{"440411":{"#nid":"440411","#data":{"type":"news","title":"Foes Can Become Friends on the Coral Reef","body":[{"value":"\u003Cp\u003EOn the coral reef, knowing who\u2019s your friend and who\u0027s your enemy can sometimes be a little complicated.\u003C\/p\u003E\u003Cp\u003ETake seaweed, for instance. Normally it\u0027s the enemy of coral, secreting toxic chemicals, blocking the sunlight, and damaging coral with its rough surfaces. But when hordes of hungry crown-of-thorns sea stars invade the reef, everything changes, reports a study published August 25 in the journal \u003Cem\u003EProceedings of the Royal Society B\u003C\/em\u003E.\u003C\/p\u003E\u003Cp\u003ESeaweeds appear to protect coral from the marauding sea stars, giving new meaning to the proverb: \u201cThe enemy of my enemy is my friend.\u201d The findings demonstrate the complexity of interactions between species in ecosystems, and provide information that could be useful for managing endangered coral reefs.\u003C\/p\u003E\u003Cp\u003E\u201cOn the reefs that we study, seaweeds reduce coral growth by both chemical and mechanical means,\u201d said \u003Ca href=\u0022http:\/\/www.biology.gatech.edu\/people\/mark-hay\u0022\u003EMark Hay\u003C\/a\u003E, a professor in the \u003Ca href=\u0022http:\/\/www.biology.gatech.edu\/\u0022\u003ESchool of Biology\u003C\/a\u003E at the Georgia Institute of Technology and the paper\u2019s senior author. \u201cBut we found that seaweeds can benefit corals by reducing predation by the crown-of-thorns sea stars. Corals surrounded by seaweeds were virtually immune to attack by the sea stars, essentially converting the seaweeds from enemies to friends.\u201d\u003C\/p\u003E\u003Cp\u003EThe research was supported by the National Science Foundation, the National Institutes of Health and the Teasley endowment at Georgia Tech.\u003C\/p\u003E\u003Cp\u003ECrown-of-thorns sea stars (\u003Cem\u003EAcanthaster planci\u003C\/em\u003E) are a major problem in the Pacific, where populations of the organisms rise and fall in cycles. On the Great Barrier Reef, for example, coral cover has declined by more than 50 percent over 25 years, and the voracious spine-covered creatures \u2013 which can travel as much as 80 meters per day \u2013 get much of the blame.\u003C\/p\u003E\u003Cp\u003E\u201cYou don\u2019t have to see the crown-of-thorns to know they have been on the reef,\u201d said Cody Clements, a Georgia Tech graduate student in Hay\u2019s lab and paper\u2019s first author. \u201cYou can see where they have been because they leave trails of bleached white coral. All they leave behind are the coral skeletons.\u201d\u003C\/p\u003E\u003Cp\u003EThe sea stars climb onto favored corals, invert their stomachs out through their mouths, and digest away the corals\u2019 living tissues \u2013 leaving white skeletons like a trail of bread crumbs that allowed Clements to not only see where the creatures had been, but also to track them to hiding places in the rocks.\u003C\/p\u003E\u003Cp\u003EDuring a two-year study in a marine protected area off the coast of the Fiji Islands, Clements used both observations and field experiments to examine the role of sea stars and seaweeds in the health of coral.\u003C\/p\u003E\u003Cp\u003E\u201cMarine protected areas where we work are often surrounded by areas of coral reef that are degraded and have lots of seaweeds,\u201d said Clements. \u201cIf seaweed is increasing in prevalence in these degraded areas, it\u2019s likely that these predators will move into protected areas with more coral and less seaweed. That could compromise conservation efforts in these relatively small marine protected areas established to protect coral.\u201d\u003C\/p\u003E\u003Cp\u003EClements first assessed the impact of seaweeds by comparing the growth of corals surrounded by varying levels of seaweed cover. To accurately measure growth, he established test colonies of the coral Montipora hispida attached to the necks of plastic soft drink bottles. Matching bottle caps were nailed into seabed rock, allowing colonies to be unscrewed from their anchorages to be accurately weighed, then returned. He placed varying amounts of the seaweed \u003Cem\u003ESargassum polycystum\u003C\/em\u003E adjacent to each test colony.\u003C\/p\u003E\u003Cp\u003E\u201cThe seaweed had a negative effect on the growth of the coral, and the more seaweed that was present, the greater the impact I observed,\u201d he said.\u003C\/p\u003E\u003Cp\u003ETo study the relationship between sea star attacks and seaweed cover, Clements used photographs to assess the amount of sea star damage to different coral colonies outside the marine protected area, and related the damage to the amount of seaweed on corals in the attacked areas. Coral colonies that had been attacked had, on average, just eight percent seaweed coverage, while nearby colonies of the same species that had not been attacked averaged 55 percent coverage of seaweeds.\u003C\/p\u003E\u003Cp\u003ETo more directly assess the protective role of the seaweed, Clements conducted an experiment. He fabricated ten cages in which he placed two Montipora coral colonies, one surrounded by varying levels of seaweed \u2013 between two and eight fronds \u2013 and the other lacking adjacent seaweeds. Into each cage he placed a sea star, then observed how much of each coral would be eaten.\u003C\/p\u003E\u003Cp\u003E\u201cAt the highest densities of seaweed, the sea stars were completely deterred,\u201d Clements said. \u201cThey wouldn\u2019t eat the coral surrounded by the seaweeds.\u201d Coral surrounded by lower densities of seaweed were sometimes eaten, while the corals without seaweed protection were always consumed by the sea stars.\u003C\/p\u003E\u003Cp\u003EResearchers aren\u2019t sure if the protective effects of the seaweed are mechanical or chemical \u2013 or perhaps both. But when Clements repeated the experiment with plastic aquarium seaweed instead of real seaweed, he found that it also had protective effects, suggesting the seaweed may be simply physical impediments making the coral difficult for the sea stars to find or consume.\u003C\/p\u003E\u003Cp\u003EFinally, Clements examined sea star feeding when the predator was given a choice between an unprotected coral it doesn\u2019t normally consume (\u003Cem\u003EPorites cylindra\u003C\/em\u003E) and Montipora \u2013 a favored prey \u2013 that had been surrounded by Sargussum. The sea stars didn\u2019t eat the Montipora, and would wait as long as ten days before finally consuming the Porites.\u003C\/p\u003E\u003Cp\u003E\u201cIf you\u2019ve got a choice between ice cream and broccoli, you\u2019re going to choose ice cream \u2013 unless broccoli is the only thing you can get,\u201d he said.\u003C\/p\u003E\u003Cp\u003EThe varying relationship between coral and seaweed illustrates the kind of complexity scientists have to understand when studying species-diverse ecosystems such as coral reefs, Clements noted.\u003C\/p\u003E\u003Cp\u003E\u201cIn a scenario that didn\u2019t involve the crown-of-thorns sea stars, interactions with the seaweed would have been negative for the coral,\u201d he noted. \u201cBut when you add the crown-of-thorns into the equation, it can be beneficial for the coral to be associated with the seaweed. Even if it suffers reduced growth, that\u2019s better than being eaten.\u201d\u003C\/p\u003E\u003Cp\u003EInformation from research like this can help scientists protect corals, which are essential to the survival of reef ecosystems.\u003C\/p\u003E\u003Cp\u003E\u201cWe are interested not only in how direct interactions between species play out, but also how these indirect interactions come into the picture and influence the wider community,\u201d said Clements. \u201cWhen it comes to coral reefs, that is very important because these interactions can affect the trajectory of an entire community of organisms.\u201d\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThis research was supported by the National Science Foundation under grant OCE- 0929119, by the Fogarty International Center of the National Institutes of Health under grants U01-TW007401 and U19TW007401, and by the Teasley Endowment to Georgia Tech. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Science Foundation or the National Institutes of Health.\u003C\/em\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ECITATION\u003C\/strong\u003E: Cody S. Clements and Mark E. Hay, \u201cCompetitors as accomplices: Seaweed competitors hide corals from predatory sea stars,\u201d (Proceedings of the Royal Society B, 2015).\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EResearch News\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EGeorgia Institute of Technology\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003E177 North Avenue\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EAtlanta, Georgia 30332-0181 USA\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003E: John Toon (404-894-6986) (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E)\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EOn the coral reef, knowing who\u2019s your friend and who\u0027s your enemy can sometimes be a little 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