What Happens in Ocean Sediment?

I never consider the status of ocean sediments and their inhabitants until I started doing research on schools at which to begin my journey back into marine sciences; in my undergraduate years I was lucky enough to spend a semester studying the coral reef dynamics and communities of the Bahamas, but even then I was not considering the sandy beaches and seagrass beds that we had to go through to get out to the reefs. However, soft-sediment habitats are extremely diverse marine environments, and you've probably seen at least two different soft-sediment habitats during your lifetime: mangrove forests and seagrass beds.

Mangrove forests are really common in Florida because they are a tropical soft-sediment habitat, and mangrove forests are easily identifiable by the mangrove knees and complex roots structures (also the fact that there are trees in the water). Mangrove forests, and seagrass beds, are important stabilizers of sediments and help prevent coastal erosion near the shore, whereas coral reefs--hard substrate habitats--prevent coastal erosion further out at sea by dampening wave action. Mangrove forests and seagrasses also are important nursery grounds for fishes and seahorses, and are inhabited by a wide variety of species. The flora in these systems are responsible for oxygenating the sediment, providing nutrients deep into the sediments for many benthic invertebrates and contribute to nutrient cycling facilitated by microphytobenthos and marine microbes. 

Benthic organisms, the organisms that live in contact with the ocean floor, may also receive protection by living within mangrove forest or seagrass bed habitats, and the flora help structure trophic interactions in shallow marine systems. Seagrasses contribute heavily to the microbial loop, the conglomeration of processes facilitated by marine microbes and their interactions with each other and the other small organism in the ocean, which can have important effects on habitat suitability and may provide settlement cues for marine organisms. Interestingly, microplastics may effect the microbial loop (but no spoilers until I start my own research). Sediment grain size can have an important role in determining the suitability of a habitat for certain species. For example, many species of bivalves (clams, oysters, etc.) prefer specific sediment grain sizes as evidenced by their ability to dig deeper into some sediments compared to others. As oysters represent a major commercial value in the United States, understanding the environmental factors that contribute to the habitat suitability for oysters is incredibly important when setting up fisheries and determining marine protected areas.

If you are interested in learning more about oyster reef conservation in the Tallahassee and Big Bend area, check out the Apalachicola Bay System Initiative that seeks to understand the causes of oyster decline in the Apalachicola Bay area.