Abstract
Cubozoan jellyfish are classified as plankton despite the strong swimming and orientation abilities of cubomedusae. How these capabilities could affect cubozoan population structures is poorly understood. Medusae of the cubozoan Copula sivickisi can uniquely attach to surfaces with the sticky pads on their bells. Biophysical modelling was used to investigate the spatial scales of connectivity in a C. sivickisi population. When the medusae were active at night they could maintain their observed distribution on fringing reef if they attached to the reef when the current speed exceeded a moderate threshold. This behaviour facilitated the isolation of a C. sivickisi population on reefs fringing Magnetic Island, Queensland, Australia. Within this distribution, there was considerable within bay retention and medusae rarely travelled > 3 km. The few (< 0.1%) medusae lost from the island habitat were largely advected into open water and away from the mainland coast which lies 8 km from the island. Given that successful emigration is unlikely, the island population probably represents a stock that is ecologically distinct from any mainland populations. The cosmopolitan distribution of C. sivickisi could contain incipient or cryptic species given the small scales of connectivity demonstrated here.
Highlights
The dynamics of populations are underpinned by their spatial structures
The population of Copula sivickisi medusae extended along the entire east coast of Magnetic Island (Fig. 1c)
C. sivickisi medusae were always absent from Middle Reef where the habitat was dominated by Sargassum sp. and coral
Summary
The dynamics of populations are underpinned by their spatial structures. The geographic ranges of marine species are generally inhabited by one or multiple metapopulations composed of mesopopulations/stocks which are largely self-contained[1,2]. Cubozoan stocks may form at relatively small spatial scales within estuarine and coastal systems given the orientation and swimming capabilities of cubomedusae, and the availability of refuges from strong current within structured estuarine and coastal habitats. Numerous techniques have been used to successfully differentiate stocks at relatively small spatial scales in other jellyfish species including: demographics23, genetics24, biogeochemistry15, morphometrics[16] and biophysical m odelling[5]. Combined hydrodynamic and behavioural models can simulate the movements of organisms in aquatic environments, considering both complex flows and species properties and behaviours These models can provide high-definition information on the scales separating stocks of aquatic species and they are useful when the behaviour of the focal organism has the potential to greatly influence its dispersal, which is true for C. sivickisi medusae. Biophysical models can be applied to elucidate the mechanisms of stock separation by systematically varying the model parameters to assess their influence on dispersal
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