Charlie B. Miller and Jennifer Crain
Studies of the U.S. GLOBEC Georges Bank Program target species Calanus finmarchicus will be extended in three directions:
I. We will continue in Phase III to work on characterizing and quantifying life history "decisions" of developing copepodites. These are a) the decision of genetic males to mature as functional males or functional females; and b) the mature or diapause decision of fifth copepodites at the end of both winter and spring generations. We are mostly using field samples from the continuing Broad-scale Survey for this work, characterizing frequencies of individuals headed toward different decisions by anatomical clues. We also use Broad-scale samples (and samples on loan from Process studies) to search for starvation events implied by proportions of individuals in different molt cycle phases. Molt cycle phases are revealed by evaluation of copepod tooth development status ("jaw facies":). We hypothesize that starvation events produce developmental delays important to population dynamics in C. finmarchicus, and important in correct modeling of advective stock transport. Because of our interest in Broad-scale samples, the Oregon project provides a worker to each Broad-scale cruise.
II. We will continue to work with individual-vector-models (IVM's) depicting the interaction of life history events in C. finmarchicus with advection and mixing in the Gulf of Maine and on Georges Bank. It is through these models that we will contribute to the goal of Phase III of the program to measure and understand cross-frontal exchange between stocks of plankton on Georges Bank and stocks in surrounding waters. It is for improvement of these models that we need better characterization of life history decisions and of field development rates.
III. Studies of developmental delays in field stocks of C. finmarchicus, delays we hypothesize come from food limitation, require calibration of morphologic indicators of starvation. For this purpose, we propose experiments intended to bring knowledge of the interaction among nutrition, growth and the molt cycle in copepods up to the standard available for decapod larvae. We will perform Point of Reserve Saturation and Point of No Return experiments with third copepodites of C. finmarchicus. Growth in planktonic crustaceans is not even through the molt cycle, but proceeds rapidly at first, with 80% of growth complete by ~40% of the molt cycle duration, then slows while morphogenetic work proceeds. After roughly this 40% of the cycle, the animal will molt even if deprived of food, so that point in the cycle is termed the point of (nutritional) reserve saturation, PRS. Because molting can proceed without food for large fractions of a stock, starvation events have complex effects on proportions of a population in different molt cycle phases. We will seek in our experiments to show that copepod development does indeed follow a PRS model, so that molt cycle proportions can be interpreted in respect to field nutrition. Starvation occurring well after molt but before PRS can only be compensated by later feeding if it occurs soon enough, before a point of no return, PNR, which occurs at about 70% of the normal molt cycle. In order to fully understand the effects of food limitation on the copepod molt cycle, we will also perform PNR experiments.