Wednesday, February 29, 2012

Nature Study Shows Squid Travel Faster in Air

There's a new study featured on Nature News which suggests that squid can travel up to five times faster in air than in water.


FYI: A squid propels itself by shooting water out of its siphon at high speed in the opposite direction to the direction of motion, just like a jet engine. In fact, this natural jet propulsion mechanism is what inspired the design of the jet engine!


Ronald O'Dor (a marine biologist from Dalhousie) and Julia Stewart (from Stanford) took a look at some rapid-succession photographs of what they think are orange-back squid (Sthenoteuthis pteropus) soaring through the air. Using the known time intervals between each photo, they calculated the squids' velocity and compared it to known values of squid propelling themselves through water.

This "flying" behaviour has been observed in squids for quite some time now, although not very often. It's widely believed that breaching is a predator-evasion tactic. However, based upon his new findings, O'Dor has suggested that squid may propel themselves through the air in order to save energy during lengthy migrations.

Some Questions


If it really is an energy-reducing measure for long distance travel, why don't we see squid leaping out of the water constantly, instead of the odd jump witnessed once in a blue moon?

Also, this study shows that squid can move faster through air than through water, but it doesn't address the logistics of propelling oneself out of the water. How much energy does it really take to break the surface? And is it worth the added speed of air travel during migration?

Finally, if squid really do jump out of water a lot more than we had previously thought, wouldn't this behaviour significantly increase their chance of predation by sea birds? (I do think this is probably true, but I also suspect predation pressure by birds is less than that of other things in the ocean, so the trade-off might be worth it).

O'Dor has proposed to investigate the proportion of time squid spend in air and in water by tracking them with tags that measure acceleration. This will give us clues as to how important flying behaviour is to the squid's lifestyle.

Thursday, February 23, 2012

Are Corals Alive?

My boyfriend and I had been meaning to visit the Royal Ontario Museum for months now. We finally went, after they just recently made Tuesdays free for post-secondary students (and those who still have a student card). We mostly loitered in the natural history section, looking at the taxidermy and animal replicas. One of my favourite things there was a large saltwater aquarium that housed a beautiful selection of reef fishes, invertebrates, and corals. As I was taking in the view, someone beside me kept repeating the question, "Are corals alive?" to which his friends had no answer.


I've noticed repeatedly that the coral is something most people know very little about. To be honest, before my second year invertebrate zoology course, I wasn't too sure what a coral was either. Since finding out, I now think it's one of the most fascinating lifeforms on the planet, and I'd love to explain what exactly a coral is.

CNIDARIA


Corals are very closely related to jellyfish (and even closer related to sea anemones). They belong to the phylum "cnidaria," a group characterized by having stinging cells called nematocytes. Actually, cnidaria in Latin means "nettle-like," from "knide" (nettle) and "aria" (like).


Cnidarians come in two body plans: swimming medusa (B), and the sessile polyp (A). A jellyfish is an example of the former, while a coral the latter. Think of a coral as a jellyfish that cannot swim around, and plants itself the bottom of the sea. That's essentially what it is.

CORAL REEFS


Unlike jellyfish, corals live in colonies. When you talk about "coral," you're really talking about a colony of several individual sessile polyps. When you say "coral reef," you're actually talking about a colony of polyps that secrete calcium carbonate to form a hard skeleton. This skeleton offers structural support and a place for polyps to retract their soft bodies when threatened.


Just as trees grow a new ring each year, reef-building corals grow a new layer of calcium carbonate skeleton each year. It can take hundreds of years to build a coral reef. The largest coral reef in the world, The Great Barrier Reef, is an estimated 6000-8000 years old. Just think about that for a minute.

FEEDING



Most corals are symbiotes. They harbour tiny photosynthetic protozoa called zooxanthellae. The zooxanthellae offer valuable energy, while in return the coral offers a home, physical protection and carbon dioxide and nitrogenous waste. Corals can also capture prey, such as plankton and small fish, by immobilizing them with their stinging nematocytes.

REPRODUCTION


Corals can have one gender or two (gonochoristic or hermaphroditic), and can reproduce sexually and asexually. Most sexual reproduction happens by releasing eggs and sperm synchronously into the environment. Asexual reproduction happens by either splitting a small polyp from an adult (budding), or by splitting the colony (fission). Actually, coral reproduction gets a lot more complicated than this, but I won't go into any more detail now.


Actually, corals in general are a lot more complicated than what I've talked about here. I just wanted to explain their basic biology, and to make it clear that corals are indeed very much alive.

Photographs from: National Geographic.

Monday, February 20, 2012

Aquaculture: Fish Farming in a Nutshell

Aquaculture is the farming of aquatic lifeforms for human consumption. It produces about half of all fish that is eaten worldwide.

As wild fish populations steadily decline, and fishery catch sizes continue to shrink, humans' unwavering demand for ocean produce has fuelled a large market for fish-farming.

Is it better to eat farmed fish than wild-caught fish? It is impossible to say for sure, but probably not. It's a complex issue. There are different types of fish farms, and different fish (or non-fish aquatic lifeforms) that are farmed, each requiring unique considerations.

In theory, fish farming could be a great alternative to fishing. In reality, it's kind of terrible.

SOME MAJOR CONCERNS

  1. Overcrowding
  2. Disease
  3. Waste products
  4. Escapes

ON-LAND FISH FARMS




Closed-system fish farms kept on-land are completely separate from ocean waters. While overcrowding (1) and disease (2) are still potential concerns, waste products (3) and escapes (4) have no environmental impact on the oceans.

OFF-SHORE FISH FARMS




Fish confined in nets located off-shore can potentially violate all the major concerns listed above. Overcrowding (1) actually contributes to the high incidence of disease (2) and toxic concentrations of waste products (3) such as ammonia, which adversely affect the immediate marine environment. Escaped farm fish (4) can spread disease to wild fish populations, and outcompete them for resources.

AT-SEA FISH FARMS




A free-floating fish farm—one that can be moved from one place to another in the ocean—is a good solution to highly concentrated waste products (3).

Overcrowding and escapes can be reduced in all fish farms, but that responsibility lies completely in the hands of the humans tending the farms. More fish in the pen may mean more money in the pocket, but at what cost?

UPDATE: I created a second post with handy-dandy infographics. Check it out.

Image Sources: (1 - Environmental Anthropology & Aquaculture) (2 - Green Report) (3 - National Geographic)