date, four indigenous seagrasses have
been identified in Dominica, namely Syringodium filiforme (0.5-18m
depth), Halodule wrightii (0.5-16m depth), Thalassia testudinum
(0.25-10m depth), and Halophila decipiens(5-25m+ depth).The
invasive species Halophila stipulacea (originating from the
Indian Ocean) has also been identified (5-25m+ depth) along vast
expanses of Dominica's west coast seagrass beds.
a mixed stand of Syringodium filiforme (thin cylindrical
and Thalassia testudinum (blade-like leaves). Right:
beds are Dominca's largest marine habitats built by organisms.
Thalassia is more dominant along the northern and eastern coast
of Dominica, generally in sheltered bays and back reef areas (e.g.
Anse Soldat, Calibishie, Hodges Bay , and Middle Bay in Marigot).
Although it mostly occurs in combination with Syringodium
it may occasionally also form monospecific assemblages, where
the calmest waters lead to stands of Thalassia that are
tall (25cm) in local intra-specific comparisons, and which
By far the largest contiuous stretches of seagrass beds are found
along the west coast between Canefield and Pointe Ronde,
dominated by Syringodium filiforme. However, the invasive
species H. stipulacea, first recognized by D. Willette,
has been identified throughout most of the west coast S.
filifome beds, in particular along its deep margins (~ 16 m)
and deeper (depth limit in Dominica not yet determined). In Prince
Rupert's Bay the invasive species has become the dominant seagrass
species by disolacing native species.
The native H. decipiens also marks the deep and shallow margins
of S. filiforme beds and and forms isolated patches. It is,
however, far less storm resistent and aggressive than the invasive
H. stipulacea, which now constitutes the second most abundant
seagrass in Dominica. Halodule wrightii has a more intermittent
distribution along the shallow margins of S. filiforme beds
(west coast) and appears to have a shallower distribution limit
at about 12m. Along the seagrass beds of Calibishie it has
occasionally been found in "open spaces" amidts mixed
stands of T. testudinum and S. syringodium.
the fringing reef systems of the north coast provide well flushed,
yet protected (turbulence) back reef areas conducive to shallow-water
(0-4 meters depth) seagrass beds, the west coast with its lack of
near shore energy-dissipating structures is not the ideal place
for shallow-water seagrass beds. Instead, seagrasses along the west
coast are generally found in waters from 4-18 meters. In these "deeper"
depths, self-shading by seagrasses with blade-like leaves (e.g.
Thalassia) would be a disadvantage and so the species with
cylindrical leaves, Syringodium, dominate the west coast.
Thalassia can occasionally be found in small patches along
the west coast in protected shallow areas such as Cachacrou.
Dominican waters, seagrass beds are not extremely wide, ranging
from 90 - 200 m. This is due to the narrow and steep shelf where
light becomes a limiting factor within a few hundred meters from
shore. Moreover, the shelf morphology offers no dissipation of physical
disturbance from waves and storms, thus limiting the expansion of
these plant communities. This setting is particularly pronounced
along the west coast where dynamic changes in the overall dimensions
and density of seagrass beds can regularly be observed after storms.
At some locations (e.g. Salisbury) entire seagrass beds "disappear"
as a combined result of erosion and burial. In other cases (e.g.
Jimmit, Anse Mulatre) seagrass beds are reduced in width by 20-30%
along their shallow margins.
the fact that the island's underwater topography is not one that
provides wide environments suitable for seagrass development, associated
organisms like the queen conch and milk conch (Strombus gigas
and S. costatus) were never abundant and not a key component
in the local fisheries. Such ecological parameters shape the artisanal
fisheries of each island, a fact often omitted in direct comparisons
of the fisheries from different regions.