You might be wondering just how we go about trying to answer questions about an octopus’s diet.

We start by looking for good sites, pouring over satellite photos and talking to locals to see if we can find good octopus habitat. Then, we just go out and get into the water to search, which is why we came equipped with wetsuits, fins, masks and snorkels. At least half of our day is spent in the water – searching, looking and collecting.

The sites we search in are specific, as Octopus cynea – the day octopus – isn’t abundant along the honeymooner’s shoreline of sand and pretty reefs:

Resized tropics

Instead, the day octopus is found in shallow, rocky water where there’s a lot of algae. In fact, many sites are so shallow that I feel a little bit ridiculous snorkeling there, my tummy wedged against the rocky bottom. And the algae? It’s a prickly kind of algae officially called Turbinaria ornate (although I have other names for it…)

Photo credit: D. Scheel

Photo credit: D. Scheel

So once we find a site and have committed to jumping in, we look for signs of hiding places, since octopuses typically hide in “dens.” We also look for evidence of recent octopus being present. One common sign is piles of shells, cleaned out and dismembered in a specific way and piled together neatly. These are called “middens” – octopuses’ gardens.

Three items found in an octopus midden, placed on a dive slate and photographed.

Three items found in an octopus midden, placed on a dive slate and photographed.

And of course, we look for the octopuses themselves. Some sites come up empty and we move on, but other sites prove to be amazing with lots of octopus activity and good octopus sightings. We had that kind of day this past Wednesday. Check out the video of a juvenile I found and named “Zeus:”

[youtube]http://www.youtube.com/watch?v=FCNfv4PR4ZA[/youtube]

Once an octopus is found, we begin our data collection. We observe the octopus and conduct an octopus personality test. This test, based on research by Dr. Mather and Dr. Anderson, ranks octopuses on a scale of ‘shy’ to ‘bold.’ Once the personality test is completed, we evaluate the habitat by running two straight 20-meter lines from the den – these lines are called “transects” – and examine the habitat, predators and flora around the octopus’s den.

An octopus den site is marked by a buoy (underwater so as to not draw the attention of local fishermen) with a transect line visible. The octopus in question, ‘Mary-Lou,’ is visible in this photo as well.

An octopus den site is marked by a buoy (underwater so as to not draw the attention of local fishermen) with a transect line visible. The octopus in question, ‘Mary-Lou,’ is visible in this photo as well.

When our time in the water is done, we take our collection bags of octopus prey remains (those middens, which are collected as part of the personality test) back to CRIOBE – the research station here we are based out of.

middens

Back in the collections room at CRIOBE, we get to work trying to ID our collected shells. This takes some time – there are 12 different books and ID guides piled across the desk as I write this (many in French – the first language here in Mo’orea), plus we also utilize 22 specimen drawers filled with specimens collected and identified in a careful hand, perhaps around twenty-plus years ago.

…and once all that’s done and the data entered? Well, then we do it all over again.

Guest blog post by Keely Langford, an interpretive delivery specialist at the Vancouver Aquarium. Keely is accompanying a team of researchers, led by Dr. Jennifer Mather of University of Lethbridge, to the South Pacific this summer. This team of researchers is studying how the day octopus (Octopus cyanea) chooses its food. Keely is sharing a series of blog post updates throughout this trip. Her first, second and third posts in these series are also available to read.

 

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One Response

  1. Jane

    Very interesting, well written article! Sounds like an interesting study! Thanks!

    Reply

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