St Eustatius National Marine 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 two most important ecosystems found on the seabed within the marine park are sea grass beds and coral reefs. Both are highly productive, fragile and valuable marine resources.  Sea grass beds are found all around the island, from approximately 10m and deeper until about 35m.  Little is known about the sandy habitats between the shores of St. Eustatius and the coral reefs. The habitat is understood to be home to various species of animals and plants including crustaceans, sea stars, shrimp, nudibranch, worms and fish. Marine plants also exist in some areas including species of seagrass and algae.  Within the Southern Marine Reserve the seabed slopes steeply towards the drop off which goes down to depths in excess of 100 metres. The reef slope here is divided by a spur and groove system with coral fingers divided by sandy channels. The ‘rock fingers’ are hardened, ancient lava flows from the Quill volcano The walls, overhangs, ledges and tops of the fingers are encrusted with corals and other organisms which thrive in deeper waters such as Plate Corals, Sea Fans and Black Corals.  Around the Southern, Western and Northern Marine Park areas, volcanic activity has produced patch reefs, where coral reef organisms have settled on volcanic boulders and blocs that have been blown out from the Quill many years ago.The basaltic rock of the Northern and Southern ends of St Eustatius slopes into the sea at a relatively shallow angle, forming large ridges, flat areas and ledges. Reef organisms have settled on these areas creating a varied and diverse habitat.

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
Coral Reef ha 5 The reef habitat in St. Eustatius generally has low levels of rugosity, and after the bleaching event of 2010, low levels of coral cover (4.9%) and algae-dominated biotic cover (12.7%). Reef habitat was the most speciose habitat sampled and a total of 60 species were distinguished. Sponges and corals were equally important in terms of both cover and species richness. The main hard corals represented were: Meandrina meandrites, Montastrea annularis, M. cavernosa, and M. faveolata, Porites astreoides and Siderastrea siderea. Of the algae, Dictyota sp. was by far the dominant species and present at all stations while Lobophora variegata was also present at all stations. From: Debrot et al. 2013. Habitat diversity and bio-diversity of the benthic seascapes of St. Eustatius (attached)
Sea grass beds
Sea Grass Beds ha 1 Two different seagrass beds were distinguished: Dense seagrass beds dominated by the invasive Halophila stipulacea (between 45-95% cover) and sparse seagrass beds dominated by the native H. decipiens (between 8-25% cover). A third seagrass species was Syringodium filiformis, which was only found at densities of 2% or less. H. decipiens seagrass beds were more diverse than H. stipulacea seagrass beds with regards to associated algae. Seagrass beds of the invasive H. stipulacea showed the highest biotic cover of all benthic habitats. Seagrass beds of Thalassia, reported as being important in St. Eustatius by McRae and Esteban (2007) appear to have disappeared. From: Debrot et al. 2013. Habitat diversity and bio-diversity of the benthic seascapes of St. Eustatius (attached)
Rocks
Rubble with algae cover ha 6 Algae fields were found principally in rubble. Algae dominated in cover as well as in number of species but a variety of sponges and coral species were also found. Dictyota sp. is always present and in many case also Lobophora variegata. This habitat had the highest concentration of adult conch From: Debrot et al. 2013. Habitat diversity and bio-diversity of the benthic seascapes of St. Eustatius (attached)
Sand cover
Sandy bottom ha 8 Bare sand. No coverage of benthic species found. Habitat mostly found close to shore, but also between coral and gorgonian patches. From: Debrot et al. 2013. Habitat diversity and bio-diversity of the benthic seascapes of St. Eustatius (attached)
Other marine ecosystems
Gorgonian Reef ha 6 Hard or rubble bottom dominated by different gorgonian species, including sea fans, wire coral, sea plumes and sea fingers. From: Debrot et al. 2013. Habitat diversity and bio-diversity of the benthic seascapes of St. Eustatius (attached)
Terrestrial ecosystems
Size (estimate)
unit Area covered