{"id":5258,"date":"2013-12-04T16:04:20","date_gmt":"2013-12-04T20:04:20","guid":{"rendered":"http:\/\/blogs.edf.org\/edfish\/?p=5258"},"modified":"2014-11-03T15:24:27","modified_gmt":"2014-11-03T19:24:27","slug":"coral-reef-thresholds-for-ecosystem-management","status":"publish","type":"post","link":"https:\/\/blogs.edf.org\/edfish\/2013\/12\/04\/coral-reef-thresholds-for-ecosystem-management\/","title":{"rendered":"Coral Reef Thresholds for Ecosystem Management"},"content":{"rendered":"
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\"(c)<\/a>
(c) Jim Patterson Photography, https:\/\/jimpattersonphotography.com\/<\/figcaption><\/figure>\n<\/dt>\n<\/dl>\n

By: Rod Fujita & Kendra Karr<\/p>\n

Fisheries management is principally focused on managing fishing pressure, with the goal of keeping individual fish stocks healthy enough to produce good yields.\u00a0 But fisheries also affect the basic processes that keep ocean ecosystems healthy.\u00a0 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.<\/p>\n

The evidence that fish are important regulators of ecosystem processes is particularly strong in coral reefs.\u00a0 The abundance and variety of fish is one of the most striking aspects of a healthy coral reef.\u00a0 Some species transport energy and nutrients between seagrass meadows and the reefs.\u00a0 Grazing fish species on a healthy coral reef keep seaweeds that would otherwise over-grow the reef in check.\u00a0\u00a0 Predators regulate populations of prey species, responding to natural variability by adjusting their feeding rates and numbers.\u00a0 On a healthy reef, many different species occupy each of these niches, and each does their job in a slightly different way.\u00a0 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.<\/p>\n

Like many complex systems with many elements that affect each other in many ways, coral reefs don\u2019t always change in a simple, linear way when one of the elements is altered.\u00a0 Similarly, your car will run, albeit a little roughly, if a single spark plug isn\u2019t working.\u00a0 But if the starter doesn\u2019t work, it won\u2019t run at all.\u00a0 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.<\/p>\n

\"Photo<\/a>
Photo Credits: Left, Kendra Karr. Right, blog.soleilorganique.com<\/figcaption><\/figure>\n

Some changes in coral reefs are gradual, but some are not.\u00a0 A tipping point occurs when small changes in human use or environmental conditions result in large, and sometimes abrupt, impacts to marine ecosystems.\u00a0 Certain factors can push coral reefs over an ecological tipping point, so that they change dramatically from one state to another.<\/p>\n

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.\u00a0 Once a tipping point is crossed, changes to the reef occur rapidly.\u00a0 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) \u2013 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.<\/p>\n

\"EDF<\/a>
EDF 2012<\/figcaption><\/figure>\n

However, if the system\u2019s resilience is reduced and\/or a driver becomes strong enough, the reef can transition (position 2) to a new, less desirable state (position 3).<\/p>\n

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.\u00a0 Moreover, just as theory predicts, some changes are abrupt and nonlinear.<\/p>\n

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.\u00a0 This may be related to the tendency for complex, regulated systems to exhibit higher variability as regulation (in this case, by fish) is reduced.\u00a0 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.<\/p>\n

A number of metrics — including the proportion of invertivore fishes, the number of fish species, and urchin density \u2013 change dramatically when fish densities fall to between 50 and 60% of unfished densities.<\/p>\n

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 \u2013 the fact that the reef is in a different state becomes obvious.<\/p>\n

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.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

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.\u00a0 But fisheries also affect the basic processes that keep ocean ecosystems healthy.\u00a0 This is why it is important to understand how many fish need to be …<\/p>\n","protected":false},"author":505,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[72448,42656],"tags":[295,657,42778,42777,524,36814],"coauthors":[],"class_list":["post-5258","post","type-post","status-publish","format-standard","hentry","category-global-fisheries-international","category-scienceresearch","tag-coral-reefs","tag-corals","tag-eco-system-management","tag-ecotourism","tag-reef-fish","tag-tipping-points"],"acf":[],"yoast_head":"\nCoral Reef Thresholds for Ecosystem Management - EDFish<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/blogs.edf.org\/edfish\/2013\/12\/04\/coral-reef-thresholds-for-ecosystem-management\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Coral Reef Thresholds for Ecosystem Management - 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