VARIATION IN THE GROWTH RATE OF MYA ARENARIA AND 



ITS RELATIONSHIP TO THE ENVIRONMENT AS ANALYZED THROUGH 



PRINCIPAL COMPONENTS ANALYSIS AND THE co PARAMETER OF 



THE VON BERTALANFFY EQUATION 



Richard S. Appeldoorn 1 



ABSTRACT 



Age-length data and environmental parameters were obtained for 25 populations of the soft-shell 

 clam, Mija arenaria. Growth rates were analyzed for 20 of the populations and variations in the 

 growth rates were related to differences in the environment. The analysis of growth was based on 

 Gallucci and Quinn's w parameter for the von Bertalanffy equation. Environmental variability was 

 analyzed, using principal components analysis which yielded three environmental factors: North- 

 ness, siltiness, and sedimentary hydrocarbons. Growth was found to be significantly related to each 

 of the three components. A distinct latitudinal growth relationship was observed, with growth de- 

 creasing towards the north. Temperature, tidal height, tidal position, and edaphic conditions sys- 

 tematically varied with latitude, with temperature being the dominant factor affecting growth. 

 Growth was negatively correlated to both siltiness and sedimentary hydrocarbons. 



The growth of the soft-shell clam, Mya a renaria, 

 has been studied by many investigators (Wilton 

 and Wilton 1929; Belding 1930; Newcombe 1936; 

 Swan 1952; Brousseau 1979; and others), and 

 much work has been done in assessing the im- 

 portance of various environmental factors in the 

 growth process. These factors include water cur- 

 rent and quality, food, temperature, salinity, 

 various edaphic parameters, and pollution. In 

 the past, investigators were obliged to study 

 these factors individually even though it was 

 realized that many were interrelated (Belding 

 1930). Because of local variations researchers 

 often disagreed on the relative importance of 

 each of these factors, and overall trends have not 

 been firmly established. 



The purpose of this study was to investigate 

 various factors contributing to growth rate vari- 

 ations in soft clam populations and to demon- 

 strate a methodology incorporating the analysis 

 of multiple factors applicable to the above inves- 

 tigation. Of specific interest was the demonstra- 

 tion of a latitudinal trend in growth and the fac- 

 tors responsible for it, since such a relationship 

 had yet to be quantified (Brousseau 1979). Prin- 

 cipal components analysis was used to analyze 



'Graduate School of Oceanography, University of Rhode 

 Island, Kingston, R.I.; present address: Department of Marine 

 Sciences, University of Puerto Rico, Mayagiiez, Puerto Rico 

 00708. 



multivariate environmental data, and the von 

 Bertalanffy model was used for the analysis of 

 growth, using the recently introduced growth 

 rate parameter w of Gallucci and Quinn (1979). 

 This study represents one of the first applica- 

 tions of w to investigate growth rate variations. 



MATERIALS AND METHODS 



Samples of Mya arenaria and environmental 

 data were obtained from 25 sites located along 

 the east coast of North America, from Maryland 

 to Nova Scotia (Fig. 1). The sites were initially 

 chosen and sampled as part of a study to investi- 

 gate the relationship between environmental 

 quality and neoplasia (Brown 1980), and as a re- 

 sult 1) the sites varied greatly in their environ- 

 mental quality, 2) the sampling design employed 

 was not specifically designed for the present 

 study, and 3) it was therefore necessary to use 

 proxy data in some cases to represent certain en- 

 vironmental characteristics. These drawbacks 

 were not severely limiting, since the particular 

 statistical techniques used could control much of 

 the induced variability in the data. Estimates of 

 the following environmental parameters were 

 obtained: Salinity, tidal position, tidal range, 

 average annual temperature, sedimentary grain 

 size, dispersion and skewness of grain sizes, per- 

 cent silt-clay, percent organic matter, and total 

 sedimentary hydrocarbons. 



Manuscript accepted June 1982. 



FISHERY BULLETIN: VOL. 81, NO. 1, 1983. 



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