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Seabirds Drive Invertebrate Communities

Scientists in New Zealand have recently revealed the diversity of invertebrates living on an island which has never been invaded by mammalian predators, and a surprising association with seabirds. Adams Island is the southern island in the Auckland Islands group. Whereas the main Auckland Island has been invaded by mice, cats and pigs, during a colourful history of attempted settlement at Hardwicke, Adams Island was spared. The biota of Adams Island have thus continued to evolve to this day in the absence of the severe negative effects of introduced mammals. The island provides a working template for what island restoration in the Southern Ocean could aspire to, on places such as nearby Antipodes Island should mice be successfully eradicated.

Adams Island - to the right of Carnley Harbour

Adams Island – to the right of Carnley Harbour (Photo: L. Mead & T. Nicklin)

The scientists used a grid of pitfall traps to sample the invertebrates. They collected 11 different invertebrate orders and a staggering 20 different species of beetles (Coleoptera). Adams Island is also famous for its seabird colonies, including a stronghold of Gibson’s wandering albatross generally extirpated from the main Auckland Island. The scientists found a strong association between the types of invertebrates found, and the density of seabird nests nearby. The reason for this surprising relationship is that seabirds transport nutrients from the marine environment to their nest sites where they are promptly ‘deposited’ all around their nests, providing a nutrient rich resource for the invertebrates. This nutrient transportation across the marine-terrestrial interface is so important that it actually subsidises the entire island ecosystem, as the nutrient importation benefits flow-up the entire food chain like a fountain. It was for this very reason that seabird islands in the past were mined for guano to be used as fertiliser. The work is published in the journal Polar Biology.