Kelp forests, which dominate temperate, coastal rocky shores, are declining around the world. Causes are local (nutrients, fishing) and global (ocean warming and its effects) effects of humans.
As reported in 2016 in the journal PNAS, a team of international experts have compiled and analysed a data set of kelp abundance at more than 1,000 sites across 34 regions around the globe. 38% of the world’s kelp forests have declined, 25% have increased in abundance; but there are many regions where kelp exists for which there are data and simply no idea of the health of the ecosystems.
Australia’s kelp forests feature heavily among the declining populations demonstrating a phenomenon known as “tropicalisation” of ecosystems. Tropicalisation occurs as ocean waters warm and tropical species start making a home in habitats previously dominated by cold-water species. In the case of NSW kelp forests, these tropical intruders are herbivorous fishes that eat the kelp – sometimes down to the ground.Kelp forests form the Great Southern Reef which stretches from Queensland to Western Australia and contributes more than A$10 billion annually to the Australian economy. In Western Australia kelp forests were wiped out during an extreme marine heatwave, which was probably a consequence of climate change. In South Australia, the kelp has succumbed to years of pollution from nutrient-rich wastewater. In Tasmania, ocean warming has enabled a kelp-eating sea urchin to jump from the mainland and graze on local kelp forests. This was compounded by overfishing of large lobsters, which normally eat the urchins.