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

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.

The 'Great Southern Reef': social, ecological and economic value of Australia's neglected kelp forests

“…The ecology of the GSR is shaped in large part by boundary currents that flow poleward along both coasts of Australia, transporting warm nutrient-poor water across Australia's temperate coastline (e.g. Wernberg et al 2013a). The Leeuwin Current flows southwards down the west coast and wraps along the southern coastline of the continent, whereas the East Australian Current extends down the east coast and penetrates along the east coast of Tasmania during summer (Condie and Dunn 2006).…”

“…Just as the Great Barrier Reef (GBR) is recognised as an entity made up of more than 2900 individual reefs dominated by corals (Day 2002), Australia's temperate reefs should be considered collectively as an entity made up of thousands of kilometres of rocky temperate reefs, dominated by kelp forests and interconnected through oceanographic (Coleman et al 2011;Wernberg et al 2013a), ecological (Irving and Connell 2006;Connell and Irving 2008;Vanderklift and Wernberg 2008) and evolutionary (Phillips 2001) processes -truly a Great Southern Reef (GSR). Here we show that lack of awareness and investment in research focussed on temperate reefs is at odds with the social, ecological and economic significance of the GSR.…”

Seaweeds in Two Oceans: Beta-Diversity

“…With the exception of the some Australian studies (Smale et al, 2010(Smale et al, , 2011Waters et al, 2010;Leaper et al, 2011;Wernberg et al, 2013), one in Europe (Tuya et al, 2012) and another two in the northwest Indian Ocean/Red Sea region (Schils and Wilson, 2006;Issa et al, 2016), studies of this scale and The partitioning represents the contribution of turnover and nestedness-resultant processes. Mean ± SD values are presented for the whole South African coast, as well as for each of the four bioregions.…”

“…It was recently suggested that studies which associate marine macroalgal distributional patterns with broad-scale temperature gradients neglect to consider alternative or additional explanations, such as that offered by connectivity due to ocean currents (Wernberg et al, 2013). It is possible that seaweeds are similarly influenced by ocean currents around South Africa, and it is temping to suggest that the direction of turnover along the east coast is from north to south, and along the south coast from east to west, as this would coincide with the direction of the Agulhas Current.…”

Life on the boundary: Environmental factors as drivers of habitat distribution in the littoral zone

“…Temperature has long been recognized as a key factor governing seaweed biogeography (e.g. Stephenson, 1944;Lewis, 1964;Lünning, 1984;Pakker et Anderson et al, 2012;Wernberg et al, 2013) and reproduction (Lüning, 1990;Ballesteros, 1991) and since it varies with latitude (Mieszkowska et al, 2006;Martínez et al 2012), it is often responsible for the distribution of northern/southern geographic boundaries of seaweeds (Breeman, 1988). Some mediolittoral habitats show a strong relationship with the seawater mean temperature gradient (17º-18.6º) from northern to southern Catalan waters.…”