Grenadine Reefs’ Health
by Emma Doyle and Patricia Kramer
Think of sailing in the Caribbean and inevitably images of blue water come to mind. Not just a single blue, but a whole spectrum of blues. A good sailor knows by colour or hue where the coral reef lies below the water.
But is that reef alive or dead? Healthy or suffering from pollution? Or becoming stressed due to high water temperatures associated with the current El Niño?
In November 2014, the Compass’s Eco-News column reported on an expedition to assess coral reef health throughout the Grenadines. Taking part were park rangers and wardens from Grenada and St. Vincent & the Grenadines, the Monitoring Coordinator from Sustainable Grenadines Inc. and a coral reef scientist with the Atlantic and Gulf Rapid Reef Assessment Program (AGRRA). The team sailed over 100 kilometres in six days aboard the catamaran Sky Flirt, whose owner Jean-Marc Sailly of Wind and Sea, kindly donated the vessel to support the expedition and to promote coral reef conservation. During the expedition, the team visited each of the six marine protected areas along the Grenada Bank to survey coral reefs, and they established long term monitoring sites to track coral reef health over time.
Why monitor coral reefs?
Coral reefs are like underwater cities and everything you see on the reef has a role to play. Coral reefs have high biodiversity, but a few things, like corals, fish and algae, are the major players in controlling overall reef health. The loss or decline of just one of these groups can have a domino effect on the entire reef ecosystem. By tracking the status of several key indicators, it’s possible to get a picture of overall coral reef health.
Within the Caribbean, the health of the Mesoamerican Reef (the world’s second longest barrier reef stretching through Mexico-Belize-Guatemala-Honduras) is carefully monitored, allowing coastal managers to better address transboundary issues between country borders. This is important since most reef organisms don’t conform to national borders. Coral reefs in long-established marine parks such as Exuma Cays Land and Sea Park in The Bahamas (established in 1958), and Florida Keys National Marine Sanctuary (1990) have also been particularly well studied.
The Grenada Bank supports the most extensive coral reefs and related habitats in the southeastern Caribbean, yet there has been comparatively little monitoring of its coral reefs. This is changing as the Grenada Bank is now home to a network of six marine protected areas, all of which have among their objectives the protection of natural resources, species and critical habitat, including coral reefs. To monitor progress in achieving this objective, it’s possible to track several key indicators of coral reef health.
What to monitor?
Firstly, the coverage of live coral on the reef is important: the more live coral the better, as coral provides habitat — shelter, food — for fish and other creatures. In contrast, the coverage of a type of algal growth referred to as “fleshy macroalgae” can be an indicator of poor reef health. Too much fleshy macroalgae can over-grow corals and take up space where baby corals could otherwise establish themselves and grow. So the less fleshy macroalgae, the better.
The number of black sea eggs on the reef is important (black spiny sea urchins or Diadema antillarum) because they graze on these algae and help keep the reef clean. Their numbers in the Caribbean were affected by a mass die-off caused by disease in the early 1980s, and only now are they recovering in some areas.
When monitoring reef fish, there are two key groups: herbivorous fish, including parrotfish and surgeonfish, that graze algae growing on the reef and help to keep it clean; and predatory fish that are often commercially important, such as snapper and grouper. A long history of fishing in the Caribbean has resulted in dramatic declines in fish stocks. Reef fish continue to be threatened today by overfishing, unsustainable fishing practices and destruction of habitat, and they are especially vulnerable to targeted overfishing of spawning aggregations. Big, old, fat fish are exponentially more productive, and by protecting them we can help their populations grow and spillover the protected area boundaries to contribute to sustainable national fisheries. The monitoring team assessed fish biomass, taking into account both the number of fish found on the reef and their size.
Managers in the Grenadines are fortunate that some of this coral reef data have been collected in the past, as far back as 1999 in the case of Tobago Cays. There are more than 2,000 sites in coral reefs in the Caribbean region that have been surveyed and provide some reference values for the Grenadines. So the 2014 Grenadines expedition used the same methodology as used in these other studies, and since several of the survey sites had been studied before, this enabled some comparison over time.
What did the expedition find?
The news about corals in the Grenadines is generally positive. Live coral cover in the marine protected areas of the Grenadines is quite good at 25 percent, which is higher than the Caribbean average of 17 percent, although lower than historic values. Among the six study sites, the highest live coral cover was found at Sandy Island/Oyster Bed Marine Protected Area (35 percent). Meanwhile, the level of fleshy macroalgae in the Grenadines study sites is on average 18 percent, which is pleasingly lower than the Caribbean regional average of 31 percent. Particularly low cover of fleshy macroalgae was found at Woburn/Clarkes Court in Grenada, which also happens to have the greatest number of black sea eggs of all the sites, and at Tobago Cays Marine Park, which has the largest biomass of herbivorous fish. Although there has been a decline since 1999 in coral cover at the survey site in Tobago Cays Marine Park, which is possibly due to hurricanes and coral bleaching, the low level of fleshy macroalgae and increasing herbivorous fish biomass means there is good potential for more coral recovery. The highest levels of fleshy macroalgae are at Moliniere-Beausejour Marine Protected Area, which is a concern especially as the marine protected area is helping herbivorous fish populations recover and numerous lobsters to thrive.
The news about reef fish in the Grenadines is less positive. Total fish biomass is much lower than both the Caribbean and Mesoamerican Reef region averages. This likely reflects heavy fishing pressure in the region and also that marine protection is newer than in other areas of the Caribbean. Focusing on herbivorous fish biomass, the Grenadines ranks as poor on average, and biomass is lower than the Mesoamerican Reef average at every site except for Tobago Cays Marine Park, which benefits from the longest history of protection. Even there, although there are more herbivorous fish in Tobago Cays than in 1999, the average size of herbivorous fish is now smaller.
Commercial fish biomass — snappers and groupers — is on average critical across the Grenadines survey sites and below both Caribbean and the Mesoamerican Reef averages. Only at Tobago Cays Marine Park (with patrols since 2007) has commercial fish biomass improved compared with 1999 levels. At the newer Sandy Island/Oyster Bed Marine Protected Area (launched in 2010), commercially important fish are low, but have the potential to increase with more time and continued protection, like herbivorous fish abundance has increased.
What of the other sites?
Coral reefs in the proposed South Coast Marine Managed Area around Blue Lagoon, St. Vincent, have good coral cover but they also have critically low levels of commercially important fish. The reefs have potential to improve but will need management actions to protect fish and to reduce pollutants and sediment entering from land. Mustique has been proactive in minimizing human influences by prohibiting the use of phosphates (e.g. in household detergents), taking steps to reduce erosion, to conserve water and to treat wastewater. Together with additional protection of herbivorous and commercial fish, these steps will help improve reef health in the Mustique Marine Conservation Area.
Of course interpreting natural science data means considering a whole host of other factors, such as hurricanes, coral bleaching, changes in local population, levels of tourism and major developments. And as anyone who has snorkeled will know, a coral reef can look quite different on different sides of the same island, for example. So the results can vary greatly depending on the site that we’re surveying. Nonetheless, knowing about change in coral reef health is vitally important for marine protected areas as they decide how best to focus their management and enforcement effort, where to target education activities and with which partner agencies on land to collaborate. The information generated by the expedition is being used by the managers of the Grenadines marine protected areas to help focus on these priority needs.
How can you help?
As individuals, we may start by doing some simple things: respect no-fishing rules; use fixed moorings or anchor only in sand (with no coral heads or seagrass); use holding tanks whenever possible, especially in marine protected areas, and if needed discharge when on passages between islands; reduce the amount of garbage you create and plastics you use and pick up trash underwater or along beaches. Next time you go snorkelling, take a child by the hand and look at coral from a fish-eye view. Think like a baby coral and work out where you would land and grow. Or follow a fish and watch where it goes and what it eats.
Keep an eye out for warmer waters and “white” corals. Forecasts from the NOAA Coral Reef Watch program’s ‘Coral Bleaching Thermal Stress Outlook’ (coralreefwatch.noaa.gov) are highlighting a very real possibility of higher than normal sea surface temperatures in the Caribbean towards the end of 2015, which can stress corals and cause them to “bleach” (turn white from expelling their symbiotic algae). Please contact the local marine protected area manager if you start to notice coral bleaching in reefs that you know well.
The monitoring expedition is now helping managers of the marine protected areas in the Grenadines better understand the health of their reefs and the threats facing them so they can take actions to protect coral reefs for a sustainable future. The expedition was organized by Sustainable Grenadines, Inc. and made possible through sponsorship from the US National Fish and Wildlife Foundation to strengthen coral reef management practices on the Grenada Bank. Why not stop by SusGren’s office in Clifton when you’re next on Union Island, to learn more about conservation efforts in the wonderful Grenadines?
Emma Doyle is Advisor on Marine Protected Areas to Sustainable Grenadines Inc. and Patricia Kramer is with the Atlantic and Gulf Rapid Reef Assessment Program (www.agrra.org).
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