Tiny sea creatures no bigger than a thumbtack are being credited for playing a key role in helping provide healthy habitats for many kinds of seafood...
Gammarus mucronatus, an amphipod grazer that can
promote healthy eelgrass beds. Copyrighted photo courtesy of Matthew
Whalen/UC Davis. (High resolution image)
“Inconspicuous creatures often play big roles in supporting productive ecosystems,” said the study'd lead author, Matt Whalen. “Think of how vital honeybees are for pollinating tree crops or what our soils would look like if we did not have earthworms. In seagrass systems, tiny grazers promote healthy seagrasses by ensuring algae is quickly consumed rather than overgrowing the seagrass. And by providing additional refuge from predators, fleshy seaweeds that drift in and out of seagrass beds can maintain larger grazer populations and enhance their positive impact on seagrass.”
USGS scientist Jim Grace, a study coauthor, says that seagrass habitats are also beneficial to people.
“Not only do these areas serve as nurseries for commercially important fish and shellfish, such as blue crabs, red drum, and some Pacific rockfish, but they also help clean our water and buffer our coastal communities by providing shoreline protection from storms,” Grace said. “These tiny animals, by going about their daily business of grazing, are integral to keeping healthy seagrass beds healthy.”
Comparison of algae fouling on eelgrass with and
without grazers. Copyrighted photo courtesy of Matthew Whalen/UC Davis.
Copyrighted photo courtesy of Matthew Whalen/UC Davis. (High resolution image)
Without these algae grazers, say the authors, algae could accumulate in a thick enough layer to block sunlight and prevent the seagrasses from photosynthesizing, which would kill them. The decline of seagrass in some areas is partly the result of excess nutrients in water that stimulates excessive algal growth on seagrasses.
J. Emmett Duffy of the Virginia Institute of Marine Science, another coauathor of the study, says that coastal managers have been concerned for years about excess fertilizer and sediment loads that hurt seagrasses. Duffy sees study results as convincing field evidence that tiny animals that graze on algae can be just as important as good water quality to prevent algal blooms and keep seagrass beds healthy.
The study, “Temporal shifts in top-down versus bottom-up control of epiphytic algae in a seagrass ecosystem,” was published in the recent issue of Ecology, a journal by the Ecological Society of America.
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