CLOSING THE LARVAL LOOP - LINKING LARVAL ECOLOGY TO THE POPULATION-DYNAMICS OF MARINE BENTHIC INVERTEBRATES

The majority of marine benthic invertebrates exhibit a complex life cy cle that includes separate planktonic larval, and bottom-dwelling juve nile and adult phases. To understand and predict changes in the spatia l and temporal distributions, abundances, population growth rate, and population structure of a species with such a complex life cycle, it i s necessary to understand the relative importance of the physical, che mical and biological properties and processes that affect individuals within both the planktonic and benthic phases. To accomplish this goal , it is necessary to study both phases within a common, quantitative f ramework defined in terms of some common currency. This can be done ef ficiently through construction and evaluation of a population dynamics model that describes the complete life cycle. Two forms that such a m odel might assume are reviewed: a stage-based, population matrix model , and a model that specifies discrete stages of the population, on the bottom and in the water column, in terms of simultaneous differential equations that may be solved in both space and time. Terms to be inco rporated in each type of model can be formulated to describe the criti cal properties and processes that can affect populations within each s tage of the life cycle. For both types of model it is shown how this m ight be accomplished using an idealized balanomorph barnacle as an exa mple species. The critical properties and processes that affect the pl anktonic and benthic phases are reviewed. For larvae, these include be nthic adult fecundity and fertilization success, growth and larval sta ge duration, mortality, larval behavior, dispersal by currents and tur bulence, and larval settlement. It is possible to predict or estimate empirically all of the key terms that should be built into the larval and benthic components of the model. Thus, the challenge of formulatin g and evaluating a full life cycle model is achievable. Development an d evaluation of such a model will be challenging because of the divers e processes which must be considered, and because of the disparities i n the spatial and temporal scales appropriate to the benthic and plank tonic larval phases. In evaluating model predictions it is critical th at sampling schemes be matched to the spatial and temporal scales of m odel resolution.