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Dispersal Boundaries and Species Composition of Hydrothermal Ecosystems on the Southern Mid-Atlantic Ridge
To What Extent do the Equatorial Atlantic Fracture Zones Impact the Dispersion, Biogeography and Evolution of Vent-Endemic Fauna?
Shank
The tight coupling between geological processes and living organisms at hydrothermal vents provides a singular opportunity to study how fundamental planetary processes shape the evolution of life. These tightly linked geological-biological systems have yielded a global network of extraordinarily productive chemosynthetic communities. The spatial and temporal variability within this network has created distinct biogeographic provinces that are influenced by a variety of underlying forces. Significant advances in our understanding of how ridge crest processes shape life can be achieved by identifying key mid-ocean ridge localities that will yield large first order "jumps" in our knowledge of faunal evolution and biogeography.
Fracture Zones of the equatorial Atlantic.
The Romanche
FZ separates the N. Atlantic from the S. Atlantic. The large offsets
in the
ridge crest caused by the Romanche and Chain Fracture Zone are
posited to
be the isolating mechanism between the Northern MAR and Indian
Ocean
fauna. The most southern known vent site in the Atlantic, Logatchev
(14°45N; red circle; Gebruk et al. 2001), is the closest known
Atlantic
site to the Kairei/Edmond fields on the Central Indian Ridge.
Field area
(indicated) of the proposed studies contains the only hydrothermal
signal
known in the South Atlantic.
Biogeographic patterns suggested by the recent discovery of Indian
Ocean vent fauna raise fundamental hypotheses to address the marked
“disconnect” between North Atlantic fauna and other ridge crest
hydrothermal communities. In 2005, we will test our hypotheses that
the major fracture zones of the Equatorial Atlantic prevent or inhibit
along-axis transport and communication of vent-endemic fauna into
(and out of) the South Atlantic. Specifically, the large geographic
ridge offsets posed by the Romanche and Chain Fracture Zones and
the strong regional unidirectional current flow across and through
the Equatorial Atlantic Fracture Zones represent a hydrographic,
bathymetric, and biogeographic barrier that bisects the Mid-Atlantic
Ridge into northern and southern provinces.
Location of 13 CTD stations (circles) within the segments
(enumerated) taken during a SMAR cruise (PI Chris German) in October 2001)
between the Chain and Boca Verde FZs. While evidence for hydrothermal
venting was observed at several stations, the A1 segment plume signal
anomalies (red circle) were equivalent to plume signals from known sites on
the MAR
We will determine the biological character of vent fields on the
unexplored Southern Mid-Atlantic Ridge. We also will determine how
these potentially unique ecosystems relate to the global biogeographic
framework as we investigate dispersal and evolutionary patterns
of vent fauna, by assess the role of the Equatorial Atlantic Fracture
Zones as barriers to species dispersal, and influencing the evolution
and biogeography of South Atlantic vent fauna. South Atlantic vent
communities will be characterized by determining the precise location
of active venting and quantitatively assessing the distribution,
abundance, and variation in microhabitat structure as they relate
to hydrothermal activity and geological features via detailed downlooking
imaging surveys using the autonomous vehicle ABE (Autonomous Benthic
Explorer). Anticipated sampling of these characterized vent ecosystems
on equatorial ridges connecting Atlantic Ocean basins will provide
novel insights into processes controlling basin-scale biogeographic
and evolutionary patterns. Manipulative experiments are focused
on removal and subsequent exclusion of mussels from selected regions
of mussel-dominated assemblages, coupled with detailed geochemical
and microbiological characterization of associated microhabitats
before and after mussel removal. Subsequent recruitment and colonization
within exclusion cages in denuded and control areas are being followed
through successive removal and analysis of deployed basalt blocks
over time. Concomitant chemical, physical and microbiological analyses
of fluids permit correlation of these parameters with temporal changes
in community structure.