**Chemosynthetic Communities**

Chemosynthetic communities are persistent, largely non-mobile, high
density groupings of bottom-dwelling marine animals found in areas of
natural hydrocarbon seepage. They are dependent upon chemosynthetic
bacteria for their primary food source. They were discovered in 1984
associated with natural hydrocarbon seeps in the northern GOM.

> A gas hydrate mound surrounded by tube worms on the Gulf of Mexico
> seafloor.

**Research on Unusual Communities**

Multidisciplinary research sponsored by the Minerals Management Service
(MMS) detects, locates, and describes these unusual deepwater
communities through environmental and engineering research related to
offshore mineral development. The MMS uses research results to describe
the environment potentially affected by offshore oil and gas leasing,
exploration and development activities, and assesses the possible
environmental consequences of these activities, and develops protective
measures to prevent, minimize, and mitigate unavoidable impacts to
chemosynthetic communities.

Through research on chemosynthetic communities and gas hydrates in the
GOM researchers now know that:

-   Chemosynthetic critters associated with cold seeps are similar to
    those of hydrothermal vents, but inhabit a fundamentally distinct
    ecosystem.

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-   Currents at relevant depths in the northern GOM are capable of
    dispersing chemosynthetic faunal larvae across the entire upper
    continental slope.

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-   The upper depth limit for GOM chemo

> synthetic communities is between 400 m and 500 m (1312 ft and 1640
> ft), corresponding to the area above which sustained exposures to
> temperatures greater than 10^o^ C (50^o^ F) will occur.

-   Remote sensing surveys can narrow and refine search patterns for
    chemosynthetic communities, but do not provide certainty of their
    presence or absence.

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-   ![](media/image2.jpeg){width="2.3055555555555554in"
    height="1.398611111111111in"}Larval recruitment from external
    locations could recolonize chemosynthetic community sites that
    suffer a loss of population. The DNA fingerprinting of seep mussels
    and tubeworms demonstrated that genetic exchange among study sites
    is adequate to sustain species integrity across the sites.

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-   Gas hydrates, crystalline solids consisting of gas molecules
    (usually methane) each surrounded by a cage of water molecules, look
    very much like water ice and are stable in ocean floor sediments at
    water depths greater than 300 m (984 ft). Gas hydrates appear to be
    an intermediate source for dissolved gases necessary to seep
    communities and a new species of polychaete (worm) was discovered
    living in burrows on shallow hydrate deposits.

> ![](media/image3.jpeg){width="2.25in" height="1.25in"}An Iceworm
> living in burrows on gas hydrate (orange).

-   In contrast to rapid tubeworm growth at hydrothermal vents, cold
    seep tubeworms grow very slowly. It is It is estimated that worms 2
    m in length are from 170 to 250

> years old. A large cluster of tubeworms indicates an area where
> hydrocarbons have seeped continuously for several hundred years.

-   Significant production of an oil field does not appear to affect the
    health of chemosynthetic communities. Over 10 years of observations
    have shown that the densely populated, tubeworm-dominated "Bush
    Hill" community (named for the bush-like appearance of the large
    tubeworms) continues to flourish in an active oil field where
    approximately 28 million barrels of oil and 120 trillion cubic feet
    of natural gas have been produced since 1989.

> ![](media/image4.jpeg){width="2.5in"
> height="1.445138888888889in"}Tubeworms and mussels flourishing at
> \"Bush Hill\" in the Central Gulf of Mexico.

**Protecting Chemosynthetic**

**Communities**

The MMS provides guidelines to offshore oil and gas operators regarding
implementation of a special lease stipulation or regional requirement
through a Notice to Lessees and Operators (NTL). Two GOM NTL's provide
protection for chemosynthetic communities.

1.  ![](media/image5.png){width="0.9751968503937007in"
    height="0.8901574803149607in"}![](media/image6.jpeg){width="2.3653543307086613in"
    height="0.3889763779527559in"} NTL (No. 2000-G20) provides a
    consistent and comprehensive approach to protecting high-density
    chemosynthetic communities from damage caused by oil and gas
    activities. This NTL requires that activities disturbing the
    seafloor in water depths of 400 m (1312 ft) or more maintain a
    separation distance of at least 457 m (1500 ft) from features or
    areas that could support high-density chemosynthetic communities for
    each proposed drilling discharge location. A minimum separation
    distance of 76 m (250 ft) is required for all other proposed
    seafloor disturbances, including anchors, anchor chains, wire ropes,
    seafloor template installations, and pipeline construction. If the
    offshore oil and gas industry proposes exploration or development
    activities that could disturb seafloor areas in water depths of 400
    m (1312 ft) or greater, this NTL requires the submission of
    environmental information specifically directed to chemosynthetic
    community identification and delineation.

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2.  *Remotely Operated Vehicle (ROV) Surveys in Deepwater* NTL (No.
    2001-G04) requires the acquisition of biological and physical
    information from ROV surveys before and after certain oil and gas
    exploration and development activities in the deepwater Gulf of
    Mexico \[water depths greater than 400 m (1312 ft)\]. This NTL
    provides protection to chemosynthetic communities as well as
    hardbottom and outcrop deepwater benthic communities that may be
    observed through the ROV surveys. An ROV survey plan is part of each
    offshore oil and gas Exploration Plan that proposes activities in
    water depths greater than 400 m (1312 ft) in the central and western
    Gulf of Mexico. An ROV survey plan is also required with the first
    Development Operations Coordination Document proposing a surface
    structure in each of 18 defined grid areas of ecological similarity.
    The ROV surveys are conducted in each grid to investigate the
    possible occurrence of high-density biological communities on the
    seafloor prior to development of oil fields.

In the face of increasing development of deepwater oil and natural gas
resources in the GOM, the MMS carefully designs research projects to
provide information needed for environmentally sound resource
management. The MMS applies new research results with the existing body
of information to frame protective measures for the continued health of
chemosynthetic communities in the GOM.

> ![](media/image7.jpeg){width="1.8in" height="1.1569444444444446in"}A
> manned research submersible sampling tubeworms at chemosynthetic
> community sites.