COMMUNITY STRUCTURE OF HYDROTHERMAL VENTS AT THE EASTERN-LAU SPREADING CENTER
Open Access
- Author:
- Zelnio, Kevin Andrew
- Graduate Program:
- Biology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- Charles Raymond Fisher Jr., Thesis Advisor/Co-Advisor
- Keywords:
- Sagartiogeton
Chondrophellia
Alvinactis
Cyananthea
Cnidaria
Hexacoralia
Actiniaria
Anemone
Phylogeny
Mitochondrial COI
Shrimp
Deep Sea
Southwest Pacific
Lau Basin
Alvinocarididae
Caridea
Alvinocaris
Hydrothermal Vent
Actinoscyphiidae
Hormathiidae
Sagartiidae
Community Ecology
Diversity
Distribution - Abstract:
- Deep sea hydrothermal vents form at plate boundaries and volcanic hotspots. Cold seawater seeping through fissures in the seafloor comes into contact with superheated rock above the magma chamber. The heated seawater rises carrying dissolved metals and sulfides that precipitate out of solution when it comes into contact with the cold water at seafloor’s surface, forming chimney-like structures. The Eastern-Lau Spreading Center (ELSC) in the Lau back-arc basin contains dense aggregations of chemoautotrophic macrofauna including two snails, <em>Alviniconcha</em> sp. and <em>Ifremeria nautilei</em>, and the mussel, <em>Bathymodiolus brevior. Each chemoautotrophic macrofaunal species occupies a defined thermo-chemical range. <em>Alviniconcha</em> sp. is found in areas closest to the hydrothermal source where oxygen levels are lower, temperature is higher and sulfide concentrations are higher, whereas <em>B. brevior </em> occupies a microhabitat closer to the other end of the thermo-chemical spectrum. <em>Ifremeria nautilei</em> occupies a thermo-chemical tolerance range overlapping the upper and lower distributions of <em>B. brevior</em> and <em>Alviniconcha</em> sp., respectively. In this study, 36 quantitative community samples from each of the chemoautotrophic macrofauna were collected from four sites with depths ranging from 1700 m in the south to 2800 m in the north. In general, communities associated with <em>Alviniconcha</em> sp. were lower in abundance and higher in Shannon diversity index and Pielou’s evenness index, yet had fewer numbers of species. Though Bray-Curtis similarity between <em>I. nautilei</em> and <em>B. brevior</em> hosted communities was significantly different (ANOSIM, Global R=0.82, P=0.02; Chapter 3: Table 6) there was a qualitative trend of higher abundance and biomass and lower Shannon diversity index, Pielous’s evenness index and mean number of species in collections of <em>B. brevior</em> relative to <em>I. nautilei</em> collections. There were distinct groups (ANOSIM: Global R=0.51, P=0.001; Chapter 3: see Table 6 for pairwise comparisons and Figure 6 for multidimensional scaling plot) of each community type in multi-dimensional space based on Bray-Curtis similarity. When grouped by study site, communities from southernmost Tu’i Malila had significantly higher Shannon diversity index, Pielou’s evenness index and mean number of species than the northernmost locality, Kilo Moana. In multi-dimensional space, only Tu’i Malila formed a distinct nonoverlapping group based on Bray-Curtis Similarity while the two northern sites, Kilo Moana and TowCam, formed a distinct group and collections from ABE were interspersed. This thesis also contains taxonomic work on a new species of caridean shrimp (Chapter 1) and the hexacorallian fauna of the ELSC hydrothermal vents (Chapter 2). The new species of shrimp is in the family Alvinicarididae and genus <em>Alvinocaris</em>, a taxon specialized to deep-sea chemosynthetic ecosystems. A combination of morphological characters set it apart from known described species. Autapomorphies included a well-defined mesial notch in the telson and 2 rows of accessory spinules on the third to fifth pereopods. Analysis of the mitochondrial COI gene supports its position as a new species and confirms similar patterns within the family Alvinocarididae as found in previous molecular studies. A key to family Alvinocarididae is included. Additionally, four species of anemone, from the vicinity of hydrothermal vents at ELSC are described based on morphology. They are put into the genera <em>Cyananthea</em>, <em>Alvinactis</em> (Actinoscyphiidae), <em>Chondrophellia</em> (Hormathiidae) and <em>Sagartiogeton</em> (Sagartiidae). Two additional morphotypes from the families Actinostolidae and Hormatiidae could not be further identified based on existing material but contain notes on their morphology and distribution. The morphology and distribution of the first record of an abundant zoanthid from a hydrothermal vent is also noted, but not described.