Graduation Year
2021
Document Type
Thesis
Degree
M.S.
Degree Name
Master of Science (M.S.)
Degree Granting Department
Biology (Integrative Biology)
Major Professor
Bradford Gemmell, Ph.D.
Committee Member
Susan Bell, Ph.D.
Committee Member
Kendra Daly, Ph.D.
Keywords
copepod, digestion, feeding, predator-prey
Abstract
The oceanic lobate ctenophore Ocyropsis spp. has a widespread distribution throughout the world’s tropical and sub-tropical oceans. While patchy, Ocyropsis spp. population densities are known to exceed one individual per m3. Studies of coastal ctenophores have shown that some species are capable of exerting strong predatory impacts on their ecosystems, but little is known about the potential trophic impacts of their oceanic relatives. Many oceanic genera such as Ocyropsis, Bolinopsis, and Eurhamphaea exhibit morphologies and prey capture mechanisms that are different from the more well-studied coastal species. Thus, existing data on coastal taxa may not apply to oceanic species due these major morphological and environmental differences. In this study we used high-resolution videography and imaging methods to quantify interactions of Ocyropsis spp. with natural copepod prey. We confirmed that Ocyropsis spp. uses a unique combination of muscular lobe contraction and prehensile mouth to capture evasive prey. Mean capture success on the first attempt was 61% when a single copepod was present and 0% when multiple prey were present within the ctenophore lobes, but overall capture success was 71% and 81% in single and multiple copepod interactions, respectively. Gut content analysis showed that Ocyropsis spp. consume significantly more prey at night, but prey items are smaller than during daylight hours. We found that copepods are digested within 44 minutes and this duration did not vary with ctenophore body length. Based on our findings, conservative estimates show that Ocyropsis spp. are capable of consuming approximately 40% of the daily copepod standing stock when at the high end of population densities observed in nature, and the low end of population densities could consume 0.5% of standing stocks. Through a range of densities from 14 to 1000 individuals per 1000 m3, Ocyropsis spp. have the potential to consume approximately 0.27 to 19 mg C day-1 ind-1 while Kremer et al. (1986a) estimates that O. crystallina require only 0.63 mg C day-1 to meet metabolic needs. This work suggests that when Ocyropsis spp. exist at high population densities, they are capable of exerting top-down control on copepod populations and may be acting to structure zooplankton communities in ways that few other oceanic species can. However, because Ocyropsis spp. are more commonly observed at low to moderate densities, it is more likely that they are meeting metabolic demands to grow and reproduce successfully, but do not have a strong impact on zooplankton communities.
Scholar Commons Citation
Potter, Elizabeth, "Ubiquitous yet Inconspicuous: Quantifying Trophic Impact of a Widespread Oceanic Comb Jelly (Ctenophore)" (2021). USF Tampa Graduate Theses and Dissertations.
https://digitalcommons.usf.edu/etd/9210
