Distinctive invertebrate assemblages in rockface seepages enhance lotic biodiversity in northern New Zealand

Abstract

We measured water quality, recorded physical habitat characteristics and collected aquatic invertebrates from 17 rockface seeps, five springs and five streams in a geologically diverse region of New Zealand’s North Island to investigate factors influencing invertebrate distribution and community composition within and among these habitats. A total of 147 aquatic invertebrate taxa was found; 84 taxa occurred in seepage samples and 53% of these were found only in those habitats, including several new species. Where paired stream-seepage comparisons could be made, seeps contributed on average 35% of new species to the total species pool. The invertebrate faunas of all habitats were dominated taxonomically by Trichoptera and Diptera, but seepages were relatively depauperate in Ephemeroptera and richer in Coleoptera taxa compared to streams and springs. Seepage faunas were dominated numerically by Mollusca, and had lower percent abundance of aquatic insects (23% overall) compared to springs (77%) and streams (93%). Seepages underlain by different geologies generally had distinct water quality signatures, with seeps draining greywacke, sandstone and volcanic rocks grouping close to their receiving streams in a Principal Component Analysis. Seepage invertebrate community composition reflected underlying geology and associated differences in water chemistry, as well as seepage size and cover by moss. Incorporation of seepage habitats into conservation planning and aquatic ecosystem protection, and maintenance of their function and connectivity with lotic and groundwater ecosystems are important considerations for freshwater biodiversity management. Maintenance of riparian plant cover over seepages should help sustain supplies of organic matter, moss cover and shade, providing habitat complexity and low water temperatures.