Category: Ocean Science & Marine Biology

ABy Thomas Wolcott, North Carolina State University; Donna Wolcott, North Carolina State University; John L. Largier, University of California, Davis, and Steven G. Morgan, University of California, Davis.

Many people who love the oceans never realize that a single drop of seawater is teeming with plankton, which means “drifters” in Greek. These organisms, which typically range in size from a pinhead down to the tip of a pin, spend their lives drifting with currents and form the base of ocean food chains.

Most larger marine organisms, from corals to crabs to fish, also begin life as tiny drifters. Females release eggs, or larvae, which join plankton and spend days to weeks adrift. Only larvae that arrive at the right habitats, at the right stage in their life cycles, will grow into a new generation. The rest will perish.

Scientists have long assumed that larvae are at the mercy of ocean currents. We cannot track such tiny creatures for weeks and months as ocean currents carry them over long distances, but many of us have wondered where they go and how they get there.

Thousands of miles and decades apart, members of our team independently wrestled with this puzzle. Studying land crabs on Bermuda, Tom and Donna Wolcott of North Carolina State University wondered why larvae of one species seemed to return to the islands every year from the surrounding ocean, but those of another species did not. On the California coast, Steven Morgan at the University of California at Davis documented larval behaviors of shore-dwelling species that apparently enabled them to avoid being swept offshore by strong currents. And Morgan’s colleague John Largier explored the pattern of currents in which the larvae drifted.

We needed a new tool to address these issues. The Wolcotts reasoned that they could not put transmitters on individual larvae, but they could design something that behaved like a larva. If it could be tracked, following a group of them would reveal the path of a cloud of larvae.

Over three decades they developed a robot “larval mimic” that senses its environment, mimics the vertical swimming responses of larvae and relays its location. Following a cluster of these robots would show where larvae would be carried by currents, depending on the depths the larvae chose.

This research is providing insights into how evolution has “tuned” subtle changes in larval swimming behaviors to maximize the chances that larvae drifting in the ocean will beat the enormous odds against them and arrive at suitable habitat for settlement.

Following the currents – or not

The strong and persistent currents off the northern California coast provide an excellent opportunity to test the effectiveness of larval behaviors. Upwelling occurs along coastlines that run north-south along the western margins of continents, where prevailing winds combine with the rotation of the Earth to drive surface waters away from shore. This process draws deep, cold, nutrient-rich waters to the surface, supporting some of the most productive fishing grounds in the world.

Scientists have long assumed that during upwelling, larvae developing near the surface were carried away from shore and lost at sea. But when Morgan and colleagues towed plankton nets at discrete depths throughout the water column and across the continental shelf of northern California, they found that larvae of most species remained within three kilometers of the shore where they originated.

How do such tiny organisms control their positions in the water? It has been known for decades that even though larvae cannot swim against currents, they can swim vertically from one layer of water to another moving in a different direction. The evolution of vertical swimming behaviors could help larvae to reliably stay close to shore, or to range different distances across the continental shelf.

By regulating their depth, larvae appear to have a surprising amount of control over how far from home they are transported. Many marine populations need this ability for successful reproduction. It also determines which populations exchange larvae sufficiently to remain a single genetically similar population along the coastline.

Knowing that larvae can regulate their movements in this way could affect how we design and evaluate networks of marine protected areas to conserve ecosystems and populations of economically and ecologically important species. It also is relevant for tracking the spread of invasive species, and for analyzing how marine species adapt to a warming planet by shifting their ranges north or south along the coast.

A robot that mimics larvae

Tom and Donna Wolcott named their robot the Autonomous Behaving Lagrangian Explorer, or ABLE – autonomous because it is deployed without a tether, and Lagrangian because it is carried along with the water parcel in which it is embedded. The Lagrangian approach to studying currents consists of following the movement of a parcel of water, typically with some sort of “drifter” – in this case, a drifting robot.

But the ABLE is not entirely passive: It mimics larval behavior by monitoring time and conditions around it, including depth, temperature, light, salinity and vertical water motion every 10 seconds. Then it calculates a new “target depth” appropriate for that larva and swims toward it by subtly adjusting its buoyancy. It can log up to 16 megabytes of environmental data from its sensors and upload them after the “bot” is recovered from the water.

Testing ABLE at sea and in a swimming pool.

When the Wolcotts snorkeled with several of the initial ABLEs in the Bahamas in 1994, they could see them swimming up and down as programmed. The ABLEs could also be tracked by following signals from their ultrasonic pingers – until drowned out by the din of snapping shrimp.

Next the Wolcotts created ABLEs to simulate mobile phytoplankton for research by North Carolina State University marine scientist Dan Kamykowsky on transport of “red tides,” which are dense blooms of toxic algae. The Wolcotts added a light sensor so that ABLE could calculate photosynthesis and respiration. The ABLEs could then mimic the movements of the algal cells, moving upward to meet their needs for light and photosynthesis and deeper to find essential nutrients.

These ABLEs also carried redundant tracking hardware: GPS receivers to get position fixes, VHF radio beacons to transmit those positions and LED beacons so that researchers could retrieve them from the water after dark. Bluetooth wireless connectivity enabled the bots to talk to computers while their pressure housings were sealed. This version successfully emulated red tide algae during experiments in the Gulf of Mexico.

The newest ABLEs carry a transmitter to relay the latest GPS fixes via satellites to our computers and smartphones, and a sensor to keep the robots from getting stuck on the sea bottom. Running all of this gear and simulating larval swimming behaviors requires a program that contains roughly 3,000 lines of code.

Cracking the black box

Steven Morgan first saw the Wolcotts demonstrate an ABLE prototype in a hotel pool at a 1996 conference. In 2015, after two more decades of “ABLE evolution” and field testing, we conducted the first experiments using them to understand how larvae were transported in currents near the University of California at Davis’s Bodega Marine Laboratory in northern California.

Circulation is more complex around headlands and bays than along straight coastlines, which makes it especially hard to predict where larvae go. Based on prior study of larval behavior and currents, Morgan and Largier predicted that during upwelling, larvae in surface waters would be transported far to the south, while larvae in bottom waters would stay put. They also expected larvae that remain in bottom waters during the day, rising to the surface to forage at night after winds subside, would stay put.

To test this hypothesis, we repeatedly released ABLEs programmed to simulate larvae with different vertical swimming behaviors and tracked them for 24 hours. Their movements demonstrated that larvae that remained near the surface would be transported up to 8 kilometers southward within 24 hours. In strong contrast, ABLEs that stayed deep in the water column remained near where they were released. ABLEs that migrated to the surface at night did not travel much farther than the ones that remained deep, moving less than 2 kilometers.

From these experiments, it is evident that vertical positioning in currents, even if cued only by the clock, has profound effects on larval movements. ABLE’s ability to respond to environmental cues, and its battery life of over two weeks, also will enable us to examine how changes in depth preferences affect transport of larvae during the course of development.

Larvae of many species occur near the surface in offshore-flowing currents early in their development and are carried away from shore. Older larvae descend into deep shoreward-flowing currents and return onshore to habitats in which they can metamorphose and become adults. In effect, they use currents like conveyor belts to travel out and back across the continental shelf.

Now we are deploying ABLEs with different behaviors to collect the first experimental evidence of how patterns of vertical migration by larvae determine how far offshore and alongshore they travel. This information will help us crack the “black box” and reveal where larvae of different species go.

We also plan to deploy ABLEs in different environments, such as estuaries. Eventually we plan to return to Bermuda or another isolated island to answer the Wolcotts’ original question: How do larvae find their way back to the shores of a speck in the middle of a vast ocean?

Thomas Wolcott, Professor Emeritus of Marine, Earth and Atmospheric Sciences, North Carolina State University; Donna Wolcott, Associate Professor Emerita of Marine, Earth and Atmospheric Sciences, North Carolina State University; John L. Largier, Professor of Coastal Oceanography, University of California, Davis, and Steven G. Morgan, Professor of Environmental Science and Policy, University of California, Davis

This article was originally published on The Conversation. Read the original article.

Now, Check Out:

• As climate change alters the oceans, what will happen to Dungeness crabs?
• Apparently the Oceans are Full of Glowing Fish
• Solving ‘Darwin’s Paradox’: why coral island hotspots exist in an oceanic desert
• Far more microplastics floating in oceans than thought
• We’ve been wrong about the origins of life for 90 years

By Joshua Cinner, James Cook University.

Despite substantial conservation efforts, human impacts are harming coral reefs all over the world. That in turn affects the millions of people who depend on reefs for their livelihoods. It’s a gloomy picture, but there are some bright spots.

In a study that appears on the cover of this week’s Nature, I and 38 international colleagues identify 15 places around the world where the outlook is not so bleak. Many of them are in surprising places like Pacific island states, which may not have lots of money for conservation but do have a close social connection to the health of their oceans.

Unlike scientific studies that look at averages or trends, we took a slightly different approach and focused on the outliers – the places bucking the trend. This type of “bright spot” approach has been used in a range of fields, including business, health and human development, to search for hope against backgrounds of widespread failure.

One example is in Vietnam, where the charity Save the Children looked at poor children who bucked the trend of widespread malnutrition. They discovered that poor families with healthier kids were collecting small crabs and shrimp from their rice paddies and grinding them into their kids’ food, and feeding them smaller, more frequent meals. These practices have now spread to more than 2.2 million families, cutting childhood malnutrition by 65%.

This is a great example of local habits that, once identified and spread more widely, have had a hugely beneficial impact. My colleagues and I wanted to see if we could do the same for the world’s coral reefs.

Searching for bright spots

We carried out more than 6,500 reef surveys across 46 countries, states and territories around the world and looked for places where reef fisheries should have been degraded, but weren’t.

We defined these bright spots as reefs with more fish than expected, based on their exposure to pressures like human population, poverty and unfavourable environmental conditions. To be clear, bright spots are not necessarily “pristine” reefs, but rather reefs that are doing better than they should be given the circumstances. They are reefs that are “punching above their weight”.

We identified 15 bright spots and 35 dark spots (places that were doing much worse than expected) in our global survey. The bright spots were mainly in the Pacific Ocean, and two-thirds of them were in populated places like the Solomon Islands, parts of Indonesia, Papua New Guinea and Kiribati.

Dark spots were more globally distributed; we found them in every major ocean, sometimes in places that are generally considered to be pristine, such as in the northwestern Hawaiian islands. Again, this doesn’t mean the reefs were necessarily in terrible shape – just worse than we would expect, given that in cases such as Hawaii they are remote, well protected and in a wealthy country with a strong capacity to govern their reefs.

The Great Barrier Reef, which is often considered the best-managed reef in the world, performed largely as we would expect it to, given that it is in a wealthy country with low population density, and many of its individual reefs are offshore and mostly remote from people.

What makes bright spots special?

We wanted to learn what these bright spots were doing differently. Why were they able to withstand pressures that caused other reef systems to suffer? And could lessons from these places inform reef conservation in other areas?

Our preliminary investigation showed that bright spots (and their nearby human communities) generally had four crucial characteristics:

• strong local sea traditions, which include ownership rights and/or customary practices such as periodically closing a reef to fishing
• high levels of participation in management by local people
• high levels of dependence on fishing (this seems counter-intuitive, but research shows that where people’s livelihoods depend on a resource, they are more committed to managing it responsibly)
• deep-water refuges for fish and corals.

Importantly, the first two are malleable (for instance, governments can invite local people to become more involved with reef management), whereas the latter two are less so (it is hard to change people’s livelihoods, and impossible to change the undersea landscape in a way that wouldn’t devastate reefs in the process).

We also found some common characteristics of dark spots

• use of particular types of fishing nets that can damage habitat
• widespread access to freezers, allowing fish catches to be stockpiled
• a recent history (within the past five years) of environmental disturbance such as coral bleaching or cyclone.

Where next?

We believe that the bright spots offer some hope and some solutions that can be applied more broadly across the world’s coral reefs.

Specifically, investments that foster local involvement and provide people with ownership rights to their marine resources can help people develop creative solutions and defy expectations that reefs will just continue to get more degraded.

Conversely, dark spots can highlight the development or management pathways to avoid. In particular, it is important to avoid investing in technology that allows for more intensive fishing, particularly in places with weak governance or where there have already been environmental shocks like cyclones or bleaching.

The next step is to dig deeper into the social, institutional and ecological dynamics in the bright spots. By looking to the places that are getting it right – whether by accident or design – we can hopefully make the future a bit brighter for reefs the world over.

Joshua Cinner, Senior Research Fellow, ARC Centre of Excellence, Coral Reef Studies, James Cook University

This article was originally published on The Conversation. Read the original article.

Now, Check Out:

• Sea turtle ‘hitchhikers’ could play an important role in conservation
• Apparently the Oceans are Full of Glowing Fish
• Oceanic Researchers Find Deep Hydrothermal Vents Made of Something Completely Different
• Solving ‘Darwin’s Paradox’: why coral island hotspots exist in an oceanic desert
• Here’s How Octopuses See Color Differently than Any Other Animal [Video]

A team of marine scientists has returned from nearly a month of scuba diving on coral reefs in the middle of the equatorial Pacific Ocean. What they saw will haunt them for a long time.

“It’s as if someone has thrown a fuzzy red/brown blanket over the reef, turning it all one color,” says Kim Cobb, a professor in Georgia Tech’s School of Earth and Atmospheric Sciences. “Right now it looks okay from afar, with all the coral structure still in place. But when you get up close, you see that it’s all dead, as far as the eye can see. It’s very eerie.”

“CHRISTMAS ISLAND’S CORAL REEFS ARE LIKE GHOST TOWNS NOW. THE STRUCTURES ARE ALL STILL THERE, BUT NO ONE IS HOME.”

Cobb and colleagues worked with biologist Julia Baum and her team of University of Victoria researchers on Kiritimati Island (also known as Christmas Island), the world’s largest coral atoll. Christmas Island is about 150 miles north of the equator and 1,340 miles south of Hawaii. The current El Niño is the strongest ever recorded, and it has hit this area harder than anywhere else on the planet.

When the Georgia Tech team visited the reefs last November, 50 to 90 percent of corals they saw were bleached and as many as 30 percent were already dead. This time, after months of warm waters powered by the El Niño, the numbers were starker. After extensive underwater surveys around the atoll, Baum’s team estimates that 80 percent of the corals are dead and 15 percent are bleached. Only 5 percent are still alive and healthy.

“To see the reefs change this dramatically in just a few months is shocking,” says Baum. “We were bracing ourselves for the worst, but seeing it with our own eyes was surreal. Christmas Island’s coral reefs are like ghost towns now. The structures are all still there, but no one is home.”

STARVING CORALS

Corals are communities of animals that have tiny photosynthetic algae living inside them in a mutually beneficial relationship. The algae provide corals with their vibrant corals, along with a vital source of food via photosynthesis. Corals, in turn, provide the structure that shelters their tiny algal symbionts.

Corals are very temperature-sensitive. A rise of just 1-1.5 degrees Celsius can stress coral enough to evict the algae until the heat stress subsides. This leaves a ghostly white coral skeleton and is known as “bleaching.” During protracted warm water events, such as the current El Niño, bleached corals aren’t able to bring their symbiotic plants back in, and they can die of starvation.

Temperatures on Christmas Island have been between 1.5 to 3 degrees Celsius higher than normal for the past 10 months straight. “This intense heat stress has transformed some of the world’s healthiest coral reefs into graveyards,” says Baum. “To our knowledge, this is the greatest coral mass mortality event at a single location on record.”

‘A WAKE-UP CALL’

Many other areas in the world’s oceans are also showing extensive bleaching this year, including Australia’s Great Barrier Reef, but the Christmas Island corals were pushed far beyond bleaching.

Cobb and Baum think it may take a decade or more for the Christmas Island reefs to recover, but they might never look the same because of warmer-than-average temperatures and lower ocean acidity. Both are the consequences of rising greenhouse gases.

“Aside from their sheer beauty and appeal, coral reefs provide a host of ecosystem services that are critical to a healthy ocean,” says Cobb. “When remote reefs like Christmas Island succumb to acute temperature stress, it’s a wake-up call for the rest of the world’s reefs, which will come under increasing stress from climate change.”

“Christmas Island’s people rely on the reefs for their food and their livelihoods, so they’ll be profoundly affected by this event,” says Baum. She and her team will be studying the reefs carefully over the coming years to assess the recovery and learn more about how some corals are managing to resist heat damage. At the same time, Cobb and her students will work to determine whether the record-breaking 2015/2016 El Niño event is a portent of future El Niño events under continued climate change.

“Our research will provide important new insights into how corals may be able to survive more frequent temperature extremes over the next century,” says Baum. “In the meantime, this event is a vivid reminder that the effects of climate change are happening now, and that the choices we make about greenhouse gas emissions in the next decades will have long-term effects.”

Source: Republished from Futurity.org as a derivative work under the Attribution 4.0 International license. Original article posted to Futurity by Jason Maderer-Georgia Tech.

Featured Photo Credit: Georgia Tech

Now, Check Out:

• Solving ‘Darwin’s Paradox’: why coral island hotspots exist in an oceanic desert
• As the Earth Enters its Third Mass Bleaching Event, Will Corals Survive?
• Is global warming causing marine diseases to spread?
• Explainer: El Niño and La Niña
• [Video] This Octopus has an Odd Way of Grabbing a Meal

 

Charlotte Eve Davies, Universidad Nacional Autónoma de México (UNAM)

Global climate change is altering the world’s oceans in many ways. Some impacts have received wide coverage, such as shrinking Arctic sea ice, rising sea levels and ocean warming. However, as the oceans warm, marine scientists are observing other forms of damage.

My research focuses on diseases in marine ecosystems. Humans, animals and plants are all susceptible to diseases caused by bacteria, viruses, parasites and fungi. Marine diseases, however, are an emerging field.

Infectious agents have the potential to alter ocean life in many ways. Some threaten our food security by attacking important commercial species, such as salmon. Others, such as bacteria in oysters, may directly harm human health. Still others damage valuable marine ecosystems – most notably coral reefs.

To anticipate these potential problems, we need a better understanding of marine diseases and how climate change affects their emergence and spread.

Warming waters promote marine diseases

Recent studies show that for some marine species diseases are spreading and increasing. Climate change may also promote the spread of infectious agents in oceans. Notably, warming water temperatures can expand these agents’ ranges and introduce diseases to areas where they were previously unknown.

Many diseases of marine species are secondary opportunist infections that take advantage when a host organism is stressed by other conditions, such as changes in pH, salinity or temperature. A bacterium that is dormant (and therefore noninfective) at a certain temperature may thrive at a slightly higher temperature.

One well-documented example is the emergence of epizootic shell disease (ESD) in American lobsters. This disease, thought to be caused by bacteria, is characterized by lesions that penetrate inward from a lobster’s shell surface towards the inner flesh, making infected lobsters unmarketable. ESD can also kill lobsters by making it difficult for them to shed their shells in order to grow.

In the 1990s, following almost a decade of above-normal summer temperatures, ESD affected so many lobsters that the Atlantic States Marine Fisheries Commission declared that the Southern New England fishery (Connecticut, Massachusetts, New York and Rhode Island) was in collapse and recommended closing it.
Fishery models that incorporated shell disease offered convincing evidence that ESD was a major factor in the decline of the stock. This episode underscores the importance of considering marine diseases in stock assessments and fishery management.

Now there are concerns that ESD will continue to spread north to Maine’s US$465.9 million lobster fishery. In 2015 the Gulf of Maine showed record high abundances of lobster, making it one of the most productive fisheries in the world.

However, sea surface temperatures in the Gulf of Maine have increased faster than 99 percent of the global ocean over the past decade, warming three times faster than the global average. Since temperature is a primary factor in the spread of this disease, observers fear that it could have devastating effects on Maine’s lobster fishery.

There is also a risk that ESD could spread from American lobsters to other fisheries. Seafood wholesalers have imported live American lobsters into Europe for decades, which can result in their escape into the wild. Last summer the United Kingdom’s Marine Management Organization warned U.K. fishermen that because the European lobster shares similar habitats, food sources and diseases with the American lobster, ESD could spread between the species.

As a doctoral student at Swansea University, U.K., I collaborated with the New England Aquarium in Boston, Massachusetts to investigate this possibility. While we found that European lobsters were more likely to develop shell disease when reared in the presence of American lobsters, on the positive side, they don’t seem to get the same shell disease as American lobsters.

This means that European lobsters may be better equipped to deal with outbreaks of ESD. But with sea surface temperatures in U.K. coastal waters rising since the 1980s by around 0.2-0.9 degrees Celsius per decade, it is important to monitor U.K. waters for this disease.

Tropical disease

Now I am now studying the Panuliris argus_1 virus (PaV1) in the Caribbean spiny lobster, where the picture is more dire. Discovered around 2000, this virus is present from the Florida Keys to Venezuela. It can infect up to 60 percent of lobsters in some areas. Laboratory studies indicate that lobsters held in high-temperature seawater and exposed to PaV1 develop active and more intense infections much more quickly than those held at lower temperatures.

Studies from 1982 to 2012 show that waters in the Caribbean are warming, with the most significant temperature increase occurring over the past 15 years – approximately the period when PaV1 appeared. If PaV1 continues to spread, it could have significant effects on the health of Caribbean reefs as a whole, as well as on the valuable Caribbean lobster fishery.

Monitoring more diseases

Many other species are also showing increasing effects from marine diseases. The frequency of coral diseases has increased significantly over the last 10 years, causing widespread mortality among reef-building coral, which are home to more than 25 percent of all marine fish species.

In the Pacific, more than 20 species of sea stars were devastated by a wasting disease that ranged from Mexico all the way up to Alaska in 2013 and 2014. Research suggests that 90 percent of some populations were wiped out, and some adult populations have been reduced to a quarter of pre-outbreak numbers.

Scientists believe the cause is a virus which becomes more active in warmer conditions. In both field surveys and laboratory experiments, starfish were found to react faster to the disease in warmer water than in cooler temperatures.

As the oceans continue to warm, it is crucial to understand how our actions are affecting marine life. Some species will not be able to withstand the increase in temperature. The most recent U.S. National Climate Change Assessment projects that outbreaks of marine diseases are likely to increase in frequency and severity as waters warm under climate change. Researchers are working around the world to determine whether and how species will survive disease events in our increasingly altered oceans.

Charlotte Eve Davies, Postdoctoral Researcher at the Institute of Marine Sciences and Limnology, Universidad Nacional Autónoma de México (UNAM)

This article was originally published on The Conversation. Read the original article.

Featured Photo Credit: James St. John/Flickr, CC BY

Now, Check Out:

• Solving ‘Darwin’s Paradox’: why coral island hotspots exist in an oceanic desert
• Oceanic Researchers Find Deep Hydrothermal Vents Made of Something Completely Different
• New Method for Tracking Ocean Currents From Space
• Farmed Fish Likely Not as Healthy to Consume
• A New Eco-Friendly Method for Making Plastics Discovered

Andrew Frederick Johnson, University of California, San Diego

It was Charles Darwin, almost 200 years ago, who first asked how it could be that coral reefs could flourish in relatively barren parts of the Pacific Ocean. This conundrum subsequently became known as Darwin’s Paradox.

A study published this week in Nature Communications helps answer just how coral oases can exist in oceanic deserts.

The simple explanation is the presence of microscopic aquatic plants known as phytoplankton. The more complicated, scientific answer – that asks why coral islands are such productive hotspots – is known as the Island Mass Effect (IME).

The findings of the new study provide scientists who study marine fisheries and habitats with important insights into how coral reef island systems can be so productive, acting as hotspots of species diversity which, in turn, help populate fisheries and provide coastal protection. This knowledge can help inform ocean management plans, particularly as ecosystems respond to climate change.

The Island Mass Effect (IME)

The IME, first described by the University of Hawaii botanist Maxwell S. Doty and colleagues, is a phenomenon in which the growth of phytoplankton is enhanced close to island-reef ecosystems.

Until now, all studies trying to explain the reasons for the IME have been done over small, geographically confined areas, such as a single island or coral reef group.

This is where the Nature Communications paper’s lead author, Jamison Gove of the National Oceanic and Atmospheric Administration (NOAA), and his colleagues come in.

[nextpagelink][/nextpagelink]

Pages: Page 1, Page 2