Niche partitioning in the Fiordland wrasse guild

Abstract

Niche space is a useful indicator of trophic diversity in marine ecosystems. Here we describe the characteristics of realized niche space of 3 sympatric labrids (Notolabrus celidotus, Notolabrus fucicola, and Pseudolabrus miles) in Fiordland, New Zealand. We investigate physical niche through relationships between environmental parameters and patterns in abundance at a regional scale. Abundances of P. miles and N. fucicola were best associated with high salinity, wave-exposed areas (r 2 = 0.637, 0.372 respectively) while N. celidotus was positively correlated with calm semi-estuarine conditions (r 2 = 0.452). Variation in biological habitat descriptors of wrasse abundance provided evidence for differences in the environmental correlates for abundance among species, though all were positively correlated with abundance of macroalgae (Ecklonia radiata). Stable isotope analysis identified individual variability in trophic position among species by revealing that P. miles fed at a significantly higher trophic level and had a higher percentage of macroalgae in their composition of basal organic matter than N. celidotus and N. fucicola. N. celidotus had a significantly higher dispersion of individual trophic levels and percentage macroalgae than P. miles and N. fucicola, indicating a broader trophic niche. Isotopic results were supported by prey choices identified in gut content analysis and qualitative observations of tooth morpho logy. In Fiordland, N. celidotus is a generalist species, successfully exploiting a range of resources along the gradient from inner to outer fjord habitat, while P. miles and N. fucicola are relatively specialized to wave-exposed coastal habitats. These methods provide a useful approach to the quantitative comparison of niche breadth among species. © 2012 Inter-Research.