The composition and resilience of rockpool fish assemblages on the central Hawke's Bay coast New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University

Abstract

Fish assemblages in rockpools on two intertidal platforms on the Central Hawke's Bay coast of New Zealand were studied from June 2000 to March 2001. Twenty-four species belonging to 14 families were collected from 226 rockpool censuses. The Tripterygiidae were the most speciose family, represented by 7 species. Fifty-seven percent of the total number of fish captured (n = 6133) belonged to a single species, the robust triplefin Grahamina capito. Common subtidal species contributed significantly to the taxocene, indicating that much of the rockpool fish fauna is an extension of that in the shallow subtidal fringe. However, two specialist intertidal species (Acanthoclinus fuscus and Bellapiscus medius) were relatively abundant in the collections. Significant relationships between rockpool fish assemblage structure, and rockpool habitat structure were discovered. Richness, abundance and biomass were generally greater in large pools with lots of shelter, located close to the low-tide mark. Further analysis revealed that assemblages in these pools contained many partial residents that were uncommon or absent from rockpools higher on the shore. Seasonality in the structure of rockpool fish assemblages was related primarily to recruitment events. During late spring and early summer, the abundance and density of resident species increased markedly as the result of an influx of settling larvae. However, species richness remained stable over the sampling period, probably because transient subtidal species (with the exception of the labrid, Notolabrus celidotus) did not contribute significantly to the rockpool fish community. The rockpool fish community appeared to be resilient: taxocene structure re-established between collection events. However, the level and rate of resilience appeared to be lower than described in other studies, as the effects of sampling were still measurable after 3-months. The recovery of richness, abundance and biomass of fish was seasonally dependent, being slow in winter and spring, but rapid during summer. Specialist intertidal species were generally the best recolonisers, whereas partial resident species were poor recolonisers, and relied mainly on larval recruitment to colonise rockpools.