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On the Density of Certain Amphipoda and Isopoda

Published online by Cambridge University Press:  11 May 2009

P.G. Moore ,
J. Davenport  and
N.E. Middleton
P.G. Moore
Affiliation:
University Marine Biological Station Millport, Isle of Cumbrae, Scotland, KA28 OEG.
J. Davenport
Affiliation:
University Marine Biological Station Millport, Isle of Cumbrae, Scotland, KA28 OEG.
N.E. Middleton
Affiliation:
Faculty of Applied Sciences, University of the West of England, Frenchay Campus, Coldharbour Lane, Bristol, BS16 1QY
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Extract

Data are presented on the density of ten species of Amphipoda and two species of Isopoda from terrestrial to aquatic (freshwater through brackish water to marine) habitats, derived using a new modification of the displacement method involving batch testing of animals and subsequent Probit Analysis of data.

Surprisingly few data are available in the literature concerning the densities of marine organisms. Extensive work on this topic was published some half a century ago by A.G. Lowndes. He reported widely on crabs and lobsters (Lowndes, 1943a), echinoderms (Lowndes, 1953) and fishes (Lowndes, 1955). In his paper to the Linnean Society (Lowndes, 1938a) he included data on some of the smaller freshwater Crustacea. Gross & Raymont (1942) have published on the specific gravity of the marine copepod Calanus finmarchicus.

In espousing the displacement method for dealing with live individuals (Lowndes, 1938a,b, 1942, 1943b, 1955), he dismissed summarily earlier techniques that involved ascertaining whether killed or narcotized animals sank or floated in liquids of known density. While we recognize the limitations of the old methods, Lowndes’ displacement technique, although very accurate for individuals (he quoted figures to five decimal places), is very tedious to replicate [“elegant if somewhat exacting”, according to Hutchinson, 1967] and so reliance tends to be placed on figures obtained for very few individuals, typically only one or two. Even Lowndes himself was wary of attributing significance to the last two decimal places in his estimations, since individuals will vary in density according to sex, the contents of the gut etc. (Eyden, 1923; Lowndes, 1938b; but see Fox & Mitchell, 1953).

Type
Short Communications
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 77 , Issue 1 , February 1997 , pp. 253 - 256
Copyright
Copyright © Marine Biological Association of the United Kingdom 1997

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