In Tasmania, the continued expansion of the Longspined Sea Urchin (Centrostephanus rodgersii) is one of the biggest challenges facing marine scientists and fisheries. As the urchin population shifts southwards in response to climate change, valuable and diversity-sustaining kelp habitat is rapidly destroyed, leading to the desertification of underwater landscapes. The resulting urchin barrens are unable to support populations of commercial fishery species such as abalone and rock lobster and the transformation to barren can see the loss of up to 150 native species.
The Southern Rock Lobster (Jasus edwardsii) has long been lauded as a potential predatory control mechanism for these urchins on the East Coast of Tasmania. However, with the conversion rate of reef to barren increasing at around 10% a year, it is critical we review the efficacy of current control methods.
Using experimental feeding trials, we investigated lobster prey preference to determine how likely lobsters are to prey on Longspined Sea Urchins when offered a choice of other native prey species. We found that the invasive Longspined Sea Urchins were the least preferred prey type for Southern Rock Lobsters (3.8% predation events), when compared to three local species: Black-lipped Abalone (Haliotis rubra;36.6%), Shortspined Sea Urchins (Heliocidaris erythrogramma;32.6%) and Periwinkles (Lunella undulata;27%). On top of this, we also found that habitat origin and potentially naivete of lobsters to the Longspined Sea Urchin affected urchin consumption with 85% being consumed by lobsters collected from extensive urchin barrens.
Low predation rates on Longspined Sea Urchin suggest that resident lobsters are unlikely to control further barren expansion unless a behavioural shift occurs. Results imply that control potential of Longspined Sea Urchins by Southern Rock Lobsters has previously been overestimated. Additional control methods are needed to safeguard ecological communities and important commercial fishery stocks from this climate change-induced, range-extending pest species.