This week in lab the class split and went out to two different Vancouver marinas in order to investigate the distribution of an invasive colonial tunicate called the Golden Star tunicate (Botryllus schlosseri). Tunicates are a marine invertebrate that, strangely enough, are closely related to us (the vertebrates). To learn more about the biology of tunicates click here. This locally invasive tunicate is found in the fouling communities of the Vancouver area. It has multiple colour morphs including the dark and orange shown at the bottom of the page.
As shown to the left, fouling species are ones that grow on man made surfaces, such as on the side of this marina by Jericho beach, on docks and anchored boats. This includes non-moving animals like mussels, barnacles, sponges, hydroids, and tunicates; and the predators that feed on them such as polychete worms, sea stars, limpets and many others. If you look closely at this picture you can see a purple and pink sea star not too far under the water.
Invasive species such as the Golden Star tunicate generally have negative effects on the new environment in which it establishes. They disturb native species and harm important ecological interactions and food webs. Arrival can occur due to human actions or from the natural advancement of nearby species. The green crab (Carcinus maenas), for example, came to BC in 1999 and has since then multiplied to greatly displace the local Dungeness crab. Other invasive species that are important in freshwater fouling communities are the Zebra and Quagga mussels. These are currently a warning species since they have not become fully established in BC or spread down to the North Western states of the USA. Therefore the more people that know about these species the more likely their expansion can be prevented. For more information on all types of invasive plants and animals in BC go to: bcinvasives.ca
While the Golden Star tunicate is found throughout the coasts of BC, of the two sites that we surveyed it could only be found in one. The tunicate was collected from the marina at Coal harbor. A difference in salinity is one hypothesis for why we could only locate it one, however there are many other factors that could have a large influence on its distribution. Coal harbor is a more sheltered site farther away from the estuary with the Fraser River, therefore it is less impacted by the rush of freshwater from the river as it meets the ocean. We will hopefully be doing a comparison of the salt content in the sea water from the two locations and possibly other experiments in order to see if we can gain some insight into the factors influencing the distribution of this invasive tunicate.