G. Tita et al., Size spectra, body width and morphotypes of intertidal nematodes: an ecological interpretation, J MARINE BI, 79(6), 1999, pp. 1007-1015
Citations number
33
Categorie Soggetti
Aquatic Sciences
Journal title
JOURNAL OF THE MARINE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM
Nematode species from three intertidal assemblages (St Lawrence Estuary, Qu
ebec, Canada) were studied in order to form an ecological interpretation of
three allometric attributes: body width, size spectra, and morphotypes. Th
e three assemblages were characterized by a very similar sediment grain med
ian (Md) but different silt-clay proportions: Al (upper-tidal level; Md=122
mu m; silt=34.8%), A3 (mid-tidal level; Md=182 mu m; silt=12.8%), and A5 (
lower-tidal level; Md=122 mu m; silt=6.8%). Silt-clay proportions were an i
nfluential factor in determining the mean nematode body width, used as a mo
rphological discriminant between burrowing and interstitial organisms. A pl
ot of the number of species vs the body width-classes showed two peaks: bet
ween 19.3 and 22.6 mu m (interstitial), and between 32.0 and 45.5 mu m (bur
rowers). As for the size spectra, in sandy sediments the mean nematode indi
vidual biomass was smaller than in muddy sediments. As a consequence, the e
stimated mean individual respiration rate was greater in muddy (A1=2.26 nl
O-2 h(-1)) than sandy sediments (A3=1.25 nl O-2 h(-1); A5=1.12 nl O-2 h(-1)
). In contrast, estimated metabolic ratios were lower in Al (2.78 nl O-2 h(
-1) mu g(-1) dry weight, DW) than in A3 (2.95 nl O-2 h(-1) mu g(-1) DW) and
A5 (3.01 nl O-2 h(-1) mu g(-1) DW) suggesting different productivity and/o
r physiological adaptations to different lifestyles (burrowing vs interstit
ial) between species inhabiting muddy or sandy sediments. Morphotypes (body
width/body length ratio=w/l ratio) were found to be associated with feedin
g groups. Small w/l ratios were typical of microvores, while greater ratios
were typical of epigrowth feeders and predators. Ciliate-feeders, deposit-
feeders and facultative predators had intermediate ratios. A morphotype foo
d-related hypothesis is proposed: the species morphotype reflects the quali
ty of exploited food; a small w/l ratio (i.e. long gut) would favour digest
ive efficiency and would be an adaptation to low quality food (microvores);
inversely a greater w/l ratio (i.e. short gut) would be an adaptation to h
igh quality food (epigrowth-feeders and predators).