Shallow-water hydrothermal vents occur world-wide in regions of volcanic activity. The vents located at Tutum Bay, Ambitle Island, Papua New Guinea are unique in that the vent fluids and surrounding sediments contain some of the highest concentrations of arsenic in a natural system. This study addresses the effects of the vent system on the benthic communities, focusing on the eukaryotes, macrofauna, meiofauna and bacteria. Samples were collected in November 2003 and May/June 2005. Analysis of the 2003 macrofaunal samples indicated that pH, rather than arsenic was influencing the benthic community, and that the hydrothermal influence occurred at a greater distance than expected. Results of more intensive sampling carried out in 2005 are the primary focus of this dissertation. The pore water and sediment characteristics revealed distinct physical habitats corresponding with distance from the vent. There was a trend of decreasing temperature and arsenic concentration and increasing salinity and pH with distance from the vent. The vent sediment was poorly sorted volcanic gravel, while sediments along the transect showed a gradient from fine, well sorted volcanic sands to coarser carbonate sands farther away. The macrofauna showed a trend of increasing diversity with distance from the vent and similar taxa were present in both the 2003 and 2005 samples. The vent community was dominated by the polychaete Capitella cf. capitata. The inner transect from 30 m to 140 m had low diversity. Dominant taxa included thalassinid shrimp and the amphipod Platyischnopus sp.A. The 180 m to 300 m sites had significantly higher diversity. The Danlum Bay reference site had relatively higher diversity than the nearshore transect sites and was dominated by deposit feeding polychaetes. Macrofaunal community structure was influenced by the sediment characteristics, notably by CaCO3 content, sorting and median grain size. The meiofaunal community also showed changes with distance from the vent. Chromadorid nematodes were dominant at the vent site and were a major component of the meiofauna at most sites, along with copepods. The meiofaunal community at the reference site showed greater similarity to the vent community and both sites had low abundances. Nematodes were more abundant than copepods near the vent, but copepods were more abundant farther offshore and at the reference site. Meiofaunal community structure was influenced primarily by the pore water temperature and salinity. Biological interactions with the macrofaunal community through physical disturbance and predation may also influence the meiofaunal community.  The molecular analysis of eukaryotic and bacterial diversity also revealed changes with distance from the vent. The 0 m and reference sites grouped together due to the presence of fungal sequences and the 140 m and 300 m sites grouped together due to a common molluscan sequence. Metazoans and fungi dominated the eukaryote sequences. The most abundant eukaryotic OTUs included fungi matching Paecilomyces sp. and Cladosporium cladosporioides and metazoans matching Viscosia viscosa (Nematoda) and Astarte castanea represented by 24 phyla and was dominated by Actinobacteria and γ-Proteobacteria. More bacterial phyla were present near the vent, while more overall OTUs were found at the intermediate sites along the transect. The most distant site had much lower diversity dominated by Firmicutes. The macrofaunal community had the strongest correlation with environmental variables. Comparison between the meiofauna and the metazoan sequences showed the proportion of nematodes found in both datasets were comparable, but the meiofauna analysis found a higher proportion of arthropods, while the molecular results were disproportionally high for platyhelminthes. Overall, the vents increased the complexity of the system by creating unique habitats. The extreme environment created by the hydrothermal activity maintained the surrounding habitat at an early successional stage colonized by a few opportunistic species. There was a gradation in the benthic communities away from the vent towards a more carbonate based climax community. The low pH environment had an effect on the sediment composition, which in turn influenced the benthic community. These findings can serve as a model for studying the potential effects of ocean acidification and climate change on benthic communities and marine biocomplexity.

Artificial reefs (ARs) are generally created with the intention of increasing local fish populations, biodiversity and corresponding habitat productivity, most often in support of commercial and recreational uses (e.g., diving and fishing). Numerous studies have investigated the communities that develop on artificial reefs. By contrast, far less research has focused on the surrounding infaunal communities, which represent critical trophic resources for many species that populate both natural and artificial reefs, and which may be affected both by AR deployment and the organisms that subsequently recruit to them. This study compared infaunal organism abundances at four sites between the inner and middle reefs off Broward County, Florida, before deployment of a series of Florida Department of Transportation (FDOT) AR boulders in 2009 (pre-construction) and four years later in 2013 (post-construction). Samples consisted of sediment collected in hand-held core tubes taken on open sediment adjacent to the proposed ARs and along transects at distances 3 m and 7 m from the ARs post-construction. Sample depths ranged from 12.1 to 14.6 m. Analyses were carried out on organisms retained on a >0.5 mm sieve and identified to the lowest practical taxonomic level. Data consisted of abundances rather than densities, because pre-construction samples did not record sediment volume per core. A total of 163 taxa were identified, of which only 50 were identified to genus and 64 to species. Polychaete families Spionidae, Sabellidae, Syllidae, and Hesionidae, and sipunculan superfamily Phascolosomatidea dominated pre-construction samples. Polychaetes also dominated post-construction samples, with high relative abundances of Sabellidae and Hesionidae, but with increased proportions of bivalves and amphipods. Statistical analyses (PRIMER, PERMANOVA, and SIMPER) determined whether infaunal composition, richness and, diversity differed among samples by year, site and distance from AR boulders. A slight but statistically insignificant difference in species diversity appeared between 3- and 7-m distances between years. However, composition, richness, and diversity of infauna did not differ either between pre-and post-construction samples or by sample distance from the adjacent AR boulders. The increase in homogeneity among samples post-construction may reflect recovery following the disturbance created by AR deployment, or a response to different benthic conditions generated by AR deployment. As other studies have suggested that AR fauna may influence surrounding infaunal communities to distances greater than 7 m, and that conditions may not stabilize around ARs for up to ten years following deployment, additional sampling is recommended to determine the longer-term effects of the FDOT ARs on infauna and benthic habitat (e.g., sediment composition, water movement) and assist in determining best practices for future AR deployments (e.g., composition, structure, location).