Saba Bank National Park

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Chapter 3. SITE DESCRIPTION

Flora

Brief description of the main plant assemblages significant or particular in the area:


During a ten day expedtion in 2006 three hundred sixty specimens of macrophytes were collected and a preliminary estimate of the number of macrophyte species collected from Saba Bank ranges upward from 150 to 200. However, the present annotated checklist of 98 taxa includes 43 Rhodophyta, 26 Chlorophyta, 26 Phaeophyceae, and 3 Cyanophyta (Cyanobacteria). The species accrual curve for the collections was steadily inclined after the 17 dive sites, and showed no clear asymptote, indicating Saba Bank has many more species to be collected. It is important to note that there were few filamentous and thin sheet forms indicative of stressed or physically disturbed environments observed.
Three sites surveyed were dominated by previously unknown unique algal communities. These included:

(1) ‘‘Field of Greens’’ (N 17u30.6209, W 63u27.7079) characterized by an abundance by green seaweeds (Chlorophyta) as well as some filamentous reds,

(2) ‘‘Brown Town’’ (N 17o28.0279, W 63o14.9449) dominated by large brown algae (Phaeophyceae), and

(3) ‘‘Seaweed City’’ (N 17o26.4859, W 63o16.8509) with a diversity of spectacular fleshy red algae (Rhodophyta). Possibly 12 new species of brown algae may be named following further scientific investigation. All of these macroalgae and their collection locations can be viewed as a
virtual herbarium (http://sweetgum.nybg.org/saba/algae.html), where users can search for any combination of phylum, family, genus, species, infra-specific rank, author, collector, collector number and precise location as a satellite map and longitude/latitude. Searching for a given parameter generates information associated with the specimens collected by the project under that parameter. Images taken of in situ living plants from the field are attached at the bottom of the label data.

Prior to this survey, the two most diverse areas for algae reported in the Caribbean had been Diamond Rock, Martinique and Pelican Cays, Belize, a mangrove, seagrass, and coral complex. Habitats on Saba Bank have far exceeded both of these places for species diversity per unit collection effort. A major reason for this uniqueness and richness is the sheer size and habitat range of the seamount/atoll.

The rim habitats range from windward pristine coral reefs to extensive leeward rhodolith (coralline algal spheres) beds (N 17o25.8329, W 63o40.9629) containing a high diversity of small epiphytic algal taxa. The Relative Dominance Model is useful for characterizing the health of any given coral reef. According to this model, healthy coral reefs are dominated by reef-building (hermatypic) corals, crustose coralline algae, and high populations of herbivorous fishes – all characteristic of Saba Bank’s windward eastern rim and fore-reef slope.

Vast sedimentary environments with some interspersed bedrock create relatively unstructured interior plains behind the rim communities, where seagrass beds would normally abound. However, seagrasses are absent (presumably due to excessive depths and insufficient light). Here vast plains of various groups of large and robust algal forms provide the three-dimensional structural heterogeneity. These are many of the rhizophytic (i.e., rooted) Bryopsidales forms typical of healthy seagrass beds in the sedimentary habitats. The seagrass model indicates that these sand plains of robust large epiphyte-free green algae, as in Field of Greens, indicate pristine oligotrophic conditions. The same can be said in the cases of Brown Town and Seaweed City, where especially clean robust macroalgal forms predominate on hard bottom. Few filamentous and thin sheet forms indicative of stressed or physically disturbed environments were observed.

List of plant species within the site that are in SPAW Annex I

List of species in SPAW annex I Estimate of population size Comments if any

List of plant species within the site that are in SPAW Annex III

List of species in SPAW annex III Estimate of population size Comments if any

List of plant species within the site that are in the IUCN Red List. UICN red list : http://www.iucnredlist.org/apps/redlist/search You will specify the IUCN Status (CR:critically endangered; EN:endangered; VU:vulnerable).

List of species in IUCN red list that are present in your site IUCN Status Estimate of population size Comments if any

List of plant species within the site that are in the national list of protected species

List of species in the national list of protected species that are present in your site Estimate of population size Comments if any

Fauna

Brief descript° of the main fauna populations and/or those of particular importance present (resident or migratory) in the area:


A total of 33 coral species were documented on the Saba Bank in a rapid assessment of only 17 sites during the 2005 expedition. More species of coral remain to be found. Most species are rare, so an asymptotic curve indicates that most of the common species were collected. Undocumented coral species are likely to be found through more exhaustive sampling effort in coral dominated reef habitats, at remote sites, and in deeper depths.

Biodiversity surveys were conducted on Saba Bank in 2005 and 2007, 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. The number of species known on Saba Bank was 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 available at http://www.ploscollections.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0010676 including color photographs of freshly collected specimens 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. 

In addition to all of the animals usually seen around the reefs and other marine habitats, some less frequently spotted species exist. Two turtle species use the waters as a foraging and breeding ground; Hawksbill Turtles (Eretmochelys imbricata) and Green Turtles (Chelonia mydas). Sharks are often spotted on the Bank, nurse shark, reef shark (Carcharhinus perezi), blacktip shark, (Carcharhinus limbatus), and tiger shark (Galeocerdo cuvier).

Large areas of the Saba Bank are characterized by hard substrate with communities dominated by algae, sponges and/or gorgonians.

The 2007 survey results added 28 species and 7 genera to the list of gorgonian octocorals known to occur on Saba Bank. Surveys resulted in a four-fold increase in knowledge of gorgonian species richness. Richness was higher than other sites in the region, but the species composition was not significantly different from other Western Atlantic and Caribbean sites. Our data indicate we cannot assume we collected all of even the most common species. Most species are rare, so an asymptotic function implies only that the most common species were collected. Our species accrual curve did not approach asymptote, so both rare and common species remain to be discovered. This is remarkable, considering the shallow gorgonian assemblage is already rich when compared to other places. Saba Bank has at least 43 zooxanthellate octocoral species, compared to Florida (S = 39), Providencia Island, Colombia (S = 32), and Puerto Rico (S = 38). It would be useful to compare species accrual curves at each of these localities.Two previously undescribed species were discovered: one Pterogorgia sp in shallow water and a Lytreia sp. in 130 m depth