Predator snails fend off the invasion of barnacles in Japan
Introduced species can have tremendous ecological effects and . Invasion biology tries to understand the mechanisms that .
Through global shipping routes, barnacles have been . An example is the barnacle Balanus glandula, native to the North American Pacific coast and , where it has . From Honshu, B. glandula spread to eastern Hokkaido (northern Japan), .
Furthermore, B. glandula has reached as far as the Atlantic coasts of and , with negative effects on native barnacle populations and other seafloor dwellers.
Biotic resistance is the ability of native species to limit the spread of invasive species. Working as marine ecologists at , on the Pacific coast of Hokkaido (Takefumi Yorisue, Kyosuke Momota), and the , Saint Francis Xavier University in Nova Scotia (Julius A. Ellrich), we established an international collaboration to investigate the low B. glandula densities in Hokkaido rocky intertidal habitats.
Predatory and herbivorous snails
In Hokkaido, the native predatory snails Nucella lima—more commonly known as dogwhelks—and herbivorous snails, Lottia cassis, known as limpets, are common. Dogwhelks have a particular appetite for barnacles: . These NCEs are triggered by dogwhelk chemical cues that limit barnacle cyprid larvae settlement. Cyprids swim away from dogwhelk cues .
Research has shown that as limpets graze, . These actions, known as disturbance effects (DEs), also limit .
We hypothesised that the native dogwhelks and limpets would contribute to biotic resistance against B. glandula. To test our hypothesis, we conducted a series of experiments in Akkeshi Bay, in Hokkaido. We examined and .
Native dogwhelks and limpets
First, we compared dogwhelk feeding preferences for introduced and native barnacles by providing dogwhelks with similar-sized B. glandula and C. dalli individuals. We found that the dogwhelks preferred the introduced B. glandula over the local C. dalli. Next, we compared dogwhelk feeding preferences for large and small B. glandula individuals. We found that dogwhelks preferred large B. glandula individuals.
These preferences are likely driven by prey profitability: previous research with dogwhelks on the North American Pacific coast indicated that , and .
Our findings suggest that dogwhelk predation limits the B. glandula spread in Hokkaido, .
Population control measures
We examined the effect of dogwhelk NCEs on B. glandula settlement and population growth. For that, we installed cages with mesh compartments in the harbour of Akkeshi Marine Station. The cages prevented the dogwhelks from feeding on the barnacles, and we found that .
We conducted a similar experiment using limpets in a cage with the barnacles. We found that .
Employing native dogwhelks and limpets
Our results highlight that in the case of barnacles in Japan, predation and disturbance by native species are important ecological processes that can contribute to biotic resistance against introduced species. It is essential to understand such complex processes in order to protect native species that help to maintain biotic resistance. Without biotic resistance, it is more likely that introduced species—such as B. glandula—can spread and have negative effects on native species and communities.
Understanding biotic resistance can support local organisms in protecting their ecosystems against biological invasions, eliminating the need for more extreme measures.
Provided by The Conversation
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