Reef complexity influences distribution and habitat choice of the corallivorous seastar Culcita schmideliana in the Maldives

Enrico Montalbetti,Davide Seveso,Marco Casartelli,Luca Fallati,Davide Maggioni,Paolo Galli,Simone Montano

doi:10.1007/s00338-022-02230-1

Enrico Montalbetti, Davide Seveso + Show 5 more

Open Access

https://doi.org/10.1007/s00338-022-02230-1

Copy DOI

Abstract

AbstractThe cushion seastar Culcita schmideliana has gained major attention in the last few years because of its selective predation on juvenile corals, as well as its ability to generate large demographic assemblages, causing delays in coral recovery after large mortality events in the Republic of Maldives. However, a lack of data regarding the factors affecting its distribution and habitat selection still persists in this area. Here, we adopted a novel approach in the study of corallivorous seastar habitat selection that combined ecological and digital photogrammetry data. In this regard, we tested 3 different parameters as factors influencing seastar habitat choice in the South-East region of Faafu Atoll, Republic of Maldives, namely prey abundance, Linear Rugosity Index (LRI), and Average Slope (AS). The analysis of selectivity coefficient (Ei) of seastars for different habitat types showed a preference for reefs characterized by medium AS values (Ei = 0.268), a LRI included between 2 and 2.5 (Ei = 0.180), and a juvenile coral density ranging between 10 and 20 colonies m−2 (Ei = 0.154). A multiple linear regression analysis showed that different AS and LRI values explained the 43.1% (R2 = 0.431, P = 0.007) and the 48.1% (R2 = 0.481, P = 0.024) of variance in seastars abundance, respectively, while juvenile coral densities did not significantly affect this (R2 = 0.132, P = 0.202). These results provide new information on the distribution and behaviour of an important corallivore of Maldivian reefs, such as C. schmideliana.

Highlights

Predation on scleractinian corals is a common and well described ecological phenomenon in coral reef ecosystems (Rice et al 2019)
Thirty-six ultra-high-resolution 3D models were generated from the 7946 images acquired in correspondence of the six sampling sites
The average Linear Rugosity Index (LRI) of the whole investigated area was 2.02 ± 0.10, with the maximum complexity reached in Dharamboodhoo reef (2.48 ± 0.33), which showed the highest Average Slope (AS) value (2275.42 ± 110.14), and the minimum 3-dimensionality recorded in Freeclimbing reef (1.46 ± 0.04), where the lowest AS value was obtained (697.75 ± 295.82) (Table 1)

Summary

Introduction

Predation on scleractinian corals is a common and well described ecological phenomenon in coral reef ecosystems (Rice et al 2019). The effects of corallivorous seastars are grievous considering the large number of stressors affecting coral reefs’ integrity in the last years, such as extreme climatic events and subsequent mass bleaching, or increased pollution (Carpenter et al 2008; Patricola and Wehner 2018; Rice et al 2019). In this context, it is important to consider the role of other coral feeding seastars, which, despite being still poorly studied, have been shown to affect reef resilience, in particular following large coral mortality events (Raj et al 2018; Mah 2020).

Objectives

Methods

Results