Abstract
Shore-based submersible operations, from 2006 to 2020, have allowed us to examine megabenthic assemblages along the island margin of Isla de Roatán from depths of about 150 to 750 m, including repeated observations of the same organisms. These dives were used to photo-document a diverse benthic assemblage and observe the health and condition of the sessile fauna in a well-explored but relatively undocumented area of the Mesoamerican Reef. Samples were collected by dip net, and some dives profiled the water column chemistry in the year 2011. The deep-sea coral assemblage observed off Roatan exhibits high abundance and diversity. The sessile habitat-forming taxa consist primarily of at least 20 different octocorals (e.g., Plexauridae, Primnoidae, Coralliidae, Isididae, and Ellisellidae) and 20 different sponges each (Demospongiae and Hexactinellida), with several known and unknown taxa of Zoantharia, Antipatharia (Bathypathes spp), and Scleractinia (e.g., Desmophyllum pertusum, Dendrophyllia alternata, Madracis myriaster, and solitary taxa). Crinoidea were also abundant and diverse, represented by at least nine species. Epifaunal assemblages associated with corals include at least 24 macroinvertebrate species dominated by Asteroschema laeve (Ophiuroidea) and Chirostylus spp. (Decapoda: Anomura). Repeated observations of a few large octocoral colonies over many years illustrate patterns of predation, recolonization, and epibiont host fidelity, including a 14-year record of decline in a plexaurid octocoral (putatively Paramuricea sp.) and loss of its resident ophiuroids. The shore-based submersible provides a practical and relatively inexpensive platform from which to study coral and sponge assemblages on a deep tropical island slope. The deep-sea coral gardens are likely to harbor new species and new discoveries if more samples can be acquired and made available for taxonomic research.
Highlights
Our knowledge and understanding of the ecology, physiology, biodiversity, and conservation of habitat-forming, deepand cold-water coral and sponge assemblages has broadened substantially over the last two decades (e.g., Freiwald et al 2004; Davies et al 2008; Davies and Guinotte 2011; Roberts et al 2006; Dahl et al 2012; Larsson et al 2013a, b; Cathalot et al 2015; Hourigan et al 2017; Quattrini et al 2017; Hebbeln et al 2019)
Subsequent dives were conducted to study the ecology of Crinoidea (Veitch and Baumiller 2021)
Dives recorded at least 32 morphological species of deep-water corals (6 colonial Scleractinia, 17 Octocorallia, 9 Antipatharia) at depths of ~ 150 m or greater
Summary
Our knowledge and understanding of the ecology, physiology, biodiversity, and conservation of habitat-forming, deepand cold-water coral and sponge assemblages has broadened substantially over the last two decades (e.g., Freiwald et al 2004; Davies et al 2008; Davies and Guinotte 2011; Roberts et al 2006; Dahl et al 2012; Larsson et al 2013a, b; Cathalot et al 2015; Hourigan et al 2017; Quattrini et al 2017; Hebbeln et al 2019). Fewer studies have incorporated time-series observations of the same sites and organisms over extended periods The increasingly widespread use of privately funded research submersibles (e.g., OceanX, Nekton Foundation, Curasub) offers the opportunity to conduct and expand in situ deep-sea time-series investigations. We report the preliminary results of ecological observations made using a privately owned submersible over a 14-year period. Isla de Roatán, off the north coast of Honduras, Central America, lies in the western Caribbean Sea at the southern end of the Mesoamerican Reef (Fig. 1), on the southern margin of a left-lateral strike-slip fault, the Swan Islands Transform Fault, near the west end of the Cayman Trough (Rosencrantz and Mann 1991). The deep island margin supports a high diversity of geologic and topographic features, beginning with the deep reef wall, and, below it, numerous slump blocks and a wide variety of outcrops and escarpments— limestone above ~ 400–450 m and basalt below—both exposed and sediment veneered and accompanied by extensive areas of unconsolidated sediment
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