Earlier this year, we produced a video documenting Academy researcher Luiz Rocha’s work in Belize studying invasive lionfish. These predators, originally from the Indo-Pacific, found their way to the northwest Atlantic in the 1990s—likely through an aquarium release—and have steadily moved south over the past fifteen years.

The lionfish are wreaking havoc in the area because they voraciously gobble up smaller, native fish—threatening everything from coral reef ecosystems to local economies based on fishing and tourism. In addition, eradication appears impossible and whatever is keeping them in check in their native Indo-Pacific habitats—researchers around the world are trying to find out what—appears to missing in the Atlantic.

“Prey in the Indo-Pacific could simply be more aware of the danger lionfish pose,” Rocha says. “There could also be parasites keeping the lionfish in check in their native habitats.”

Bad
A recent study in PLoS One determines that humans may be the only threat to lionfish in their new home. An international research team looked at whether native reef predators such as sharks and groupers could help control the population growth of lionfish in the Caribbean, either by eating them or out-competing them for prey.

The team surveyed 71 reefs over three years, in three different regions of the Caribbean. Their results indicate there is no relationship between the density of lionfish and that of native predators, suggesting that, “interactions with native predators do not influence” the number of lionfish in those areas.

The researchers did find that lionfish populations were smaller in protected reefs, but researchers attributed the lower numbers to targeted removal by reef managers, rather than consumption by large fishes in the protected areas. As Rocha mentioned in the video last spring, encouraging the hunting and human consumption of these spiny fish may be reefs’ only hope.

Ugly
Recent submersible dives deep off the coast of Fort Lauderdale, Florida reveal that these invasive lionfish populations aren’t just spreading southward—they’re also heading to great depths, out of the reach of their only predators, human hunters.

“We expected some populations of lionfish at that depth [300 feet], but their numbers and size were a surprise,” says Stephanie Green, of Oregon State University, who participated in the dives.

The lionfish are growing to an unusually large size—as much as 16 inches. “A lionfish will eat almost any fish smaller than it is,” Green says. “Regarding the large fish we observed in the submersible dives, a real concern is that they could migrate to shallower depths as well and eat many of the fish there. And the control measures we’re using at shallower depths—catch them and let people eat them—are not as practical at great depth.”

Rocha confirms this. “Even if control efforts are successful in shallow water, we can’t reach these deep fish.” And the lionfish at great depths can easily move to shallower areas. In addition, “these larger fish produce more eggs,” Rocha says, creating even larger populations.

(Rocha is hoping to join on subsequent dives. He was invited on this recent submersible dive, but was attending a conference on Indo-Pacific fish in Japan at the time. A video of the dives is available here.)

Good
We want to end on an upbeat note, and Rocha has a recent study in Marine Ecology Progress Series about the spread of lionfish down the coast of South America and into Brazil. The fish haven’t reached that far yet, but given their rapid spread, it seems to be only a matter of time.

Working with other Brazilian researchers, Rocha investigated movements of various fish species across the Amazon-Orinoco plume (AOP), where the Amazon and Orinoco rivers meet the Atlantic Ocean. The study describes the AOP as “a large freshwater and sediment runoff between the Caribbean and the Brazilian Provinces that represents a ‘porous’ barrier to dispersal for reef organisms.”

The scientists found that while a few “vagrant” species recently crossed the barrier heading north, “species headed south don’t spread as quickly,” according to Rocha. “The currents make it tricky to cross.”

This could be the first bit of good news in stopping the spread of lionfish. “This means we can keep an eye on it and control the lionfish as they cross, keeping their numbers down,” Rocha says.

Next
Rocha and colleagues here at the Academy and in Europe are beginning a population genomic study of the invasive lionfish. This study will look at fine-scale genetic diversity of lionfish among the different Caribbean islands. Rocha will start collecting samples in two weeks in Curaçao. The samples will then be analyzed by Academy researchers—including Rocha’s wife, Claudia—here at the Center for Comparative Genomics.

“We want to see if there is gene exchange between different island populations,” Rocha explains. “This will help us determine how successful local efforts to control lionfish can be if larvae are coming from other locations. This study can help inform how resources are used to control different populations.”

The fight against invasive lionfish continues…

Image: Alexander Vasenin/Wikipedia

Oysters, like many bivalves, are important for marine ecosystems. The organisms filter water through their feathered gills, removing impurities as they inhale and exhale. In fact, native and invasive bivalves might filter the entire volume of the San Francisco Bay every 3-4 days!

However, oysters around the world are threatened by ocean acidification. The acidity breaks down the calcium carbonate shells of the oysters, as we reported in a video several months ago.

Recently, researchers discovered other effects of acidification on oysters and what the breakdown of the oysters’ calcium carbonate shells could mean for the acidic balance. Science Today sat down with the Academy’s own oyster expert, Dr. Peter Roopnarine, curator and chair of Invertebrate Zoology and Geology, to get some perspective on these recent studies.

In the first study, published earlier this month, scientists reported that acidification has negative effects for oysters in the larval stage. The acidity in the water makes the larvae expend much more energy than in neutral waters to make their shells.

“As the oyster larvae struggle early on and expend that embryonic energy,” Roopnarine says, “they have difficulty cranking up their own feeding.”

According to the paper’s lead author, George Waldbusser, “It becomes a death race of sorts. Can the oyster build its shell quickly enough to allow its feeding mechanisms to develop before it runs out of energy from the egg? They must build their first shell quickly on a limited amount of energy—and along with the shell comes the organ to capture external food more effectively.”

Last month, headlines reported that “Oyster Shells are an Antacid to the Oceans,” based on a study of oyster reefs in Chesapeake Bay. Roopnarine explains how oyster reefs are built over time, “Oysters do best on hard ground. The first oysters in a soft bottom environment eventually become the hard substrate that future oysters build upon. As the reef grows, the presence of the shells promotes a healthy, low acidic environment.” Or as the study’s introduction states, “Active and dense populations of filter-feeding bivalves couple production of organic-rich waste with precipitation of calcium carbonate minerals, creating conditions favorable for alkalinity regeneration.”

On a micro-scale, like the Chesapeake Bay, Roopnarine agrees that this could work. Restoration of oyster reefs could contribute to the reduction of ocean acidification problems. On a macro-scale, over geological time and large ocean mass, however, it seems that these oyster reefs could do little to undo the large amounts of CO₂ humans have been pumping into air (that’s absorbed by the oceans) for over a hundred years.

I asked Roopnarine about the San Francisco Bay’s oyster population. We had native oysters before overharvesting, pollution and sedimentation from gold mining in the Sierras buried the oyster reefs, Roopnarine says. A few are still found around the bay, but their numbers are small.

The oysters farmed locally are Japanese oysters, which, until a few years ago, were only found in hatcheries. Wild populations are now establishing themselves in the bay, Roopnarine says, which could be due to warmer temperatures. He and colleagues wrote a study a few years ago that looks at the Japanese oyster population locally.

With the important work these marine organisms do, it’s important we learn more about them to restore oyster reefs.

A former Academy staff-member, Jill Bible, is doing just this near Bodega Bay. To learn more watch this great video by the UC Communications team.

Image: Oysters showing the effects of ocean acidification, OSU

What the…?

Remember this video we produced a while ago about the super cool mimic octopus? It compresses and conforms itself to look like a sea snake, flatfish, or lionfish—adjusting its look for different situations. Thanks to these brazen habits, it can swim in the open with relatively little fear of predators.

Well, it now appears the mimic octopus has a companion mimic. Last summer, Godehard Kopp of the University of Gottingen, Germany took this video while diving in Indonesia. A black-marble jawfish is seen closely following a mimic octopus as it moves across the sandy bottom. The jawfish has brown-and-white markings similar to the octopus and is difficult to spot among the many arms. The octopus, for its part, doesn’t seem to notice or care.

Kopp sent the video to Rich Ross and Luiz Rocha here at the Academy, who identified the jawfish species. Since this association had not been recorded before, they published their observations last month in the scientific journal Coral Reefs. The authors surmise that the jawfish hitches a ride with the octopus for protection, allowing it to venture away from its burrow to look for food—a case of “opportunistic mimicry.”

“This is a unique case in the reefs not only because the model for the jawfish is a mimic itself, but also because this is the first case of a jawfish involved in mimicry,” says Rocha, assistant curator of ichthyology. “Unfortunately, reefs in the Coral Triangle area of southeast Asia are rapidly declining mostly due to harmful human activities, and we may lose species involved in unique interactions like this even before we get to know them.”

Luiz Rocha and his colleagues set about finding out how coral reef fish make long distance journeys across the Atlantic (about 3500km/2200 miles near the equator) or the freshwater and sediment discharges of the Amazon and Orinoco rivers in South America (about 2300 km/1500 miles).

Coral reef fish don’t move a lot as adults, so the long held belief was that the fish dispersed in their larval stage. The larval stage can last 10 days for some species and 100 days for others and it may take 50 days to cross the Atlantic. Looking at the variables and the distribution for 985 species, the researchers found that the larval stage actually had little to do with which fish crossed the large distances and barriers—or how they managed to do it.

Dispersal seems to factor on other specifics—the size of the adult fish, whether the fish could use flotsam, or sargassum mats, as habitats across the barriers and if the fish were generalists—able to adapt to new habitats and food. Luiz and his collaborators published their findings last week in the Proceedings of the Royal Society: B. From the abstract:

Successful establishment after crossing both barriers may be facilitated by broad environmental tolerance associated with large body size and wide latitudinal-range. These results highlight the need to look beyond larval-dispersal potential and assess adult-biology traits when assessing determinants of successful movements across marine barriers.

Luiz gave us some examples:

The Brown Chromis (Chromis multilineata) is a great example of a fish that has a short larval stage but crosses barriers using floating substrate.

Many species of parrotfishes in the Caribbean have long larval stages but are restricted to the Caribbean, and found neither in Brazil nor in the other side of the Atlantic.

Some species of wrasses of the genus Halichoeres cross the Amazon barrier but don’t survive on the other side because they can’t find their preferred habitat. In this genus, the specialists tend to have smaller geographical ranges than the generalists. One of the examples is Halichoeres poeyi, a wrasse that lives not only in coral reefs, but also rocky reefs and seagrass. This wrasse is continuously distributed from South Brazil to Florida, and all of the other (more specialized) species in this genus are different in either side of the Amazon barrier.

The study built upon a paper the team published in 2008—a culmination of five years of work, creating a database of 1,300 Atlantic species of coral reef fish. The database includes many variables for each species—biogeographic data, reproductive mode (which is a proxy for length of the larval stage), spawning information, size as an adult, habitat needs, and more.

Luiz Rocha joined the Academy less than a month ago, as a curator of ichthyology, specializing in coral reef fish. Originally from Brazil, he fell in love with these fish at an early age—snorkeling since the age of five! He comes to the Academy from the University of Texas. Stay tuned for more of his research.

Image by John E. Randall, WorldFish Center – FishBase, EOL

In case you were wondering what an atoll is, according to the Encyclopedia of Earth:

Atolls are circular, oval, or horseshoe-shaped arrays of coral reef islands that are perched around an oceanic volcanic seamount and encircle a shallow central lagoon…. Because atoll formation requires coral reef building, atolls are limited to tropical waters.

(View this great animation here of an atoll forming over 30 million years.)

Healthy Fishing

To gain new insights on the ecology of reef fishing, Stanford researchers are comparing and contrasting the reefs of two atolls—Palmyra and Tabuaeran.

Palmyra is a protected U.S. wildlife refuge and prohibits fishing along its shores. Tabuaeran is part of the Republic of Kiribati and is home to about 2,500 people who depend on the reef for food and income.

Signs of a healthy marine ecosystem usually include the presence of large fish and sharks. “Palmyra has some of the highest densities of sharks and other large fish of any coral reef in the world,” said Douglas McCauley, a graduate student at Stanford. “That’s clear within seconds of jumping in the water there.”

But in Tabuaeran, where fishing is a way of life, sharks and other large species are in short supply, McCauley said. “That was surprising, because Tabuaeran is a somewhat lightly populated island. Most people arrived only a few decades ago, and fishing there is still very artisanal in nature.”

Big fish grow and reproduce slowly, so their populations take longer to recover, he added. “It appears that it takes very little harvesting to reduce populations of these sensitive, large reef fish.”

The Stanford researchers are hoping to pass this information along to the people of Tabuaeran so they can fish more sustainably. Over the past three years, the team taught science classes at local schools on topics such as reef ecology and genetics and conducted town hall meetings at every village on the atoll.

Because the livelihoods of so many Tabuaerans depend on healthy fisheries, locals are eager to preserve fish numbers, McCauley said. “Those who depend most on the environment can and should be its best stewards,” he added.

Millennium Atoll: A Pristine Ecosystem

Millennium Atoll, also part of the Republic of Kiribati, is one of the most remote, pristine atolls in the world. Its lagoon is highly enclosed, sealing it away from the outside world. Californian and Hawaiian scientists studied its life and published their findings last week in PLoS One:

This is the first comprehensive survey of the lagoon at Millennium Atoll, which contains some of the few remaining coral reefs that are relatively unaltered by human activity. The lagoon of the atoll is home to a variety of unique organisms that are threatened in many areas of the world.

Valuable resource species such as clams, sharks, Napoleon wrasse, sea turtles, and lobster are fairly abundant at Millennium but have been seriously overexploited elsewhere around the world.

Protection of Millennium’s coral reefs should be a priority for the Republic of Kiritbati as these habitats are not only unique but are some of the world’s least impacted reef systems.

Atolls Growing, Not Shrinking

Finally, last month Australian researchers published the incredible finding that despite warnings of small atolls and islands disappearing with sea level rise, they have found that in the Pacific, some have actually grown in the last 60 years.

Despite evidence of the sea level rising as high as five inches in the region, of the 27 islands they studied, four decreased in size, but the rest remained the same or grew.

It may simply be due to the nature of atoll formation itself. From New Scientist:

Because the corals are alive, they provide a continuous supply of material. “Atolls are composed of once-living material,” says Arthur Webb, “so you have a continual growth.”

The researchers stress these results reflect a small portion of atolls in one area in the Pacific and that “warnings about rising sea levels must still be taken seriously.”

With so much research emerging about atolls, it’s obvious we still have a lot to learn. These little islands are making big waves in the scientific community.