Age and Growth of An Outbreaking Acanthaster cf. solaris Population within the Great Barrier Reef

M Macneil,Deborah Pratchett,Karen Chong-Seng,Vanessa Messmer,Casssandra Thompson,Morgan Pratchett

doi:10.3390/d9010018

Abstract

Despite having been studied for more than 40 years, much about the basic life history of crown-of-thorns starfish (CoTS; Acanthaster spp.) remains poorly understood. Size at age—a key metric of productivity for any animal population—has yet to be clearly defined, primarily due to difficulties in obtaining validated ages and potentially indeterminate growth due to factors such as starvation; within-population variability is entirely unknown. Here we develop age and growth estimates for an outbreaking CoTS population in Australian waters by integrating prior information with data from CoTS collected from multiple outbreaking reefs. Age estimates were made from un-validated band counts of 2038 individual starfish. Results from our three-parameter von Bertalanffy Bayesian hierarchical model show that, under 2013–2014 outbreak conditions, CoTS on the GBR grew to a 349 (326, 380) mm (posterior median (95% uncertainty interval)) total diameter at a 0.54 (0.43, 0.66) intrinsic rate of increase. However, we also found substantial evidence (ΔDIC > 200) for inter-reef variability in both maximum size (SD 38 (19, 76)) and intrinsic rate of increase (SD 0.32 (0.20, 0.49)) within the CoTS outbreak initiation area. These results suggest that CoTS demography can vary widely with reef-scale environmental conditions, supporting location-based mechanisms for CoTS outbreaks generally. These findings should help improve population and metapopulation models of CoTS dynamics and better predict the potential damage they may cause in the future.

Highlights

Population outbreaks of crown-of-thorns starfish (CoTS; Acanthaster spp.) are a major contributor to coral loss throughout the Indo-Pacific [1,2,3,4]
On the Great Barrier Reef (GBR), for example, there have been four distinct episodes of outbreaks since the 1960s [5], and coral loss caused by these outbreaks is equal or greater than that caused by other major disturbances
The demography of Acanthaster spp. is considered to be extremely plastic, whereby adult growth growth and longevity are strongly dependent on local environmental conditions, such as food and longevity are strongly dependent on local environmental conditions, such as food availability, availability, temperature, and wave exposure [19,20,30]

Summary

Introduction

Population outbreaks of crown-of-thorns starfish (CoTS; Acanthaster spp.) are a major contributor to coral loss throughout the Indo-Pacific [1,2,3,4]. Minimizing or preventing outbreaks of Acanthaster spp. is considered one of the foremost management strategies to reverse sustained coral loss on the GBR (e.g., [6]). Outbreaks of Acanthaster spp. are variously attributed to their inherent life history characteristics, such as exceptional fecundity [9,10], versus anthropogenic and environmental changes that disrupt normal regulatory processes [11,12,13]. There is limited data on differences in population demographics within outbreak or non-outbreak populations of CoTS, which would help to resolve the relative importance of intrinsic versus extrinsic processes. Most studies of CoTS (e.g., [14,15,16])

Methods

Results

Discussion

Conclusion