It all started at Sapelo Island, Georgia, a place that once was thought to provide the evidence to support the hypothesis that the marsh grass production is controlled by bottom-up forces. Now, due to the experimentation done by Silliman and Bertness at the the turn of the century, we find these facts to be flipped. It is odd to think that for so long we could be wrong about this. No one dared to challenge the bottom-up theory; it simply became a widely accepted fact that primary producers controlled salt marsh cordgrass production. What I wonder is what were the conditions and methods of the experiment done prior to Silliman and Bertness’? Were there drastic errors involved and how did they prove their hypothesis of bottom-up control?
In any case, it was very strategic for Silliman and Bertness to conduct their experiment in the very location that this bottom-up theory was produced. Using the same natural environment to conduct their 2 year long experiment on Littoraria irrorata (periwinkle snail), what they graze on (cordgrass), and who their predators (blue crabs). The results they found were shocking. The fact that in the controlled environments without predation, grazing snails took one of the most productive grassland systems in the world and turned it to a barren mudflat in only 8 months, is insane. Now take this idea and apply it to all the grassland systems, unimaginable but could become a reality. As Silliman proves, if there are no predators left to eat the grazers in these ecosystems, all of the biomass will be lost.
A key quote I found that I feel exemplifies the purpose of this study is, “Understanding how marshes respond to such perturbations is key to the survival of these ecologically and economically important habitats.” Humans must realize that the resources are not infinite. Everything we do has repercussions, and the Earth can only give so much.
Where do we go from here? Since the publication date of Silliman paper, is there anything in action to protect the Blue Crabs? One would hope there are laws in place limiting the amount of Callinectes sapidus taken from the marshes so we can protect Blue Crabs from being over-fished, and thus causing these precious ecosystems to stay intact rather than be flattened to mud pits.
It seems Silliman forgot to include the top most level of the top-down control hierarchy in Figure 2. Us.
4 Responses to Bottom-Up? Think Again.