Amphidromy Links a Newly Documented Fish Community of Continental Australian Streams, to Oceanic Islands of the West Pacific

BACKGROUND: Indo-Pacific high island streams experience extreme hydrological variation, and are characterised by freshwater fish species with an amphidromous life history. Amphidromy is a likely adaptation for colonisation of island streams following stochastic events that lead to local extirpation. In the Wet Tropics of north-eastern Australia, steep coastal mountain streams share similar physical characteristics to island systems. These streams are poorly surveyed, but may provide suitable habitat for amphidromous species. However, due to their ephemeral nature, common non-diadromous freshwater species of continental Australia are unlikely to persist. Consequently, we hypothesise that coastal Wet Tropics streams are faunally more similar, to distant Pacific island communities, than to nearby faunas of large continental rivers. METHODS/PRINCIPAL FINDINGS: Surveys of coastal Wet Tropics streams recorded 26 species, 10 of which are first records for Australia, with three species undescribed. This fish community is unique in an Australian context in that it contains mostly amphidromous species, including sicydiine gobies of the genera Sicyopterus, Sicyopus, Smilosicyopus and Stiphodon. Species presence/absence data of coastal Wet Tropics streams were compared to both Wet Tropics river networks and Pacific island faunas. ANOSIM indicated the fish fauna of north-eastern Australian coastal streams were more similar to distant Pacific islands (R = 0.76), than to nearby continental rivers (R = 0.98). MAIN CONCLUSIONS/SIGNIFICANCE: Coastal Wet Tropics streams are faunally more similar to distant Pacific islands (79% of species shared), than to nearby continental fauna due to two factors. First, coastal Wet Tropics streams lack many non-diadromous freshwater fish which are common in nearby large rivers. Second, many amphidromous species found in coastal Wet Tropics streams and Indo-Pacific islands remain absent from large rivers of the Wet Tropics. The evolutionary and conservation significance of this newly discovered Australian fauna requires clarification in the context of the wider amphidromous fish community of the Pacific

Map of the West Pacific freshwater fish communities used in analyses.

<p>Map indicating the Wet Tropics of north-eastern Australia, in relation to Papua New Guinea and West Pacific island groups. Open circles denote regions were freshwater fish communities were included for analyses.</p

Life histories of West Pacific freshwater fish communities.

<p>Proportion of the freshwater fish community from differing sub-regions of the West Pacific that display an amphidromous life history (solid bars) and are non-diadromous (open bars).</p

Phenogram of West Pacific freshwater fish communities.

<p>Phenogram derived from a Bray-Curtis similarity matrix of presence/absence data of freshwater fish fauna from sub-regions of the West Pacific (Key: <b>PNGR</b>  =  Papua New Guinea rivers, <b>WPIS</b>  =  West Pacific island streams, <b>WTR  = </b> Wet Tropics rivers, <b>WTS</b>  =  Wet Tropics streams, <b>CWTS</b>  =  coastal Wet Tropics streams).</p

Physical characteristics of five coastal north-east Australian Wet Tropics streams.

<p>Physical characteristics of five coastal north-east Australian Wet Tropics streams.</p

Map of study sites in north-eastern Australia.

<p>Location of five study sites in the Wet Tropics of north-eastern Australia. Solid triangles denote where freshwater fish surveys were conducted.</p

MDS ordination of West Pacific freshwater fish communities.

<p>Two-dimensional MDS ordination of freshwater fish assemblage presence/absence data for sub-regions of the West Pacific.</p

Species richness of family groups in coastal north-east Australian Wet Tropics streams.

<p>Species richness of family groups in coastal north-east Australian Wet Tropics streams.</p

Species richness of coastal north-east Australian Wet Tropics streams.

<p>*A - previously recorded in Australia; B - new species occurrence to Australia, i.e. from Thuesen <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026685#pone.0026685-Thuesen1" target="_blank">[23]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026685#pone.0026685-Thuesen2" target="_blank">[24]</a>, Ebner & Thuesen <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026685#pone.0026685-Ebner1" target="_blank">[25]</a> and current study. # Species shared with Pacific island groups.</p><p>∧0 = species absent from site; 1 =  species present at site.</p

ANOSIM of West Pacific fish communities.

<p>R-stat values for pairwise ANOSIM comparisons of the fish assemblages from differing sub-regions of the West Pacific. N.B. Significant differences are represented by *<i>P></i>0.05, ** <i>P></i>0.01. Global R = 0.852 *. (Key: <b>PNGR</b>  =  Papua New Guinea rivers, <b>WPIS</b>  =  West Pacific island streams, <b>WTR  = </b> Wet Tropics rivers, <b>WTS</b>  =  Wet Tropics streams, <b>CWTS</b>  =  coastal Wet Tropics streams.</p