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Abstract The high-latitude copepod Neocalanus flemingeri exploits the spring phytoplankton bloom to accumulate lipids for survival during food-limited periods and to fuel reproduction. At some point during development, lipid-accumulation ends and pre-adults molt into adults, descend to depth and enter a state of dormancy termed diapause. How and when they determine to make this transition is still unresolved. According to one hypothesis, the trigger is their attaining a threshold amount of lipid fullness. Alternatively, they might follow a genetic program, entering diapause within a narrow developmental window. To better understand the decision, a 5-week laboratory experiment was conducted to assess the effect of food quantity and type on lipid accumulation, biomass and gene expression in N. flemingeri copepodite stage CV. In fed individuals, the initial rate of lipid accumulation slowed by week 5, as a portion of CVs began to molt into adults. While changes in gene expression common to all fed individuals between weeks 1 and 3 were consistent with a developmental program, the duration of the CV stage was variable. Unfed individuals maintained lipid stores initially, suggesting physiological acclimatization to conserve energy. A comparison with gene expression profiles of field-collected individuals suggests similar responses to resources in the environment. 

Abstract In the South Atlantic Bight (SAB), responses of zooplankton communities to physical dynamics were evaluated monthly at two sites on the continental shelf offshore from Savannah, GA, USA, between December 2015 and December 2017. Zooplankton were collected in oblique net tows (202-μm). Samples were collected in two regions of the middle shelf: inner edge (Site 1: 25 m isobath, n = 22) and outer edge (Site 2: 40 m isobath, n = 21). Samples were also collected at a third site on the 40 m isobath, ~20 nm south of Site 2 in July and August 2016. Temperature, salinity and fluorescence data were recorded at each site. Overall, 57 taxa were identified with total abundances varying from 1 × 103 to 81 × 103 ind.m−3. Small copepods predominated; notably Paracalanus spp. The highest abundance was recorded in October 2016 at Site 1, following deep mixing induced by Hurricane Matthew. Interannual variability of zooplankton abundance was significant, with higher abundances in 2016 compared with 2017, reflecting higher river runoff in 2016. Samples from Site 3 yielded the largest Dolioletta gegenbauri bloom documented in the SAB. This 2-year time-series, for the first time, suggests that zooplankton communities on the SAB middle shelf region are significantly influenced by continental precipitation patterns.