Temporal variation of intertidal seagrasses in Southern China (2008-2014)

Background/Question/Methods

To examine interannual and seasonal variations of the intertidal Halophila ovalis community in southern China, we sampled quarterly with SeagrassNet methodology and assessed environmental conditions as well as direct anthropogenic impacts to the seagrass meadow from July 2008 to October 2014. 

Results/Conclusions

Our study demonstrated strong inter-annual and seasonal dynamics of the intertidal seagrass community in the study area. The range of mean seasonal average seagrass cover (0.1% in April 2012 vs. 27.5% in July 2013), shoot density (29 shoots/m² in April 2012 vs. 2180 shoots/m² in July 2013), above-ground biomass (0.260 dry g/m² in April 2012 vs. 14.989 dry g/m² in July 2013), below-ground biomass (0.168 dry g/m² in April 2012 vs. 8.124 dry g/m² in July 2013), and total biomass (0.428 dry g/m² in April 2012 vs. 23.112 dry g/m² in July 2013), varied widely within two order of magnitude over the monitoring period. For leaf area index (0.01 m²/m² in April 2012 vs. 0.60 m²/m² in July 2013), spans within one order of magnitude. The seagrass meadow was almost disappeared in April 2012. Generally, the community has best performance (highest seagrass cover, leaf area, shoot density, total biomass) in summer and worst in spring among 4 seasons. Even so, the ecological growth conditions of H. ovalis in the study site could be physiologically sub-optimal. The temporal variations of seagrass community attributes (e.g. above-ground biomass) were significantly affected by precipitation, visibility, and salinity, while leaf width was significantly correlated with temperature, visibility and salinity (negative effect). However, we didn’t see significant effect of human physical disturbances on seagrass dynamics in the study area, which may be explained by the relative low degree perturbations and the high resilience of the small colonizing species, H. ovalis.