Importance of considering grain and extent for the analysis on spatial dynamics: perspectives from comparison between theory and empirical example on seagrass bed dynamics in Tokyo Bay

AbstractThe term scale has been used in many ways. In continuous landscape analysis, the spatial scale consists of two components; grain and extent. Most previous studies on the scale issue were conducted in limited range or on one component of the scale. To further step up, we compared theory of scaling by applying indices developed for terrestrial static landscape to underwater vegetation. The result suggested that changing grain shows power-low scaling relationships for the most of landscape indices. Changing extent increased variation of above scaling relationships. We conclude that changing both components reveal the possibility to extrapolate these indices into different scales or places. For the conservation of ecosystems, recognition of scaling relationships is necessary to build more spatially explicit planning and understanding of phenomenon

Species diversity and abundance of seagrasses in southwestern Thailand under different influence of river discharge

Seagrass beds are among the most important components in coastal ecosystem, but are susceptible to human-induced changes in terrestrial ecosystem. As a first step to understand the effects of terrestrial input through river discharge on tropical seagrass ecosystems, we carried out quantitative mapping of seagrass beds at Pang-gna and Trang Provinces, southwestern Thailand to examine spatial variation in species composition, species diversity and biomass of seagrasses. Five seagrass beds were chosen as study sites that locate at different distances from the major river mouths, and thus subjected to different impacts of river discharge. These seagrass beds differed greatly in environmental conditions, seagrass diversity and abundance. Seagrass beds located near large river mouths showed higher silt-clay content in the sediments and light attenuation of water, possibly due to transportation of sediment from rivers and its resuspension. A total of nine seagrass species occurred. Enhalus acoroides and Halophila ovalis occurred in all the stations, whereas distribution of other species were mostly confined to seagrass beds with small or moderate degree of siltation and light attenuation. Seagrass species diversity measured by species richness and Simpson\u27s diversity index was lower in seagrass beds near the river mouth. These findings highlight negative impacts of terrestrial ecosystems through river discharge on seagrass biodiversity and its functioning along the coastal areas of southwestern Thailand

Distributed under Creative Commons CC-BY 4.0 OPEN ACCESS Influence of different types of sessile epibionts on the community structure of mobile invertebrates in an eelgrass bed

ABSTRACT Eelgrass (Zostera marina) beds are known to have high ecological and economical values within coastal ecosystems of the temperate northern hemisphere although their biodiversity and functions varied greatly from sites to sites. The variation in the biomass, abundance and diversity of mobile invertebrates in eelgrass beds has been examined in relation to various abiotic and biotic factors, such as water temperature, salinity, eelgrass biomass and epiphytic microalgae presence. However, the importance of sessile epibionts, such as macroalgae and calcific spirorbid polychaetes attached to eelgrass blades, has not been the focus of previous studies. In the present study, we examined the effects of three different sessile epibionts, namely, branched red algae, filamentous green algae, and calcific spirorbid polychaetes, on the biomass and diversity of mobile invertebrates in the eelgrass beds of Akkeshi in northeastern Japan. The relationships between seven abiotic and biotic variables including three types of epibionts, and biomass of 11 dominant mobile invertebrate species as well as three community-level variables (the total biomass of mobile invertebrates, species richness and the ShannonWiener species diversity index) were analyzed using a linear mixed model. Our results show that branched red algae are correlated with Pontogeneia rostrata, Lacuna spp., Nereis sp., Syllis sp. and the total biomass of mobile invertebrates, filamentous green algae with P. rostrata, Ansola angustata and the species diversity of mobile invertebrates, and spirorbid polychaetes with A. angustata, Lacuna spp., Siphonacmea oblongata, Syllis sp., the species richness and diversity of mobile invertebrates. The effect size of the epibionts was similar or even higher than that of abiotic and eelgrass factors on the total biomass of mobile invertebrates, species richness, species diversity and most of dominant invertebrate populations across the taxonomic groups. Consequently, epibiotic macroalgae and spirorbid polychaetes can be good predictors of the variation in the total biomass, species richness and species diversity of mobile invertebrates and the biomass of major dominant species, especially for species that have a relatively high dependency on eelgrass blades. These results suggest that the different functional groups of sessile epibionts have significant roles in determining the biomass and diversity of mobile invertebrates in eelgrass beds

Anti-epiphyte defenses in the red seaweed Gracilaria vermiculophylla : non-native algae are better defended than their native conspecifics

Epibiosis in the marine environment is a stressor that may determine invasion success in introduced species. Previous comparisons showed resistance to epibionts can be higher in non-native than in resident seaweed species, but we do not know whether it is an intrinsic trait of the non-natives or it has been acquired during the invasion process. To elucidate this question, a comparison between native and non-native populations of the same species is needed. Resistance against two groups of epiphytes was assessed in living thalli and in artificial substrata coated with surface extracts, both gained from four Asian (native) and four European (non-native) populations of the red alga Gracilaria vermiculophylla. Two diatom species and two filamentous macroalgae were used as micro- and macro-epiphytes, and one of each type was collected in Asia, while the other came from Europe. Laboratory assays were done in both distributional ranges of G. vermiculophylla and in different seasons. We used G. vermiculophylla from four populations in each range and used a fully crossed design with the factors (i) ‘Origin of Gracilaria’, (ii) ‘Origin of epiphytes’, (iii) ‘Season’ and (iv) ‘Solvent used for extraction’. Both groups of epiphytes, regardless of their origin, attached less to living thalli and to surface extracts from non-native G. vermiculophylla. Fewer diatoms attached to hexane-based extracts, while fewer Ceramium filaments settled on extracts gained with dichloromethane. Synthesis. Our results show for the first time that non-native individuals of a marine organism are better defended against epiphytes than native conspecifics. Furthermore, we found evidence that at least a part of the defence is based on extractable secondary metabolites. We discuss several mechanisms that could explain the increased resistance to epiphytes in non-native individuals, including the release from enemies in the non-native range, which could lead to an increase in algal performance during the invasion process. We suggest that an enhanced defence against epiphytes after introduction is one reason for G. vermiculophylla's invasion success. Our observation may also apply to other basibiont–epibiont and host–enemy systems, including plant–plant, plant–animal and animal–animal interactions, in aquatic environments and could be a key feature of bioinvasions

Assessment of Artificial MiRNA Architectures for Higher Knockdown Efficiencies without the Undesired Effects in Mice.

RNAi-based strategies have been used for hypomorphic analyses. However, there are technical challenges to achieve robust, reproducible knockdown effect. Here we examined the artificial microRNA (amiRNA) architectures that could provide higher knockdown efficiencies. Using transient and stable transfection assays in cells, we found that simple amiRNA-expression cassettes, that did not contain a marker gene (-MG), displayed higher amiRNA expression and more efficient knockdown than those that contained a marker gene (+MG). Further, we tested this phenomenon in vivo, by analyzing amiRNA-expressing mice that were produced by the pronuclear injection-based targeted transgenesis (PITT) method. While we observed significant silencing of the target gene (eGFP) in +MG hemizygous mice, obtaining -MG amiRNA expression mice, even hemizygotes, was difficult and the animals died perinatally. We obtained only mosaic mice having both -MG amiRNA cells and amiRNA low-expression cells but they exhibited growth retardation and cataracts, and they could not transmit the -MG amiRNA allele to the next generation. Furthermore, +MG amiRNA homozygotes could not be obtained. These results suggested that excessive amiRNAs transcribed by -MG expression cassettes cause deleterious effects in mice, and the amiRNA expression level in hemizygous +MG amiRNA mice is near the upper limit, where mice can develop normally. In conclusion, the PITT-(+MG amiRNA) system demonstrated here can generate knockdown mouse models that reliably express highest and tolerable levels of amiRNAs

How do microbiota associated with an invasive seaweed vary across scales?

Communities are shaped by scale dependent processes. To study the diversity and variation of microbial communities across scales, the invasive and widespread seaweed Agarophyton vermiculophyllum presents a unique opportunity. We characterized pro‐ and eukaryotic communities associated with this holobiont across its known distribution range, which stretches over the northern hemisphere. Our data reveal that community composition and diversity in the holobiont vary at local but also larger geographic scales. While processes acting at the local scale (i.e., within population) are the main structuring drivers of associated microbial communities, changes in community composition also depend on processes acting at larger geographic scales. Interestingly, the largest analysed scale (i.e., native and non‐native ranges) explained variation in the prevalence of predicted functional groups, which could suggest a functional shift in microbiota occurred over the course of the invasion process. While high variability in microbiota at the local scale supports A. vermiculophyllum to be a generalist host, we also identified a number of core taxa. These geographically independent holobiont members imply that cointroduction of specific microbiota may have additionally promoted the invasion process

Distribution, productivity, life history and biodiversity of seagrass community along Sanriku Coast: A review

The seagrass flora in Japan is characterized by the occurrence of several species of Zosteraceae that are considered to be endemic to the northwestern Pacific. In seagrass beds along Sanriku Coast, northeastern Honshu Island of Japan, the endemic Zostera spp. generally occur at subtidal soft bottom, usually forming multispecific seagrass beds with the cosmopolitan eelgrass Z. marina. This paper reviews some of the recent studies on ecology of the seagrass community conducted at Otsuchi Bay, Funakoshi Bay and Yamada Bay along Sanriku Coast of Iwate Prefecture. We specially focus on following subjects ; (1) spatial distribution of Z. caespitosa in Yamada Bay surveyed using eco-sounding techniques, (2) comparative studies on morphological and life history traits of Zostera spp., (3) quantitative estimation on shoot dynamics, growth and primary production of Z. caulescens, (4) ecology of epifaunal community on the aboveground parts of seagrasses, and (5) population genetic structure and gene flow among populations of Z. caespitosa analyzed using molecular data. The results of these studies showed that the seagrass community along Sanriku Coast is one of the most productive parts of the coastal ecosystem, and that various environmental and biological factors are involved in a complex manner to produce observed patterns of population structure and dynamics of the seagrass community