Biomass Spectra of Aquatic Ecosystems in Relation to Fisheries Yield

Abstract

1992. Biomass spectra of aquatic ecosystems in relation to fisheries yield Can. j. Fish. Aquat. Sci. 49: 1528-1 538.The biomass density of aquatic ecosystems can be expressed as an allsmetric function of organism body sine. The log-log plot of this relation, termed the biomass spectrum, is used to cornpare aquatic ecosystems in various parts of the world. We develop a standardized presentation for several example environments where detailed data on biomass density by body size in the trophic positions, phytoplankton, zooplankton, benthos, and fish, make it possible to establish overall or primary spectral slopes. The basic methodology is adapted for application to other ecosystems where less detailed data are available, Spectra from all the different environments exhibit a unifc~rrn low slope, but with different intercepts that appear to reflect ecosystem differences in nutrient circulation and availability. Detail on the secondary structuring at various positions in the trophic system appears to provide information useful for distinguishing between long-term changes in productivity and short-term perturbations in biomass or abundance.La densite de la biomasse presente dans un 6cosystGme aquatique peut &re exprimee ssus forme de fonction allom6trique de la taille des srganisrnes. On utilise le graphe log-log de cette relation, appelee spectre de biomasse, pour cornparer les 6cosystemes aquatiques de diverses parties du globe. On dabore aussi une presentation normalisee de plusieurs types d'ersvironnernents pour lesqslels des donnees detaillkes sur la densit6 de la biomasse en fonction de la taille des srganisrnes au niveau trophique, nooplancton, phytoplancton, benthos et pisson, permettent d'etablir la pente globaleou primaire du spectre. On adapte les methodes fondamentales pour qu'elles s'appliquent A d'aartres 6cosyst&rnes pour lesquels des dsnnees dktaill6es ne sont pas disponibles. Les spectres obtenus de tous les differents environnernents rnontrent une faible pente uniforrne, mais les differents interceptes semblent r6fl6ter des difgrences dans le cycle et la disponibilit6 des aliments au rsiveau des 6cosyst6mes. Bes details sur la structure secondaire 2 diverses positions du systerne trophique semblent fournir de B'informatisn utile dans la separation des variations 21 long terme de la prsductivit6 et des perturbations 3 court terme de la biomasse ou de t'absndance.(xuesa redicting biological production in communities from energy flux through its trophic components has been a prime focus of ecology. Attempts to use Lindeman's (1942) original fornulation, specifying predator-prey trophic linkages between species grouped into "levels, ' have demonstrated the difficulties of arriving at models that are both sufficiently realistic and sufficiently general (Lane and Collins 1985). The practical failure of the trophic level calculations (Mmn et al. 1989) in the past is due partly to the complexity of the systems modelled and partly to continued uncertainty about the time and space scales on which it is possibl...

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