MORAN, A.L.*; MANAHAN, D.T.; Univ. of North Carolina, Chapel Hill; Univ. of Southern California, Los Angeles: Energy Budgets of Marine Larvae: Why Don’t They Add Up?

Larval energy budgets are an important tool for understanding the ecology, evolution and physiology of marine invertebrate life histories. For nonfeeding larvae or prefeeding planktotrophic stages, budgets are most often based on the physiological costs of development balanced against the energy available from use of maternally endowed energy reserves in eggs. Three types of budgets are possible: 1) a perfect balance, in which energy expenditure matches depletion of larval reserves: 2) an energy surplus, in which physiological costs exceed the observed depletion of endogenous reserves: and 3) an apparent energy deficit, in which larval expenditures (based on measured biochemical constituent changes) are less than physiological costs. Not surprisingly, perfect balances are rare; yet, in many cases energy surpluses or deficits are too great to be attributable to reasonable propagation of experimental error. In oysters, we found that larvae survived without food for 33 days and did not utilize any of their endogenous protein reserves (the major biochemical constituent). Physiological costs exceeded the entire egg energy investment by 8 d post-fertilization. The explanation likely lies in the ability of soft-bodied marine invertebrate larvae to utilize alternative sources of exogenous energy such as dissolved organic material (DOM) or bacteria. In contrast, our studies on nonfeeding abalone larvae showed that depletion of energy reserves over development exceeded measured metabolic costs. These data suggest that (1) for soft-bodied larvae, water �quality� in terms of DOM and bacterial content will substantially affect larval energetics; and (2) oxyenthalphic values for protein, lipid and carbohydrate may overestimate the energy available from endogenous reserves if these substrates are not completely oxidized when used as metabolic substrates.