Content on this page was last updated in 2006. Some of the content may be out of date. For more information: http://www.fws.gov/caribbean/Refuges/Navassa/
Macroalgae (seaweeds) appear to be the dominant benthic groups of the shallow and deeper locations. Prominent genera are the brown algae, Lobophora, Sargassum,Dictyota, and Stypopodium, and the green alga, Halimeda. Lobophora variegata is of pharmaceutical interest because it produces a potent antifungal compound used as a natural antibiotic to defend itself against infection. Some coralline algae and Foraminifera are found at depths much greater than expected, indicating very clear water around Navassa.
Lobophora variegata, a dominant macroalgal species (photo: US. Geological survey)
Prominent brown alga, Dictyota sp, is found in the shallow and deeper marine habitats of Navassa Island. (Photo: U.S. Geological Survey)
Large, brightly colored sponges in the genus Agelas cover 10-20 percent of the reef area at most locations sampled (Miller, et al., 2005). Species of barrel sponge (Xestospongia) and other Demospongiae (Grace, et al. 2000) are also found in these reef habitats. The dominant sponge across all habitats was the touch-me-not sponge, Neofibularia nolitangere.
The touch-me-not sponge, Fibularia nolitangere. (Photo: NOAA/Frank and Joyce Burek)
A Coral and two sponges (Photo: NOAA)
Within the benthic communities, live coral cover ranges from three percent on the northern shelf hard bottom communities to over 40 percent on some deep patch reefs. Shallow shelf and spur and groove habitats average almost 20 percent live coral cover (Miller, 2003). The dominant hard corals deeper than 25 meters are species of star corals (Montastraea sp), lettuce corals (Agaricia sp), and finger corals (Porites porites). Other corals deeper than 25 meters are the mustard hill coral (Porites astreoides), brain coral (Diploria sp) , pencil coral (Madracis sp), fire coral (Millepora sp), smooth flower coral (Eusmilia fastigiata), boulder brain coral (Colpophyllia natans), cactus coral (Mycetophyllia danae), maze coral (Meandrina meandites), and the massive starlet coral (Siderastrea siderea). Lettuce coral (Agaricia sp) is the dominant coral in the shallower sites (Miller et al., 2005).
The marine snail, Coralliophila abbreviate, feeding on living coral polyps (Photo: Andrew Bruckner/NOAA)
Miller (2003, 2005) reports that the elkhorn coral (Acropora palmata) is increasing in abundance, compared to earlier observations in 2002. Staghorn coral (Acropora cervicornis), however, remains rare and in poor condition.
Threats to the live coral are few, but include the short coral snail, Coralliophila abbreviata, a voracious predator on corals, invasion by bio-eroding sponges, Cliona sp, and a disease of unknown origin, but similar to white plague, in deeper habitats that affects the brain corals, Diploria spp and Colpophyllia natans (Miller 2003, 2005). In general, the overall condition of corals in shallow habitats is good with little incidence of disease.
The star coral (Montastraea cavernosa) from Navassa Island (Photo: USGS)
The black sea fan (Iciligorgia schrammi) (Photo: Geoff Schultz)
Twenty-one species of gorgonians (sea fans) typical of Caribbean shallow water gorgonians, are found at habitats from 15 to 20 meters. The population densities of gorgonians are relatively low at the shallow depths, but may be greater at other habitats. The dominant species in the northwest is the purple sea fan, Gorgonia ventalina. The black sea fan, Iciligorgia schrammi, is usually found along vertical walls or slope breaks in deeper waters with very clear water and high currents. It has not been observed in the shallow waters of Lulu Bay or in the northwestern sector of the island. Other gorgonians observed at study sites are the forked or bipinnate sea feather, Pseudopterogorgia bipinnata, the bottle-brush coral, Muriceopsis flavida, the shelf knob sea rod, Eunicea succinea, the tan bushy soft coral, Plexaura flexosa, the common bushy soft coral, Plexaura homomalla, the purple sea plume, Pseudopterogorgia acerosa, and the spiny sea fan, Muricea muricata.
Maze coral (Meandrina meandites) (Photo:CCMA/NOAA)
The black sea fan (Iciligorgia schrammi) (Photo: Geoff Schultz)
Mollusks and Other Invertebrates
Conch surveys in 2006 indicated low abundances of mostly adult queen conchs (Strombus gigas) (Piniak et al., 2006)
A partial list of mollusks, other invertebrates, and algae observed at Navassa Island appears in Grace et al, 2000.
Numerically, approximately 71 percent of the fishes of Navassa Island are plankton-feeding species. Herbivores constitute about 18 percent of the remaining fish assemblages and the remainder is composed of fish-eating and invertebrate-eating species. Large individuals of all species were notably absent (Miller, 2003, Collette et al., 2003).
In the spring of 1999, Collette et al. (2003) collected or recorded 224 species of fishes from 66 families, making a total of 237 species known from Navassa. Miller (2003) added an additional 35 species, making a total of 272 species. Most of the Navassa fishes are reef species that are widely-distributed throughout the Caribbean sea (Collette et al., 2003).
The princess parrotfish, Scarus taeniopterus (Photo: gmc travel)
The red band parrotfish Sparisoma aurofrenatum (Photo: Dr. John E. Randall)
Navassa lacks families associated with the continental shelf or seagrass meadows. Forage fishes such as herrings and anchovies are also absent. Most medium to large sized fishes such as grunts (Haemulidae), groupers (Serranidae), snappers (Lutjanidae), and parrotfishes (Scaridae) were rare or absent from the shallower and accessible areas at the northwestern end of the island. There were more large fishes in the deeper and less accessible southern end of the island. This marked difference may be the result of the heavy fishing pressure by the Haitian fishers. Piniak et al. (2006) surveyed the fish communities along the deep shelf (28-34 meters) and observed numerous squirrelfishes, triggerfishes, and parrotfishes. Groupers and snappers were also present, but no small individuals were observed. The three most common families of fishes were parrotfishes (Scaridae), triggerfishes (Balistidae), and surgeonfishes (Acanthuridae).
Miller (2003) reported that the most abundant species, comprising nearly 60 percent of the total number, are the blue chromis (Chromis cyanea), creole wrasse (Clepticus parrae), bluehead wrasse (Thalassoma bifasciatum) and bicolor damselfish (Stegastes partitus). Species with the highest frequency of occurrence from all of the samples were the blue tang (Acanthurus coeruleus), followed by the princess parrotfish (Scarus taeniopteru), redband parrotfish (Sparisoma aurofrenatum), bluehead wrasse, bicolor damselfish, and black durgon (Melichthys niger).
The bicolor damselfish (Stegastes partitus) (Photo: Dr John E. Randall)
The scalloped hammerhead shark (Sphyrna lewini) (Photo: Dr John E. Randall)
Collette et al. (2003) published an annotated and illustrated list of shore fishes of Navassa Island. A list of fish species with collection and observational methods is given in Grace et al., 2000.
Captures by bottom longline include the bull shark (Carcharhinus leucas), smooth dogfish (Mustelus canis), scalloped hammerhead (Sphyrna lewini), great barracuda (Sphyraena barracuda), silk snapper (Lutjanus vivanus), and misty grouper (Epinephelus mystacinus).