Flora

Background:

Located in the Dutch Windward Islands, Saba Bank is a flat-topped seamount (20–45 m deep in the shallower regions). The primary goals of the survey were to improve knowledge of biodiversity for one of the world’s most significant, but little-known, seamounts and to increase basic data and analyses to promote the development of an improved management plan.

Methodology/Principal Findings:

Our team of three divers used scuba to collect algal samples to depths of 50 m at 17 dive sites. Over 360 macrophyte specimens (12 putative new species) were collected, more than 1,000 photographs were taken in truly exceptional habitats, and three astonishing new seaweed community types were discovered. These included: (1) ‘‘Field of Greens’’ (N 17u30.6209, W 63u27.7079) dominated by green seaweeds as well as some filamentous reds, (2) ‘‘Brown Town’’ (N 17u28.0279, W 63u14.9449) dominated by large brown algae, and (3) ‘‘Seaweed City’’ (N 17u26.4859, W 63u16.8509) with a diversity of spectacular fleshy red algae.

Conclusions/Significance:

Dives to 30 m in the more two-dimensional interior habitats revealed particularly robust specimens of algae typical of shallower seagrass beds, but here in the total absence of any seagrasses (seagrasses generally do not grow below 20 m). Our preliminary estimate of the number of total seaweed species on Saba Bank ranges from a minimum of 150 to 200. Few filamentous and thin sheet forms indicative of stressed or physically disturbed environments were observed. A more precise number still awaits further microscopic and molecular examinations in the laboratory. The expedition, while intensive, has only scratched the surface of this unique submerged seamount/atoll. 

Reefs of the windward Netherlands Antilles (Saba, Saba Bank, St. Eustatius, St. Maarten) were assessed at 24 sites in the late 1999. The Atlantic and Gulf Rapid Reef Assessment (AGGRA) protocol was used with modifications to detect recent hurricane impacts. Live coral cover averaged 18%. The assemblage of >10 cm stony corals was primarily composed of small-sized colonies (mean diameter = 37 cm) of which the Montastraea annularis complex was the most abundant (30% of colonies). Overall, =1% of the individually surveyed colonies had been physically damaged by Hurricane Lenny but injury levels were higher in Saba (2.6%). Bleaching was noted in 23% of colonies at the time of the assessment with the greatest percentage occurring on St. Maarten (44%) and the lowest on Saba Bank (9%). Total (recent + old) partial mortality of reef-building corals averaged less than 18% although levels were higher (26%) in Colpophyllia natans. Coral recruitment densities were relatively consistent (mean = 5 recruits/m2) across sites. Commercially significant fish species (i.e. serranids, lutjanids, haemulids >5 cm) were present with mean densities of 4.5 individuals/100 m2. High biomass (mean = 5.8 kg/100 m2) of grazing, herbivorous fishes (acanthurids, scarids >5 cm, Microspathodon chrysurus) partially explains the relatively low macroalgal cover (mean = 7%) throughout this area. Saba’s fish community had a greater total biomass than those in the other three geographic areas (mean = 11 kg/100 m2 versus 7 kg/100 m2). While the coral reefs of St. Maarten show signs of disturbance (i.e., increased bleaching and sedimentation), those of Saba, Saba Bank, and southern St. Eustatius have been relatively little disturbed by coastal development and remain potential sources of marine life. Nevertheless, reef development in the windward Netherlands Antilles is limited by frequent hurricanes.