Upside-down Jellyfish: A Bioindicator of the Consequences of the Halophila stipulacea

Nina Scott and Edwin Cruz-Rivera, University of the Virgin Islands, Charlotte Amalie, United States
Cassiopea xamachana are particularly vulnerable to various environmental changes. New evidence suggests that they are a bioindicator species. In this study, we determine if the rapid spread of invasive seagrass Halophila stipulacea will negatively impact Cassiopea xamachana populations in St. Thomas, USVI. While not much is understood about their ecology, we do know that these photosynthetic jellies require open sandy areas with high light exposure. Halophila is now occupying this same space throughout in St. Thomas, which could potentially compromise the stability of Cassiopea populations. The project analyzes behavior and physiological stress responses to various bottom types such as sand, grass (local and introduced species) and mud (simulating mangrove bottom type). Here we tested the hypothesis that the overall productivity of upside-down jellyfish will decrease due to competition with the seagrass and the signs of physiological stress will increase. This was accomplished first by hosting weekly surveys to observe habitat preference and measure movement for a month in John Brewer’s Bay. Next, a jellyfish placement behavioral experiment was conducted in the field where bell contractions as well as how long an individual remained in that original plot was observed. We also conducted a caged field experiment that uses P.A.M. fluorometry to measure the photosynthetic productivity of jellies after 1-week sessions on either sand or grass substrate. So far upside-down jellies have only been found sandy bottoms during surveys, implying habitat preference and we anticipate that our results reflect this. Identifying Cassiopea xamachana as a bioindicator of the negative ecological impacts of Halophila stipulacea will help scientists’ further study how the seagrass will affect other vulnerable species within the same habitats.