Cryptic species in sympatry: nonrandom small-scale distribution patterns in Bostrychia intricata (Ceramiales, Rhodophyta)

Sympatric coexistence of cryptic species, indistinguishable morphological taxa, has increasingly been detected on the basis of molecular data. This discovery raises the interesting question of how cryptic species can coexist, as hypothetically they would need identical ecological resources. The red alga Bostrychia intricata is commonly found along New Zealand shores. Previous studies indicated several cryptic species within this morphospecies, and that some populations have multiple species. This study aimed to determine how coexisting cryptic B. intricata distribute at a small scale. Along the shore of Moa Point, Wellington, we conducted intensive sampling of B. intricata in different habitats with respect to tidal position, wave and sun exposure levels. Our genetic data clearly documented the coexistence of three cryptic species of B. intricata: N2, N4 and N5. Multiple samples from individual algal patches indicated that each patch was made of the same ramet. Our analyses revealed a habitat-related pattern in small-scale distribution of different cryptic B. intricata, suggesting that the distribution of these cryptic species was not random. Cryptic species N4 was found at a higher tidal position than species N2 and N5, whereas cryptic species N2 occurred in more wave-exposed areas than the other species. Discriminant analysis indicated that tidal height strongly influenced the distribution pattern among these cryptic species. Our observations demonstrated that the co-occurrence of three cryptic B. intricata can partly be explained by their occupation of different intertidal habitats, highlighting the nonrandom distribution of coexisting cryptic algal species.