The effect of environmental gradient on biodiversity and similarity of invertebrate communities in eelgrass (Zostera marina) beds

Abstract

Environmental filtering and dispersal limitation are important processes within the metacommunity concept. Non-random species turnover occurs in places where environmental filtering plays the key role in determining local community structure, whereas dispersal limitation causes nested patterns of species assemblages organized by non-random colonization processes. However, factors that modify the relative importance of these processes remain unclear for many ecosystems. We tested whether salinity gradient affect the relative importance of environmental filtering and dispersal limitation for structuring epifaunal and infaunal communities in three lagoons in Hokkaido, Japan, that have different salinity gradients. Specifically, we compared patterns of species diversity and similarity of eelgrass-associated invertebrate assemblages across space. Beta diversity (i.e., species turnover among different sites in each lagoon) was highest in Akkeshi, the lagoon with the salinity gradients.Variation partitioning of similarity components showed that spatial variation in the community assemblage pattern was mostly explained by environmental filtering in Akkeshi, but that it was explained more by species dispersal patterns and the difference in eelgrass biomass and shoot density in Notoro and Saroma, the lagoons without clear salinity gradient. Redundancy analysis showed that spatial variation in community structure was related to salinity and eelgrass biomass in Akkeshi, and to eelgrass aboveground biomass in Notoro and Saroma. Our findings highlight the effects of environmental heterogeneity on beta diversity and community structure and indicate that environmental gradients can be a key factor causing a shift in the relative importance of different metacommunity processes and the role of the foundation species in provisioning habitat. K E Y W O R D Seastern Hokkaido, environmental filtering, epifauna and infauna, metacommunity, salinity gradient.

Increased salinity stress changes plant productivity and biomass by altering the top‐down controls in eelgrass beds

“…Eelgrass, epiphytic microalgae attached to the aboveground eelgrass, and gastropod L. decorata collected at A1, A2, N1, and N2 were used for the experiment. This gastropod is one of the most abundant and widely distributed species in eelgrass beds in both Akkeshi and Notoro sites and is found in natural habitats with both unstable and stable salinity (Namba et al 2020). Living on the aboveground parts of eelgrass, they feed on various food sources, including microalgae and eelgrass leaves (Kanamori et al 2004, Kajihara et al 2010).…”

“…A uniform loss of grazers, especially the studied Lacuna snails, from the sites in Notoro would occur when salinity decline occurs more frequently or in the long term. As the snail species was the dominant grazer in the lagoon (Namba et al 2020), this would affect the top-down control operated by the grazers until species turnover occurs or community compositions shift to be more adapted to low salinity regimes occur.…”

“…Environmental stress is defined as unfavorable deflection of environmental conditions (Odum et al 1979). The degree of environmental stress varies among and within ecosystems (Barnes and Ellwood 2012, Cheng and Grosholz 2016, Namba et al 2020, while spatial variation creates stress gradients. Organism/individual responses, such as changes in respiration, feeding, growth, and reproductive rates (Salo et al 2014, McDonald et al 2016, and population responses, such as changes in abundance and biomass (Rodr ıguez-Gallego et al 2015), can vary along stress gradients.…”

“…Stress responses of organisms and their effects on species interactions have been studied along various stress gradients, such as altitudinal gradients (Bertness and Callaway 1994, Mori et al 2013, Sch€ ob et al 2013, distances from the shoreline (Alberti et al 2010), and salinity gradients in estuaries (Barnes and Ellwood 2012, Namba and Nakaoka 2018, Namba et al 2020. Natural disturbances such as storms and anthropogenic disturbances such as coastal development affect communities, populations, and organisms, resulting in changes to ecosystem functioning (e.g., Mori et al 2013).…”

Marine ecology – Learn about a tough but wonderful world

“…The motivation for the publication of this Special Feature was a symposium held at the 65th annual meeting of the Ecological Society of Japan in March 2018 (“Marine ecology—Learn about a tough but wonderful world”). This feature covers a wide range of topics in the field of marine ecology, including coastal seaweed and its associated diversity (Hamaoka, Kamiyama, & Hori, ; Namba et al, ; Sudo, Watanabe, Yotsukura, & Nakaoka, ), community population processes of marine animals including species interactions (Kanamori, Iwasaki, Oda, & Noda, ; Morita & Fukuwaka, ), and marine mammal population dynamics (Mizuguchi, Kato, Okamoto, Hattori, & Sakurai, ). Additionally, there are applied studies, such as those that investigated impacts on biological communities after the devastating tsunami caused by the Great East Japan Earthquake in 2011 (Hamaoka et al, ; Kanamori et al, ) and those on population processes associated with climate change (Mizuguchi et al, ; Sudo et al, ).…”