Ecological And Metabolic Studies On Free-Living Nematodes From An Estuarine Mud-Flat

Nematodes from a mud-flat in the river Lynher estuary, Cornwall, U.K., have a population density ranging between 8 and 9 × 106 m−2 in the winter months, corresponding to a dry weight of 1·4 and 1·6 g m−2. They reach a peak abundance of 22·86 × 106 m−2 (3·4 g) in May. About 40 species are present, and the species composition remained seasonally stable over the period of study. Analysis of age-structure suggests that the major species have continuous asynchronous reproduction. Respiration rates of 16 species have been determined at 20 °C using Cartesian diver respirometry. For five species, respiration/body size regressions were obtained in the form log10R = log10a+b log10V, where R = respiration in nl O2 ind−1 h−1 and V = body volume in nl: Mesotheristus setosus (log10a = −0·04,b = 0·74), Sphaerolaimus hirsutus (log10a = 0·11, b = 0·68), Axonolaimus paraspinosus (log10a = 0·00, b = 0·79), Metachromadora vivipara (log10a = −0·59, b = 1·07), Praeacanthonchus punctatus (log10a = 0·00, b = 0·55). For the remaining 11 species, several animals were used in each diver and, by assuming b = 0·75, log10a′ values were calculated: Viscosia viscosa (log10a′ = 0·188), Innocuonema tentabundum (−0·012), Ptycholaimellus ponticus (−0·081), Odontophora setosa (−0·092), Sphaerolaimus balticus (−0·112), Dichromadora cephalata (−0·133), Atrochromadora microlaima (−0·142), Cylindrotheristus normandicus (−0·150), Terschellingialongicaudata (−0·170), Sabatieria pulchra (−0·197), Terschellingia communis (−0·277). These values are compared with recalculated values for other species from the literature. Annual respiration of the nematode community is 28·01 O2 m−2, equivalent to 11·2 g carbon metabolised. Community respiration is compared with figures from N. American saltmarshes. At 20 °C, a respiration of about 61 O2 m−2 year−1 g−1 wet weight of nematodes appears to be typical. Annual production is estimated to be 6·6 g C m−2. The correlation between feeding-group, body-size, habitat and the repiration rate of individual species is discussed.

Measurement Of The Responses Of Individuals To Environmental-Stress And Pollution - Studies With Bivalve Mollusks

Certain physiological differences between individuals in different populations of the mussel, Mytilus edulis, are described. In particular, the scope for growth differs in space and time and may be used to assess the animals' physiological condition. When the required measurements are made in the field, the rates of growth predicted from the physiological data agree well with observed rates of growth. An alternative approach utilizes mussels transplanted to various waters, with indices of condition then measured in the laboratory under standard conditions; an example of this approach is illustrated. Laboratory experiments are used to equate various levels of physiological condition with fecundity, in an attempt to equate physiological effects on the individual with likely population damage. A cytochemical index of stress is described, based on the latency of lysosomal enzymes; spatial variability in this index, and its relation with the scope for growth, are discussed. Finally, the results of some experiments on the effects of petroleum hydrocarbons on mussels are described and the presence of inducible activity of NADPH-dependent tetrazolium reductase in the blood cells is demonstrated. Certain considerations that apply in adopting similar measurements of biological effects of pollution in environmental monitoring programmes are discussed.