Abstract
Many species of birds breeding on ocean beaches and in coastal dunes are of global conservation concern. Most of these species rely on invertebrates (e.g. insects, small crustaceans) as an irreplaceable food source, foraging primarily around the strandline on the upper beach near the dunes. Sandy beaches are also prime sites for human recreation, which impacts these food resources via negative trampling effects. We quantified acute trampling impacts on assemblages of upper shore invertebrates in a controlled experiment over a range of foot traffic intensities (up to 56 steps per square metre) on a temperate beach in Victoria, Australia. Trampling significantly altered assemblage structure (species composition and density) and was correlated with significant declines in invertebrate abundance and species richness. Trampling effects were strongest for rare species. In heavily trafficked plots the abundance of sand hoppers (Amphipoda), a principal prey item of threatened Hooded Plovers breeding on this beach, was halved. In contrast to the consistently strong effects of trampling, natural habitat attributes (e.g. sediment grain size, compactness) were much less influential predictors. If acute suppression of invertebrates caused by trampling, as demonstrated here, is more widespread on beaches it may constitute a significant threat to endangered vertebrates reliant on these invertebrates. This calls for a re-thinking of conservation actions by considering active management of food resources, possibly through enhancement of wrack or direct augmentation of prey items to breeding territories.
Highlights
A bird came down the walk: He did not know I saw; He bit an angle-worm in halves And ate the fellow, raw
Here we examine whether intense human trampling acutely alters upper-shore invertebrate populations on a beach that supports a breeding population of the threatened Hooded Plover, Thinornis rubricollis
Anthropogenic habitat change resulting from recreational activities is widespread on sandy coastlines [4]
Summary
A bird came down the walk: He did not know I saw; He bit an angle-worm in halves And ate the fellow, raw. The two studies that could attribute changes in shallow-buried beach invertebrates to human trampling show declines in abundance for species of the middle and lower shore [7, 8]. It is, largely unknown whether—and to which extent—trampling may impact invertebrates on the upper shore where many shorebirds feed and human foot traffic is concentrated during high tides [9]
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