Category Archives: fisheries

Seaweed Kills Corals by Touch

Seaweed With a Deadly Touch – ScienceNOW.


Green plague. In Fiji, rarely fished reefs (top) abound with colorful corals, but seaweeds start their invasions in exploited locales (bottom)

“Attack of the killer seaweed” may sound like a cheesy horror flick, but for many coral species, murderous multicellular algae have become real-life villains. A new study of reefs in the South Pacific suggests that some algae can poison coral on contact. This chemical warfare may be increasing the pressure on struggling reef communities worldwide, researchers say.

Along the reefs dotting Fiji, overfishing has pitted corals against algae in a battle royale. On swaths of coastline where fishing is restricted, corals such as the tall and branching Acropora millepora rule, says study co-author Mark Hay, a marine ecologist at the Georgia Institute of Technology in Atlanta.

But where Fijians spear lots of herbivores such as bird-beaked parrotfish, few fish remain to prune back the region’s seaweeds, a blanket term for many types of big algae. These algae then creep in, extending their tendrils over close to 60% of the ocean bottom, Hay estimates, and turning waters a sludgy green. Such “seaweed-covered parking lots” aren’t unique to Fiji, either, he says.

Recent studies have hinted that this ocean greenery may be carrying out a subtle chemical war on sensitive reefs. To investigate this covert struggle, Hay and colleagues strung eight different species of Fijian seaweed across growing corals, including A. millepora colonies. True to the researchers’ suspicions, many of these algal species seemed to wield a poison touch. In less than 2 weeks, the test coral often began to discolor and even die where it rubbed against the seaweeds, the team reports today in the Proceedings of the National Academy of Sciences. Faux seaweeds made of plastic had no such effect.

Hay and colleagues then mashed up several of these seaweeds to identify their killer concoction. The key ingredient turned out to be chemicals called terpenes, which some algae use to sicken fish that feed on them. Terpene extracts alone killed off corals, the researchers found. But some algae seemed to be more liberal with their toxins than others, Hay notes. When one particularly nasty specimen called turtle weed (Chlorodesmis fastigiata) rubs against A. millepora, for instance, wide bands of dying tissue girdle the coral.

This seaweed is so nasty, in fact, that most marine herbivores avoid it on sight—except for one species of rabbitfish that quivers with excitement every time it spots this not-so-common algae. That interaction highlights the importance of prudent fishing practices, he adds. If Fijians developed a particular taste for that one rabbitfish, for instance, turtle weed might begin to grow out of control, launching its bid for world, or at least South Pacific, domination. Hay would like to work with Fijians to identify and protect the herbivores most responsible for trimming back deadly seaweeds, giving sensitive corals a fighting chance.

“It’s certainly a novel finding,” says John Bruno, a marine ecologist at the University of North Carolina, Chapel Hill. But not all seaweeds are poisonous, he adds. Many scientists argue that algae—toxins or no—rarely kill off adult corals en masse. Instead, these opportunistic organisms may simply be capitalizing on the slow death of the invertebrates due to pollution, climate change, or other factors. He adds, however, that the seaweeds Hay and colleagues studied would likely be exceptionally toxic to young, coin-sized corals that have yet to grow big and hale.

Terpenes from seaweed are almost certainly not the only reason for the mysterious global decline of corals, says Jennifer Smith, a marine ecologist at the University of California, San Diego. Most scientists rank overfishing, pollution, and warming oceans among the biggest overall contributors. But corals may suffer from other nasty tricks played by seaweed. In a 2006 study, Smith and colleagues sleuthed out that some California algae could take the epidemic route to domination. In the lab, these seaweeds leak huge quantities of dissolved carbon that then fuels the spread of potentially infectious microbes on coral surfaces. “You can imagine that [algae and corals] have evolved over the years different mechanisms for battling each other and fighting these turf wars,” Smith says.

Raindrop Tracker Point to Better Environmental Awareness

Go with the flow : Nature : Nature Publishing Group.

It might seem impossible to get lost in the modern world with its ubiquity of digital maps, but there is more than one way to be lost. Truly knowing where you are goes beyond pinpointing your position. It means knowing where your water comes from and where it goes, where your electricity is generated and where your rubbish ends up. It means being aware of what plants and animals live nearby and what kind of soil lies beneath your feet.

For example, an undergraduate at a rainy Butler University in Indianapolis, Indiana, can use his or her smartphone to instantly calculate a route to the nearest Starbucks coffee shop. But chances are that he or she remains ignorant of how the rain flows through the city on its way to the White River, the Mississippi and, finally, the Gulf of Mexico.

Enter Raindrop, a phone application that combines sewer and watercourse maps with the software that makes getting a caffeine fix so easy. Tap the map and watch the path of a single raindrop flow from your location through streams, culverts and pipes into the river. The app, due to launch next month, was funded by the US National Oceanic and Atmospheric Administration and put together by a team led by ecologist Timothy Carter at Butler. It is currently limited to Indianapolis, but similar efforts could be designed for other cities.

A better appreciation of watercourses and other hidden networks can only strengthen human connections to ecosystems, biogeochemical cycles and resource flows, and will arguably make people more likely to support science and environmental causes. Making available the data that science and society produce in these innovative ways can help people to find themselves — even if they had no idea that they were lost.

Warming seas could smother seafood

Warming seas could smother seafood – environment – 08 September 2011 – New Scientist.

Seafood could be going off a lot of menus as the world warms. More than half of a group of fish crucial for the marine food web might die if, as predicted, global warming reduces the amount of oxygen dissolved in some critical areas of the ocean – including some of our richest fisheries.

The prediction is based on a unique set of records that goes back to 1951. California has regularly surveyed its marine plankton and baby fish to support the sardine fishery. “There is almost no other dataset going back so far that includes every kind of fish,” says Tony Koslow of the Scripps Institution of Oceanography in La Jolla, California, who heads the survey. The survey records also include information on water temperature, salinity and the dissolved oxygen content.

Koslow’s team studied records of 86 fish species found consistently in the samples and discovered that the abundance of 27 of them correlated strongly with the amount of oxygen 200 to 400 metres down: a 20 per cent drop in oxygen meant a 63 per cent drop in the fish. There have been several episodes of low oxygen during the period in question, mainly in the 1950s and since 1984.

Global climate models predict that 20 to 40 per cent of the oxygen at these depths will disappear over the next century due to warming, says Koslow – mainly because these waters get oxygen by mixing with surface waters. Warmer, lighter surface waters are less likely to mix with the colder, denser waters beneath.

Of the 27 species most affected by low oxygen, says Koslow, 24 were “mesopelagic”: fish that spend the daytime in deep, dark waters below 200 metres to avoid predators such as squid that hunt by sight. There are 10 billion tonnes of mesopelagic fish globally – 10 times the annual global commercial catch – and they are a vital food for other fish and marine birds and mammals.

Out of the depths

In large segments of the Indian, eastern Pacific and Atlantic Oceans called oxygen minimum zones (OMZs), patterns of ocean currents already permit little downward mixing of surface water, so the dark depths where mesopelagics hide have barely enough oxygen for survival. Worldwide, OMZs are expanding both in area and vertically, pushing “hypoxic” water – water with too little oxygen for survival – to ever-shallower levels. Last year, Japanese researchers reported that this has nearly halved the depths inhabited by Pacific cod.

The California coast is an OMZ. When oxygen levels are even lower than usual, the hypoxic zone starts up to 90 metres closer to the surface. This means fish must stay in shallower, more brightly lit water, says Koslow, at greater risk from predators – which, he suspects, is what kills them. In the California data, predatory rockfish in fact boomed during periods of low oxygen.

“This is important work,” says William Gilly of Stanford University’s marine lab in Pacific Grove, California. He studies Humboldt squid, an OMZ predator whose recent movements seem consistent with Koslow’s idea.

“These findings are an example of the kinds of changes we will see more broadly throughout our oceans in coming decades, especially in OMZs,” says Frank Whitney of the Institute of Ocean Sciences in Sidney, British Columbia, Canada. Unfortunately, he notes, water and nutrient movements within OMZs make them among our richest fishing grounds.

Journal reference: Marine Ecology Progress Series, DOI: 10.3354/meps09270

Overfishing eats away at genetic diversity of fish

Overfishing eats away at genetic diversity of fish – environment – 15 July 2011 – New Scientist.

Plenty more fish in the sea? Maybe not for much longer. Overfishing is damaging the genetic diversity of fish to a greater degree than expected, leaving at-risk species vulnerable.

It was thought that even badly overfished species would remain genetically diverse, since millions of individual fish remain even in the most depleted species.

To test this assumption, Malin Pinsky and Stephen Palumbi of Stanford University in California gathered published data on genetic diversity in 37 overfished species and compared it with diversity in 51 of their lightly fished relatives.

To their surprise, they found that the overfished species carried, on average, about 18 per cent fewer genetic variants than their lightly fished relatives. “Contrary to what we expected, it looks like the [genetic] effects of overfishing are quite widespread,” Pinsky says.

At first glance, a drop in genetic diversity of just 18 per cent may seem small, given that some overfished species are thought to have suffered severe population crashes. However, widespread overfishing is just a few decades old, and if it continues it may lead to a further erosion of genetic diversity, says Pinsky.

Meanwhile, Michael Alfaro of the University of California, Los Angeles, and his colleagues have found another ominous sign for fish stocks.

Speedy evolution

They analysed the family tree of fish to see how quickly body size changes in each lineage, then noted which lineages are most heavily fished. The team found that species with unusually fast rates of evolution in body size are preferentially targeted by fishing.

Since changes in body size often lead to changes in other ecologically relevant traits, this means that fishing targets the most evolutionarily active groups of fish, Alfaro says.

“Humans are eating away the richest branches of the fish tree of life,” says Alfaro. “If you were going to come up with a plan to assault the fish tree of life, you would want to do it like this.”

The results add urgency to biologists’ call for more aggressive management of commercial fisheries. “These are not trends we would wish to see continue,” says Paul Bentzen, a fisheries geneticist at Dalhousie University in Halifax, Canada. “We need to be managing fisheries more effectively.”

That could involve measures such as shorter fishing seasons and an increase in the number of no-fishing zones. But the bottom line is that people need to catch fewer fish, Bentzen says.

Pinsky and Alfaro presented their findings at a meeting of the Society for the Study of Evolution in Norman, Oklahoma, last month