The influence of resource availability on flowering intensity in Zostera marina (L.)

Ηighlights
- Resource availability can impact flowering intensity in Zostera marina.
- Duration and magnitude of resource regime may dictate impact on Z. marina flowering.
- A critical shoot age requirement for flowering shoot production may not exist.

The impact of resource availability on investment between asexual and sexual reproduction in seagrasses remains poorly understood. In this study, the effects of sediment nutrients and light availability on sexual and asexual reproduction in the seagrass Zostera marina (L.) were investigated. Field manipulations were combined with observational surveys to identify whether nutrient and light availability influenced flowering intensity of Z. marina in Chesapeake Bay, Virginia. A positive relationship between pore water ammonium and the percentage of flowering shoots was observed across locations with differing sediment nutrient types. In addition, short-term elevation of sediment nutrients increased the number of spathes per flowering shoot, but did not alter flowering shoot densities. Surveys around existing residential piers, used as observational surrogates for long-term shading, found seagrass directly below piers exhibited lower percentages of flower shoots than adjacent unshaded seagrass. In contrast, seasonal light reductions of seagrass did not significantly affect flowering intensity in experimental plots. Thus, increasing nutrient resources over both the seasonal and longer terms appeared to increase several aspects of investment in sexual reproduction, while only long-term reductions in shading decreased investment in sexual reproduction. Therefore, any factors which influence the duration and magnitude of nutrient and light resource availability to seagrass, may have important implications for the sustainability and resiliency of these valuable populations and the services they provide within increasingly threatened coastal systems.