Tag Archives: crustacean

Skinny seals and hungry cod point to trouble in the Baltic Sea

Not all is well in the Baltic Sea, new research suggests — the local food networks are in trouble.

Baltic sea sky.

Image credits Michal Jarmoluk.

The top predators of the area, gray seals and cod, are losing weight, the study reports. This development is linked to the worsening health of the cornerstones of the Baltic’s local food networks: bottom-living crustaceans, isopods, and amphipods.

Sinking food stocks

“It is important that you understand how the food web works when managing a fishery. It is not enough to manage how the fish and fisheries are changing. The availability and quality of food is at least as important,” explains Lena Bergström, researcher at the Department of Aquatic Resources at the Swedish Agricultural University and the study’s corresponding author.

The study, a collaboration between several universities, looked at the health and abundance of key species over the last two decades in the Bothnian Sea and the Baltic Proper. Seal, cod, herring, sprat, isopods, amphipods, and zooplankton all made the object of this study, as they are important players at different levels of the local food webs. These networks are very complex, the team writes, and the same species can be both prey and predator — for example, herrings eat zooplankton and bottom fauna while being hunted by cod and seals in turn.

The authors show that there is a link between the health of cod and seals, the top predators in this ecosystem, and that of bottom-dwelling species, which are the lowest rung on the ladder. Seals are indirectly linked to these bottom-feeders, as they dine on herrings (who in turn dine on the bottom-dwelling species). The worsening health of both cod and seals, the authors explain, is tied to climate change and eutrophication. Eutrophication is an excess of nutrients in a body of water, frequently due to run-off from land, which causes a dense growth of bacteria and algae.

“Oxygen levels in Baltic Sea have reduced since the 1990s, in big part due to eutrophication, creating vast oxygen-free areas. This leads to less living space for the bottom-living prey animals,” says Agnes Karlsson, lead author and researcher at the Department of Ecology, Environment, and Plant Sciences (DEEP) at Stockholm University.

“This has, among other things, led to the fact that the isopods have become fewer and smaller, making them a poorer food choice for cod.”

The team explains that, while the mean weight and fat content of herring in the Bothnian Sea have recently been on the uptick — made possible by an increase in the quantity of bottom-living amphipods — this isn’t an improvement; it’s a recovery. These crustaceans were almost wiped out by a period of extremely heavy rains in the early 2000s which changed the quality of local waters.

“The upturn is relative, because the amphipod in the Bothnian Sea collapsed in the early 2000s and what we now see are signs of a recovery,” Karlsson adds.

“With climate change it is likely that we will see similar extreme events more frequently in the future,” Bergström adds. “If activities that lead to eutrophication are not reduced, oxygen shortage in the Baltic Sea will likely continue, leading to further reductions in the numbers of bottom-living animals. This can have far reaching effects for the economy, with reference to the fish species that are important commercially. To manage a fishery, we must also manage the environment and the food web.”

The paper “Linking consumer physiological status to food-web structure and prey food value in the Baltic Sea” has been published in the journal Ambio.

Experiment shows that crabs and lobsters feel pain, suggests we don’t really understand animal pain

I have never in my life eaten a crab or a lobster, because ever since I was a kid, boiling an animal alive seemed extremely cruel; it just didn’t make sense that an animal doesn’t feel pain – and even today, it doesn’t, to me. Pain is your body’s way of telling you something is damaged and needs fixing. It makes all the sense in the world to know when your body is damaged, so why would crabs miss out on this?

Nociception and crustaceans


Robert Elwood, an animal behaviour researcher at Queen’s University Belfast delivered a strong speech at the Behaviour 2013 meeting in Newcastle, UK, today, explaining that we need to refine our ideas about animal pain.

Crustaceans — crabs, prawns, lobsters and other creatures — are generally not protected by animal-welfare laws, despite huge numbers of them being caught or farmed for human consumption. The idea people hid behind was that they don’t feel pain, they just exhibit nociception, a reflex response to move away from a noxious stimulus.

Extreme cruelty


Defended by this false belief, people subjected crustaceans to extremely cruel practices: their legs were removed while they were still alive, they were tightly bound for days in markets, and prawns were impaled on sticks and eaten alive.

Researchers showed that crustaceans not only respond to noxious stimuli simply by nociceptive reflex – instead, long-term motivational change that enables discrimination learning has been demonstrated. To put this simply (and just a bit loosely), they feel pain just like cats and dogs feel it. So either we need to rethink our beliefs on animal pain, or we shouldn’t have any problems about boiling cats and dogs as well. Lobsters shouldn’t be treated any worse than cows are.

Assessing pain

In order to reach this conclusion, Elwood and his team conducted two separate experiments. The first one focused on what is called avoidance learning: can the animals actually learn from pain, or do they simply respond in a reflex type of reaction?

To answer this, Elwood and his colleague Barry Magee presented shore crabs with a choice of two different shelters – one of them would shock the creature if it went inside, while the other one was a safe haven. After the second time the experiment was conducted, crabs overwhelmingly chose the safe one. This, says Elwood, shows that the shock is aversive.

In the second experiment, he presented crabs with two types of shell, one of which the animals are known to prefer, and gave them shocks when they chose this. Whenever they were presented with a new shell, even one which they didn’t prefer, they chose it over the first one.

“Assessing pain is difficult, even within humans,” Elwood told the Newcastle meeting. But there is a “clear, long-term motivational change [in these experiments] that is entirely consistent with the idea of pain”.

So the conclusion is simple – we’re not treating all animals equally; we like cats, dogs, and even cows, but we simply ignore the horrendous pain crustaceans are put through.

“We’re behaving in an illogical way at the moment” by protecting mice but not crustaceans, he notes.

Scientific reference

120 million crabs hit the streets

Image by Lilolebob.

Every year, around this time of year, more than 100 million determined crabs take to the streets in a massive attempt to get to their spawning grounds as soon as possible; as a result, they literally flood the streets in Christmas island, covering the streets and forcing rangers to divert traffic and use some quite creative methods of protecting the crustaceans.

Photo by Ian Usher.

However, despite the absolutely huge number of crabs, there have been no reports of violence, from any one of the islands 1200 inhabitants. “It is difficult to see crabs in the houses,” one local resident told BBC Brasil. However, the efforts local rangers have been sustaining are nothing short of laudable; they constructed plastic bridges and fences to keep them from more populated areas and even help them across difficult areas (I don’t know, but I’m guessing difficult urbanized obstacles).

At 135 square km and located 370 km off of Indonesia, this Australian territory is often called the “Galapagos of the Indian Ocean” for its diversity of both plant and animal life. It’s also home to 14 different species of crabs, including the coconut crab, the largest invertebrate in the world. The efforts I mentioned earlier are even more impressive taking into account the 1.5 million people who come to see the amazing wildlife display each year.


First ‘rule’ of evolution suggests life will become more and more complex

crustaceanScientists from the University of Bath have revealed what may very well be the first law of evolution, which has a huge importance. The study was published in Proceedings of the National Academy of Sciences and it shows the fact that evolution drives animals to become increasingly more complex.

They analyzed fossils from the crustacean family tree and drawed conclusions from the different evolutionary branches of the last 550 million years. They were expecting to find animals that evolved to be simpler and more effective, but instead they found that as the evolutionary tree grows, animals tend to be more and more complex than their ancestors.

“If you start with the simplest possible animal body, then there’s only one direction to evolve in – you have to become more complex,” said Dr Matthew Wills from the Department of Biology & Biochemistry at the University of Bath who worked with colleagues Sarah Adamowicz from from the University of Waterloo (Canada) and Andy Purvis from Imperial College London.

But although it may seem strange, 550 mil years may just not be enough time to draw the right conclusions. Dr. Wills adds:

“Sooner or later, however, you reach a level of complexity where it’s possible to go backwards and become simpler again. What’s astonishing is that hardly any crustaceans have taken this backwards route. Instead, almost all branches have evolved in the same direction, becoming more complex in parallel. This is the nearest thing to a pervasive evolutionary rule that’s been found.”

“Of course, there are exceptions within the crustacean family tree, but most of these are parasites, or animals living in remote habitats such as isolated marine caves.