Etnoyer, P.J.

The second Saba Bank Expedition in October 2008 aimed at improving the knowledge of the gorgonacea by generating a comprehensive species list for shallow and deep water species with georeferenced in-situ photographs and voucher specimens for each sample taken.
Gorgonian species were common and conspicuous at all sites surveyed, except perhaps in some deep water (~60m) rubble flats south of Poison Bank. A total of 47 species were collected, including two new species in the genera Pterogorgia and Lytreia. Pterogorgia n. sp. was collected twice from 20m depth in the D zone. Lytreia n. sp. was collected twice from 50m depth near the A zone. The total number of gorgonian species collected from shallow water was 39. The number of gorgonian species from deep water (>50m) was 12. There was some overlap in the zones, with 4 shallow water species (Muriceopsis flavida, Eunicea clavigera, Pseudopterogorgia acerosa, and Ps. bipinnata) occurring below 50m. The species accumulation curve for shallow water species indicates the slope of the fitted line decreases with effort, but the line shows no clear asymptote. The species accumulation curve for deep water collections is still climbing. The line could be interpreted as a linear rise in deep-water species richness. There is no indication we have collected all the gorgonian species from the Saba Bank

The survey results add 38 species to the list of gorgonacea known to occur on Saba bank. The discovery of a new species of Pterogorgia was surprising because a) the discovery was made in shallow, easily accessible water depths and b) the new species was collected from the relatively depauperate reef flats in the “D zone”. This suggests the reef flat area in the interior of the Bank may be largely unexplored and the true diversity of the reef flat areas may be somewhat underappreciated.

Saba Bank is a large submerged platform (~2200 km2), average depth 30 m, located 4 km southwest of Saba Island in Netherlands Antilles, Caribbean Sea. Ships traveling to and from oil terminals on nearby St. Eustatius routinely anchor on the Bank, damaging benthic megafauna. Gorgonian octocorals are vulnerable to anchor damage, and they are common and conspicuous in shallow water (15–50 m) around the banks. This prompted a rapid assessment of octocoral habitat and diversity. The primary objectives were to estimate total species richness and to characterize habitats vis a vis gorgonians. Landsat imagery and multibeam bathymetry were employed to identify random sites for quantitative transects. A Seabotix LBV200L remotely operated vehicle (ROV) and SCUBA were used to collect and survey to 130 m. A total of 14 scuba dives and 3 ROV dives were completed in 10 days. During that time, 48 octocoral species were collected, including two likely undescribed species in the genera Pterogorgia and Lytreia. Gorgonian richness was exceptional, but not all species were collected, because the species accumulation curve remained steeply inclined after all surveys. Two shallow-water gorgonian habitat types were identified using multidimensional scaling and hierarchical cluster analyses: 1) a high diversity, high density fore-reef environment characterized by Eunicea spp., Gorgonia spp., and Pseudopterogorgia spp. and 2) a low diversity, low density plateau environment characterized by Pseudopterogorgia acerosa, Pterogorgia guadalupensis, and Gorgonia mariae. The analyses support hypotheses of broad (~15 km) habitat homogeneity (ANOSIM, P>0.05), but a significant difference between fore-reef and plateau environments (ANOSIM, P<0.05). However, there was some indication of habitat heterogeneity along the 15 km study section of the 50 km platform edge along the southeast rim. Our results highlight the complexity and biodiversity of the Saba Bank, and emphasize the need for more scientific exploration. 

Findings:

Combining the findings of this study with that of other studies, the authors conclude that the coral assemblage on the Saba Bank is diverse and healthy; it is representative and typical of those found elsewhere in the Caribbean.

Coral Richness

• A total of 43 species were documented.
• There were no significant differences in coral composition amongst bottom types or depth classes.
• There was a significant difference between sites near and far from the platform edge. The number of coral species observed ranged from 0 and 1 in algal dominated habitats to 23 at a reef habitat on the Bank’s southern edge.
• Coral species richness was higher on reef dominated areas as opposed to algal dominated ones.

Coral Condition

• Bleaching was evident at 82% of the sites assessed with 43 colonies bleached.
• Only three coral colonies were observed to have disease.
• Five reef sites had stands of Staghorn Coral (Acropora cervicornis), a critically endangered species on the IUCN Red List.
• No physical damage consistent with anchor usage or sand scour from shipping activity was noted at any of the sites assessed.

Management Recommendations

1. Immediate action is necessary to protect the diverse coral reef habitats documented.
2. The five healthy stands of staghorn coral (A. cervicornis) and their surrounding should be given highest priority for full protection in the zoning use plan under development (in consultation with all stakeholders).
3. More information is needed on the Saba Bank to create a comprehensive zone use plan. For example, more sites need to be studied so as to get a more comprehensive coverage of the bank’s coral composition.

Abstract:

Biodiversity surveys were conducted on Saba Bank, Netherlands Antilles, to assess ichthyofaunal richness and to compare with published surveys of other Caribbean localities. The primary objective was to estimate the total species richness of the Saba Bank ichthyofauna. A variety of sampling techniques was utilized to survey the fish species of both the visually accessible megafauna and the camouflaged and small-sized species comprising the cryptic ichthyofauna. Based on results presented herein, the number of species known on Saba Bank is increased from 42 previously known species to 270 species. Expected species-accumulation curves demonstrate that the current estimate of species richness of fishes for Saba Bank under represents the actual richness, and our knowledge of the ichthyofauna has not plateaued. The total expected fish species richness may be somewhere between 320 and 411 species. The Saba Bank ichthyofaunal assemblage is compared to fish assemblages found elsewhere in the Caribbean. Despite the absence of shallow or emergent shore habitats like mangroves, Saba Bank ranks as having the eighth highest ichthyofaunal richness of surveyed localities in the Greater Caribbean. Some degree of habitat heterogeneity was evident. Fore-reef, patch-reef, and lagoonal habitats were sampled. Fish assemblages were significantly different between habitats. Species richness was highest on the fore reef, but 11 species were found only at lagoonal sites. A comprehensive, annotated list of the fishes currently known to occur on Saba Bank, Netherland Antilles, is provided and color photographs of freshly collected specimens are presented for 165 of the listed species of Saba Bank fishes to facilitate identification and taxonomic comparison with similar taxa at other localities. Coloration of some species is shown for the first time. Preliminary analysis indicates that at least six undescribed new species were collected during the survey and these are indicated in the annotated list.