Tracking Coral Reef Health
RHI
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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
ID Sub-
region 1 Grenada
South Wide shallow shelf, thickets of finger corals (Porites porites).
Hardbottom reefs - abundant crustose coralline algae (CCA), small-
sized corals, Diadema urchins and some elkhorn corals (Acropora
palmata). Woburn Clark’s Court MPA. Nearby seagrass, mangroves. 1
2 Grenada
West Central: Narrow shelf, high relief spur and grove reefs near Flamingo
Bay, high coral cover, high fleshy macroalgae, few Diadema. Complex
reef structure has many small fish and lobster. Moliniere Beausejour
MPA. Reefs affected by upland run off. Southwest: Wide shallow
shelf, low relief reefs, small corals, abundant CCA and Diadema; deep
high relief fringing reefs, high coral & macroalgal cover, few large fish. 9
3
4
5 Grenada:
East
North
Rhonde Reef surveys not available for these areas. Subregions East (3) & North
(4): Broad shallow shelf, high wave energy, hardground/gorgonian
plains. Subregion 5: Rhonde Island & Les Tantes, high wave energy.
Kick’em Jenny submarine volcano. Reefs need to be surveyed. 0
6 Sandy Island & Mabouya - high relief deep fringing reefs, many finger
Carriacou corals (Madracis, Porites), high macroalgae, few Diadema; Nearshore
West
areas with patch reefs, hardbottom/gorgonian plains, more Diadema. 9
7 Carricaou East: Wide, shallow shelf with lower relief, low coral cover
Carriacou patch reefs and hardbottom/gorgonian plains. Frigate and Saline
East
Islands and Petite Martinique have better developed reefs. 8
Grenada
The Reef Health Index includes comparable
data from different surveys. Grenada: 2
surveys in 2014 by Grenadines Network of
Marine Protected Areas (GNMPA) (1 long
term monitoring site (LTM) in Moliniere
Beausejour Marine Protected Area (MPA), 1
in Woburn Clark Court MPA) and 8 surveys
in 2015 by Steve Nimrod/ The Nature
Conservancy (TNC)/ Fisheries. Carriacou: 14
sites in 2005 by TNC, 2 surveys in 2014 by
Robert Steneck of University of Maine and
1 LTM site by GNMPA in 2014. Grenada is
divided into subregions based on similar
biogeographic features. Data were not
available for 3 subregions. Subregions for the
6 ECMMAN countries are numbered 1 to 41
from Grenada north to St. Kitts and Nevis.
Indicator
Corals
Description of Grenada’s Reef Health
Corals build the reef’s 3D structure, provide habitat, and protect coastlines
• Coral cover high, lower than historic, corals small but healthy
• West coast reefs more complex, more live coral, but more macroalgae
• Thickets of finger coral common and several healthy elkhorn corals
• Reefs affected by chronic disturbance & bleaching events (2005)
Fleshy macroalgae, when too abundant, outcompete corals
• West coast deep reefs often have more seaweed than live coral
• Crustose coralline algae were abundant on east coast and shallow reefs
• Less macroalgae on reefs with abundant Diadema
Fleshy
macroalgae • Nutrients and lack of herbivory contributing to higher macroalgae
Herbivorous
Fish Herbivorous fish clean algae off reefs, large parrotfish remove more algae
• Herbivorous fish are often most abundant fish, but small in size
• Few large parrotfish, less grazing of algae
• Several larger parrotfish found in MMAs
• Parrotfish are overharvested, but could increase if protected
Commercial
Fish Groupers & snappers are key predators that keep food chain in balance
• Groupers & snappers were rare, small sizes, few mature adults
• More fish on reefs with complex structure and deeper water
• Predatory fish are overharvested, may take time to recover in MMAs
• Protecting nearby mangroves/seagrass nurseries is important
Diadema
Coral
Recruits
3
#
Sites
Subregion Description
Diadema urchins clean algae off reefs and open space for coral recruits
• East coast reefs and shallow reefs had more Diadema
• Reefs with more urchins had less seaweed and more coral cover
• Diadema urchins are important since few large herbivorous fish
• If nutrients and sediments reduced, urchins could increase
Coral recruits are “baby” corals. Recruits prefer macroalgal free areas
• Recruits present, mostly smaller-sized coral species
• High macroalgae & increased sediments reduced space for coral recruits
• Coral recruits on reefs with crustose coralline algae
• Reducing sediments and increasing herbivory will improve substrate
Threatened
Score
Healthy
Ken Marks Ken Marks
Ken Marks Ken Marks
Ken Marks Ken Marks
Emma Doyle Ken Marks
Clare Morrall Ken Marks
Clare Morrall Ken Marks