I’m celebrating that this week has – finally – seen the publication of a paper my colleague Sam Bowser and I have been working on with some others for a very long time. You can check it out here (it’s OA).
The paper pulls together various bits of evidence gathered over almost two decades of study on a few species of benthic Foraminifera – single-celled organisms (affectionately called ‘forams’) that live on the seafloor – in Explorers Cove, McMurdo Sound, Antarctica. Among other things, we were able to demonstrate that the species Astrammina rara is ingesting small multicellular organisms (metazoa) in its natural environment.
What fascinates us about this is that it challenges preconceived ideas. In oceanography, the thought of a food web that ultimately leads from the smallest and simplest to the biggest and most complex organism (and back) is often engrained in people’s heads – in the benthos for example, this would mean that bacteria get consumed by protozoans, protozoans get eaten by bigger, multicellular organisms (metazoans), such as nematodes, harpacticoids (small crustaceans) or other beasties, they in turn get eaten by polychaetes (a marine group of annelid “worms”), which get eaten by larger animals and so on. The other factor in this is that the assumption is often made that protozoa are somehow ‘simple’ organisms. In the case of Astrammina rara (and many of its colleagues), this concept just doesn’t work.
First of all, at up to 4.5 mm, the single-celled organism here is bigger than many of the smaller metazoans found in the sediment around it. Secondly, it doesn’t get eaten by the small metazoans – instead, it consumes them. And not only that: it seems to trap them in a net of reticulopods that, almost like a spider web, covers the sediment surface around the foram’s test, and subsequently rips them apart, carrying the tasty chunks of crustacean, worm, or maybe larvae of echinoderms, bivalves, or other larger organisms bit by bit towards its cell body, where they get enveloped and digested. We’d like to think that this would have some consequences for the environments where these forams occur in higher densities; for example, they might negatively affect settling rates of larvae of bigger organisms.
I mentioned the underdog appeal of forams before. Well, here’s the underdog winning, preciousss….
Congrats on your paper, Steffi! Good thing those forams don’t grow larger than 4.5 mm or so; they sound positively ferocious ….
One of my cousins, a geophysicist, spent some time doing research in Antarctica- he says it’s an amazing place.
Nice post Steffi – I had no idea you could get single-celled organisms of that size!
And I got to learn about two new ‘vores’ on the same day. First, Kristi’s locavore, and now your ‘detritivore’.
Thanks Kristi and Stephen! Two of the other species mentioned in the paper, Notodentrodes antarctikos and N. hyalinosphaira, actually grow several centimeters big. They’re beautiful, ‘tree’ and ‘flower’-shaped things. Shallow-water forams carrying algal symbionts also get many centimeters big. There are other protozoans that get massive, but I digress.. :)
Stephen – ‘detritivore’ just sounds better than ‘dirt eater’, doesn’t it?
Well done, Steffi. Amazing, but then I still haven’t gotten over the idea of carnivorous sponges and tunicates.
I was wondering how long it would be before Henry picked up on this…
Steffi – I particularly like the term detritiviore because it reminds me of my children…!
Two of the other species mentioned in the paper, Notodentrodes antarctikos and N. hyalinosphaira, actually grow several centimeters big
So what’s the upper limit on size for a protozoan, and is there something(s) in particular about forams that allow certain species to attain a size of several centimeters? Is it the test?
I particularly like the term detritiviore because it reminds me of my children
Actual dirt-eating in humans is called pica, which is one of my favorite medical terms (along with bezoar).
Thanks Henry. The SF-like aspect of a lot of marine life is probably among its most intriguing qualities ;)
Stephen – my son would be an ‘extreme pickyvore’, I’m afraid. of course, in benthic biology the term ‘detritus’ is used for any particulate organic matter, big or small, that ends up on the sediment surface: this can be anything from relatively fresh phytoplankton to zooplankton fecal pellets (another of my favourite terms), but is most often a mix of it all – a rain of stuff from the water column..
Kristi: well, as far as the ‘biggest protozoan’ goes, forams don’t win – I think a slime mould does, but was side-tracked while I was trying to find a reference.
And yes, for forams it’s probably primarily the test that allows them to grow so big. It’s important to add that the test is not entirely filled with the cell body, either, and that most foram species are much smaller – these guys are the exception, not the rule.
And this is why I got sidetracked. Am digesting that now and trying to find more background..
What has me going on this is whether the tracks are real – Gromia sphaerica is not new (yes, that’s Sam again on that paper, and my PhD advisor Andy Gooday) – and it’s sad that the researcher who discovered the ‘tracks’ says in this video they’re ‘amoebas’ (he does correct himself then, but still – one gets touchy).
It’s not new (at all) that forams move, so it’s possible that Gromia, which is a relative, might do as well.
My problem is that all the tracks seem to go more or less in the same direction. Looks like a case of bottom currents, sediment deposition and possibly slightly premature media hype to me..
Ok, done rambling. All better for now.