Large-scale comparison of biomass and reproductive phenology among native and non-native populations of the seagrass Zostera japonica

Ma Ito,Hj Lin,M Nakaoka,Mi O’Connor

doi:10.3354/meps13884

Abstract

Large-scale analysis along latitude or temperature gradients can be an effective method for exploring the potential roles of light and temperature in controlling seagrass phenology. In this study, we investigated effects of latitude and temperature on seagrass biomass and reproductive seasonality. Zostera japonica is an intertidal seagrass with a wide latitudinal distribution expanding from tropical to temperate zones in its native range in Asia, with an additional non-native distribution in North America. We collated available data on phenological traits (timings of peak biomass or reproduction, durations of biomass growth and reproductive season, and maximum biomass or reproductive ratio) from publications and our own observations. Traits were compared among geographic groups: Asia-tropical, Asia-temperate, and North America-temperate. We further examined relationships between traits and latitude and temperature for 3 population groups: Asian, North American, and all populations. Our analysis revealed significant variation among geographic groups in maximum biomass, peak reproductive timing, and maximum reproductive ratio, but not in other traits. Maximum biomass and peak reproductive timing for Asian and all populations were significantly correlated with latitude and temperature. Maximum biomass was highest at mid-latitudes or intermediate temperatures and decreased toward distribution range limits, and peak reproductive timing occurred later in the year at higher latitudes or cooler sites. North American populations showed shorter growth durations and greater reproductive ratios at higher latitude. Different responses observed for North American populations may reflect effects of introduction. Our study demonstrates potential variation among geographic regions and between native and non-native populations.

Highlights

Seagrasses are marine angiosperms that form extensive meadows in shallow coastal environments, which are known as seagrass beds (Hemminga &Duarte 2000)
The intertidal seagrass Zostera japonica showed no geographical variation in peak biomass timing and growth duration, nor was it affected by latitude or temperature, except for the North American populations where latitude and temperature had significant effects on their growth duration
Our study demonstrates that the effects of latitude and temperature on seagrass biomass and reproduction vary among analyzed traits and among geographic groups

Summary

Introduction

Seagrasses are marine angiosperms that form extensive meadows in shallow coastal environments, which are known as seagrass beds (Hemminga &Duarte 2000). Seagrass meadows provide multiple important ecosystem services and are recognized as one of the most valuable habitats in the world (Costanza et al 1997). Despite their importance, seagrasses are rapidly declining worldwide due to various types of anthropogenic stressors and disturbances that act at different scales (Orth et al 2006, Waycott et al 2009). Increased temperatures are expected to shift seagrass distribution to higher latitudes, alter growth rates and other physical functions, and change sexual reproduction patterns (Short & Neckles 1999, Duarte 2002, Hyndes et al 2016). To predict future changes in seagrass meadows and to promote effective conservation, it is important to understand how life history traits of each seagrass species vary with environmental conditions

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