U.S. GLOBEC: Egg production, Growth and Mortality of Calanus finmarchicus and Pseudocalanus on Georges Bank

E. Durbin (URI), J. Runge (DFO), R. Campbell (URI), C. Ashjian (WHOI), M. Ohman (UCSD)

Our Phase I results showed that the abundance and production rates of Calanus finmarchicus and Pseudocalanus spp. differ greatly between the shallow well-mixed crest waters of Georges Bank and the deeper waters of the northeast peak and the southern flank. We suggest that differing physical processes which control the advection of water and organisms from the Gulf of Maine onto different regions of the bank during the winter, and differences in growth and mortality patterns of the target copepod species within the different regions of the bank, control the population sizes they attain during the spring and early summer.

We will address these questions by carrying out the following specific objectives: (1) Describe the recruitment of Calanus and Pseudocalanus on Georges Bank during the winter/spring period, as inferred from the distribution of nauplii and early copepodites collected with pump samples during the broad scale survey. (2) From broadscale and process cruise data, map the distribution of water column egg production for the dominant broadcast spawning copepods (Calanus, Temora, Centropages) and water column birth rates for dominant egg-carrying copepods (e.g. Pseudocalanus). Determine whether there are distinct and persistant centers of recruitment for each of the dominant species. Determine the spatial, seasonal and interannual variation in egg production and birth rates for the dominant species including Calanus and Pseudocalanus. (3) From process cruises determine the spatial, seasonal and interannual variations in egg viability, egg and naupliar mortality rates, and naupliar development rates. Determine whether egg and naupliar mortality rates are correlated with abundances of potential predators. (4) Provide the modeling group with data on copepod distribution, recruitment, growth and mortality rates.

This proposal is composed of four separate components which have been combined in one proposal. These components are: (1) the broad-scale pump survey, (2) the egg laying rate measurements of Calanus and Pseudocalanus, (3) the growth rate measurements of Calanus and Pseudocalanus, and (4) the estimation of egg and naupliar mortality of Calanus and Pseudocalanus. The pump survey will take place during each of the broad scale survey cruises while the latter three components will be carried out during each of the process cruises although broad scale survey female abundance data will be used in bank-wide egg production estimates. E. Durbin will supervise the first and third component, J. Runge will supervise the second, and M. Ohman will supervise the fourth.

This measurement of regional differences in vital rates (fecundity, development, growth, and mortality) that determine the abundance and population growth rates of planktonic copepods is critically important to the overall goals of the Georges Bank GLOBEC Program. This will also be the first comprehensive study of all of the component population dynamic processes for marine copepods in a field study with detailed physical observations and modeling.