Biology and invastion ecology of sessile animals

Sessile marine animals have lifestyles unseen in their terrestrial counterparts; studying their reproduction and development provides fascinating insights into the evolution of sex, gender allocation and ageing, while ascidians in particular can cast light on the origin of the vertebrates. Our work on reproduction has focussed on spermcast mating, a widespread process in sessile faunas that involves the release of sperm into the water to be taken up by conspecifics to fertilize eggs that have been retained rather than spawned, generally followed by brooding of the resulting embryos. One group of sessile animals combines this with the splitting of each embryo into multiple genetically identical copies that develop independently, a process termed polyembryony which seems hard to explain in evolutionary terms—an apparent paradox that we are investigating.

Non-native species, introduced beyond their natural geographical range by human activities, pose serious threats to native species and ecosystems and can damage both human health and economic interests. Sessile marine organisms, living attached to solid surfaces, are easily transported from place to place as fouling, and accordingly feature prominently in inventories of marine non-natives.