Growth and age determination of the tropical Australian cubozoan Chiropsalmus sp.

Abstract

Chiropsalmus sp. medusae collected in this study ranged from 3 to 71 mm diagonal bell width and displayed growth best described by the following equation: size (mm) ¼ 74.9 · exp ()exp(0.041 (time since metamorphosis (day) )35.6674))). Growth rates of up to 7 mm week )1 increase in diagonal bell width are theoretically possible, with animals able to reach sexual maturity in approximately 70 days. Correlation of the number of rings on the statoliths with the predicted age of the individual from the field produced a relationship that indicates the growth rings are laid down daily and as such could be used to infer age of the medusae. Over the 1998-1999 season, there were four influxes of juvenile cohorts, each occurring approximately 14 days after a major rainfall event.

Growth, Development and Temporal Variation in the Onset of Six Chironex fleckeri Medusae Seasons: A Contribution to Understanding Jellyfish Ecology

“…Rather, if successive rings were added on a daily basis, medusae collected within this study would have ranged between one and three months of age. Not only are these realistic age estimates, given that medusae are unlikely to survive between seasons, but growth rings are added on a daily basis in three other species of cubozoa [35], [38], [39], [40], [41]. In this scenario, alternating dark and light bands would reflect the diurnal behaviours of medusae [25], [43].…”

“…While the development to a specific number of tentacles [32] and the presence of photosymbiotic algae [33] have also been suggested as potential cues for metamorphosis, these links have not been validated quantitatively. Similarly, while the correlation between rainfall events and successive pulses of juvenile cubomedusae [34], [35] may implicate salinity as a cue for metamorphosis, quantitative data demonstrating this link is lacking. Given this paucity in data, a need therefore exists for research distinguishing between those mechanisms driving polyp metamorphosis and those merely correlated with this process.…”

“…While such growth patterns are reported for a number of scyphozoan species [36], for cubomedusae, it is only for Chiropsella bronzei Gershwin that growth parameters have been quantified [34], [35]. This paucity in data is largely due to the lack of a reliable method by which cubomedusae can be aged.…”

“…While some authors have used the number of tentacles per pedalium as an indicator of development [25], tentacles are added across a size range, and hence, may still be somewhat dependent upon feeding regime. More recently, the statoliths contained within the statocysts of cubomedusae rhopalia (eye bearing sensory structures) have been shown to contain fine growth rings that are added on a daily basis [35], [38], [39], [40], [41].…”

“…For example, several cohorts of C. bronzei medusae occurring within a single season, as well as a correlation between cohort appearance and significant rainfall events, were elucidated from population structure data [34], [35]. Comparable data for C. fleckeri populations is, however, currently limited to the generalisation that an abundance of small individuals early in the season progresses to fewer but larger medusae late in the season [15].…”