The Footprint of Continental-Scale Ocean Currents on the Biogeography of Seaweeds

Thomas Wernberg,Mads S Thomsen,Bayden D Russell,Carlos F D Gurgel,Craig Sanderson,Gerald T Kraft,Jonathan M Waters,Sean D Connell,Giuseppe C Zuccarello,John A West

doi:10.1371/journal.pone.0080168

Abstract

Explaining spatial patterns of biological organisation remains a central challenge for biogeographic studies. In marine systems, large-scale ocean currents can modify broad-scale biological patterns by simultaneously connecting environmental (e.g. temperature, salinity and nutrients) and biological (e.g. amounts and types of dispersed propagules) properties of adjacent and distant regions. For example, steep environmental gradients and highly variable, disrupted flow should lead to heterogeneity in regional communities and high species turnover. In this study, we investigated the possible imprint of the Leeuwin (LC) and East Australia (EAC) Currents on seaweed communities across ~7,000 km of coastline in temperate Australia. These currents flow poleward along the west and east coasts of Australia, respectively, but have markedly different characteristics. We tested the hypothesis that, regional seaweed communities show serial change in the direction of current flow and that, because the LC is characterised by a weaker temperature gradient and more un-interrupted along-shore flow compared to the EAC, then coasts influenced by the LC have less variable seaweed communities and lower species turnover across regions than the EAC. This hypothesis was supported. We suggest that this pattern is likely caused by a combination of seaweed temperature tolerances and current-driven dispersal. In conclusion, our findings support the idea that the characteristics of continental-scale currents can influence regional community organisation, and that the coupling of ocean currents and marine biological structure is a general feature that transcends taxa and spatial scales.

Highlights

Understanding how regional-scale processes contribute to geographic structuring of biodiversity is challenging because many possible environmental drivers often correlate across broad spatial scales
The present study shows a strong imprint of continental-scale ocean currents on the biological community structure of seaweeds across temperate Australia, with high community variability and rapid regional species turnover coinciding with large-scale heterogeneity of current patterns and a strong temperature gradient
Our study adds to the increasing support for the idea that broad-scale patterns of species distribution and community structure can be mediated by a combination of well-known temperature gradients and less-studied flow patterns [11,13]

Summary

Introduction

Understanding how regional-scale processes contribute to geographic structuring of biodiversity is challenging because many possible environmental drivers often correlate across broad spatial scales. In addition to documenting biogeographic patterns, distance decay curves provide insights into the nature of the processes which underpin these patterns, through variation in the rates of distance decay of community similarity – species turnover - between geographical regions [1,2]. Temperature, in particular, has been invoked to explain biogeographic patterns for centuries [5,6]. These early accounts are supported by contemporary quantitative studies which show how temperature can be a strong predictor of spatial changes in species composition and biodiversity [7,8,9,10]. Marine biogeographers have drawn attention to the role of physical connectivity mediated by current flow and water movement, even across large distances [11,12,13,14]

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Discussion

Conclusion