Growth and development rates of Calanus finmarchicus nauplii during a diatom spring bloom

Growth and development rates were determined for nauplii of Calanus finmarc hicus (Gunnerus) in the near-shore waters of a western Norwegian fjord from ill situ mesocosm incubations. The major food source for the nauplii was d iatoms, but Phaeocystis sp.. dinoflagellates and ciliates were also part of the diet. At local temperatures ranging from 4.8 to 5.2 degrees C the cumu lative median development time from hatching to Nauplius VI was 19 d. The t ime taken to molt to the next naupliar stage was approximately constant (3 d) from Stages IV to VI, but Stage III needed the longest development time (5 d). The instantaneous growth rate in terms of body carbon was negative f rom hatching to Nauplius Stage II, but as high as 0.25 to 0.30 d(-1) from S tage III to V. Enhancement of food resources by nutrient addition led to no significant change in specific growth rates. Additionally, the cohorts fro m different nutrient regimes showed almost equal development time, size and body carbon within stages. Length-weight relationships of nauplii from the two different food resources were: W-low resources = 4.17 x 10(-6) x L-2.0 3 (r(2) = 0.84) and W-high resources = 4.29 x 10(-6) x L-2.04 (r(2) = 0.92) , where weight (W) is in micrograms of C and body length (L) in micrometers . The natural body morphology of naupliar stages I to VI is illustrated wit h digital images, including the final molt from Nauplius VI to Copepodid St age I. In general, development of the nauplii was faster than that of the c opepodids of C. finmarchicus, and structural growth was exponential from na upliar stages III to VI. This study validates our earlier results that naup lii of C. finmarchicus can obtain high growth and nearly maximal developmen tal rates at relatively low food levels (similar to 50 mu g C l(-1)), sugge sting that nauplii exhibit far less dependence on food supply than copepodi ds.