Eelgrass in Drakes Estero

NPS Assertion: The oyster farm causes harm to eelgrass

The claim was first made in an article by Dr. Sarah Allen (PRNS staff scientist), Jules Evens, and John Kelly published in the local newspaper, the Point Reyes Light, entitled “Coastal Wilderness,” saying “Eelgrass beds … are especially vulnerable to oyster operations. Oyster racks prevent eelgrass beds from establishing and degrade existing beds by over-shading the substratum increasing sedimentation…”

There is no known evidence for the claim.

DBOC Assertion: Not only does oyster culture not harm eelgrass, it is known to enhance it.

Eelgrass habitat in Drakes Estero is known to have doubled between 1991 and 2007.

The National Academy of Science report on mariculture in Drakes Estero points out that while a small portion of eelgrass is scarred by the oyster farm’s skiff during harvesting operations, overall, eelgrass in Drakes Estero is extremely healthy. On page 4, the NAS report states “Research elsewhere demonstrates that damaged eelgrass blades have rapid regeneration capacity and that eelgrass productivity can be locally enhanced by the cultured oysters through a reduction in turbidity and fertilization via nutrient regeneration.” The report says “there is no empirical evidence of enhanced organic content or sediment hypoxia in eelgrass beds proximate to oyster culture racks.” The NAS report also explains that oyster culture contributes to a healthy estero via benthic-pelagic coupling, a process by which materials including nutrients and organic carbon are transferred from the water column to the sediments on the bottom.

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