High ecological resilience of the sea fan Gorgonia ventalina during two severe hurricanes

Since about the turn of the millennium, octocorals have been increasing in abundance on Caribbean reefs. The mechanisms underlying this trend have not been resolved, but the emergent species assemblage appears to be more resilient than the scleractinians they are replacing. The sea fan Gorgonia ventalina is an iconic species in the contemporary octocoral fauna, and here its population dynamics are described from St. John, US Virgin Islands, from 2013 to 2019. Mean densities of G. ventalina at Yawzi Point (9-m depth) varied from 1.4–1.5 colonies m−2, and their mean heights from 24–30 cm; nearby at Tektite (14-m depth), they varied from 0.6–0.8 colonies m−2 and from 25–33 cm. These reefs were impacted by two Category 5 hurricanes in 2017, but neither the density of G. ventalina, the density of their recruits (< 5-cm tall), nor the height of colonies, differed among years, although growth was depressed after the hurricanes. Nevertheless, at Tektite, colony height trended upwards over time, in part because colonies 10.1–20 cm tall were reduced in abundance after the hurricanes. These trends were sustained without density-associated effects mediating recruitment or self-thinning of adults. The dynamics of G. ventalina over seven years reveals the high resilience of this species that will contribute to the persistence of octocorals as a dominant state on Caribbean reefs.

Pathology of multifocal purple spots, a nonspecific lesion morphology of Caribbean sea fans Gorgonia spp.

Disease is contributing to the decline of coral reefs globally, but the cause and pathogenesis of most coral diseases are poorly understood. Using Gorgonia ventalina and G. flabellum as a model for coral disease diagnosis, we histologically and microbiologically examined 45 biopsies of lesions resembling Gorgonia multifocal purple spots (MFPS) with the aim of forming a comprehensive case definition based on gross and microscopic morphologic descriptions and associated etiologies. Macroscopically, all lesions were small circular areas of purple pigmentation. Gross morphologies included pigmentation only (4/45, 9%), or pigmentation with branchlet expansion and fusion (19/45, 22%), sessile masses (17/45, 38%), or hard nodules (5/45, 9%). Histological morphologic diagnoses included amoebocyte encapsulation (9/45, 20%), coenenchymal amoebocytosis (6/45, 13%), melanin (17/45, 38%), and gorgonin deposition (13/45, 29%). Sixty-four percent of instances of fungi and 86% of labyrinthulomycetes were localized to grossly normal portions of the biopsy, whereas barnacles were only within lesions, and 87% of instances of algae and 82% of cyanobacteria were within lesioned area of the biopsy. Penicillium (n = 12) was the predominant genus of fungi isolated from biopsies. Barnacles were identified as Conopea sp. using molecular techniques. The pathology and etiology underlying MFPS lesions are diverse, consistent with a highly nonspecific lesion pattern rather than a specific disease. This study demonstrates the importance of microscopic examination of tissues for accurate classification of coral diseases and lesion patterns.

Unprecedented densities of Gorgonia sea fans on coral reefs in St. John, US Virgin Islands?

Gorgonia ventalina is an iconic member of the octocoral fauna of shallow Caribbean reefs, and here we report unprecedentedly high population densities on the south shore of St. John, 35 mo after being hit by two hurricanes.

Comparison of chemical compounds associated with sclerites from healthy and diseased sea fan corals (Gorgonia ventalina)

Background The roles of gorgonian sclerites as structural components and predator deterrents have been widely studied. Yet their role as barriers against microbes has only recently been investigated, and even less is known about the diversity and roles of the chemical compounds associated with sclerites. Methods Here, we examine the semi-volatile organic compound fraction (SVOCs) associated with sclerites from healthy and diseased Gorgonia ventalina sea fan corals to understand their possible role as a stress response or in defense of infection. We also measured the oxidative potential of compounds from diseased and healthy G. ventalina colonies. Results The results showed that sclerites harbor a great diversity of SVOCs. Overall, 70 compounds were identified, the majority of which are novel with unknown biological roles. The majority of SVOCs identified exhibit multiple immune-related roles including antimicrobial and radical scavenging functions. The free radical activity assays further confirmed the anti-oxidative potential of some these compounds. The anti-oxidative activity was, nonetheless, similar across sclerites regardless of the health condition of the colony, although sclerites from diseased sea fans display slightly higher anti-oxidative activity than the healthy ones. Discussion Sclerites harbor great SVOCs diversity, the majority of which are novel to sea fans or any other corals. Yet the scientific literature consulted showed that the roles of compounds found in sclerites vary from antioxidant to antimicrobial compounds. However, this study fell short in determine the origin of the SVOCs identified, undermining our capacity to determine the biological roles of the SVOCs on sclerites and sea fans.