An Assessment of Environmental Conditions That Define Suitable Habitat for the Upside-down Jellyfish (Cassiopea spp.) on Oʻahu
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Authors
Allie Rayna Bilson
Issue Date
2025
Type
Thesis
Language
en_US
Keywords
Marine Science
Alternative Title
Abstract
The upside-down jellyfish, Cassiopea, is a genus of scyphozoans that in the past few decades, has become widely invasive across the subtropics and tropics, including the island of Oʻahu. Their biology, including a mechanism that allows them to pump out nutrient-rich porewater as well as a symbiosis with photosynthetic zooxanthellae, give Cassiopea spp. high tolerance to stressors and may increase their invasibility as the effects of climate change intensify. This study investigated what factors influence seasonal presence of the jellyfish, what constitutes suitable habitat, and how the jellyfish potentially impact nutrient cycling in their nonnative environments. The first part of this study focused on a temporal survey over ten months at the interior end of the Ala Wai Canal in Waikīkī, during which water and sediment nutrients were analyzed and used alongside water quality measurements to construct a logistic regression to determine which were most important for jellyfish presence. Only a few jellyfish were found at two of 18 sampling intervals. In the second part of the study, I conducted a spatial survey of ten sites across Oʻahu that currently or previously hosted invasive populations of Cassiopea spp. Water quality measurements and nutrient concentrations in porewater and the water column were used to construct several generalized linear models in order to determine the most influential factors for jellyfish presence, density, and size. Water column turbidity and nitrate concentration both had negative relationships with jellyfish presence and density, reinforcing the importance of the symbionts as well as posing new questions about nitrate tolerance and whether elevated nitrate could disrupt physiological processes. Salinity and sediment organic matter were also found to be positively related to jellyfish presence, which reinforces current understanding of preferred habitat conditions for the genus, sources of nutrition, and how they may benefit from anthropogenic impacts. Jellyfish tended to be larger at sites with higher pH, suggesting that the health of these populations may begin to suffer in the future as ocean acidification intensifies. These findings suggest that several environmental factors may be key in crafting a multifaceted management solution for preventing and eliminating invasions of Cassiopea spp.
Description
Citation
Publisher
Hawai‘i Pacific University