Comparison of Methods for Estimating Annual Productivity of the Copepods Acartia hudsonica and Eurytemora herdmani in Passamaquoddy Bay, New Brunswick

Annual productivity of the copepods Acartia hudsonica and Eurytemora herdmani was estimated over a 12-mo period at three sites in Passamaquoddy Bay, New Brunswick. The sites were chosen to represent the range of habitats present in the bay. Samples were collected in vertical hauls of a 64-μm-mesh plankton net. Annual productivity was estimated by three methods. Estimates by the temperature–biomass method were 578–677 kJ∙m−2∙yr−1 for A. hudsonica and 63–173 kJ∙m−2∙yr−1 for E. herdmani. Both the mass-specific and cohort P/B methods yielded productivity estimates comparable with those calculated by the temperature–biomass method for E. herdmani. Acartia hudsonica estimates by the P/B methods were lower. We suspect that the cause of this discrepancy is the incorporation of periods of diapause and nonmaximal growth in estimating a mean biomass value for A. hudsonica. Other temporally abundant copepods observed in the bay included Tortanus discaudatus, Temora longicornis, Pseudocalanus sp., Oithona similis, and Centropages typicus. Total copepod productivity, assuming productivity by the rare species to be proportional to their relative numeric contribution, was estimated to be 800–850 kJ∙m−2∙yr−1. Through comparison of these estimates with previously published estimates, we suggest that copepod productivity in coastal areas may be similar over broad geographic areas.

Similar nucleus numbers among copepods

First nauplius stages (NI) of Pseudocalanus sp., Eurytemora herdmani, Calanus finmarchicus, and C. hyperboreas all have on average about 2000 nuclei. First copepodid stages (CI) of Acartia hudsonica, Pseudocalanus sp., E. herdmani, C. finmarchicus and C. glacialis have about 9600–13 000 nuclei. Body volumes among the same species differ ca. 8-fold in NI and 30-fold in CI. Larger species have much larger nuclei, but close correspondence of body size to nucleus size (amount of DNA) may only occur among closely related species. Nucleocytoplasmic ratios must also vary seasonally within species.

UNUSUAL VARIATIONS IN NUCLEAR DNA CONTENTS IN THE MARINE COPEPOD PSEUDOCALANUS

Variations in DNA/nucleus within adult females are similar, when normalized for mean differences, in the copepods Pseudocalanus sp. and Eurytemora herdmani. However, Pseudocalanus shows great variation among individuals, with no evidence of significant groupings (species?), except perhaps for a few individuals with abnormally small DNA values. Body lengths of adult female Pseudocalanus are approximately proportional to the cube root of DNA/nucleus. It is inferred that nuclear size, not nuclear number, determines body size, and this is supported by generally similar nuclear counts in newly hatched nauplii and among first copepodid stages. Although body size and development rate of Pseudocalanus had earlier been shown to be strongly heritable, an offspring-parent regression reflected no heritability of DNA/nucleus (and some abnormally small offspring values) under the probably suboptimal conditions of rearing. Some variability in DNA content of adult somatic nuclei may be related to chromatin diminution during embryogenesis. An unusual loss of nonchromosomal, Feulgen-positive material is documented for first cleavage in Pseudocalanus, but not E. herdmani.

Temperature-Dependent Growth and Production by a Marine Copepod

Highly synchronous cohorts of the copepod Eurytemora herdmani at a station near Halifax, Nova Scotia, were followed in samples taken during late July and early August, 1980. Individuals from the same population were reared in the laboratory from copepodite I (CI) to adult in conditions of food satiation. Development times and adult body sizes in nature were about the same as predicted for comparable temperatures in the laboratory. Weight increments between CI and adult male in samples from nature were exponential. Females became heavier, because of eggs, after CIII, but developed more slowly, so that their specific growth rates were about the same as for males. Production estimated from weights and stage increments in successive samples (cohort method) was adequately predicted from biomasses in samples and temperature-dependent development times from the laboratory. Production of egg matter by adult females was also adequately predicted by temperature-dependent growth rates of younger stages. These "rules" of development, growth, and production need wider empirical testing and theoretical justification.Key words: Copepoda, temperature, life cycles, development, growth, production