Benthic Zone Biomes of the Gulf of Mexico

The most amazing communities of the benthic zone, the bottom layer, of the Gulf of Mexico are the cold seeps. They are proof of the diversity of life, and of its persistence under conditions that we surface dwellers would find impossible.

Not every form of life on earth depends upon sunlight. On the continents and in the upper oceans, plants make food through photosynthesis. They turn sunlight, water, and carbon dioxide into food, and animals take their food from plants. In parts of the deep oceans though, and in certain other environments, photosynthesis is irrelevant. Life sustains itself in another way.

The bacteria of the cold seeps of the Gulf of Mexico survive by chemosynthesis, the production of carbohydrates from gases such as methane and hydrogen sulfide and from oil. Instead of powering the reactions that build sugars with sunlight, they power them with the energy given off by chemical reactions.

They live in an environment utterly different from ours. Some seeps have mounds of methane hydrate ice, frozen crystals of water and methane, like the materials that impeded the dome that BP tried to place over the Deepwater Horizon spill. Also part of the terrain are pools of concentrated brine, often full of methane and strong enough to kill ocean fish.

On the other hand, the seeps have no bad weather, and their colonies appear to be stable and long lasting. Most of the deep sea is a wet desert, marine biologists believe. Very little lives in the darkness. The cold seeps, and the hydrothermal vents found elsewhere on the ocean floor, are fantastic oases full of alien life.

Bizarre (to us) creatures live there, feeding off the products of the chemosynthetic bacteria. Long-lived tubeworms with blood-red tentacles live in symbiotic (mutually sharing) relationships with the bacteria inside them. The tubeworms provide shelter and share the oxygen they gather in the hemoglobin of their tentacles. The bacteria synthesize sugars that feed the tubeworms.

Specialized mollusks also shelter bacteria, and live off the food they provide. Other members of the community, the biome, live off these creatures.

Clams, mussels, or tubeworms dominate various biomes, but all cold seeps appear to have bacterial mats, surfaces of  bacteria that provide the basis of the food chain with chemosynthesis. Some seeps have mud pots at their lowest depths, where seepage is rapid and boils up through the ocean bottom. Some have gardens of coral at their heights, where corals (also symbionts) grow on crags of carbonate rock precipitated out of the mineral rich water.

It is actually doubtful that the Deepwater spill will harm the cold seeps. They live on the energy that flows from under the sea, so it is possible that this energy spill will in some sense benefit them. Research done for the MMS by Texas A & M University seems to indicate that tubeworms are more prevalent in communities with more liquid hydrocarbons, while mussels are more likely in communities dominated by methane-rich brine seeps.

The spill may actually nourish some of the life on the sea floor, encouraging it to grow and thrive. It may favor some life forms, or it may encourage them all. Added life in the sea may help with global warming, by taking up carbon and releasing oxygen.

We don’t know. So far, more research has gone into energy production than into studying these incredible creatures of the benthic zone.


NOAA has frequently updated scientific information on conditions in the Gulf of Mexico, and many links to information from ongoing research on cold seeps.