Are chaetognaths gelatinous? You be the judge
(Apologies in advance for the perhaps obscure and esoteric content of this entry.)
The "Jelly Ocean Hypothesis" suggests that due to human-driven changes in the environment, we are headed toward an ocean dominated by jellyfish. Before determining whether this scientifically intriguing dystopian nightmare comes to pass, we need to agree on what classifies as a "gelatinous zooplankton".
Some people assert that chaetognaths fit into this category; others do not. Since we are debating this in the lab now, here is some information for context. What we need is a measure of how gelatinous something is. Ideally we would like to have a measure of carbon-to-volume ratio for each taxon--basically a measure of organic density--but for now, dry weight as a percentage of wet weight (DW as %WW) will have to do. --Basically the amount of the organism that is not water.
ctenophore copepod chaetognath
gelatinous not gelatinous ??
Here are the numbers:
Euphausiid DW as %WW: range 20-24% (depending on stage) +/- ~3
(Iguchi & Ikeda 1998 table 1)
Copepod DW as %WW: average ~19% +/- 10
(computed from Mauchline 1998 fig 50)
Chaetognath DW as % WW: 8%
(Sameoto 1972 reported in Feigenbaum 1982)
Thaliacea DW as %WW: average 5.5% +/- 2.47
Ctenophora DW as %WW: average 3.53% +/- 0.92
Cnidaria DW as % WW: average 4.07% +/- 1.23
(Lucas et al. 2011)
And in graphical format:
<--------- more gelatinous less gelatinous --------->
I think this crude and cursory analysis settles the debate. Now we can get back to talking about copepods.
Nick Record, signing off
Lucas CH, Pitt KA, Purcell JE, Lebrato M, Condon RH (2011) What's in a jellyfish? Proximate and elemental composition and biometric relationships for use in biogeochemical studies. Ecology 92:1704.
Feigenbaum D (1982) Feeding by the chaetognath, Sagitta elegans, at low temperatures in Vineyard Sound, Massachusetts. Limnol. Oceanogr. 27(4): 699-706.
Iguchi N, Ikeda T (1998) Elemental composition (C, H, N) of the euphausiid Euphausia pacifica in Toyama Bay, southern Japan Sea. Plankton Biol. Ecol. 45(1): 79-84.
Mauchline (1998) The biology of calanoid copepods
Sameoto DD (1972) Yearly respiration rate and estimated energy budget for Sagittu elegans. J. Fish. Res. Bd. Can. 29: 987-996.