The secret lives of mangroves: Exploring New Zealand's urban mangroves with integrated biodiversity assessments

Abstract

Integrated biodiversity assessments were conducted at four mangrove sites bordering urban parks in the Manukau Harbour, Auckland, New Zealand. Mangrove habitat complexity was also surveyed. Sites selected were adjacent to areas of mangrove removal between 2010 and 2018. Assessments were conducted in late summer 2018 and with a duration of one week per site. This study provides a snap-shot of biodiversity within mangroves and a baseline dataset on many species little studied in these habitats. A wide-range of equipment and techniques were used in order to record both terrestrial and marine vertebrates and invertebrates, through the least invasive methods. Forty-nine arboreal arthropod, fifteen bird, six mammalian, two fish, two crab, one shrimp, one gastropod, one jellyfish and one amphipod species were recorded in the study period. Results show much heterogeneity in terms of habitat complexity among sites. Habitat complexity parameters of adult tree density, average crown spread and height of adult trees explained 39% of arboreal arthropod abundance at the sites. Sites with lowest tree density, height and greatest crown spread had the highest relative abundance of arboreal arthropods. There was a significant difference between species richness of arthropods among sites, and sites with lowest adult tree density have the greatest richness. All eleven habitat complexity parameters contributed 34.4% of overall differences in richness among sites. Area of connected mangrove was negatively correlated with both arboreal arthropod abundance (r2 = 0.77) and richness (r2 = 0.99). This research shows that mangroves are important habitats for a wide variety of both native and non-native animal species in New Zealand. Simple non-invasive techniques can be used to record different species occupying mangroves throughout tidal cycles. Long-term integrated ecological monitoring is required in these habitats and removal of mangrove should be considered on a site-by-site basis.