Saba Bank National Park

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Chapter 3. SITE DESCRIPTION

c - Biological features

Habitats

Brief description of dominant and particular habitats (marine and terrestrial)*: List here the habitats and ecosystems that are representative and/or of importance for the WCR (i.e. mangroves, coral reefs, etc):


The marine habitats represented within the Saba Bank can be categorized as follows:

  •  Open water: supporting planktonic and pelagic sea creatures including fish and migratory species such as whales, dolphin, and sea turtles,
  • sea bed (benthos): supporting coral reefs, algae (and possibly sea grass beds), and infauna (burrowing creatures like mollusks and worms), benthic invertebrates and fish.

There is regular exchange of water, energy and materials between each of these habitats. Organisms also move freely between the different environments for feeding and reproduction. As the waters around the Saba Bank are very deep the Bank has very little, if any, exposure to terrestrial influences. This includes freshwater runoff, sediments, nutrients and any form of coastal pollution, which all stress and eventually kill marine organisms.

Open Water

The open water supports pelagic fish populations, most of which are highly migratory such as Tuna (Thunnus sp.), Dolphin (Dorado / Coryphaena hippurus) and Wahoo (Acanthocybium solandri) as well as Marlin (Makaira sp.) and swordfish (Xiphias gladius) which are found primarily around the edges of the Bank.

 

While there is little documented information of Caribbean species of turtle that can be found on Saba Bank, there have been several confirmed sightings of Hawksbills (Eretmochelys imbricata) during the 2007 survey, indicating the Bank is a foraging area for them. It is quite likely that the Bank is an important foraging are for Green Turtles (Chelonia mydas) as well due to the large algae fields. Leatherbacks (Dermochelys coriacea), and Loggerheads (Caretta caretta) have been seen on the Bank so it is quite likely that they also use the Bank for foraging, though the leaterbacks were likely only migrating through.

 

A number of Cetaceans are present on the Saba Bank, including; Humpback Whales (Megaptera novaeangliae), Sperm Whales (Physeter macrocephalus), Spinner Dolphins (Stenella longirostris), and Bottlenose Dolphins (Tursiops truncatus). Humpback whales, migrating north to their mating grounds, are occasionally seen in the channel between Saba and the Bank. A humpback whale with calf was seen on the Bank in the area known as Moonfish Bank during the 2006 expedition. During dives in February 2002 and in January 2006, humpback whale song was heard.

 

There are a number of birds that live almost exclusively in the open ocean environment, using Saba as a breeding ground or migratory stop over. These include Frigate Birds (Fregata magnificens), Red Billed Tropicbirds (Phaethon aethereus), Brown Pelicans (Pelecanus occidentalis) and Audubon’s Shearwater (Puffinus lherminieri).

 

Pelagic zone

With the exception of the seabed, everything in blue water beyond the 30m depth contour can be considered the pelagic zone. The pelagic environment is commonly thought of as being made up of number of different ecological zones; most importantly, the epipelagic, mesopelagic and the bathypelagic; we will only be discussing the epipelagic zone.

 

  • Epipelagic: The epipelagic zone stretches from the surface down to 200 meters. This is where most plants and animals (flora and fauna) live due to the abundance of light and nutrients. Pelagic fish species are found in this part of the sea around the edges of the Saba Bank. This includes small bait fish such as Herring (Clupea harengus) – a major food source for marine mammals, and larger, predatory fish such as the blackfin tuna (Thunnus atlanticus), Wahoo (Acanthocybium solandri) and Dolphin (Dorado - Coryphaena hippurus) all of which are commercially important species.

 

Healthy and abundant migratory pelagic fish stocks of Tuna, Dolphin and Wahoo are critical to support Saba’s small scale local fishing industry. Globally endangered cetaceans and sea turtles regularly migrate through Saba waters.

 

Sea Bed

Deep sea bottom

Soft-bottom habitats make up some of the deep areas along the south east edge. The sediments are usually comprised of a mixture of biologically fixed silica and calcium carbonate, as well as silts, and sand sediments.

There is little known about the deep water environments on the Saba Bank which are beyond the reach of SCUBA divers. However, with the use of a remotely operated vehicle (ROV) it was possible to examine a number of deeper sites on the Bank. Observations made from the ROV indicate that substrate and benthic communities show consistent zonation patterns along the depth gradient of the front reef slope. A transition in the reef fish assemblage was also evident, though less pronounced, along this same depth gradient. Fish diversity was greatest in the reef crest zone and declined with depth, however sightings of commercially important lutjanid species such as silk and blackfin snapper increased with depth.

Some experimental deep water fishing was conducted during the October survey. Some of the fish caught included the snowy grouper (Epinephelus niveatus), saddled moray (Gymnothorax conspersus), sharktooth moray (Gymnothorax maderensis), grey conger (Conger esculentus), and a deep body boarfish (Antigonia capros).

In addition to the surveys at Overall Bank, four ROV surveys were made at two other Saba Bank areas: Poison Bank and Grapplers Bank. The substrate at Poison Bank was comprised of coralline algal nodules or “rhodoliths” which formed extensive rhodolith beds. At Grapplers Bank, a steep rocky escarpment was explored. The near-vertical rocky scarp began at 120 m depth and extended down slope beyond the limits of the ROV survey (157 m depth). Observations made from ROV at Overall Bank suggested a continuous reef system that is relatively uniform and predictable at mid-depths in terms of its structure, substrate composition, and community zonation patterns. In contrast, the few observations made by ROV at Poison Bank and Grapplers Bank revealed habitats that were quite different from those at Overall Bank. This implies that explorations to new areas of Saba Bank are likely to reveal still greater diversity in mid-depth habitat types.

Research voyages in the Florida Keys which have explored deep water environments have recorded considerable numbers of new invertebrate and fish species. There is every reason to believe that the same would be true of the deep water benthic environment on the Saba Bank. In 2007 two new species of gorgonians were discovered with 8 dives with the ROV. With further sampling it is quite possible that more new species would be discovered.

Coral reefs

The coral reefs are found primarily along the east and southeast edges of the Bank and are rich in terms of cover and diversity of reef-building corals. There are a variety of reef types on the Saba Bank, from patch reefs through spur and groove type reefs with sandy channels. Each of these provides a hard substrate for coral and other animals to settle on, which in turn attracts fish and an abundance of other invertebrates.

The coral reefs are home to many fish species including, Angelfish (Holocanthus sp. and many others), Groupers, Triggerfish, Scorpionfish, Moray eels (e.g. Gymnothorax moringa), Wrasses and Chromis, Parrotfish, and roaming schools of Blue Tangs (Acanthurus coeruleus). In sandy areas Garden eels (Heteroconger halis), Peacock Flounder (Bothus lunatus), Stingrays (Dasyatis Americana) and Flying Gurnard (Dactylopterus volitans) can all be seen. Near to the reefs in the blue water, Black Jacks (Caranx lugubris), Bar jacks (Caranx ruber), Barracuda (Sphyraena sp.) and schools of Horse-eye jacks (Caranx latus) and Wahoo (Acanthocybium solandri) roam around looking to feed off the smaller reef fish.

The value of the coral reef of the Bank is not based on tourism, as is the case with the reefs of the Saba Marine Park, with respect to their economic importance to Saba, but its value is in the biodiversity and the habitat they provide for many animals and plants, which commercial and artisanal fisheries depend on. The coral reefs provide a habitat for a wide variety of creatures other than fish and coral. Countless species of crustaceans, worms, anemones, jellyfish, mollusks, echinoderms (sea-cucumbers and starfish), bryozoans, and sponges live on the reefs.

In addition to all of the animals and plants 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).

Colonized pavement

Distributed throughout the remaining available habitat, wherever there is hard substrate available, there are communities dominated by algae, sponges and/or gorgonians. These communities typically have a less complex substrate with almost no slopes, varying amounts of sand cover, and a moderate energy regime.

Although the structural heterogeneity that supports reef biodiversity is absent, these areas do provide food, refuge, and much sought after space to numerous invertebrates such as lobster, queen conch, and fishes. These communities provide linkages to surrounding marine communities. According to preliminary benthic habitat maps, these communities dominate the seafloor of the central area of the Bank.

 

Detail for each habitat/ecosystem the area it covers:

Marine / coastal ecosystem categories
Detail for each habitat / ecosystem the area covers
Size (estimate) Description and comments
unit Area covered
Coral reefs
Eastern and Southern fringe ha 1750
Other marine ecosystems
hard bottom macro-algal communities ha not given Main ecosystem of the Saba Bank. Variously characterized by presence of large gorgonians or sponges in addition to the dominance of macro-algae
Terrestrial ecosystems
Size (estimate)
unit Area covered