Though marine waters are dominated by several species of algae, there is one true flowering plant, namely eelgrass (Zostera marina) that is extremely important to many animal populations. A member of the Zosteraceae family, eelgrass forms large beds in subtidal waters up and down the Atlantic coastline.
During the early 1930ís this plant was ravaged by an aquatic fungus and most of the populations disappeared. A few decades later it recovered only to be subjected to additional environmental stressors such as algae population blooms, the effects of overdevelopment, and the impact of hydraulic dredging of shellfish. Invasive algae species such as Codium fragile grow abundantly on the surface, blocking sunlight and lowering dissolved oxygen during the process of decomposition.
Yet, eelgrass is vital for many commercially useful species such as scallops, flounder, and blue crabs. Brant geese, and other aquatic birds, feed on the long, slender leaves. Eelgrass branches grow up to six feet long and provide shelter for numerous and tiny animals in both larval and adult stages. The strong roots are embedded in the sand and mud and help to buffer wave action, thus reducing coastal erosion.
Eelgrass can spread into open waters either vegetatively or by producing seeds. Strong currents will spread the fruits and seeds during the summer. There has also been several successful recolonization or transplanting projects that have increased and stabilized eelgrass populations.
An eelgrass bed is a small ecosystem that supports numerous species of animals. Invertebrates such as sponges, worms, shrimp and bryozoans cling to the blades. In addition to the commercially important species mentioned earlier there are pipefish, sticklebacks, and mummichogs hiding in the eelgrass from predators. The bay scallop industry is completely dependent on this plant. When eelgrass declines, so do the scallops.
Letís consider the stages that take place when an excess of nutrients, mainly in the form of nitrogen, wash into a bay. Some species of algae such as Ulva or Codium undergo a rapid increase in population. These algae species shade out the eelgrass beds below preventing photosynthesis. Thus, a weakened eelgrass population is unable to compete for the important sunlight that it needs.
It seems that if we are to protect these significant resources, then we must improve our land management practices. Controlling nitrogen loading, a major issue on Cape Cod, is essential for the maintenance of healthy eelgrass beds.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.