Comparative physiological studies on the growth of cryptic species of Bostrychia intricata (Rhodomelaceae,Rhodophyta) in various salinity and temperature conditions

Inter‐ and intra‐specific physiological variations of intertidal macroalgae have been well investigated. However, studies on physiological responses of cryptic algal species have been poorly documented. Bostrychia intricata is a widespread marine red alga in the Southern Hemisphere, and has many cryptic species. We investigated the effect of different salinities and temperatures on the specific growth rate of three cryptic species (N2, N4 and N5) of B. intricata from New Zealand. Our data indicated that all cryptic species grew at the full range of salinities and temperatures tested, but exhibited a significant difference in their specific growth rates. Cryptic species N4 had a higher growth rate than the other two cryptic species under all experimental conditions, whereas cryptic species N2 occasionally showed a higher growth rate than cryptic species N5 at high salinities and lower temperatures. The distinct physiological properties of these cryptic species may explain their distribution pattern (a wider distribution of cryptic species N4 than N2 and N5) in New Zealand. The physiological divergence between the cryptic species could be related to their levels of evolutionary divergence, with more similar physiology between cryptic species, which share a more recent common ancestor (N2 and N5). Our findings underline that morphologically indistinguishable cryptic algal species are different in many other aspects and are truly independent entities.