Effects of food quality on naupliar development in Calanus glacialis at subzero temperatures

We studied the naupliar development of the calanoid copepod Calanus glacialis, a key herbivore in the Arctic marine ecosystem. Eggs obtained from females collected at 78 degrees N in Svalbard, Norway, in May 2008 were reared at -1.2 degrees C in a temperature-controlled room. Stage-specific naupliar development time, survival and naupliar size were studied in response to different food qualities, i.e. low versus high proportions of polyunsaturated fatty acids (PUFAs) and low versus high element molar ratios (C:N and C:P). Length measurements of consecutive naupliar stages were obtained from image analysis of digital photos taken every second day. A length-frequency analysis revealed distinct size classes for each stage. Stage duration of the 6 naupliar stages varied between 6 and 27 d. The longest stage duration was measured for Stage NIII. Development time from hatching to Stage NVI was shortest (41.9 d) for nauplii reared under high algal bloom chlorophyll a (chl a) concentrations (similar to 20 mu g chl a l(-1)) with algae of high food quality (control). Starved nauplii developed the slowest and showed highest mortality. High mortality was also recorded for nauplii fed with algae grown under a phosphorous limitation that were offered at the same chl a concentrations as the control treatment. These algae had lower PUFA concentrations and higher element molar ratios and were, thus, of lower food quality than the control algae. However, comparable development times and naupliar sizes were found for nauplii fed with algae of high or low food quality. This is the first study that successfully follows the entire naupliar development of Calanus glacialis at subzero temperatures.