Predation Cues Lead to Reduced Foraging of Invasive Siganus rivulatus in the Mediterranean

Daphna Shapiro Goldberg,Gil Rilov,Sébastien Villéger,Jonathan Belmaker

doi:10.3389/fmars.2021.678848

Abstract

Invasive species are one of many anthropogenic challenges to maintaining a healthy marine ecosystem. Two rabbitfish species (Siganus rivulatusandSiganus luridus) are among the more successful migrants from the Red Sea to the Mediterranean, where their intense foraging has caused damage to the algae community, thus reducing primary production and habitat complexity, and impacting nurseries for early life stages. Anecdotal evidence suggests that the impact of rabbitfish on algae is lower in Marine Protected Areas (MPAs) although rabbitfish densities are similar in protected and fished areas. One explanation could be that fear of predators, more often present inside MPAs and an important component of a healthy marine ecosystem, reduces the ecological impacts of rabbitfish. This research aimed to test if such fear effects do occur in rabbitfish. Using controlled mesocosm experiments, we testedS. rivulatusreactions to two chemical predation cues: chemical alarm cues released from a recently killed conspecific fish, and water-borne cues from a tank with a live grouper predator,Epinephelus marginatus.We found that rabbitfish significantly reduce their overall food consumption as well as their bites per minute when exposed to the alarm cue, but not when exposed to the grouper water cue. These results support the idea that MPAs, which effectively increase the density of large piscivores and hence predation, can mitigate the impact of invasive herbivorous species. If the mesocosm results can scale up to natural systems, predation cues may be artificially introduced to other target areas in order to reduce rabbitfish grazing outside reserves. Thus, this study provides information that can be used to manage the ecological impacts caused by invasive rabbitfish, both inside and outside of marine reserves.

Highlights

The Mediterranean Sea is under an ongoing invasion by hundreds of exotic species, in large part due to the opening of the Suez Canal in 1869 (Belmaker et al, 2009; Katsanevakis et al, 2014; Galil et al, 2015; Castellanos-Galindo et al, 2020; Golani, 2021)
The rabbitfish in the treatment tanks had an overall lower bite rate per minute when exposed to a chemical alarm cue released by a recently killed conspecific fish (Predator effect: p = 0.008; Table 1)
There was a higher percentage of food portions remaining over time, i.e., lower foraging impact, in treatment tanks with an alarm cue than in tanks with no predation cue (Figure 3), confirmed by the lower change in food consumption over time between consecutive days with no predation cue (Predator × Time: p < 0.001; Table 2)

Summary

Introduction

The Mediterranean Sea is under an ongoing invasion by hundreds of exotic species, in large part due to the opening of the Suez Canal in 1869 (Belmaker et al, 2009; Katsanevakis et al, 2014; Galil et al, 2015; Castellanos-Galindo et al, 2020; Golani, 2021). Rabbitfish have been observed to graze on both established algae and on turf which contains macroalgal recruits (Verges et al, 2014), in contrast to native Mediterranean herbivores who feed primarily on adult macrophytes. All of this disturbs the larger ecological community that depends on macroalgae and seagrass for many ecosystem functions, including primary production, nutrient recycling, habitat formation, and nurseries for many marine species (Mineur et al, 2015; Teagle et al, 2017) and leads to a shift in ecosystem functions (Rilov et al, 2020)

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