Fish mitigate trophic depletion in marine cave ecosystems

Simona Bussotti,Serge Planes,Jean Vincent Vieux-Ingrassia,Paolo Guidetti,Lea Egea,Antonio Di Franco,Alexis Pey,Pierre Chevaldonné,Luigi Musco,Emanuela Fanelli,Carlo Nike Bianchi,Carlos Navarro-Barranco,Christophe Lejeusne

doi:10.1038/s41598-018-27491-1

Abstract

Dark marine habitats are often characterized by a food-limited condition. Peculiar dark habitats include marine caves, characterized by the absence of light and limited water flow, which lead to reduced fluxes of organic matter for cave-dwelling organisms. We investigated whether the most abundant and common cave-dwelling fish Apogon imberbis has the potential to play the role of trophic vector in Mediterranean marine caves. We first analysed stomach contents to check whether repletion changes according to a nycthemeral cycle. We then identified the prey items, to see whether they belong to species associated with cave habitats or not. Finally, we assessed whether A. imberbis moves outside marine caves at night to feed, by collecting visual census data on A. imberbis density both inside and outside caves, by day and by night. The stomach repletion of individuals sampled early in the morning was significantly higher than later in the day. Most prey were typical of habitats other than caves. A. imberbis was on average more abundant within caves during the day and outside during the night. Our study supports the hypothesis regarding the crucial trophic role of A. imberbis in connecting Mediterranean marine caves with external habitats.

Highlights

Dark marine habitats are often characterized by a food-limited condition
We addressed three questions: (1) Do cave-dwelling A. imberbis feed at night? (2) Do prey items of cave-dwelling A. imberbis belong to taxa typically associated with habitats outside the caves? (3) Are there changes in the abundance patterns of A. imberbis within and outside caves during the night/day cycle?
The logistic regression performed on the Apogon imberbis stomach repletion data from the 14 caves investigated shows a significant effect of the time-interval between sunrise and sampling time on the feeding pattern of A. imberbis (Wald = 86.930, df = 1, p < 0.01), with a significant decrease of stomach repletion with increasing time-interval (Fig. 3)

Summary

Introduction

Dark marine habitats are often characterized by a food-limited condition. Peculiar dark habitats include marine caves, characterized by the absence of light and limited water flow, which lead to reduced fluxes of organic matter for cave-dwelling organisms. Dark marine habitats are environments where the light is limited if not completely absent (aphotic areas), leading to a consequent shortage or total lack of autochthonous photosynthesis[1]. Setting aside chemosynthetic processes in deep ocean ridges and similar habitats[2], the low/absent autochthonous primary production makes dark habitats food-limited environments. Their functioning, depends (partially or totally) on allochthonous primary production[3]. Water movement can more or less effectively transport Particulate Organic Matter (POM) from outside habitats into the cave, a process that may affect the assemblages living inside, e.g. in terms of abundance, cover, biomass, species composition and overall assemblage structure[19,20,21,22]. The trophic depletion within caves is the result of the shortage of the total food input, but it is associated with an impoverishment of its nutritional value (C/N ratio, complex/simple organic matter ratio, and pheophitin-chlorophyll ratio inside the cave[7])

Methods

Results

Discussion

Conclusion