Deceiving the Naked Eye: Marine Invasive Species

Guest blog by Adam Obaza – Paua Marine Research Group

Invasive species can have nasty effects on local ecosystems. Disturbingly, increased commerce and travel have led to an exponential increase in species introductions. Instead of spending precious blog-space on rehashing that information, I will point you towards a few pieces of literature and be on my way (Pimental et al 2005; Charles and Dukes 2008; Simberloff 2013).

One reality of studying coastal ecosystems is that major changes don’t always appear in an obvious way. I always expected changes in species composition from human-driven causes, such as the introduction of an exotic species that grows in number to a point that it affects other species, would announce themselves in some loud manner, making it impossible for even casual observers to miss.  In some cases, this is true: a local example is the expansion of Sargassum horneri at Catalina Island. However, the opposite is frequently true as well.

I’ll be honest, this little piece of roadkill didn’t look like ecosystem collapse

I’ll be honest, this little piece of roadkill didn’t look like ecosystem collapse. Photo by Adam Obaza.

I completed my graduate work in the Florida Everglades and spent many hours traipsing through waist-deep water learning about seasonal movements of tiny fish. It was during this time that the python invasion in the region was getting a lot of press (mom was not thrilled). This invasion was likely caused by irresponsible pet owners purchasing tiny snakes only to find out they can live for many years and grow to sizes capable of eating their dog or small child. This realization led to many snakes being unleashed in the local wetland where they had few predators, plenty of food and time to make baby snakes. During all my hours in the Everglades, I only saw a single python. It was small and had been run over by a car. This low encounter rate was definitely contrary to the news media giving the impression I would have to shovel them out of the way to walk just a few feet. Despite their lack of visibility, pythons had been eating all of the small mammals in the Everglades (seriously – Dorcas et al 2012). It was an excellent lesson in not trusting your own anecdotal observations to make determinations on ecosystem changes.

An ongoing challenge in management of invasive species is generating public interest. It’s true that government agencies should create and enforce policies that reduce the likelihood of a species introduction. In many cases, they are. The National Oceanic and Atmospheric Administration and California Department of Fish and Wildlife developed a Caulerpa Control Protocol to avoid another introduction of the aggressive seaweed eradicated in the early 2000s and the California State Lands Commission is in the process of implementing one of the world’s first hull fouling policies. However, a diverse group of stakeholders that includes the public can further the prevention and early detection efforts that are paramount in managing invasive species. As per the previous paragraph, this task is made more difficult by the often low-key manner in which non-native species can establish themselves. How can you communicate the sense of urgency without Hollywood level impacts? I believe the answer (at least partially) is to think more like a detective and less like a disaster-relief worker.

To understand what I mean, head to your local marina. The water will be populated by many floating structures. Take a walk down one (a public one, please. I am not responsible for trespassing!) and check out the dock section below the waterline. Most likely, there will be many little invertebrates growing. These are known as fouling species and are frequently a nuisance to boaters as they recruit to their hulls and increase drag and negatively affect steering. Turns out, most of those invertebrates are non-native. The native critters that inhabit bays and harbors in Southern California are less adept at exploiting these artificial habitats than invertebrates introduced through hull fouling or other means. So there you go, without knowing it you have probably walked by countless non-native species on strolls through the marina.


The last picture from many a smart phone. Photo by Adam Obaza.

But the story doesn’t end there. If the non-native invertebrates stayed on the docks, it probably wouldn’t be cause for concern. But you may have guessed I wouldn’t be sharing this information if that was the case. Look at the pictures above and below. Above, you might notice some red frilly stuff. That’s actually a bryozoan called Watersipora subtorquata. It’s an introduced species and grows in just about every harbor in Southern California and has even been seen on reefs in Monterey Bay. I’ve also seen it growing on eelgrass (below), which is super important in creating fish habitat, cycling nutrients and preventing erosion. Unfortunately, I can’t tell you the exact impact of Watersipora on eelgrass. To my knowledge, it has not been researched. Anecdotally, most eelgrass with Watersipora growing on it looks to be in poor shape, but the bryozoan could just be taking advantage of eelgrass that was already dying. Studies on fouling species and eelgrass in other parts of the world have shown negative effects (Wong and Vercaemer 2012). What’s the message here? Watersipora is just one of many non-native species that grow on these artificial structures and could well negatively affect one of the most important marine habitats in Southern California.

Watersipora subtorquata growing on eelgrass

Watersipora subtorquata growing on eelgrass. Photo by Adam Obaza.

How does this relate to being an invasive species detective? Learn what species naturally occur in southern California, and some that don’t. Check out some of the great resources online (listed below) and enhance your knowledge base. And finally, get involved with productive groups like Los Angeles Waterkeeper, that are taking some great steps to understand the local marine ecosystems.


Literature Cited

Charles, H. and J.S. Dukes. 2008. Impacts of invasive species on ecosystem services. In Biological Invasions 217-237. Springer Berlin Heidelberg.

Dorcas, M.E., J.D. Willson, R.N. Reed, R.W. Snow, M.R. Rochford, M.A.Miller, W.E. Meshaka, Jr., P.T. Andreadis, F.J. Mazzotti, C.M. Romagosa, and K.M. Hart. 2012. Severe mammal declines coincide with proliferation of invasive Burmese pythons in Everglades National Park. Proceedings of the National Academy of Sciences 109(7): 2418-2422

Pimental, D., R. Zuniga and D. Morrison. 2005. Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecological Economics 52(3): 273-288

Simberloff, D. 2013. Invasive species: what everyone needs to know. Oxford University Press.

Wong, M.C. and B. Vercaemer. 2012. Effects of the invasive colonial tunicates and a native sponge on the growth, survival and light attenuation of eelgrass (Zostera marina). Aquatic Invasions 7(3): 315-326

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