The Beacon

Blog Tags: Algae

Corals Call on Fish Bodyguards for Protection

A goby finds shelter and food in its host coral ©Georgia Tech/Danielle Dixson

When there’s invading seaweed in your neighborhood, who you gonna call? Well, a new study by scientists at Georgia Tech shows that when corals are threatened by toxic algae they use chemical signals to call for help from their “bodyguards”, the unassuming goby fish.

The study, carried out on coral reefs in Fiji and published in the November 8 issue of the journal Science, shows that within moments of the coral’s “911 call” the gobies respond to these chemical distress signals and pick off the offending seaweed. What’s in it for the fish? Gobies spend their entire lives with the same patch of coral, using it for protection from predators and even feeding on mucus produced by the coral. It comes as little surprise then that the goby takes any threat to its shelter very seriously.

"The fish are getting protection in a safe place to live and food from the coral," said Mark Hay, a biology professor at Georgia Tech and the study’s co-author. "The coral gets a bodyguard in exchange for a small amount of food. It's kind of like paying taxes in exchange for police protection."

For one species of goby, feeding on the toxic algae has the secondary effect of making the fish itself more toxic to predators.

Coral is under threat worldwide from pollution and ocean acidification from human activity. When corals are stressed, aggressive algae competing for sunlit patches of ocean floor can represent a death blow to coral reefs and the magnificent ecosystems they support. At least one fish, though, isn’t letting the reef go down without a fight.


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Creature Feature: Seahorse

Camouflaging in coral ©Wikimedia Commons

Though you won’t see them saddled and ready to ride anytime soon, seahorses are pretty fascinating little sea creatures.

Named for their resemblance to the horses that we’re used to seeing on land, the seahorse is one of the slowest moving fish in the ocean. They swim upright, unlike their cousin the pipefish, and flutter their dorsal fin up to 30-40 times per second to move around (more like a hummingbird than a horse).

There are 47 distinct species of seahorses, and all are in the genus Hippocampus, which comes from the Ancient Greek for “sea monster.” You can find them in shallow waters throughout the world, especially in seagrass beds, coral reefs, and mangroves, where they can take cover and hide from bigger fish that might want to make a meal out of them.

Seahorses are fairly small, ranging from 0.6 to 14 inches. But the smallest of all are the pygmy seahorses. Scientists are continuing to discover new species of pygmy seahorse, but they’re tough to find because they camouflage themselves and live in or near coral, algae, or seaweed, where they blend so well that they’re nearly impossible to spot. They often use their tails to anchor themselves to a surface, then use their snouts to catch brine shrimp and other small crustaceans floating by.

One of the seahorse’s most unique characteristics is that males carry the fertilized eggs instead of females. The male seahorse has a brood pouch on his front side where the female deposits eggs during mating. He carries the eggs until they’re fully developed, then releases the tiny seahorses out into the ocean to fend for themselves. A single brood can contain up to 1,500 young!

Because seahorses are so elusive, we don’t know very much about their populations worldwide. But the coral reefs, seagrass beds, and other areas they call home are endangered by habitat depletion, pollution, and ocean acidification, which has made some species of seahorse vulnerable to extinction.


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New Report: Why Healthy Oceans Need Sea Turtles

Imagine a healthy, beautiful ocean. Now remove the sea turtles, one by one.

Not so healthy anymore, is it?

That’s the gist of the report we released today, Why Healthy Oceans Need Sea Turtles: The Importance of Sea Turtles to Marine Ecosystems. The report describes the vital roles sea turtles play in the ecosystem, and how the Gulf of Mexico oil spill is further threatening their ability to fulfill those roles.

As the report outlines, sea turtles provide the following important ecosystem services:

  • Maintain healthy seagrass beds through grazing
  • Maintain healthy coral reefs by removing sponges when foraging
  • Facilitate nutrient cycling by supplying a concentrated source of high-protein nutrients when nesting
  • Balance marine food webs by maintaining jellyfish populations
  • Provide a food source for fish by carrying around barnacles, algae and other similar organisms
  • Increase the rate of nutrient recycling on the ocean floor by breaking up shells while foraging
  • Provide habitat for small marine organisms as well as offer an oasis for fish and seabirds in the open ocean

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