ESTIMATING SECONDARY PRODUCTION IN NATURAL POPULATIONS OF POLYCHAETES: SOME GENERAL CONSTRAINTS
Sardá, R.; Pinedo, S. & Dueso, A.
Centre d'Estudis Avançats de Blanes (C.S.I.C.). Camí Sta. Barbara s/n., 17300-Blanes (Girona). Spain
The measurement of production as part of energy flow through ecosystems has been one of the major goals in benthic ecology during the last decades. Secondary production deals with the formation of heterotrophic biomass through time, regardless of taxon and trophic status and it has been widely reviewed. Secondary production in natural populations is primarily a function of growth of individuals and of patterns of recruitment as well as mortality observed in nature. Therefore, it is directly related to the life-cycle of the species. However, spatial scales and processes affecting natural populations should also be considered such as migration patterns, larval dispersion, etc. All these factors need to be considered at the beginning of production computation for polychaete species. Furthermore, traditional methodologies to estimate secondary production are time-consuming and labor-intensive, and to alleviate these efforts there is a general tendency to replace these traditional estimates by empirical relationships. The use of these relationship should also be made cautiously. Several studies have been conducted lately by the authors. In this paper we present secondary production estimates for three species of polychaetes which present life-cycles longer than a year. These species inhabit three different habitats and locations and will be employed to summarise problems that need to be considered when production estimates for polychaete population are given. Leitoscoloplos fragilis is a vagrant species, living in sandy sediments of salt marsh areas in the Northamerican Atlantic Coast; the distribution of juveniles and adults in the marsh is not regular, and production estimates (2.8-13.0) as well as population P/Bs can have wide variations if we do not sample the different habitats inhabited by different size-classes of this worm. Owenia fusiformis is one of the most important and highly productive sublittoral species in the Bay of Blanes (Western Mediterranean, Spain); in this species larval dispersion is very high, and production estimates (5.1-10.3) as well as population P/Bs need to take into consideration this factor. Nereis (Hediste) diversicolor is one of the most common species in brackish European waters. The species is able to move from one place to other in its habitat; this migrating behavior can also have importance for the productivity of the species that can be very high. We will present this three cases, we will show different production estimates depending of the designed sampling, and we will also give values obtained by theoretical general relationships.