Award: OCE-1061973

This project investigated the impacts of unusual phytosterols, many associated with harmful algal blooms, on zooplankton growth and reproduction. Cholesterol is an essential component of cell membranes and a precursor to steroid hormones, but crustacean zooplankton are unable to synthesize cholesterol and must acquire cholesterol or phytosterol precursors from their diet. Phytoplankton contain a broad range of phytosterols, some of which can be converted to cholesterol with varying efficiencies and others which cannot be converted. A number of unusual phytosterols have recently been discovered in phytoplankton species associated with harmful algal blooms. As there has been considerable interest over the past several decades in bioactive compounds produced by phytoplankton that inhibit growth and reproduction in zooplankton, we investigated whether these unusual phytosterols serve a similar function. In this collaborative project Dr. José Giner investigated the metabolic pathways of ingested phytosterols. By labeling phytosterols synthesized in the lab with a stable carbon isotope, we could determine whether the ingested phytosterol is metabolized by zooplankton. In my portion of the project, in addition to culturing zooplankton to incorporate the labeled phytosterols, I tested whether any of these phytosterols had deleterious effects on zooplankton (copepods and brine shrimp) by supplementing the diet of the zooplankton with a range of phytosterols, including those known to be metabolized, as well as a range of novel phytosterols, many from harmful algal species. Experiments were conducted to determine growth rates of the brine shrimp Artemia salina, development of the copepod Eurytemora affinis, and egg production and egg viability of the copepod Acartia tonsa on supplemented diets. Adults and later developmental stages appeared to be unaffected by the supplements. There was no effect observed on egg production or egg viability of Acartia tonsa on any of the phytosterol supplements. Longer-term growth and development experiments with Artemia salina and Eurytemora affinis did find several phytosterols that inhibited growth of the zooplankton. Results of the experiments suggest that the impacts were on early developmental stages, and may have been due to high ingestion of the supplemented sterols by some individuals in the population. These results indicate that several of these novel phytosterols could be deleterious to zooplankton if present at high concentrations in the diet, although under normal field conditions the main effect of dietary phytosterols would likely depend on the ability of the zooplankton to metabolize the phytosterol to cholesterol. As part of a collaborative proposal with lead PI Dr. José Giner a total of nine journal articles and 20 conference presentations were produced through Dr. Giner's lab. Spectral data of 13C-labeled sterols are publically available (http://www.bco-dmo.org/dataset/565297). Two undergraduates participated in the project at Ohio University and The Mount Desert Island Biological Laboratory (MDIBL). Public science outreach was done each summer at MDIBL as part of a Family Science Night. Last Modified: 12/20/2017 Submitted by: R. Patrick Hassett