Takashi Noda

Predator–prey interactions have long been recognized as important selective forces in the evolution and maintenance of multiple traits in both predators and prey. Certain animal species leave information intentionally or unintentionally, in the form of urine, faeces, feeding traces and chemical trails, even after they have moved. This residual information, left behind by animals, has the potential to affect predation efficiency. However, information warfare—the use of information between predator and prey, in which predators exploit prey cues to increase predation efficiency, while prey exploit predator cues to reduce it—remains largely unexplored, especially in the context of residual information. Marine gastropods leave a mucus trail that contains individual information as they crawl. In this study, we investigated the existence of information warfare between the predator snail Reishia clavigera and the prey limpet Siphonaria sirius through mucus trails. We observed the responses of predators and prey to their respective mucus trails under laboratory conditions. The predators followed the prey's mucus trails. In contrast, the prey exhibited movements, such as looping, upon confrontation with the predator's mucus trails. The looping behaviour reduced the probability of the predator reaching the endpoint of the prey's mucus trail. These results suggest a potential strategy whereby predators exploit prey mucus trails for localization, along with a counter‐strategy through which prey minimize the risk of detection. Our findings provide novel insights into how information shapes predator–prey interactions, indicating the potential existence of an information‐induced arms race.

There has been a limited number of studies on the effects of harmful algal blooms (HABs) on natural rocky intertidal ecosystems. From mid-September to early November 2021, an unprecedented HAB caused by Karenia selliformis hit the Pacific coast of southeast Hokkaido, Japan, for the first time, causing massive mortalities among marine organisms. To clarify the immediate impacts of the HAB on the abundance of 10 rocky intertidal species in four functional groups (macroalgae, sessile invertebrates, molluscan grazers, and molluscan carnivores), we focused on two questions: (1) How did the HAB affect the abundance of each species differently at the regional scale? and (2) How did the impacts of the HAB on the abundance of each functional groups vary spatially, and was the spatial variation of the HAB impacts related to the spatial distribution of the cell density of HAB species? To study these issues, we compared census data for 17 years before the HAB and within one month after it for five shores on the southeast coast of Hokkaido. The results showed that two macroalgae species and all three molluscan grazer species declined significantly after the HAB. Moreover, the decrease in molluscan grazers was significantly correlated with cell density. These results suggest that the impacts of the HAB in southeast Hokkaido on the abundance of rocky intertidal organisms are highly variable depending on species and locality, presumably because of differences in species-specific tolerances to HAB toxins and the spatial variation in the density of the HAB organisms.

To elucidate how the population dynamics of the acorn barnacle Balanus glandula transitioned after its invasion in 2000 along the Pacific coast of Japan, a population census was conducted from 2004 to 2014 at five shores along 49 km of coastline 144–193 km east outside of the invasion front. Survey areas at each shore consisted of five paired plots (cleared recruitment plots and control plots). Larval recruitment was first detected in 2004 but benthic individuals were not detected until 2 years later. The abundance and occurrence of B. glandula increased until around 2010; abundance then decreased but occurrence remained high (70%) until 2014, suggesting that the metapopulation of this barnacle approached a maximum around 2011. From 2011, the population dynamics of B. glandula changed considerably at two contrasting spatial scales: at a regional scale, the dependency of the number of larvae on stock size decreased, whereas at a local scale, the relative contribution of larval supply as a determinant of local population dynamics decreased. These findings suggest that the major driving force of population dynamics of the introduced barnacle changed in just a few years after invasion; therefore, population census data from just after an invasion, including larval recruitment monitoring just outside the invasion front, is essential to understanding invasion dynamics by sessile marine organisms.

Both natural and anthropogenic disturbances have significant impacts on populations in terrestrial and marine habitats. Despite evidence that population recovery after large‐scale disturbances in terrestrial habitats varies substantially among species depending on species traits and types of disturbance, little is known about interspecific differences in population recovery in marine habitats. In this study, we evaluated the course and status of recovery of the vertical distribution of nine intertidal sessile species over 6 years following the 2011 Great East Japan Earthquake. First, we characterized temporal changes in the vertical position of zonation as the spatial distribution, and total coverage as the local population size after the 2011 earthquake. Then, we evaluated the differences in successional status that explain interspecific differences in zonation recovery speed. Finally, we revealed that temporal changes in the vertical position and abundance after the earthquake differed according to species. The interspecific differences in the speed of recovery of zonation after 2014 were correlated with successional status, with later successional species having a delayed recovery rate. These results indicated that intertidal sessile assemblages continued to change 6 years after the large earthquake, suggesting that evaluations of the impacts of disturbances on assemblages and the course of community recovery require long periods of time.

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