Influence of variability in larval development on recruitment success in the euphausiid Euphausia pacifica:: elasticity and sensitivity analyses

Simple life-history models were employed to identify those larval stages of Euphausia pacifica (Hansen) with the greatest potential contribution to variability in recruitment success. Using stage-specific vital parameters (i.e. stage duration and specific mortality) the models explored the influence of developmental variability without ascribing the variability to any particular cause or forcing. Through such a non-mechanistic modelling approach, the critical periods in larval development were determined. The results led to inferences about larval population responses to temperature/food heterogeneity in the natural environment. Peaks in recruitment-success elasticity were evident for variability imposed during the egg and Furcilia I and II stages. The high elasticity of the egg stage suggested the importance of female nutrition and the timing and location of egg release in determining their viability and subsequent recruitment success. Peak elasticity during the Furcilia I and II stages supported the notion that indirect developmental pathways of pleopod development during these stages may be associated with diminished recruitment success. Sensitivity analyses further highlighted the influence of these early furcilia stages in determining recruitment success, and also suggested the importance of the Furcilia III and VII stages. The robustness of elasticity and sensitivity results with respect to the life-history structure utilized is discussed. A criterion is presented for the identification of life-history structures which might obscure the true elasticity relationships of a developmental sequence.