(Invasive Species + Marine Ecosystems) x Climate Change = Ocean Commotion?

That's right folks, the national press is true. Invasive species aren't limited to the terrestrial environment and so this blog shouldn't be either. For now, we're waving goodbye to dry land and waving hello to some, erm... waves?

As Hannah Mallinson touched upon in her blog, our oceans are facing a number of threats, including the 'deadly trio':  ocean acidification, ocean warming and deoxygenation (Bijma et al. 2013). But this is an invasive species blog so..

Successful marine invasions can significantly modify ecosystem structure, trophic networks and even cause local extinctions of natives (Artioli et al. 2013). This can have a large impact when considering a broader picture, with potential disruptions to ecosystem functions and ecosystem services (the functions that humans make active use of) such as fisheries (which already also face numerous threats). 

The connections are everywhere

But why are marine ecosystems suffering invasions? Well one reason, luckily enough for a blog on the subject of 'Global Environmental Change', is climate change. But as we will see, just like last week, humans can also play a direct role.

Climate change and invasive species are among the most serious marine ecosystem threats (Cockrell and Sorte, 2013). As a combination, climate change can lead to ocean warming (remember the 'deadly trio'?) which can accelerate invader growth rate and fecundity (Dijkstra et al, 2011). 

This phenomenon has recently been investigated by Cockrell and Sorte (2013) in the marine epibenthic community of Bodega Harbor, California. The Harbor has experienced increases in water temperature and invasive species abundance over the last 35 years, meaning that the ecosystem community is currently ~70% non-native (Sorte and Stachowicz, 2011).

The invasive tunicate Botryllus schlosseri first appeared off the Californian coast in the 1940s (Cohen & Carlton, 1995). Cockrell and Sorte's data indicate that its growth rate increases with increasing water temperature, so much so that at a temperature increase of 4°C could, in favourable conditions, cause a 19 fold population increase in 90 days. 

Botryllus schlosseri, close up on right.

Given its highly invasive and cosmopolitan nature, implications of the potential B. schlosseri population explosion are extremely serious worldwide. One ecosystem service that could suffer is aquaculture. Fouling organisms such as B. schlosseri encrust manmade structures used in aquaculture and can out-compete commercial species such as oysters and scallops, leading to reduced aquaculture yields (Rosa et al. 2013).

Tunicates have invaded many other countries coastal waters in recent decades. They usually arrive on ship's hulls or in ballast water (what is it with us humans instigating these invasions...?) They can also be introduced via mollusc shells brought in for marine cultivation. One region experiencing this issue is the Mediterranean (see section on Ascidians if your interest has been piqued). 

Invasive species are by no means our oceans' biggest threat, but they certainly represent one. Their importance is evidenced by the fact that marine ecosystem invasion susceptibility was raised at 2013's European Geosciences Union General Assembly. The issue will likely become evermore prevalent as climate change continues to make marine ecosystems increasingly invadable, thus it is more than worthy of our attention now.

Over and out

The Invader Inspector