Geological effects on faunal distributions on the Cleft segment, Juan de Fuca Ridge
Date
1993
Authors
Milligan, Barry
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Abstract
Biological samples comprising high and low temperature vents ranging from a few to hundreds of years of age were taken within a few years of an eruption on the Cleft Segment of the Juan de Fuca Ridge. Cleft Segment is characterized by four active venting areas ranging from years to hundreds of years old. I hypothesized that older venting areas on Cleft Segment would be more speciose than younger areas. Cleft Segment is characterized by a very low number of species (24), although Cleft Segment represents the greatest areal extent, the most vents sampled, and the most specimens processed. Cleft Segment is taxonomically dominated by phyllodocid and terebellid polychaetes and archaeogastropods, and numerically dominated by 6 species (Ridgeia piscesae, Paralvinella pandorae, Lepetodrilus fucensis, Depressigyra globulus, Amphisamytha galapagensis, and Paralvinella sulfincola). Poor species richness may be explained by young age and very recent magmatic and tectonic activity, less habitat heterogeneity (possibly reducing niche availability), and regional current patterns that may not foster larval influx. The species composition of Cleft Segment is similar to that of other Northeast Pacific vents, suggesting good dispersive ability of Cleft inhabitants. The presence of vent organisms on the New Pillow Mounds (NPM) demonstrates that vent animals are colonizing new vents within at most 2 to 6 years.
There is a significant difference in species composition, but not species diversity or richness, among active venting areas of Cleft Segment. P. pandorae and L. fucensis is more abundant at South Cleft and D. globulus is more abundant at Young Sheet Flow (YSF) and Older Northern Lavas (ONL). Ridgeia piscesae dominated at South Cleft and ONL while A. galapagensis was absent from South Cleft and P. sulfincola was absent from YSF. Differences in species assemblages corresponded to differences in temperature and/or substratum, and distance the sample was taken from the active venting source or orifice. Within areas, and even within vents, there are differences in community structure corresponding to differences in temperature or substrata to which vent organisms are exposed. Paralvinella pandorae, L. fucensis, and A. galapagensis appear adapted to low temperature venting whereas R. piscesae, D. globulus, and P. sulfincola appear adapted to high temperature venting. Factors such as restricted settling space and competition do not appear to be important in structuring community assemblages at Cleft Segment. However, one cannot rule out the possibility that competition is occurring, or has occurred, at Cleft Segment. The documented decline of vent flow and vent fauna during this study indicate that underlying geological and chemical processes have a serious effect on community composition.
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UN SDG 14: Life Below Water