Finish your salps, please …

Today, I’m going to write a bit more about how increasing numbers of salps in the Southern Ocean might alter the diets of fish, squid, whales, seals and penguins (these are organisms usually feasting on krill). Now, whenever I think about reporting on the dietary preferences of an animal, I don’t picture David Attenborough. Instead, I picture this classic commentary …

If anyone hasn’t seen This Is Spinal Tap, life is short and PLEASE GET ONTO IT.

There’s no bread on the menu today, but two foods that are somewhat comparable to chicken (krill) and jelly (salps). If you had to choose between those two options for dinner, what would you pick? Actually, maybe humans should stay out of this. We (I) are (am) highly emotive when it comes to food choices, and some days I know we (I) would love nothing more than to crawl up into a ball, watch This Is Spinal Tap and eat jelly.

But what about a whale (or fish, squid, seabird, seal or penguin)? What would a whale choose? Now, before I go making any assumptions, I acknowledge that whales can have tough days and sometimes they might feel like a simple, soothing plate of jelly. I’m not one to judge, but, for now, I’ll say that the whale is going to make a dinner decision based on the energy they’ll have to spend finding, eating and digesting their food, and the nutritional payoff. At the end of the day, a whale wants a dinner option that is …

  1. Readily accessible, and accessible in very large amounts. (Actually, whales are definitely kind of like us, in the respect that they want something quick and easy.)
  2. Nutritious.
  3. Easy to digest.

The reason whales don’t want to spend too much energy on finding and eating food is because they would rather invest their energy into growing, looking after their young, dodging whaling vessels, and other important whale tasks.

So what can satisfy every whale’s dinner desires? ANTARCTIC KRILL, of course. Antarctic krill are high in protein and calories (no diets down here in the Southern Ocean), they are easily broken down in the stomach and gut, and their swarming nature means that a whale can go ahead and binge eat.

But …

Last time I talked about salps, I mentioned the possibility of the species moving further down south, and mixing in with krill swarms. Now is also a great time to mention that studies have found salps to contain less than half the calories and protein of krill (keep that in mind as you continue reading).

So, what if salps DO mix in with krill swarms? A whale might come and take a big bite from what it thinks is a pure krill swarm, and find itself with a mouthful of krill AND its cheap imitation (salps). Will a whale spit the salps back out? Unlikely. They are just going to have to suck it up. Or suck them up I should say.

A whale might also be faced with a different scenario, in which they are surrounded by salp blooms with NOT A KRILL IN SIGHT. What are they gonna do then, huh? Will they travel further in search of krill, or will they think, stuff it, and eat the salps? There are risks associated with either choice. If the whale stays and eats salps, it has a guaranteed, albeit less nutritious, meal. If the whale goes, it has a better chance at landing a decent feed, but, then again, it could be left empty-flippered.

I was wrong in saying there aren’t any diets down in the Southern Ocean. The Salp Diet could be the next weight-loss regime to sweep Antarctica. And that’s not good. Antarctica and the Southern Ocean are extreme environments and obviously very, very cold. Whales need to maintain their lipid stores by eating lots of hearty krill. Based on calorie and protein content, salps just don’t cut it and it’s possible that prolonged feeding on this gelatinous organism could compromise the condition of species that typically feed on krill.

I’m going to leave it there for now, as next time I’ll be talking about what methods I’m using to investigate the above questions. I’m also going to be diving into a concept called ecosystem energy flow, and I’ll be using this concept to discuss how changes in small organisms like krill and salps can change AN ENTIRE ECOSYSTEM.

If only whales could talk, hey? Although, if whales could talk, I reckon they’d have some heavy questions to ask us about human behaviours …

whale-01

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