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By John Toon
Corals under attack by toxic seaweed do what anyone might do when threatened – they call for help. A study reported this week in the journal Science shows that threatened corals send signals to fish “bodyguards” that quickly respond to trim back the noxious alga – which can kill the coral if not promptly removed.
Scientists at the Georgia Institute of Technology have found evidence that these “mutualistic” fish respond to chemical signals from the coral like a 911 emergency call – in a matter of minutes. The inch-long fish – known as gobies – spend their entire lives in the crevices of specific corals, receiving protection from their own predators while removing threats to the corals.
This symbiotic relationship between the fish and the coral on which they live is the first known example of one species chemically signaling a consumer species to remove competitors. It is similar to the symbiotic relationship between Acacia trees and mutualist ants in which the ants receive food and shelter while protecting the trees from both competitors and consumers.
“This species of coral is recruiting inch-long bodyguards,” said Mark Hay, a professor in the School of Biology at Georgia Tech. “There is a careful and nuanced dance of the odors that makes all this happen. The fish have evolved to cue on the odor released into the water by the coral, and they very quickly take care of the problem.”
The research, supported the National Science Foundation, the National Institutes of Health and the Teasley Endowment at Georgia Tech, was reported November 8 in the journal Science. The research was done as part of a long-term study of chemical signaling on Fiji Island coral reefs aimed at understanding these threatened ecosystems and discovering chemicals that may be useful as pharmaceuticals.
Because they control the growth of seaweeds that damage coral, the importance of large herbivorous fish to maintaining the health of coral reefs has been known for some time. But Georgia Tech postdoctoral fellow Danielle Dixson suspected that the role of the gobies might be more complicated. To study that relationship, she and Hay set up a series of experiments to observe how the fish would respond when the coral that shelters them was threatened.
They studied Acropora nasuta, a species in a genus of coral important to reef ecosystems because it grows rapidly and provides much of the structure for reefs. To threaten the coral, the researchers moved filaments of Chlorodesmis fastigiata, a species of seaweed that is particularly chemically toxic to corals, into contact with the coral. Within a few minutes of the seaweed contacting the coral, two species of gobies – Gobidon histrio and Paragobidon enchinocephalus – moved toward the site of contact and began neatly trimming away the offending seaweed.
“These little fish would come out and mow the seaweed off so it didn’t touch the coral,” said Hay, who holds the Harry and Linda Teasley Chair in Environmental Biology at Georgia Tech. “This takes place very rapidly, which means it must be very important to both the coral and the fish. The coral releases a chemical and the fish respond right away.”
In corals occupied by the gobies, the amount of offending seaweed declined 30 percent over a three-day period, and the amount of damage to the coral declined by 70 to 80 percent. Control corals that had no gobies living with them had no change in the amount of toxic seaweed and were badly damaged by the seaweed.
To determine what was attracting the fish, Dixson and Hay collected samples of water from locations (1) near the seaweed by itself, (2) where the seaweed was contacting the coral, and (3) from coral that had been in contact with the seaweed – 20 minutes after the seaweed had been removed. They released the samples near other corals that hosted gobies, which were attracted to the samples taken from the seaweed-coral contact area and the damaged coral – but not the seaweed by itself.
“We demonstrated that the coral is emitting some signal or cue that attracts the fish to remove the encroaching seaweed,” Hay said. “The fish are not responding to the seaweed itself.”
Similar waters collected from a different species of coral placed in contact with the seaweed did not attract the fish, suggesting they were only interested in removing seaweed from their host coral.
Finally, the researchers obtained the chemical extract of the toxic seaweed and placed it onto nylon filaments designed to stimulate the mechanical effects of seaweed. They also created simulated seaweed samples without the toxic extract. When placed in contact with the coral, the fish were attracted to areas in which the chemical-containing mimic contacted the coral, but not to the area contacting the mimic without the chemical.
By studying the contents of the fish digestive systems, the researchers learned that one species – Gobidon histrio – actually eats the noxious seaweed, while the other fish apparently bites it off without eating it. In the former, consuming the toxic seaweed makes the fish less attractive to predators.
The two species of fish also eat mucus from the coral, as well as algae from the coral base and zooplankton from the water column. By defending the corals, the gobies are thus defending the home in which they shelter and feed.
“The fish are getting protection in a safe place to live and food from the coral,” Hay noted. “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.”
As a next step, Hay and Dixson would like to determine if other species of coral and fish have similar symbiotic relationships. And they’d like to understand more about how the chemical signaling and symbiotic relationship came into being.
“These kinds of positive interactions needs to be better understood because they tell us something about the pressures that have gone on through time on these corals,” said Hay. “If they have evolved to signal these gobies when a competitor shows up, then competition has been important throughout evolutionary time.”
Source: Danielle L. Dixson and Mark E. Hay, Corals chemically signal mutualistic fishes to remove competing seaweeds, Science (2012).
Photograph by Georgia Tech, Danielle Dixson
Posted November 9th, 2012. Add a comment
By Trevor Stokes, LiveScience Contributor
Clownfish, the orange-, black- and white-striped fish made famous in the movie “Finding Nemo,” are a gossipy bunch, popping and clicking amid their anemone homes to defend and reinforce their social status, according to new research.
Unlike the 360 other species of territorial marine fish in the Pomacentridae family, clownfish don’t make a peep when mating. Researchers wondering why clownfish would bother to make noise in other circumstances discovered that their chatter helps maintain the rank and file among group members.
“Sound could be an interesting strategy for preventing conflict between group members,” lead study author Orphal Colleye, a postdoctoral fellow at the University of Liège, Belgium, told LiveScience. “In terms of cost energy, you don’t have to interact with another individual to determine which is the dominant and which is the subordinate, you just need to make a sound.”
Photograph by Orphal Colleye.
Posted November 8th, 2012. Add a comment
Coral specialist Dr. Bert W. Hoeksema of Naturalis Biodiversity Center in Leiden, The Netherlands, recently published the description of a new coral species that lives on the ceilings of caves in Indo-Pacific coral reefs. It differs from its closest relatives by its small polyp size and by the absence of symbiotic algae, so-called zooxanthellae. Its distribution range overlaps with the Coral Triangle, an area that is famous for its high marine species richness. Marine zoologists of Naturalis visit this area frequently to explore its marine biodiversity.
Reef corals in shallow tropical seas normally need the symbiotic algae for their survival and growth. Without these algae, many coral reefs would not exist. During periods of elevated seawater temperature, most reef corals lose their algae, which is visible as a dramatic whitening of the reefs, a coral disease known as bleaching.
Most reef corals generally do not occur over 40 m depth, a twilight zone where sunlight is not bright anymore, but some species of the genus Leptoseris are exceptional and may even occur much deeper. At greater depths, seawater is generally colder and corals here may be less susceptible to bleaching than those at shallower depths. Despite the lack of zooxanthellae and its small size, the skeleton structures of the new species indicate that it is closely related to these Leptoseris corals, although it has not been found deeper than 35 m so far.
The species is named Leptoseris troglodyta. The word troglodyta is derived from ancient Greek and means “one who dwells in holes”, a cave dweller. The discovery sheds new light on the relation of reef corals with symbiotic algae. The new species has adapted to a life without them. Consequently, it may not grow fast, which would be convenient because space is limited on cave ceilings. The species description is published in the open access journal ZooKeys.
Source: Pensoft Publishers
Photograph by Dr. Bert W. Hoeksema / Naturalis
Posted October 12th, 2012. Add a comment
A recent study conducted in the Great Barrier Reef of Australia has revealed much about the daily routines of the majestic manta ray, including when they eat, cruise, and get cleaned by other fish. The study focused on Lady Elliot Island, a small land mass in the Reef. Using three years of observations, some by local scuba divers and boat captains, researchers from the University of Queensland charted how ocean conditions influence where manta rays gather and what they do.
Manta rays were found to cluster around the island when wind speeds are lower and when the moon is new or full. They also go to specific locations depending on activity. A number of sites, where they have been seen filtering plankton from the water, are apparently used mainly for foraging. Other sites are reserved for cleaning.
Photo: PLoS ONE
Sea cucumbers and sea urchins are able to change the elasticity of collagen within their bodies, and could hold the key to maintaining a youthful appearance, according to scientists at Queen Mary, University of London.
The researchers investigated the genes of marine creatures such as sea urchins and sea cucumbers, known as echinoderms. They found the genes for “messenger molecules” known as peptides, which are released by cells and tell other cells in their bodies what to do.
The study was published online in the journals PLOS One and General and Comparative Endocrinology.
Project leader Professor Maurice Elphick, from Queen Mary’s School of Biological and Chemical Sciences, said: “Probably the most exciting discovery from our research was finding genes encoding peptides that cause rapid stiffening or softening of collagen in the body wall of sea cucumbers.
“Although sea urchins and sea cucumbers may not look much like us, we are actually quite closely related to them. As we get older, changes in collagen cause wrinkling of our skin, so if we can find out how peptides cause the body wall of a sea cucumber to quickly become stiff or soft then our research might lead to new ways to keeping skin looking young and healthy.”
The scientists analysed the DNA sequences of thousands of genes in the purple sea urchin Strongylocentrotus purpuratus and the edible sea cucumber Apostichopus japonicus and specifically searched for genes encoding peptide messenger molecules. Rapid advances in technology used to sequence genes made the research possible.
“When the human genome was sequenced over a decade ago it cost millions of pounds – now all of the genes in an animal can be sequenced for just a few thousand pounds,” Professor Elphick said.
“We also found that sea urchins have a peptide that is very similar to calcitonin, a hormone that regulates our bones to make sure that they remain strong,” Professor Elphick said.
“So it will be fascinating to find out if calcitonin-type peptides have a similar sort of role in spiny-skinned creatures like sea urchins.”
“These types of advances in basic science are fascinating in their own right but they are also important because they underpin the medical breakthroughs that lead to improvement in the quality of people’s lives.”
Source: Queen Mary, University of London
Photograph by John O’Malley
Scientists have discovered that Caribbean coral coverage has plummeted. In the 1970s, there was 50 to 60 percent coral cover present, but those numbers have now dropped to less than 10 percent. Much of the decline has to do with the massive die-off of sea urchins in the 1970s, possibly due to disease. These creatures keep vegetation in check; without them, algae and grass levels have increased, pushing corals aside. The overfishing of certain fish species that perform similar tasks, such as parrotfish, have also had an effect, in addition to global warming.
Source: National Geographic
Photo: Mazyar Jalayer
Posted September 10th, 2012. Add a comment
Oceanographers with the Nova Southeastern University have found that some deep-sea crabs have eyes sensitive to ultraviolet light, which help them locate and sort glowing plankton, their source of food. The crabs live in the deep-sea zone, a pitch-dark area at the bottom of the ocean, typically resting on glowing, toxic corals. It is believed that the bioluminescence helps the crabs differentiate between the two; the corals glow blue-green and green, while the plankton they eat glow blue. The crabs’ sensitivity to shorter ultraviolet wavelengths may give them a form of color vision that ensures they gather food rather than poison.
Source: Nova Southeastern University
Photo: Nova Southeastern University
Posted September 10th, 2012. Add a comment
According to the journal Zootaxa, a new species of fish was recently discovered in Vietnam. Like all members of the genus Phallostethus, the newly discovered Phallostethus cuulong, has its reproductive organs located on its head just below the mouth. In fact, the genus name Phallostethus means “penis chest,” referring to the unusual placement of their reproductive organs.
These are small fish, less than an inch long, that are mostly translucent with a bright white blotch over the top of their head. They were collected from shallow areas with slow-flowing water in canals and rivers in Vietnam. They prefer to stay in heavily vegetated areas.
You can read the full study about this newly discovered little fish in Zootaxa.
Photograph courtesy of Magnolia Press.
Weedy sea dragon with its babies.
The Monterey Bay Aquarium animal care team and a nurturing weedy sea dragon dad have achieved a milestone reached by only four other aquariums in North America: the birth of a brood of sea dragon babies.
More than 80 of the inch-long fish – Australian relatives of the seahorse – began hatching on July 22. The father, who carried the eggs in a brood pouch under his tail, delivered the young in a sea dragon display that’s part of the aquarium’s special exhibition, “The Secret Lives of Seahorses.” The last eggs hatched on August 2.
The young are being raised behind the scenes for now, said Associate Curator of Fish and Invertebrates Jonelle Verdugo, who heads the seahorse husbandry team at the aquarium. If they survive and thrive, visitors may get to see them as part of the special exhibition. Others will be transferred to colleague institutions with the Association of Zoos and Aquariums.
“We are so excited about these births,” Verdugo said. “We’ve had success with a couple species of pipefish and half a dozen species of seahorses, but this is a first for our weedy sea dragons.”
Verdugo said her team drew on the experiences of colleagues at the Aquarium of the Pacific in Long Beach, the Georgia Aquarium in Atlanta and Melbourne Aquarium in Australia, all of whom generously shared information about their own work breeding sea dragons.
Verdugo was also in touch with SeaWorld Orlando, whose sea dragon was carrying eggs and gave birth around the same time. Tennessee Aquarium in Chattanooga has also bred weedy sea dragons.
Verdugo said the papa weedy sea dragon remained on exhibit and was free to swim about as usual while he was giving birth. Each day, the young were moved behind the scenes as they hatched, and placed in smaller aquariums to receive closer attention from caregivers.
“Sea dragon pregnancies pose a lot of challenges for us,” she said. “We’ve gotten through several of them and now have living baby sea dragons. We know there are more challenges ahead, and we hope we’ll be able to raise all of the babies to adulthood.”
“Just having the pregnancy and births is a great indication that we’ve created an environment in which our sea dragons are thriving,” she added.
Like their more flamboyant cousins, the leafy sea dragons, weedy sea dragons are native to the southern and eastern coasts of Australia. While not classified as threatened in the wild, they are considered vulnerable due to over collecting for the home aquarium trade. Both species are protected under Australian law, and it is illegal to take or export them without a permit.
“If we and other aquariums continue to have success in breeding weedy sea dragons, that will go a long way toward eliminating the pressure to collect sea dragons from the wild,” Verdugo said.
Leafy and weedy sea dragons are closely related to seahorses and pipefish. With all of these fishes it’s the males who carry the young.
Sea dragons have long, slender bodies with leaflike projections that help them blend in with the seaweeds where they live. Weedy sea dragons can grow to be 18 inches long, and are usually reddish in color with yellow spots.
During breeding, males and females hover side by side, mirroring each other’s movements but with tails curved away from each other. They rise up in the water column, just like seahorses, to transfer the eggs onto a brood patch on the underside of the male’s tail.
Gestation typically lasts 6-8 weeks, and the babies hatch out over the course of a few days. In the wild, as the babies hatch, the male will change his swim pattern to distribute the young over a larger area.
The mission of the Monterey Bay Aquarium is to inspire conservation of the oceans.
Source: Monterey Bay Aquarium
Photograph by Monterey Bay Aquarium/Randy Wilder.
From an article by Jessica Nimon.
While aquariums provide a relaxing pastime for humans on Earth, recreation is not the goal behind the new Aquatic Habitat, or AQH, aboard the International Space Station. Instead, researchers will use this unique facility to look at how microgravity impacts marine life.
Sponsored by the Japanese Space Agency, or JAXA, this habitat is a closed-water circulatory system, which provides a new facility option for station research. Scientists will use the habitat to study small, freshwater fish on orbit. For the first investigations, they plan to examine the Medaka (Oryzias latipes) fish.
Photograph courtesy of JAXA.
Source: Science Daily