Assessing the Drivers behind the Structure and Diversity of Fish Assemblages Associated with Rocky Shores in the Galapagos Archipelago

Wout Van Echelpoel,José Ponton-Cevallos,Peter Goethals,Nancy De Saeyer,Niels De Troyer,Stijn Luca,Tom Moens,Long Ho,Rafael Bermudez,Ruth Vandeputte,Heleen Raat,Ratha Sor,Luis Dominguez-Granda,Marie Anne Eurie Forio,Stijn Bruneel,Amber Schoeters,Christine Van der heyden

doi:10.3390/jmse9040375

Abstract

Oceanic islands harbor unique yet fragile marine ecosystems that require evidence-based environmental management. Among these islands, the Galapagos archipelago is well known for its fish diversity, but the factors that structure communities within and between its islands remain poorly understood. In this study, water quality, physical habitats and geographical distance were assessed as potential predictors for the diversity and structure of fish assemblages. Differences in the structure of fish assemblages of the two studied islands (Santa Cruz and Floreana) were most likely driven by temperature and nutrient concentrations. In the relatively highly populated island Santa Cruz, the structure of fish assemblages was more affected by water conditions than physical habitats while the contrary was true for the more pristine area of Floreana. A wide variety of species with different geographical origins were distributed over the different islands, which indicates that most fish species are able to reach the islands of the archipelago. However, temperature gradients and elevated nutrient levels cause large differences in the structure of local fish assemblages. In addition, in Santa Cruz nutrient concentrations were negatively correlated with α diversity. Since pollution is a clear pressure on the fish assemblages of oceanic islands, environmental management of the coastal areas is of paramount importance.

Highlights

Due to their isolated position, oceanic islands harbor some of the last near-pristine marine ecosystems and associated fish assemblages [1,2]
Rocky habitats were targeted for the transects, sandy patches were often unavoidable and sand cover was significantly higher in Santa Cruz (the abiotic data is depicted visually in Principal Component Analysis (PCA) plots (Figures S4.1–S4.3)
Because the series of variables were characterized by many correlations among their variables, there was no sound statistical ground to separate the effects of geographical distance, water quality and physical habitats on diversity and the structure of fish assemblages based on this observation alone

Summary

Introduction

Due to their isolated position, oceanic islands harbor some of the last near-pristine marine ecosystems and associated fish assemblages [1,2] Anthropogenic pressures, such as fishery, pollution, and the introduction of invasive species, threaten, many of these already fragile marine communities, and sound evidence-based management is required to protect them from extinction [3,4]. Among these oceanic islands, the Galapagos archipelago is key due to its exceptionally rich biodiversity and its role as stepping stone between the Tropical Eastern and Central Pacific [5,6].

Objectives

Methods

Results

Discussion

Conclusion