Impact of small-scale environmental perturbations on local marine food resources: a case study of a predator, the little penguin

Abstract

Although the impact of environmental changes on the demographic parameters of top predators is well established, the mechanisms by which populations are affected remain poorly understood. Here, we show that a reduction in the thermal stratification of coastal water masses between 2005 and 2006 was associated with reduced foraging and breeding success of little penguins Eudyptula minor, major bio-indicators of the Bass Strait ecosystem in southern Australia. The foraging patterns of the penguins suggest that their prey disperse widely in poorly stratified waters, leading to reduced foraging efficiency and poor breeding success. Mixed water regimes resulting from storms are currently unusual during the breeding period of these birds, but are expected to become more frequent due to climate change.

Figure 1.

Location of the study site showing the major currents liable to influence the waters of the Bass Strait (excerpt from Google Earth).

Figure 2.

Temperature profiles (lines) of the water masses around Phillip Island, Australia, recorded by miniature bio-loggers attached to foraging little penguins. Note the clear thermal stratification of the water in (a) 2005 (with a thermocline around 20–25 m), compared with the situation in (b) 2006, a weak El Niño year (see text). Bars indicate the distribution of those depths where penguins encountered prey (bars at 0–10 m are not represented as the index of prey encounter at these depths is influenced by biomechanical factors related to the buoyancy of the animal).