Population dynamics of the invasive upside-down jellyfish Cassiopea in Lake Macquarie: identification, seasonality, and distribution.

Abstract

Scyphozoans of the genus Cassiopea are notable for their unusual benthic habitat of lying upside-down with their exumbrella resting on the substrate and oral arms facing upwards, resulting in their common name “upside-down jellyfish”. Cassiopea are model examples of an invasive species that have been historically confused because of their taxonomic ambiguity and can have significant economic and environmental consequences as their blooms are known to impact fisheries, tourism, and trophic structures. Cassiopea were first reported in temperate Lake Macquarie, New South Wales, in 2017, though historically these jellyfish have a more northern tropical distribution in Eastern Australia. This project aims to provide baseline information on the identification and presence of Cassiopea in Lake Macquarie and inform potential management strategies. This study used a genetic analysis to confirm two species of Cassiopea are expanding their range down the east coast of Australia, with a focus on C. xamachana, the species occurring in Lake Macquarie. A morphometric analysis identified the features that can be used to distinguish these species, and these results combined with the genetic analysis confirmed that C. maremetens, described in 2010 from southern Queensland, is a junior synonym of C. xamachana. Additionally, the results from this study confirm that Cassiopea abundance peaks during Austral Autumn and Winter, before experiencing a population crash in August. This appears to be controlled by temperature and turbidity, but their density and distribution is expected to increase with climate change. Additionally, no polyps have been found in the area and only females have been recorded, suggesting there was only one invasion event into Lake Macquarie, and since then, the polyps have been asexually reproducing. As a result, long-term monitoring is recommended and this study demonstrates that drones are a precise and efficient method for doing this.