For this week's semi-random post topic, I drew the copepod genus Bryocamptus. Copepods have made an appearance on this site before (see here, here and here), seeing as these minute crustaceans inhabit almost all the world's waters. Bryocamptus belongs within the harpacticoids, one of the three main groups of free-living copepods (the others are the calanoids and cyclopoids), and like other harpacticoids members of this genus have a more-or-less parallel-sided, somewhat wormlike form, though Bryocamptus species are shorter than some. Within the harpacticoids, this genus belongs to the family Canthocamptidae, members of which have the first segment of the body bearing swimming legs fused to the cephalothorax (Caramujo & Boavida 2009).
There are over 100 recognised species of Bryocamptus, found in a wide range of fresh-watery habitats (Lee & Chang 2006). They may be found in mountain streams, in springs and temporary pools, or in subterranean groundwaters. Some may even be found 'terrestrially', living in the water film around leaf-litter, mosses or within the soil (Fiers 2013). One type of habitat that I haven't found reference to Bryocamptus living in is larger water bodies such as lakes. This is not particularly unusual: nutrients and micro-organisms tend to accumulate along boundaries, so habitats with a high proportion of edges tend to attract a higher diversity than the relative deserts that are larger water bodies.
Sometimes these habitats can be very small indeed. Groundwater species, for instance, may be restricted to the cracks within formations only some tens of metres in extent. Cottarelli et al. (2012) described Bryocamptus stillae from Conza Cave near Palermo in Sicily. This species was found in seasonal rimstone pools within the cave: temporary pools that would be filled by water dripping from the ceiling during the winter, only to dry up in the summer. However, the copepods are unable to survive out of water, and canthocamptids do not have a resistant phase in their life cycle that could survive the ppols drying out. Cottarelli et al. therefore inferred that the pools were not the copepods' primary habitat; rather, the copepods normally lived in the epikarst, the layer of limestone above the cave. Despite being only a few metres thick, this limestone layer retained enough pockets of moisture to provide a home for the copepods. During the rainy season, when water was more actively flowing through the epikarst, some of the more unfortunate copepods would be carried by the water as it dripped through the cave ceiling into the pools below. They would survive (and even breed) so long as the pools remained wet but they would be doomed to die off over the summer, with the following year's copepods representing an entirely new batch. Interestingly, though, Cottarelli et al. found B. stillae in only one group of pools in the cave. In a second group of pools, only about ten or fifteen metres away, an entirely different copepod species was found. Cottarelli et al. collected in the cave over three separate seasons, and each time the same species was found in the same pools. The evidence indicated that, even though these pools were so close, the water dripping into them came from separate, isolated epikarst formations, each one home to its own species of highly localised copepods.
REFERENCES
Caramujo, M.-J., & M.-J. Boavida. 2009. The practical identification of harpacticoids (Copepoda, Harpacticoida) in inland waters of central Portugal for applied studies. Crustaceana 82 (4): 385–409.
Cottarelli, V., M. C. Bruno, M. T. Spena & R. Grasso. 2012. Studies on subterranean copepods from Italy, with descriptions of two new epikarstic species from a cave in Sicily. Zoological Studies 51 (4): 556–582.
Fiers, F. 2013. Bryocamptus (Bryocamptus) gauthieri (Roy, 1924): a Mediterranean edaphic specialist (Crustacea: Copepoda: Harpacticoida). Revue Suisse de Zoologie 120 (3): 357–371.
Lee, J. M., & C. Y. Chang. 2006. Taxonomy on freshwater canthocamptid harpacticoids from South Korea V. Genus Bryocamptus. Korean J. Syst. Zool. 22 (2): 195–208.
To a copepod, the terrestial-aquatic dichotomy might appear somewhat artificial, if copepods were prone to higher cognition.
ReplyDeletePresumably, strongly localized species have high turnover rates? One exceptionally dry year and that piece of epikarst might dry out?
So, just how minute is B. minutus? From the description of its habitat, I assume it's FAIRLY minute, but the source of your image doesn't have a scale bar.
ReplyDeleteAllen: we're talking in the range of half a millimetre or shorter.
ReplyDeleteAndreas: I was wondering the same thing about turnover myself, and what sort of population size might be involved. For instance, a 300 metre cubed formation (10 m by 10 m by 3 m) would, I'm guessing, be about the volume of a large living room. At face value, that's a pretty big space for a half-millimetre copepod, you could fit millions in there. But of course, the actual inhabitable fissures are only a small fraction of what is mostly rock, so how much actual space do we have?
Chris-- Thanks! So roughly in the same size range as the copepod that makes it into school textbooks, Cyclops. For comparison… if the scale bar in the illustration in the Wikipedia article on "krill" is to be trusted, Euphausia superb is on the order of a hundred times as long. So, a miniaturized blue whale (B.-- for Balaenoptera -- minutus) feeding on these things would be under a foot long!
ReplyDeleteYeah, I could be wrong, but my impression is that krill are actually quite large as planktonic crustaceans go. Indeed, I'm not sure if they even count as plankton or as nekton.
DeleteSince the specific name of the real blue whale is musculus "little mouse", shouldn't a footlong relative be gigantocetus or something? ;)
DeleteOops… I seem to have misremembered: Cyclops is apparently bigger, a whole millimetre long (which, going by the scale bar in the photo on the Wikipedia page, doesn't include the tail feathers).
ReplyDeleteContinental cyclopoid copepods (including genus Cyclops) range from about 0.3 mm for tiny interstitial forms to 3 mm or above for pond and lake plankton. Continental harpacticoid copepods also start at ~0.3 mm and others can be ~1.5 mm or larger. These measurements don't include the "tail feathers" (caudal setae).
DeleteHow do you go about "drawing" a semi-random taxon? When I read these posts, I think about doing a similar series for our local flora--certainly would be an interesting way to get to know it better (if time allows, as always).
ReplyDeleteWithout going into too much pointless detail, I basically have a list of taxa in a Word document (it's the source document for the stuff I put up at Variety of Life). Every week I cycle a certain number of pages through the document and see where I land. So it's not really 'random' and there is a pattern if you look closely (a typical cycle will go plant, arthropod, arthropod, arthropod, mollusc, vertebrate, vertebrate) but, meh, it does the trick.
DeleteGetting to know these things better was my own motivation for writing these posts. Putting something together on a subject that I know next to nothing about (like, say, copepods) can be a challenge, but it forces me to investigate things I might not otherwise be investigating.
Thanks, that's helpful. I can see adding some structure--to avoid inadvertently spending too much time on one group and ignoring others. I think I'm going to give this a try. I like the idea of being surprised by a post topic!--adds a little fun to the endeavor. But my ambitions are not nearly as great as yours--I'll stick with plants ;-)
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