorallia presented the need for this regional guide. Specifically, some members of the former Paramuriceidae (now Plexauridae) occurring in the shallow SAB have not been treated for several decades apart from inclusion in checklists and technical reports. This work aims to bridge this gap and is intended to assist scientists, managers, educators and students to identify, through the use of keys, species notes, and images, the octocorals present from depths less than 200 m in the SAB.
Prior work
The taxonomy and classification of western Atlantic octocorals were treated extensively by Deichmann (1936), who included in her monograph all western Atlantic shallow- and deep-water species known at the time and she also described several new species. Her work was a continuation of A. E. Verrill’s study of material collected during the Blake Expedition of 1877–1878, a manuscript he was unable to complete before his death. Nearly 30 years later, Bayer (1961) presented an updated taxonomic treatment of western Atlantic tropical and subtropical shallow water octocorals and then produced a key (Bayer, 1981a) to the non-pennatulacean genera of world-wide Octocorallia. Subsequently, Williams (1995) published a world key to the pennatulacean octocorals which complemented Bayer’s (1981a) key, and the two works comprise a standard for the modern classification of the Octocorallia. In the shadow of these important taxonomic works, the rationale for developing a regional key to the octocorals of the SAB was based on the following: a) since the publishing of Deichmann’s (1936) western Atlantic key many new species have been described, four of which are included in the present work, and octocoral classification has changed significantly; b) although works by Bayer (1981a) and Williams (1995) contain modern classifications, they treat worldwide genera and do not have species diagnoses; c) Bayer (1961) and Deichmann (1936) included many species that do not occur in the shallow SAB, creating the necessity of a regional, concise, user-friendly guide; d) there is a current lack of color and in situ images of growth forms of many species which are included in this guide.
Bayer (1961) did not include a key to the species or descriptions of the former Paramuriceidae (now Plexauridae) because they occurred too deep in the West Indian region. These species do occur in shallow water (<200 m) in the SAB and are included in this key. Also included are five range extensions not previously recorded in shallow water at this latitude range. Future collections will undoubtedly reveal new species, although none are described in this work. See Table 1 for an updated taxonomic listing of octocoral species recorded in the shallow SAB.
This document relies heavily on the prior work of F. M. Bayer and the reader is encouraged to refer to his relevant papers when identifying difficult specimens. In particular, his illustrations of octocoral sclerites are unparalleled and, in the absence of scanning electron microscope imagery, are the only quality reproductions of the sclerites of many species. Since the identification of virtually all octocoral species relies on sclerite morphology, his skillful illustrations are a valuable resource.
Unless otherwise noted, all references, key characteristics, diagnoses, etc. in this document are applicable to octocoral species in the shallow SAB and do not necessarily represent world species.
The South Atlantic Bight
For the purposes of this paper, the SAB is defined as the coastal waters of the United States between Cape Hatteras, North Carolina and Cape Canaveral, Florida (Figure 1). This region of the Atlantic encompasses the continental shelf, slope and rise, and includes the Blake Plateau. This work discusses only octocorals found in 200 m or less in the SAB, as the continental slope rapidly drops off at that point and becomes habitat to a significantly different assemblage of octocoral species. The sub-tropical and tropical areas to the south of Cape Canaveral have a more diverse group of octocorals, specifically gorgoniids and plexaurids, but some species overlap. Several species discussed in this work occur through the tropical latitudes and into the coast of South America, but for a few the southern tip of Florida is the limit to their southern range. Some of these species are absent in Florida and the Caribbean, but reappear in the Gulf of Mexico. Bayer (1954, 1961) discussed the concept of Carolinian fauna and disjunct populations in the northern Gulf of Mexico.
The following abbreviations have been used: GML-
Grice Marine Laboratory, College of Charleston, Charleston, SC;
NMNH - National Museum of Natural History (Smithsonian
Institution); SAB - South Atlantic Bight; SCDNR
– South Carolina Department of Natural Resources; SERTC
– Southeastern Regional Taxonomic Center, Charleston, SC;
USNM - United States National Museum, used for
previously cataloged material.
