Benthic Zone

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Introduction

The benthic zone is the lowest level of a marine or freshwater system and includes the sediment surface, the water just above it, and some sub-surface layers. Benthic zones exist all over the world in every appreciable water system, be it an ocean, lake, pond, river, or stream. The benthic zone starts at the shore and extends down along the bottom of the lake or ocean. This means that it could be as shallow as a few inches at its start, but may reach depths of 6,000 meters as it coincides with the abyssal plain at the bottom of the ocean. Because of the depths it can reach, the benthic zone is often characterized by low sunlight and low temperatures. This usually attributes to little life and biodiversity, so one would be inclined to assume that it is a vast waste. However, the presence of sediment layers at the benthic zone provides many nutrients and adds greatly to species richness. Because the benthic zone has such a range of depths, many kinds of organisms may live there. Crustaceans, sponges, bivalves, snails, sea stars, polychaetes, fish, and many others can inhabit the zone.

The nutrients at the sediment layer are usually the limiting source of energy for the organisms that inhabit the benthic zone. These nutrients actually originate from dead or decaying organic matter from higher up in the water column. This organic matter drifts down continuously from shallower depths and settles on the bottom, where it is consumed and is the main driver of the benthic zone food chain. The organisms in the benthic zone are classified into those which dwell on the surface and those which burrow into the sea floor. They are the epifauna and infauna, respectively. Organisms inhabiting the benthic zone are collectively called the benthos. The name benthos comes from the Greek noun βένθος, which means “depths of the sea”.

Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.

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Legend/credit: Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.
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In the introduction, briefly describe the habitat that is the topic of this page. Introduce the habitat, its ecological significance, and the importance of microorganisms in this environment. (What processes do they carry out? What functions do they perform?)

Physical environment

Physical Characteristics

Because the benthic zone can occur in such a wide range of environments, physical characteristics vary largely and are almost always context dependent.

Temperature

Temperature in the benthic zone ranges from warm normal temperatures at shallow depths, but may drop to 2 °C to 3 °C at the most extreme depths of the abyssal zone. At such cold temperatures, abundance of life quite low and things move at a very slow pace. Warmer waters at shallower depths provide much more energy and can host much more complex systems.

Pressure

Pressures range from very little in a few inches of water to tremendously great at the bottom of the ocean. For an extreme example, the deepest spot in the Mariana Trench (the deepest trench in the ocean) is around 36,000 feet below sea level and experiences pressures of about 16,000 psi; standard pressure at sea level is 14.7 psi.

At particularly great depths, the benthic zone is under extreme pressure. This high pressure restricts the movement of particles, so the environment is not affected by outside disturbances, such as those from tidal forces. This makes for a very homogenous environment that produces a number of peculiar traits among organisms. One such peculiarity is the enhanced size of certain organisms. At great depths in arctic and antarctic waters, dissolved oxygen content is quite high. This allows organisms to grow much larger when compared to close relatives in temperate zones (.naturalsciences.be).

Microbial communities

What kind of microbes do we typically find in this environment? Or associated with important processes in this environment? Describe key groups of microbes that we find in this environment, and any special adaptations they may have evolved to survive in this environment. List examples of specific microbes that represent key groups or are associated with important processes found in this environment. Link to other MicrobeWiki pages where possible.

Are there important biological interactions that are important in this environment? Do these interactions influence microbial populations and their activities? How do these interactions influence other organisms? Describe biological interactions that might take place in this environment, using as many sections/subsections as you require. Look at other topics available in MicrobeWiki. Create links where relevant.

Benthic microorganisms are almost exclusively microalgae and bacteria, but other others include: ciliates, amoeba, and flagellates. Most organisms there are detritivores and scavengers because of the abundance of dead or decaying organic matter. In addition to these heterotrophs, there are chemoautotrophs present that use the substrate to make biomass. There are also photoautotrophs present at shallower depths where sunlight is abundant.

Microbial processes

What microbial processes define this environment? Describe microbial processes that are important in this habitat, adding sections/subsections as needed. Look at other topics in MicrobeWiki. Are some of these processes already described? Create links where relevant.

Benthic microorganisms are key to controlling nutrient flow between sediment layers and the water column. As nutrients are taken in and stored by microorganisms, their flow through the system is greatly slowed. This process can act as a buffer. Buffers are essential in all natural systems and prevent excessive flux of elements. One such example is seen when microalgae buffer nutrients to prevent phytoplankton overexploitation, which often results in eutrophication (web.vims.edu). The impacts of benthic microorganisms spread, much like the impacts of all other microbes, across the community as a whole. They provide essential energy and nutrients at the lower levels of the food chain and are imperative to the success of other forms of life.

Current Research

Enter summaries of recent research here--at least three required

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by <your name>, a student of Angela Kent at the University of Illinois at Urbana-Champaign.