Thermal stratification drives movement of a coastal apex predator

Eneko Aspillaga,Frederic Bartumeus,Mikel Zabala,David Díaz,Richard M Starr,Cristina Linares,Àngel López-Sanz,Bernat Hereu,Joaquim Garrabou

doi:10.1038/s41598-017-00576-z

Abstract

A characterization of the thermal ecology of fishes is needed to better understand changes in ecosystems and species distributions arising from global warming. The movement of wild animals during changing environmental conditions provides essential information to help predict the future thermal response of large marine predators. We used acoustic telemetry to monitor the vertical movement activity of the common dentex (Dentex dentex), a Mediterranean coastal predator, in relation to the oscillations of the seasonal thermocline during two summer periods in the Medes Islands marine reserve (NW Mediterranean Sea). During the summer stratification period, the common dentex presented a clear preference for the warm suprathermoclinal layer, and adjusted their vertical movements following the depth changes of the thermocline. The same preference was also observed during the night, when fish were less active. Due to this behaviour, we hypothesize that inter-annual thermal oscillations and the predicted lengthening of summer conditions will have a significant positive impact on the metabolic efficiency, activity levels, and population dynamics of this species, particularly in its northern limit of distribution. These changes in the dynamics of an ecosystem’s keystone predator might cascade down to lower trophic levels, potentially re-defining the coastal fish communities of the future.

Highlights

Temperature is a key environmental factor that, through profound physiological effects, influences the fitness and survival of ectothermic organisms[1,2,3]
In this study we focused on the common dentex, Dentex dentex (L. 1758), one of the main coastal apex predators in the Mediterranean Sea and an important fishery resource for both artisanal and recreational fisheries[26,27,28]
During the study period we observed the typical seasonal thermal cycle for the NW Mediterranean Sea, which is characterized by a mixed phase followed by a thermal stratification period[35]

Summary

Introduction

Temperature is a key environmental factor that, through profound physiological effects, influences the fitness and survival of ectothermic organisms[1,2,3]. As with many other mobile animals, marine fishes can readily exploit thermal gradients to regulate their body temperature and increase their metabolic efficiency[15, 16]. Controlled laboratory experiments have shown that fish move across thermal gradients to attain a preferred temperature[17, 18], and have allowed the researchers to investigate the response of an individual’s internal temperature to a fluctuating environment[16]. Thermoclines set up a heterogeneous thermal environment wherein mobile organisms have developed behavioural responses according to the trade-off between their physiological requirements and energy demands. In order to exploit those food resources, several tuna species[15, 20, 21] as well as the ocean sunfish[22] rewarm during relatively long periods in the suprathermoclinal layer before performing short excursions below the thermocline to forage. In this study we focused on the common dentex, Dentex dentex (L. 1758), one of the main coastal apex predators in the Mediterranean Sea and an important fishery resource for both artisanal and recreational fisheries[26,27,28]

Objectives

Methods

Results

Conclusion