Spatial patterns and predictor variables vary among different types of primary producers and consumers in eelgrass (Zostera marina) beds

Abstract

Eelgrass (Zostera marina) forms extensive beds in coastal and estuarine environments and provides various ecosystem functions. The aboveground part of eelgrass provides habitats for other types of primary producers such as epiphytic microalgae and for epifaunal invertebrate grazers. Because of the different sizes, generation times and resource requirements, these different types of producers and consumers may be affected by different sets of biotic/abiotic factors over multiple spatial scales. We examined the spatial variations in three functional groups of eelgrass beds (eelgrass, epiphytic microalgae and epifaunal invertebrates) and the abiotic/biotic factors responsible for these variations in three lagoons with different environmental properties at the eastern region of Hokkaido Island, Japan. The spatial scale responsible for the variation in the biomasses of the three functional groups varied, where within-lagoon variation was important for eelgrass and epifauna but among-lagoon variation was important for microalgae. The environmental predictors for the observed spatial variations also differed among the different functional groups, with variation in eelgrass biomass related to depth, nutrient and salinity, epiphytes to water temperature, eelgrass biomass and water column chlorophyll and epifauna mainly to eelgrass biomass. These results revealed that the level of importance of among- and within-lagoon environmental gradients vary in the different functional groups of the eelgrass bed community. The large-scale variation in pelagic productivity, which is tightly related to the ocean current regimes, is likely responsible for the great among-lagoon variation in microalgae. The local variations in environmental factors such as salinity and nutrients, which change with alterations in terrestrial river inputs, are likely related to the great variations in eelgrass and epifauna within the ecosystem. The observed relationship of epifauna with eelgrass biomass indicates the importance of non-trophic plant-animal interactions because epifauna utilize eelgrass as habitat. We therefore emphasize the importance of evaluating spatial variations at multiple scales to further understand the functions of coastal and estuarine ecosystems.

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

“…Environmental conditions and eelgrass bed properties for each site are summarized in Table 1 (also see Namba & Nakaoka, 2018). Overall, 104 species of epifauna and 37 species of infauna were found across all samples (Table S1).…”

“…To examine the effect of salinity gradient on community structures of epifauna and infauna in eelgrass beds, we sampled eelgrass-associated benthic organisms in three semi-enclosed lagoons (i.e., Akkeshi-ko Lagoon, Notoroko Lagoon and Saroma-ko Lagoon) in eastern Hokkaido, Japan (Figure 1; the detailed descriptions can be found in Namba & Nakaoka, 2018). In all the three lagoons, eelgrass beds are found in the shallow subtidal zone (0.2-1.6 m).…”

“…Because Akkeshi had an eelgrass bed thoroughly in the lagoon, whereas that in Notoro and Saroma is limited to nearshore part of the lagoons, the number of sites was different among the lagoons. Salinity and water temperature data were obtained by conductivity temperature depth sensors (RINKO Profiler ASTD102-ALC-R02: JFE Advantech Co., Ltd., Japan) at each site (Namba & Nakaoka, 2018). To measure SOM via the loss on ignition technique, we collected three replicate sediment cores at each site.…”

The phenology of epiphytic diatoms and epifauna observed on <i>Zostera marina</i> of Arikawa Bay, Nagasaki Prefecture, Japan

“…The phenological response of the state of the epiflora and epifauna of seagrass leaves is a well-researched topic (Jacobs et al 1983, Nakaoka et al 2001, Namba & Nakaoka 2018. Many studies have examined the interactions between epiflora and epifauna; however, evaluations on the interactions between seagrass leaves and epiflora are rare.…”

“…Herbivores (i.e., epifauna) that partly feed on epiphytic diatoms find refuge in macrophytes, and in terms of seagrass ecosystems, small crustaceans, gastropods, and polychaetes are the predominant groups (Lewis & Hollingworth 1982, Baden 1990, Nakaoka et al 2001, Namba & Nakaoka 2018. The factors affecting grazer-epiphyte interactions in seagrass ecosystems are complex (Jernakoff et al 1996), and the inclusion and exclusion of predators have immediate effects on grazers and epiphyte abundance (Reynolds et al 2014(Reynolds et al , Östman et al 2016.…”