Size spectra, body width and morphotypes of intertidal nematodes: an ecological interpretation

Abstract

Nematode species from three intertidal assemblages (St Lawrence Estuary, Quebec, Canada) were studied in order to form an ecological interpretation of three allometric attributes: body width, size spectra, and morphotypes. The three assemblages were characterized by a very similar sediment grain median (Md) but different silt–clay proportions: A1 (upper-tidal level; Md=122 μm; silt=34.8%), A3 (mid-tidal level; Md=182 μm; silt=12.8%), and A5 (lower-tidal level; Md=122 μm; silt=6.8%). Silt–clay proportions were an influential factor in determining the mean nematode body width, used as a morphological discriminant between burrowing and interstitial organisms. A plot of the number of species vs the body width-classes showed two peaks: between 19.3 and 22.6 μm (interstitial), and between 32.0 and 45.5 μm (burrowers). As for the size spectra, in sandy sediments the mean nematode individual biomass was smaller than in muddy sediments. As a consequence, the estimated mean individual respiration rate was greater in muddy (A1=2.26 nl O2 h−1) than sandy sediments (A3=1.25 nl O2 h−1; A5=1.12 nl O2 h−1). In contrast, estimated metabolic ratios were lower in A1 (2.78 nl O2 h−1 μg−1 dry weight, DW) than in A3 (2.95 nl O2 h−1 μg−1 DW) and A5 (3.01 nl O2 h−1 μg−1 DW) suggesting different productivity and/or physiological adaptations to different lifestyles (burrowing vs interstitial) between species inhabiting muddy or sandy sediments. Morphotypes (body width/body length ratio=w/l ratio) were found to be associated with feeding 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 food-related hypothesis is proposed: the species morphotype reflects the quality of exploited food; a small w/l ratio (i.e. long gut) would favour digestive 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 high quality food (epigrowth-feeders and predators).

Can field distributions of marine predacious nematodes be explained by sediment constraints on their foraging success?

“…This is in agreement with the field distribution of E. longispiculosus at the Paulina site: Enoploides densities correlated positively with the fine sand fraction (125 to 250 µm) but negatively with the percentage of very fine sand (63 to 125 µm) and showed no correlation with the medium sand fraction (250 to 500 µm). Active carnivores and omnivores live as epifauna or in the semifluid sediment surface where they behave as interstitial forms (Jumars & Fauchald 1977, Schwinghamer 1981, Tita et al 1999. Wieser (1959) argued that sediments with a median particle diameter of approx.…”

Taxonomic resolution and Biological Traits Analysis (BTA) approaches in estuarine free-living nematodes

“…According to Thistle et al (1995), insights based on tail shape give additional information to that incorporated by the buccal-morphology groups, making them potentially useful as ecological indicators. Losi et al (2013) found nematode body shape to be an informative parameter which was suggested to be related with the available food and biogeochemical conditions of the sediment (Tita et al, 1999;Soetaert et al, 2002;Vanaverbeke et al, 2004). This trait was the least informative regarding the separation of areas since slender bodies dominated in all areas and sampling occasions, not presenting any clear relation with the environmental factors analysed.…”

Ecology of Marine Meiofauna

“…Mesmo dentro do meiobentos, diferentes animais vivem em diferentes tipos de sedimentos e evoluíram estilos de vida distintos (intersticiais, epibênticos, construtores de galerias, etc.) que exigem uma variação de tamanhos (TITA et al, 1999). As numerosas características distintivas do meiobentos para o macrobentos estão resumidas na Tabela 2.…”

“…A relação proporcional entre o tamanho do corpo e a taxa de respiração foi atribuída a diferentes zonas de hábitat por Tita et al (1999). Os nematoides mais pesados de praias com sedimentos lamosos (biomassa média individual de 0,8 mg de peso seco) consumiram mais oxigênio do que os nematoides menores da zona entremarés de praias arenosas (biomassa média individual de 0,4 mg de peso seco).…”