Award: OCE-1255697

Intellectual Merit: The most abundant metazoans in the open sea are often the earliest developmental stages of copepods, their nauplii. Nauplii remain under-studied due to the limitations of conventional techniques and an historical emphasis on studying the larger mesozooplankton. However, there is increasing recognition that nauplii play important roles in food web dynamics, and considerable evidence suggests that nauplii may be important trophic intermediaries between microbial and classical food webs, due to their high abundance, high weight-specific ingestion rates, and ability to feed on relatively small particles. Novel approaches are needed to resolve the ecosystem roles of these metazoan micro-grazers in planktonic marine ecosystems. This team of investigators developed a novel molecular approach to studying diverse populations of nauplii in mixed field samples based on quantitative PCR (qPCR). Targeting fragments of the mitochondrial cytochrome c oxidase subunit I gene, the assays were highly species-specific, amplifying a single product in the presence of target DNA at levels as low as 2 pg total DNA, and in mixed-species samples where the target species represented <1 % of the total DNA. Tests on cultured P. crassirostris mtCOI copy number compared to measurements of carbon across developmental stage found a log-linear relationship across a five order of magnitude in animal biomass. The qPCR assay developed here is sensitive and accurate; it can be used to obtain reliable estimates of species-specific biomass in mixed community samples. Using this novel molecular approach to enumerate early-stage copepods in field populations, we investigated the copepod community response to storm events in Kane?ohe Bay, Oahu, the largest coastal embayment in the state of Hawai?i. Event-scale perturbations, such as storms, are important drivers of plankton community dynamics in many coastal marine ecosystems. Storm-associated runoff provides a pulse of nutrients, fueling rapid spikes in phytoplankton production that are often followed by dramatic increases in abundance of the early life stages of copepods (copepod nauplii). In Kane?ohe Bay, recruitment of nauplii of three species was found to be low but stable during non-storm ecosystem states. In contrast, a first-flush winter storm resulted in a rapid increase in early-stage nauplii, with ephemeral shifts in species dominance within the naupliar community. Within 2-4 days following the storm, Parvocalanus crassirostris naupliar DNA quantities were up to an order of magnitude greater than pre-storm levels; while the response in the other species was more modest (up to five-fold increase), and in the case of Oithona attenuata, delayed. Despite the rapid increase in naupliar biomass, the majority of the early naupliar production was lost within 10 days of the storm. Up to 99% of daily early naupliar biomass and a maximum of 13 mg C m-3 d-1 of Oithona simplex was removed from the naupliar community before reaching mid-stage nauplii. These results underscore how responses to ecosystem perturbation differ among species and the ephemeral nature of the response, observations made possible by the novel qPCR approach. The trophic roles of copepod nauplii in planktonic food webs in Kane?ohe Bay also were investigated. Ingestion rates of Parvocalanus crassirostris and Bestiolina similis mid-stage (N3-N4) nauplii on natural prey assemblages were measured to evaluate prey preferences and estimate the trophic impact of grazing by each species. The two species overlapped in the range of prey removed, however P. crassirostris nauplii grazed less selectively than nauplii of B. similis, which avoided 2-5 µm prey while showing positive selection for 20-35 µm prey. Parvocalanus crassirostris had a greater trophic impact on prey populations due to in situ naupliar abundances that were 2 to 11-fold higher than B. similis. The combined grazing impacts by the two species ranged from 1.0 to 8.7% of the 2-35 µm prey biomass. Our results demonstrate that naupliar ingestion rates and prey selectivity is species-specific and can vary on timescales of 2-3 days, and also that nauplii can have a significant grazing impact on prey populations, particularly through positive selection for less abundant (larger) prey. Broader Impacts This award supported mentoring and training of undergraduate students, graduate students, and postdoctoral fellows towards careers in ocean science, including several women early career scientists. Michelle Jungbluth completed a MS (2012) and PhD (2016) based on research related to this award. Two postdoctoral fellows also conducted research on copepod nauplii in association with this award (Carolyn Faithfull, Katherine Hanson), as well as four undergraduate students that received training in laboratory and field research. Our research in Kaneohe Bay served as the basis for outreach to the public in the SOEST Open House (2013, 2015), educating 1000s of school children about planktonic organisms and their ecosystem roles. In addition, PI Goetze draws extensively from research conducted in the Bay to support place-based learning in a large-enrollment undergraduate course in marine science at the University of Hawaii at Manoa (Science of the Sea, 380 students enrolled in 2016-17 AY). Last Modified: 05/15/2017 Submitted by: Erica Goetze