Is predation of juvenile crown-of-thorns seastars (Acanthaster cf. solaris) by peppermint shrimp (Lysmata vittata) dependent on age, size, or diet?

Outbreaks of crown-of-thorns seastars (CoTS) are one of the leading causes of coral decline on Indo-Pacific coral reefs. Predator removal has been proposed to be a possible mechanism contributing to CoTS outbreaks in this region. Although some data exist on predation of adults, little work has been conducted on predators of juvenile CoTS. The aim of this study was therefore to establish whether predation of juvenile CoTS (1-9 months old after settlement) by peppermint shrimp (L. vittata) is affected by the age, size, or diet of juvenile CoTS. Through a set of ten predation experiments and statistical modeling, this study demonstrated that both age and size of juvenile CoTS are important factors affecting partial and lethal predation. Age was, however, found to be a better predictor of changes in probability (P) of lethal and partial predation (based on smaller AICc). Up to the age of similar to 4 months post-settlement, the probability of lethal predation over a span of 3 d of the experiment was nearly 1. Juvenile CoTS > 4 months old were rarely consumed entirely (P lethal predation = 0) yet showed increased partial predation (such as arm removal or damage to the center of the body) with probabilities increasing after 6 months post-settlement. A subset of CoTS over the age of 4 months was offered either coral or crustose coralline algae (CCA) as food to test for the effect of diet on predation. Diet did not significantly impact either partial or lethal predation. Thus, peppermint shrimp were identified as predators of juvenile CoTS up to an age of 4 months post-settlement, yet partial predation past this age still occurs, which may have consequences on population dynamics. The present study and future research on other juvenile predators fill important gaps in understanding CoTS population outbreaks.

Automated summary

The study revealed that the age and size of juvenile crown-of-thorns seastars play important roles in predation by peppermint shrimp, with younger individuals more likely to be completely consumed by the predators. Individuals over 4 months old were rarely consumed entirely but showed increased partial predation, with diet having no significant impact on predation. Peppermint shrimp were identified as predators of juvenile CoTS up to an age of 4 months post-settlement, highlighting potential consequences for population dynamics.