Reef Health Index
Subregion 6 Windward Reef
Grenada ’ s Reef Health Index ( RHI )
The national Reef Health Index was 2.5 ( out of 5 ). Coral cover is ‘ good ’ ( score = 4 ), suggesting these reefs could support greater fish populations . Herbivorous fish are abundant but small in size so biomass estimates are low ( score = 2 ). Fleshy macroalgae ( score = 2 ) is abundant in areas without herbivory and could be reduced if herbivorous fish , especially parrotfish , were protected . Commercial fish biomass is low , although more larger-sized fish were found in protected areas ( score = 2 ).
|
Sandy Is
( Deep )
Jack-a-Dan
|
Mabouya N |
Mabouya S |
Lighthouse Reef |
Sister |
Lighthouse |
Rocks |
Sandy Is |
Pt Cistern |
( Shallow ) |
Casada Bay
Saline Is Channel
White Is Shallow White Is
Watering Bay
Petite Martinique
Thibault Reef
Carriacou
Subregion 7
Key findings :
• Grenada has many different coral reef types , each provides important habitat
• More fish found on reefs with complex structure and deeper water
• Reefs with abundant Diadema urchins had less macroalgae
• Lack of large-sized female fish means fewer eggs to replenish populations
• Marine managed areas are helping fish recover , but increases will take time
• Reefs at high risk to chronic upland impacts and coral bleaching
• Reefs in ‘ poor ’ condition may recover if human impacts are reduced
Grenada site names : Bold = Nimrod / TNC 2015 Italics = GNMPA 2014
Frigate Is
0 2 4 Km
Carriacou site names in bold = TNC 2005 , in italics = GNMPA 2014 , in grey = Steneck 2014
Subregion 5
Grenada ’ s Reef Health Index ( RHI )
Indicator Year Score Average Trend Caribbean **
Subregion 2
Subregion 4
Subregion 3
Coral Cover Fleshy Macroalgae Herbivorous Fish Commercial Fish
2015 Good
2015 Poor 2015 2015
Poor Poor
22 20 1004 692 n / a n / a n / a n / a
14 30 3928 2823
Reef Health Index Scores
The Reef Health Index “ scores ” are calculated by converting the average data value of each indicator into a condition ranking from ‘ critical ’ to ‘ very good ’ based on reference values ( table below ). The four scores are averaged to obtain the overall RHI score . The pie displays the overall RHI ( middle ) and each individual indicator to show how each indicator affects the score .
The Reef Health Index ( RHI )
Reef Health Index Reference Values * Critical 1-1.8
Poor 1.9-2.6
Fair 2.7-3.4
Good 3.5-4.2
Very Good 4.3-5
Coral Cover (%) < 5 5.0-9.9 10.0-19.9 20.0-39.9 ≥40 Fleshy Macroalgal Cover (%) > 25.0 12.1-25 5.1-12.0 1.0-5.0 0-0.9 Herbivorous Fish ( g / 100m 2 ) < 960 960-1919 1920-2879 2880-3479 ≥3480
Subregion 1
Commercial Fish ( g / 100m 2 ) < 420 420-839 840-1259 1260-1679 ≥1680
* Reef Health Index developed by Healthy Reefs Initiative ( www . healthyreefs . org ) ** Caribbean average based on AGRRA regional database 2011-2014 ( www . agrra . org ) A trend is calculated after an indicator has been assessed for at least two years , otherwise it is listed as not available ( n / a ). For data , maps , and references see www . caribnode . org .
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