Abstract
The population biology and production of the stout razor clam Tagelus plebeius Lightfoot, 1786 were investigated on an intertidal sandflat on the southeast coast of Brazil (Enseada Beach, Sao Sebastiao, state of Sao Paulo) between April 1997 and April 1998. Two rectangular sites of 50 X 10 m parallel to the waterline were established, site A (upper intertidal level) and site B (middle intertidal level), where the samples were taken in an 0.5 x 0.5 m quadrat. High abundances were recorded in winter and spring, with no significant differences between the sites. The high bivalve abundances were related to the presence of very fine homogeneous sediment with low salinities. Tagelus plebeius had negative allometric growth, characteristic of deep burrowers for the relationships DM/SL and AFDM/SL. Parameters of the modified von Bertalanffy growth function were: L∞ = 67.01 mm, K = 1.73 year-1, t0 = -0.11 year, C = 0.43, WP = 0.96. The instantaneous mortality (Z) was 3.12 year-1, relatively high in comparison to other tropical bivalve populations. Secondary production was 1.53 g AFDM m-2 year-1, with a P/B ratio reaching 1.37 year-1. This high turnover ratio (P/B) was related to a rapid population replacement, connected with the short life span and high mortality of the species.
Highlights
Traditional descriptive studies on benthic soft-bottom communities have elucidated the interactions that determine their spatial and temporal structures; such studies provide little information about the species (CRAIG 1994)
Tagelus plebeius Lightfoot, 1786 is a solecurtid bivalve, common in estuaries and intertidal zones of sandy beaches, occurring in stable sediments from the upper intertidal level to depths of approximately 10 m, and with growth rates ranging according to the elevation above the mean low intertidal level (CHANLEY & CASTAGNA 1971, HOLLAND & DEAN 1977a,b, LOMOVASKI et al 2006)
Even though T. plebeius has a wide distribution in the coastal region of Brazil, and is used as a fishery resource by several coastal communities, only VIÉGAS (1982) analyzed the growth and secondary production of this species in an estuary in Maceió, and ABRAHÃO & AMARAL (1999) described its abundance and spatial distribution in a beach on the northern coast of São Paulo
Summary
Traditional descriptive studies on benthic soft-bottom communities have elucidated the interactions that determine their spatial and temporal structures; such studies provide little information about the species (CRAIG 1994). Bivalves stand out for their diversity of species, numerical dominance, high biomass, and ecological importance in marine soft-bottom substrates (ÓLAFSSON et al 1993, URBAN 1994) They occur in a variety of coastal environments, including estuaries and sandy beaches, where they are exposed to different factors such as temperature, salinity, and water currents. Even though T. plebeius has a wide distribution in the coastal region of Brazil, and is used as a fishery resource by several coastal communities, only VIÉGAS (1982) analyzed the growth and secondary production of this species in an estuary in Maceió, and ABRAHÃO & AMARAL (1999) described its abundance and spatial distribution in a beach on the northern coast of São Paulo In this context, the present study aimed to analyze the population dynamics and secondary production of T. plebeius at an intertidal zone of a sandflat in southeast Brazil
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