“Poster children” of invasion over-represented in marine research

Isabelle M. Côté is a professor of marine ecology and leads the Marine Ecology Lab, which engages in extensive applied research on marine ecosystems. A prolific researcher and skilled science communicator, she recently published her milestone 200th academic paper. She is currently Chair of SFU’s Department of Biological Sciences.

Over the past three decades her research has provided a comprehensive overview of ecological changes on coral reefs and of the effectiveness of Marine Protected Areas from Canada to the Caribbean, and influenced policy and practice for more effective management of shallow-water ecosystems.

She recently published Research biases create over-represented “poster children” of marine invasion ecology, along with PhD students Jillian Dunic, Hannah Watkins and Helen Yan, looking at what was missing from current research and understanding of non-native marine species. They conducted a comprehensive review of over 2200 academic articles, finding that the ecological impact of less than ten percent of the world’s non-native marine species had been studied. This represents a significant gap in knowledge about most marine invasive species, while creating a disproportionately well-known few that become representatives or “poster children” of marine invasion.    

Non-native marine species have been transported and introduced all over the world’s coastal oceans. They are increasingly recognized as a threat, yet not all are detrimental to their environments – some even have positive effects as environmental engineers or new sources of prey. Others, however, readily become invasive and compete with or prey upon native species, putting biodiversity and habitat at risk. The researchers argue that filling in the knowledge gap will help better address the threat of global marine invaders.

For the study, the researchers chose to focus on nine major groups of marine animals. These included well-known animals like corals, crabs, sea stars and fishes, but also lesser-known groups, like comb jellies, moss animals and tunicates - a type of jelly-like filter-feeders related to fishes.

Using the Institute of Scientific Information Web of Science database, they gathered original, English-language academic articles on non-native species collected within all invaded regions of the world. This initial, deliberately broad search yielded more than 28,000 hits, which had to be whittled down to articles that were directly relevant to the subject. From the remaining 2200 papers, the authors noted the location of study, the non-native species and habitat types examined, and whether the article assessed impact.

They then compared their list of species with the total number of non-native species from the World Register of Introduced Marine Species (WRiMS). They cross-referenced ranges and names to create a comprehensive, taxonomically corrected list of global marine introduced species.

The findings revealed that few of the introduced species in WRiMS had been studied, and many that had been studied were not listed in WRiMS, which is the largest global database for marine introduced species. Fishes and mollusks were the most studied of all non-native species, while only a handful of studies were found for sea stars and their relatives (e.g., sea urchins, sand dollars, etc.), and for comb jellies.

Most studies focused on basic general knowledge about non-native species, such as their ecology (i.e., what habitat they are found in; 41 percent of studies) and their geographic distribution (35 percent of studies).

More troubling is that relatively few studies – less than ten percent – measured the impact of introduced species on the native species found in the new habitat. Even fewer, just two percent examined the effectiveness of strategies to minimize these impacts. These types of studies are essential to understand, predict and manage marine invasions.

The researchers also found strong geographic biases in studies, with mismatches between the number of recorded non-native marine species and research effort. Given similar numbers of non-native species, some regions, such as the east coast of North America and northwestern Europe, are very well studied while polar and equatorial regions were understudied.

Additionally, the researchers identified species that were the most studied in each major group. In four of the groups, one species made up more than half of the literature, effectively acting as a “poster child” of invasion for that group. Examples of poster children included the sea walnut Mnemiopsis leidyi (for the phylum Ctenophora), the Northern Pacific sea star Asterias amurensis (phylum Echinodermata), the purse sponge Paraleucilla magna (phylum Porifera), and the Indo-Pacific lionfish Pterois volitans/miles (phylum Chordata).  

“Finding that non-native marine species are consistently understudied presents a concern both for the development of invasion ecology theory and for management and conservation,” concludes Côté. “Furthermore, there is a mismatch between the peer-reviewed literature and WRiMS – which is arguably the most comprehensive database of introduced marine species. We found studies for less than 40 percent of the species listed in WRiMS, while uncovering many papers on non-native species that were not listed in this database.”

Why are some species more studied than others? Côté suggests this bias is driven by the perceived large impact of species that have become well known to researchers and to the public. As a result, more investment is provided to aid in the management of the worst offenders. However, investing in just a few “poster children” of invasion ignores the many species that are not being investigated.

It means that marine managers must choose between assuming that “poster children” invaders are representative of all non-native species and spread their resources thinly across all invaders, or target the worst offenders while leaving marine ecosystems vulnerable to the potential impacts of other species.

Detecting and mitigating the potential damage caused by non-native marine species is a growing concern as the world becomes increasingly interconnected. In 2010, countries signatory to the Convention on Biological Diversity of the United Nations addressed the issue of filling the knowledge gap on invasive species and highlighted the urgency for greater understanding of their impacts.

Côté agrees a concerted effort from the scientific community is needed to address this information deficit, by diverting focus from the “poster children” toward understudied non-native species. “Studying a poorly understood non-native species could have greater value for effectively triaging species for management than a similar study on a species whose detrimental impacts are already known,” she says. 

“Only through diversifying research to a wider array of non-native marine species can we begin to build a stronger foundation upon which this growing threat can be confidently addressed.”