Researching the habitat of the upside-down jellyfish (Erik Wurz photo)
PHILIPSBURG--Researchers from Wageningen University & Research and the University of Amsterdam report on a fascinating case of competition between an animal and an invasive pIant. The invasive seagrass Halophila stipulacea has been very successful in new habitats both in the Mediterranean and Caribbean seas, at the expense of native jellyfish.
The seagrass can quickly colonise new habitats because small fragments break off, remain viable and spread via currents. In the new paper Battle for the mounds: Niche competition between upside-down jellyfish and invasive seagrass, published in the scientific journal Ecology, the researchers report on their discovery that the invasive seagrass uses little mounds – created by burrowing animals such as shrimp or sea cucumbers – as a new habitat to settle and expand from. The mounds provide new space with sufficient light, opening up the dense meadows of native seagrass where the invasive seagrass otherwise cannot settle. From there, they observed that the invasive seagrass can spread.
In tropical ecosystems, photosynthesising organisms are continuously competing for space and light. Researchers found that this can cause problems for native species. “The upside-down jellyfish (Cassiopea spp) lies upside down because it has photosynthetic algae in its tentacles. Therefore, these organisms also need light and prefer open spaces such as these mounds created by burrowing animals,” according to Fee Smulders of Wageningen University & Research, and lead author of the study.
Master of Science student Naomi Slikboer recorded the presence of both invasive seagrass and upside-down jellyfish on many of these mounds on the island of Curaçao. She found that often the invasive seagrass pushes the upside-down jellyfish out of these habitats over time.
Due to rapid overgrowth of H. stipulacea, jellyfish has to move more often, and therefore use more energy. Additionally, the authors hypothesise that the interplay between invasive seagrass and burrowing mounds will lead to unstable, dynamic seagrass meadows, unfavourable for valuable native seagrass species.
Smulders: “We need to keep a close watch on this invasive seagrass and investigate the impact on both native species as well as the seascape patch dynamics in Caribbean seagrass meadows.”
