Selected tags: Coral Reefs

Coral Reef Thresholds for Ecosystem Management

(c) Jim Patterson Photography,

(c) Jim Patterson Photography,

By: Rod Fujita & Kendra Karr

Fisheries management is principally focused on managing fishing pressure, with the goal of keeping individual fish stocks healthy enough to produce good yields.  But fisheries also affect the basic processes that keep ocean ecosystems healthy.  This is why it is important to understand how many fish need to be in the system to maintain the many important services that an ocean ecosystem can produce — including the maintenance of biodiversity, tourism value, and fisheries — and to manage fisheries so that fish populations remain at about that level.

The evidence that fish are important regulators of ecosystem processes is particularly strong in coral reefs.  The abundance and variety of fish is one of the most striking aspects of a healthy coral reef.  Some species transport energy and nutrients between seagrass meadows and the reefs.  Grazing fish species on a healthy coral reef keep seaweeds that would otherwise over-grow the reef in check.   Predators regulate populations of prey species, responding to natural variability by adjusting their feeding rates and numbers.  On a healthy reef, many different species occupy each of these niches, and each does their job in a slightly different way.  This enables the reef to resist threats and other changes (like hurricanes) and to recover from very storms or human impacts, within limits of course.

Like many complex systems with many elements that affect each other in many ways, coral reefs don’t always change in a simple, linear way when one of the elements is altered.  Similarly, your car will run, albeit a little roughly, if a single spark plug isn’t working.  But if the starter doesn’t work, it won’t run at all.  Coral reefs can exist in many different states, ranging from one in which live coral dominates, supporting a highly diverse mix of species and generating high levels of multiple ecosystem services to a state in which most of the coral is dead, species diversity is low, and the reef is no longer producing valued ecosystem services.

Photo Credits: Left, Kendra Karr. Right,

Photo Credits: Left, Kendra Karr. Right,

Some changes in coral reefs are gradual, but some are not.  A tipping point occurs when small changes in human use or environmental conditions result in large, and sometimes abrupt, impacts to marine ecosystems.  Certain factors can push coral reefs over an ecological tipping point, so that they change dramatically from one state to another.

Because fish are such important regulators of the processes that maintain coral reefs in these different states, fishing can act as a driver, pushing the reef toward a tipping point.  Once a tipping point is crossed, changes to the reef occur rapidly.  In the figure below, the levels of various drivers of change are at levels which enable the reef to exist in a healthy state (position 1) – the width of the basin in which it rests and the height of the ridge that defines the basin depend on how many species are present, how many are playing redundant roles, how high productivity is, and many other factors that contribute to the resilience of the reef.

EDF 2012

EDF 2012

However, if the system’s resilience is reduced and/or a driver becomes strong enough, the reef can transition (position 2) to a new, less desirable state (position 3).

Our analysis of coral reef health metrics and fish abundance (collected over 20 years, from 1994 to 2011, across 19 countries throughout the Caribbean) shows that coral reef metrics shift in response to changes in fish density, a measure of abundance.  Moreover, just as theory predicts, some changes are abrupt and nonlinear.

Macroalgal cover increases as fish density decreases to about 90% of the maximum levels in the data set (which we take to be a proxy for unfished levels), and variance becomes very high.  This may be related to the tendency for complex, regulated systems to exhibit higher variability as regulation (in this case, by fish) is reduced.  For example, if the thermostat in your house is partially broken, the temperature in your house may fluctuate between 60 and 70 degrees, instead of being held within a narrow range of temperatures by a well-functioning thermostat.

A number of metrics — including the proportion of invertivore fishes, the number of fish species, and urchin density – change dramatically when fish densities fall to between 50 and 60% of unfished densities.

When fish densities reach 30% of unfished densities, the ratio of macroalgae to coral increases, the proportion of herbivorous fish in the fish community decreases, and coral cover drops markedly – the fact that the reef is in a different state becomes obvious.

EDF will continue to refine the use of coral reef ecosystem thresholds and advocate their use in setting aggregate catch limits in order to keep healthy reefs healthy and to restore reefs that are in transition or in less desirable states.


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A Big Step Forward for Better Rigs To Reef Management

A large group of chub (Kyphosus sp.) school under the platform. Photo: Schmahl/FGBNMS (From NOAA)

As I’ve written before, the Rigs to Reefs permitting process of the federal and state agencies in the Gulf of Mexico is a good example of “finding ways that work.”  This cooperative process enables the owners of oil and gas platforms to use those structures to support artificial reefs.  In fact, this means the rigs continue serving as artificial reefs because they have already attracted fish, coral, and other marine life as the rigs produced oil or gas.

Over the past few years, the issue of rig removal has become a heated topic among anglers as the federal government undertook more aggressive measures to remove retired rigs.  The officials responsible for safe retirement of end-of-service rigs and the anglers and divers who benefit from the marine life around those rigs have been at odds over the best ways to maintain reef habitats while also providing for other uses of the Gulf. That tension was reduced this week when the Bureau of Safety and Environmental Enforcement, a division of the Department of Interior, issued a new policy addressing several sticking points that arose in recent years.  Most of the log jam has been caused by basic questions of process:  how many rigs would remain as reef habitat, where would they be placed, and how would they be secured?

The pressure built as the number of rigs reaching the end of their productive life and the end of their leases began to rise.  Starting in 2005, the number of applications for removals spiked, and Hurricane Katrina damaged even more platforms and disrupted existing artificial reefs.  These pressures complicated the challenge for the Department of Interior to assure safe disposition of an increasing number of platforms.

In 2010 – after the Deepwater Horizon disaster – the department issued a notice to lease-holders that it was modifying procedures to ensure faster removals in the interest of safety.  Anglers and divers began to see more rigs being removed, and many were removed using explosives that would leave hundreds of dead fish floating in the wake of the project.

The clamor, however, also involved effective coordination among all concerned.  The Bureau of Safety and Environmental Enforcement, working with the White House National Ocean Council, the other cabinet agencies, scientists, and stakeholders, developed changes to policy that will ease the process.  Sportsmen groups such as the Congressional Sportsmen’s Foundation played a leading role.  EDF, after stepping forward as an early supporter of revising the 2010 policy, encouraged and supplied data to these discussions.  We are proud to say that we were the only major ENGO to speak out for the interests of anglers in this debate.

The most important features of the new policy are that it drops the requirement for distance between reef sites, adds an allowance for creating a reef where a rig currently stands, and extends deadlines for removal for platform owners seeking approval for a reefing project.

This improved approach is a step in the right direction, and we are hopeful that it will lead to better fish habitat, populations, and recreational opportunities.  It is especially welcome as reef-fish issues and red snapper management in particular are hot topics in the Gulf right now.

Congratulations are due to all those who are dedicated to finding ways that work.

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Protecting Cuba's Abundant Coral Reefs

Two of the authors, Doug Rader and Dan Whittle with a goliath grouper.

*Re-posted with permission from Sailors for the Sea

This month's ocean watch essay comes to us from theEnvironmental Defense Fund(EDF), and was written by:Dan Whittle the senior attorney at Environmental Defense Fund and director of its Cuba ProgramDoug Rader, PhD, EDF's Chief Oceans Scientist, and Violet Dixon the Marketing Communications Associate for EDF's Oceans program. All images by Noel Lopez Fernandez.

In the waters off the Southeast coast of Cuba there's a near-pristine coral reef reserve called Jardines de la Reina, or the Gardens of the Queen. In this national park, groupers, snappers and many other reef fish flourish, along with several species of sharks. Although many of the world's best-known reefs face destruction in the face of global warming and other threats, large portions of the Gardens of the Queen remain remarkably healthy. Relative isolation from human influence helps make Cuba's coral reefs unique. Protecting these ecosystems — and species that rely on them — requires careful collaboration and cooperation among managers, scientists, fishermen and local fishing communities. Well-designed marine protected areas (MPAs), combined with innovative fisheries management, are the foundation for both sustainable commercial and recreational fisheries and a thriving eco-tourism sector.The abundance of big predators, like these Caribbean reef sharks, is a sure sign of an ecosystem in balance. The Gardens has six to eight times as many sharks as elsewhere in the Caribbean.

Seeing under the sea
Healthy coral reefs, mangrove swamps and seagrass beds support thriving fish populations, which in turn support local fishing communities and attract ocean enthusiasts. Scuba divers come from around the world, for example, to witness the myriad of sea animals and breathtaking underwater ecosystems in the Gardens of the Queen.

On these dives, they encounter numerous species of shark including Caribbean reef sharks, silky sharks, nurse sharks and occasional lemon and blacktip sharks.  Depending on the season and other factors, visitors also occasionally encounter whale sharks, the largest known fish species. Read More »

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