| Summary: | Maintenance and Update Frequency: notPlanned Statement: We selected eight geographically proximate and environmentally similar islands in Cook Strait, New Zealand to investigate long-term changes in nitrogen stable isotopes levels across islands with different restoration treatments: never-invaded islands - Takapourewa/Stephens and Kuru Pongi/ Middle Trio, invaded islands - Moutiti/Victory and Tawhitinui, eradicated islands - Wakaterepapanui and Nukuwaiata, and actively seabird restored islands - Te Hoiere/Maud and Mana. Each island was originally sampled for a stable isotope study in 2006/07 by Jones (2010b) and we re-visited each island in 2022 for this study. Soil, plant (taupata - Coprosma repens, karamu - C. robusta, and māpou - Myrsine australis) and spider (family Porrhothelidae) samples were collected from inside and outside seabird colonies (no burrows found within a 3m radius of the sampling location) at between 9 and 47 sampling locations on each island. At each sampling location soil and as many of the three plant species as were present were collected. Plants were sampled by picking three new growth leaves from separate individuals of the same species, if available. Soil was sampled by scraping back the litter layer and collecting approximately 100 g using a small hand trowel down to 10 cm depth. Up to three spiders were collected from inside and three from outside seabird colonies opportunistically on each island (because spider tunnels were not always present in each sampling locale) by digging up their tunnels. On each island with a seabird colony, we also collected three seabird guano samples. Spider samples were stored in 70% ethanol for transportation off the island. All samples were then washed in distilled water and oven dried at 60°C for 48 hours to prevent decomposition and in preparation for stable isotope analysis. Dried soil samples were passed through a 0.5 mm sieve, then all samples were hand ground to a fine powder using a mortar and pestle. Stable isotope analysis was conducted ...
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