Marine Biology (1996) 125:119-127 Springer-Verlag 1996 J. A. Pechenik T. J. Hilbish . L. S. Eyster D. Marshall Relationship between larval and juvenile growth rates in two marine gastropods, Crepidula plana and C. fornicata Received: 11 August 1995/Accepted: 12 October 1995 Abstract Previous studies on various marine mollusc species have shown that both larval and juvenile growth rates are substantially heritable, but few workers have examined the extent to which larval and juvenile growth rates covary. We examined the rela- tionship between larval and juvenile growth rates in seven laboratory experiments conducted between 1986 and 1993, using the prosobranch gastropods Crepidula plana Say and C. fornicata (L.). In most experiments larvae were reared individually, measured twice non- destructively to determine larval growth rate, allowed or stimulated (daily 5-h exposure to 20 mM excess K + in seawater) to metamorphose, and then measured at least twice after metamorphosis to determine juve- nile growth rates. Generally, there was no significant (p > 0.10) relationship between larval and juvenile growth rates, suggesting that in these two species selec- tion can act independently on the two stages of devel- opment. A positive correlation (p = 0.007) between lar- val and juvenile growth rates was observed for C. fornicata in one experiment, but only for offspring from females maturing the most rapidly in laboratory cul- ture. Even for these larvae, however, variation in larval growth rate explained <2% of the variation in juve- Communicated by J.P. Grassle, New Brunswick J.A. Pechenik ([~) Biology Department, Tufts University, Medford, Massachusetts 02155, USA T.J. Hilbish Marine Sciences Program, Belle W. Baruch Institute for Marine Biology and Coastal Research, Columbia, South Carolina 29208, USA L.S. Eyster Science Department, Milton Academy, Milton, Massachusetts 02186, USA D. Marshall Academic Computing, Tufts University, Medford, Massachusetts 02155, USA nile growth rate, so that larval and juvenile growth rates are at most only weakly associated in this species. Introduction The influence of environmental factors on larval (reviewed by Pechenik 1987) and juvenile (e.g., Kirby- Smith 1972; MacDonald and Thompson 1985; Brown 1988; Rice and Pechenik 1992) growth rates have been much studied for many marine molluscs. For any given set of environmental conditions, larval and juvenile growth rates vary considerably among individuals; this variation is substantially heritable both before and after metamorphosis (Innes and Haley 1977; Newkirk 1978; Newkirk et al. 1981; Mallet et al. 1986; StrSmgren and Nielsen 1989; Rawson and Hilbish 1990; Hadley et al. 1991; Hilbish et al. 1993). However, few studies have considered the extent to which larval and juvenile growth rates covary; that is, the extent to which relative growth rates among larvae predict relative post-meta- morphic growth rates. In addition to its obvious practi- cal application in aquaculture operations, the extent to which larval and juvenile growth rates are coupled, either positively or inversely, will influence the degree to which selection can bring about shifts in growth rates in either stage (Ebenman 1992; Stearns 1992; Hilbish et al. 1993). Hilbish et al. (1993) discuss the common assumption that variations in larval and juvenile growth have a common genetic basis. For example, Haley and Newkirk (1977) and Newkirk et al. (1977) suggest that juvenile growth rates in the eastern oyster, Crassostrea virginica, may be increased by selecting for fast-growing larvae, based on measurements of spat shell length made 9 mo after the larvae metamorphosed. Larval growth rates were not directly determined in that study; rather it was assumed that the first larvae to metamor- phose grew the fastest. However, we now know that rates of shell and biomass growth may be easily