Effects of physiological integration on the survival and growth of ramets and clonal fragments in the seagrass Syringodium filiforme

Mesocosm experiments examined the importance of clonal integration to the growth of Syringodium filiforme ramets (short shoots with their associated section of rhizome and roots) and clonal fragments. High mortality and reduced growth following isolation from parent clones indicated that. young ramets are dependent on clonal integration for survival and growth. In contrast, older ramets survived isolation, grew, and branched forming a new rhizome apical meristem (RAM) and additional ramets. Similar results were obtained from an experiment examining the survival and growth of clonal fragments. Older fragments produced longer branches and more new ramets than did younger fragments during the same time period, Cutting the rhizome behind a ramet led to a decrease in ramet growth compared to cutting the rhizome in front of a ramet. These results indicate that S. filiforme RAMs and young ramets act as physiological sinks, drawing resources from and reducing the growth potential of older ramets. These results also suggest that restoration projects should utilize planting units comprised of older clonal fragments due to increased survival and growth potential. Using older portions of clones as planting units negates the need for an intact RAM, as these fragments are capable of producing multiple new growth axes. Finally, our results indicate that in order to gain an accurate picture of seagrass meadow health in disturbance prone environments, rhizome condition and ramet position relative to the RAM should be considered in addition to the standard measurements of ramet productivity.