Diversity and distribution of coralline algae in southern New Zealand

Abstract

Coralline algae (Corallinophycideae) are calcifying red algae that form the foundation of many shallow marine ecosystems globally, providing settlement sites for a range of invertebrate larvae, stabilisation of reefs and habitat for grazing and cryptofaunal species. This group of macroalgae are vulnerable to increased anthropogenic disturbances, in particular ocean acidification. Despite their ecological importance and vulnerability, little is known about their diversity, distribution and ecology, globally and within New Zealand. The primary objective of this work was to document the diversity and distribution of coralline algae in New Zealand, and examine the abiotic and biotic factors potentially influencing this distribution across different spatial scales. This body of work used DNA based phylogenetic methods to identify species of corallines collected in the southern region of New Zealand, incorporating data previously collected from central and northern New Zealand. A high level of diversity was revealed in southern New Zealand (77 species identified and 99 predicted), which is in line with what is currently being uncovered globally, with diversity that is two to four times higher than previously estimates that were based on morpho-anatomical identifications. Multivariate clustering and constrained ordination techniques, grouping sites based on similarities in coralline algae community structure and relating this to selected environmental parameters, identified sea surface temperature and light at the seabed as variables significantly correlated with these community groupings across the New Zealand region. Similarly, linear model analysis identified depth, likely a proxy for light, and the type of substrate as being the most important variables explaining the abundance of coralline algae (independent of species identity) across an often overlooked biogenic environment across Foveaux Strait. At local spatial scales (10-100's m) patterns in coralline algal community structure revealed stochastic dispersal processes likely determine which species establish, followed by competitive interactions driving differences in abundances. These local scale processes are unlikely to influence diversity patterns seen at larger scales across the New Zealand region. Furthermore, high local scale diversity was observed, with few abundant and many rare species. This research provides an important molecular framework and information on distributional patterns of coralline algae needed to further advance knowledge on this ecologically important group.