Award: DEB-1542673

The deep sea is more than 90 percent of the inhabitable space on Earth, yet life there is largely a mystery to science. Ctenophores, also known as comb jellies, are marine predators found in all oceans, inhabiting both deep and shallow seas. Although fragile and difficult to study, they are ecologically important components of planktonic food webs. Also, they appear to have been the first group of animals to split off from all other organisms during evolution, even before sponges and jellyfish. Comb jellies are different from cnidarian jellyfish, because they use colloblasts (aka glue cells) to capture prey instead of stinging cells. Ctenophores also use rows of cilia, arranged in bands of combs, to swim instead of jet propulsion. Over evolutionary time, many marine animals have transitioned their home ranges between shallow and deep environments despite the huge differences between these two habitats, including light, temperature, and pressure. Such habitat shifts required dramatic genetic and physiological changes to these animals over evolutionary time. In this project, we examined the diversity of biochemical characteristics of ctenophores with particular focus on species from a wide variety of habitats off California and Hawaii and in Puget Sound. Enzymes are proteins used in metabolism and are important for feeding, locomotion, etc. Using 320 specimens of 39 species, we described the relationships between activities of metabolic enzymes in relation to biological and environmental parameters. We found a significant positive relationship between creatine kinase (CK) activity and comb plate density. Significant correlation of enzymatic activities to body mass were observed at the for ctenophore orders, but not at the whole phylum level. This demonstrates that the different orders have diverse strategies for coping with metabolic demands. Ctenophores did not display metabolic differences between shallow and deep species, in support of the visual-interactions hypothesis, which predicts no trend in metabolic differences for animals without vision. Using 177 specimens from 27 species we examined the effects of high pressure on 3 metabolic enzymes, CK, malate dehydrogenase (MDH), and pyruvate kinase (PK). species inhabiting similar vertical ranges can display unique pressure tolerance characteristics. Some ctenophore species displayed broad pressure tolerances, while others were constrained to their respective habitat depth. The decreased residual rate followed by a spike at recovery in CK and PK activities indicate permanent conformational damage to the enzyme after the pressure has been introduced. The enzymatic rates of CK were variable across species and pressures. Of the three enzymes studied, PK was the most affected by increasing pressures. MDH activity remained relatively stable as pressure was introduced to the system. We also examined the ultrastructural diversity of colloblasts in 20 species of ctenophores using scanning electron microscopy. This was the most extensive survey of colloblast diversity ever undertaken, and our observations revealed the unique morphology of these structures. Comparative measurements of colloblasts revealed that the shape of the collosphere (the organizational unit of sticky granules) falls into 3 classifications: spherical, ellipsoidal, or non-uniform. Novel observations were also made on the cap cell membrane, spiral filament and patterns of external secretion granule deposition. This project provided research training for 2 graduate students, who completed their masters degrees, 10 undergraduate students, 1 high school teacher and 1 high school student. Our outreach activities included participation in the Partners in Science program of the Murdock Charitable Trust whereby a high school teacher spent two summers working with our project. The 2 graduate students were keynote speakers at the Expanding Your Horizons program, a nationwide STEM initiative to attract middle school girls to careers in the sciences. We also provided research opportunities to collaborating scientists aboard our research expeditions in Hawaii. A more extensive illustrated report summarizing the activities of all three NSF-funded Dimensions of Biodiversity ctenophore projects can be found at https://jellywatch.org/nsf-deepc.pdf. Last Modified: 12/13/2021 Submitted by: Erik V Thuesen