Tracking Coral Reef Health
RHI
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Dominica
The Reef Health Index (RHI) integrates four indicators to measure coral reef health (coral cover, fleshy
macroalgae, herbivorous fish and commercial fish). The RHI “pie” symbol on the map is displayed at the site,
subregional and national levels.* (For more information visit www.caribnode.org)
No
Data
Very
Good
The Reef Health Index for Dominica is based
on data shared by Sascha Steiner of Institute
for Tropical Marine Ecology (ITME) for 16 sites
surveyed in 2005 and additional research
reports. 1 These surveys were conducted during
the severe 2005 coral bleaching event. Additional
impacts from the 2010 bleaching event and years
of continued local impacts have occurred. Thus,
the RHI shown here may not be representative
of the current condition today, but it provides an
island wide baseline. Dominica is divided into 2
subregions since west coast reefs are different
from the east. Subregions for the 6 ECMMAN
countries are numbered 1 to 41 from Grenada
north to St. Kitts and Nevis.
Indicator
29
30
Sub
region
West
Coast
East
Coast
Subregion Description 1 #
Sites
Protected narrow shelf has steep slopes near rivers and
coastal calderas. North west: Isolated patch reefs near
Morne Espagnol, Toucari Bay. Boulder fields near Cabrits
and Hermitage River. Central west: Greater coral diversity,
complex reef structure, deep fringing reefs. Largest reefs
between Batali and Mero, south Prince Ruperts Bay and
Grande Savane. South west: Main reefs at a) Fond Colet/
Roseau patch reef, some of oldest large corals, b) Soufriere
north fringing reef, and c) Cachacrou, north Scott’s Head
Peninsula. 15
Windward side, higher wave energy. East and South east
coast: Coral reefs are found in a few small protected bays.
Unique NE coast: wider, semi-protected areas extends ~3
km offshore between Wesley and Marigot. The largest reefs,
between Anse Soldat and Calibishie, have coral framework
of dead elkhorn skeletons with some live elkhorn and small
corals like Diploria and Porites. The back reef area behind
the reef crest provides important habitat for seagrass
communities to grow.
Description of Dominica’s Reef Health 1
Corals Corals build the reef’s 3D structure, provide habitat and protect coastlines
• Coral cover was high (10-53%) prior to 2005 bleaching event
• Cover declined >28% in 1 year, >75% of corals were bleached
• Significant loss of large mountainous star corals in deep reefs
• Reefs at risk to local chronic impacts and bleaching events
Fleshy
macroalgae Fleshy macroalgae, when too abundant, outcompete corals
• Fleshy macroalgae was very low prior to 2005 coral bleaching
• Turf and fleshy macroalgae overgrew corals that died in 2005
• Crustose coralline algae were low on most reefs
• High sedimentation reduces coral recruitment substrate
Threatened
Score
1
Healthy
Sascha Steiner Sascha Steiner
Andy Bruckner Ken Marks
Herbivorous fish clean algae off reefs, large parrotfish remove more algae
• Herbivorous fish were abundant, numerous surgeonfish
• Fish were small in size (11-21cm) which means less grazing
Herbivorous
• More large parrotfish found in Soufriere-Scott’s Head MR
Fish
• Parrotfish are harvested, but could recover if protected Clare Morrall Ken Marks
Commercial
Fish Groupers & snappers are key predators that keep food chain in balance
• Majority of groupers & snappers were small in size
• More fish on reefs with complex structure and deeper water
• Larger-sized fish found in protected areas
• Predatory fish are overharvested, may recover if protected Emma Doyle Ken Marks
Diadema
antillarum Diadema urchins clean algae off reefs and open space for coral recruits
• Diadema found on all sites but Calibishie
• Urchins increased >60% over a 5 year period (2001-2005)
• Reefs with more urchins had less seaweed and more coral cover
• Diadema urchins are important since few large herbivorous fish Clare Morrall Patricia Kramer
Coral recruits are “baby” corals. Recruits prefer macroalgae free areas
• Recruits were abundant prior to 2005 coral bleaching
• Number of recruits decreased by >65% after event
• Large star corals had new tissue regrowing over dead skeleton
• More coral recruits found on reefs with abundant urchins Clare Morrall Andy Bruckner
Coral
Recruits
3
ID