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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