Benthic Predators Influence Microhabitat Preferences and Settlement Success of Crown-of-Thorns Starfish (Acanthaster cf. solaris)

Zara-Louise Cowan,Morgan Pratchett,Ciemon Caballes,Symon Dworjanyn

doi:10.3390/d8040027

Zara-Louise Cowan, Morgan Pratchett + Show 2 more

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https://doi.org/10.3390/d8040027

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Abstract

Like most coral reef organisms, crown-of-thorns starfish (Acanthaster spp.) are expected to be highly vulnerable to predation as they transition from a planktonic larval phase to settling among reef habitats. Accordingly, crown-of-thorns starfish might be expected to exhibit behavioural adaptations which moderate exposure to predation at this critical stage in their life history. Using pairwise choice experiments and settlement assays, we explored the ability of competent larvae of Acanthaster cf. solaris to first detect and then actively avoid benthic predators during settlement. Pairwise choice experiments revealed that late stage brachiolaria larvae are able to detect predators in the substrate and where possible, will preferentially settle in microhabitats without predators. Settlement assays (without choices) revealed that larvae do not necessarily delay settlement in the presence of predators, but high levels of predation on settling larvae by benthic predators significantly reduce the number of larvae that settle successfully. Taken together, these results show that crown-of-thorns starfish are highly vulnerable to benthic predators during settlement, and that variation in the abundance of benthic predators may exert a significant influence on patterns of settlement for crown-of-thorns starfish.

Highlights

As for many benthic reef organisms, settlement is expected to represent one of the major bottlenecks in the life history of crown-of-thorns starfish (Acanthaster spp.), whereby relatively naïve planktonic larvae will be exposed to an entirely new suite of potential predators as they transition to living in benthic reef habitats [1]
All three benthic predators tested in this study (polychaetes, trapeziid crabs threecategories categoriesofofpotential potential benthic predators tested in this study caused rates of mortality lateamong stage brachiolaria crabsscleractinian and scleractinian corals) elevated caused elevated rates of among mortality late stage larvae of crown-of-thorns starfish
This study shows that settling larvae of Acanthaster cf. solaris are highly vulnerable to a range of different benthic predators, including scleractinian corals and their commensals, as well as polychaete worms that were commonly found on freshly collected pieces of coral rubble, adding to the wide range of predators known to feed on early life-stages of Acanthaster spp. (e.g., [2,3,4,26])

Summary

Introduction

As for many benthic reef organisms, settlement is expected to represent one of the major bottlenecks in the life history of crown-of-thorns starfish (Acanthaster spp.), whereby relatively naïve planktonic larvae will be exposed to an entirely new suite of potential predators as they transition to living in benthic reef habitats [1]. Reef-based predators include both planktivorous fishes and sessile invertebrates (e.g., corals) that intercept larvae as they swim towards benthic habitats [2,3], as well as infaunal invertebrate predators that will feed on starfish that settle to specific microhabitats [4]. Both pre- and post-settlement mortality play important roles in structuring populations of marine organisms (e.g., [5]), but predation rates are generally highest (≥30% day−1 ) immediately after settlement (reviewed by Gosselin and Qian [6]). There will be strong selection for settling larvae to choose microhabitats that minimise predation risk [9], either by avoiding habitats with high abundance of potential predators or preferentially settling in complex microhabitats that provide greater refuge from predators.

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