Reproductive investment in the intertidal bivalve Macoma balthica

Bivalve eggs generally contain large amounts of lipids which, in comparison with proteins and carbohydrates, have high energy contents and are thus co stly in energetic terms. As lipid contents vary between species, comparison s of reproductive investments should not only include numbers and sizes of eggs, but also their energy content. We estimated the investment in egg mat erial of mature females of the Baltic tellin Macoma balthica (L.) in terms of both mass and energy content. All mass below a minimum body mass (below which no eggs are produced) was defined as structural mass. This threshold amounts to a body mass index (BMI) of 5.6 (ash-free dry mass per cubic shel l length in mg cm(-3)). More than half (55%) of the mass above the structur al mass was invested in egg material and 45% in extra somatic tissue and ti ssue for production and storage of gametes. This means that the amount of e ggs spawned ranged from 0 (at BMI = 5.6 mg cm(-3)) to 33% of the total ash- free dry mass (at a high BMI value of 14 mg cm(-3)). Eggs contained a relat ively large amount of Lipids, about 30% of their ash-free dry mass, whereas non-egg material contained only about 7% lipids. Eggs of two other bivalve s in the Wadden Sea, the cockle Cerastoderma edule and the mussel Mytilus e dulis, were smaller and contained only about 11% and 20% lipids, respective ly. Energy content of M. balthica eggs amounted to similar to 0.006 J, in t he other two species to similar to 0.002 J. The function of the more expens ive eggs in M. balthica may be related to its early spawning in spring, cau sing slower larval development until first feeding. (C) 1999 Elsevier Scien ce B.V. All rights reserved.