Estimating secondary production in natural populations of polycahetes: Some general constraints

Secondary production estimates are presented for three species of polychaetes. The selected species have life-spans longer than 1 yr and inhabit three different habitats. The differences in locations were employed to illustrate some problems such as migration patterns, patchiness or larval dispersal that should be considered when production estimates are calculated for polychaete species. Leitoscoloplos fragilis is a vagrant species that can be found in the sandy, non-organic sediments of beaches, and salt marsh areas of the North American Atlantic coast. Juvenile and adult individuals do not share the same locations and the production estimates (2,3-12,9 g dw m-2 yr-1) obtained in this study as well as population production/biomass ratios (P/B) showed wide variations depending on the different sites sampled. Owenia fusiformis is one of the most important and highly productive sublittoral species in the bay of Blanes (Western Mediterranean, Spain). Larval dispersion is very high causing heterogeneous distribution of the species in the bay. Consequently, production estimates (4,8-10,3 g dw m-2 yr-1) and population P/B's can also be very different between sites. Nereis (Hediste) diversicolor is a common species in brackish European waters. This species is able to move from one place to another within its habitat. This migrating behavior can also influence the productivity of the species (10,6-11,6 g dw m-2 yr-1). These three cases illustrate the importance of knowledge of the life cycle of the species in order to evaluate the ecological significance of production estimates in the field. Different methodologies used for estimating secondary production might result in different accuracy of estimation. During the last two decades, several relationships have been developed to estimate secondary production. These methods were then applied to these three examples to compare the accuracy of such methods. These relationships overestimated productivity of adult based populations, and underestimated productivity of juvenile based populations for the three species. Although a calibration of these relationship models is strongly recommended, the relationships described by Robertson (1979), Brey (1990), and Tumbiolo and Downing (1994) seem to be the more adequate ones to be employed for polychaete species.