The composition, recruitment rates and fine-scale spatial dynamics of the sessile benthic community occupying hard substrata off Lee Stocking Island, The Bahamas, was determined through photography and the deployment of artificial substrata from September 1993 to September 1996. The study spanned 10 to 250 meters in depth. The benthic community exhibited a pronounced bathymetric zonation. Filamentous and macroalgae dominated the shallow communities , but were replaced by corals, sponges and endolithic algae with increasing depth. Living cover was high above 100 m, but declined significantly below this depth, being replaced by increasing amounts of bare and sediment-covered rock surfaces. Benthic zonation was shifted downward with respect to other locations in the western Atlantic, possibly due to the clear waters of Exuma Sound allowing relatively deep light penetration. Recruitment experiments were deployed during two time inten :als from 1994 to 1995. The experiments enabled the analysis of the effects of five treatments which differed in depth, orientation and degree of exposure. Recruitment of all sessile taxa declined sharply with depth. Peak recruitment for most taxa occurred between 20 m and 50 m. Recruitment experiments retrieved from sites located above 50 m exhibited high cover of :filamentous and macroalgae on exposed surfaces. Sponges, corals and other invertebrates dominated the cryptic surfaces. Dominance by polychaetes characterized the deeper sites. Fine-scale changes in community structure were determined through repeat photography of natural substrata and artificial settling panels. Numerical change indices were generated for changes in cover and additions and losses of individual organisms occurring over time. Each change index began at a relatively low value at the 10 m depth, increased to a maximum value at 30 m or 50 m and then declined with increasing depth. Numbers of fish grazing scars were positively correlated with the loss index and negatively correlated \\ith algal cover, suggesting that fish contribute to fine-scale changes in the sessile community. Important contributors to fine-scale spatial changes within the benthic community shift from algae to corals to sponges with increasing depth.

PhD, Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2010 / The aim of this investigation was to provide a proper design procedure for Merensky crush pillars, based primarily on underground measurements. Three sites with a variety of geotechnical conditions were selected. An interaction between the pillars and the rock mass around the stopes was shown by the literature, relevant laboratory tests and numerical modelling. During the investigations, nonlinear rock behaviour was observed at one of the sites. Further studies revealed that nonlinear behaviour also occurred in samples extracted from high stress conditions at the other sites, but the rock mass was not nonlinear at these sites. A methodology for determining stress from strain measured in nonlinear rock was established. The research also established that there is an approximately linear relationship between peak pillar strength and w/h ratio at ratios between about 1.2 and 8. The so called ‘squat’ effect is not observed because pillar failure is not contained within the pillar but extends into the foundations. A linear peak pillar strength formula was established from back analyses of underground pillar failures and was confirmed by numerical modelling. Pillar behaviour was established from underground measurements on one stability pillar and six crush pillars, which included peak and residual strengths. Also, stable and unstable loading conditions were established from an analysis of pillar bursts and the minimum strata stiffness for stable pillar failure was determined. This stiffness is only achieved near the advancing face and pillars that fail in the back areas are likely to burst. For this reason, pillar design needs to include the peak strength as large pillars may be too strong and fail in the back area. The residual strength also needs to be considered as the load-bearing capacity of these pillars needs to satisfy the criterion of 1 MPa across the stope to prevent back-breaks. This translates into a pillar stress of between 8 MPa and 13 MPa if the pillar lines are spaced 30 m apart. The peak and residual requirements have been included in a design chart, and the relationship between w/h ratio and residual strength is provided in a graph for easy design.

Artificial reefs are important management tools for red snapper, Lutjanus campechanus, fisheries in the Northern Gulf of Mexico. I deployed fish traps (0.97 m long; 0.64 m height; 175 x 115 mm funnel mouth size) to collect red snapper < 406 mm total length (TL) associated with pyramid-shaped artificial reef structures (3.7 m triangular base; 2.4 m height; 3.2 metric tons) to evaluate two reef distribution designs: (1) five closely-spaced pyramid units, and (2) five closely-spaced pyramids with two sets of two pyramids at 30.5, 61.0, and 91.5 m from the five pyramids. In 26 sampling trips, 927 red snapper were captured. Catch per unit effort (fish/hour) did not differ significantly among patterns (P= 0.396). Red snapper lengths differed significantly among patterns (P= 0.005), with the largest mean total length (235 mm, SE= 5.14) occurring at the pattern with 61.0-m spacing.

No description available.

No description available.

Productivity, diversity and survival of estuaries are threatened by explosive coastal population growth and associated recreational activities. One major area of recreational growth has been the number of small pleasure craft motoring in shallow waters at high speeds. On the east coast of Central Florida in the Indian River Lagoon system, intense boating activity occurs year-round and intertidal reefs of the eastern oyster Crassostrea virginica with dead margins (piles of disarticulated shells) on their seaward edges are commonly found adjacent to major boating channels. The cause(s) of the dead margins is unclear. However, the disarticulated shells may be reducing reef sustainability if these surfaces are unavailable for larvae. Recruitment trials were run on eight reefs (4 with dead margins, 4 without) in three 8-week trials in 2001/2002. Significant differences were found for location on reef and season. For survival of recruits, significant differences were found for reef type, location on reef, and season. Sediment loads, percent silt/clay, and relative water motion were all found to be significantly higher on impacted reefs. Spring months were found to be the optimal time for larval recruitment to increase larval set and survival and to also decrease the effects of sedimentation and water motion. Based on these results, experimental restoration began May 2003 to develop an ecologically and economically feasible restoration protocol for this intertidal region. Four different densities of shells (0, 16, 25, 36) were attached to vexar mesh mats (45 X 45 cm) displaying shells perpendicular to the substrate. 360 mats were randomly deployed at one of six dentified optimum recruitment locations. Recruitment increased through June and was significantly higher on mats with 36 shells. This was followed by a large, expected decline in recruitment and survival in July/August, due to competition, predation and/or extreme high temperatures. Total live oysters on the restoration mats significantly increased during October 2003 through February 2003. These newly-created oyster reefs are moveable and provide optimal substrate and larval set to be transported post-recruitment to areas resource managers have slated for restoration to aid in reef sustainability. To determine the potential negative effects of flow and sediment levels on oyster larval settlement, which may be associated with an increase in boating actitivity, laboratory experiments were conducted. Eighteen trials, with competent oyster larvae, nine in flowing-water and nine in still-water were run at three sediment levels: no sediment, low sediment, and high sediment loads. Larval settlement was significantly higher in the still-water trials and both high and low sediment loads significantly reduced larval settlement.

<p> Four coral reef sites were observed in Spermonde Archipelago, off Southwest Sulawesi, Indonesia The sites were located at different distances from the mainland: Kayangan reef ('affected' site) is the closest and Samalona, Barang Lompo, and Kapoposan ('comparison' sites) are successively farther from the mainland and Ujung Pandang city. </p> <p> Coral cover, number of species at 3m and 1Om depths, and coral growth rates (Porites lobata) were observed to describe coral conditions. Environmental parameters suspended particulate matter (SPM), resuspended sediment, salinity, clarity, chlorophyll a, phosphate, nitrate, ammonium and o15N values ofcoral tissue (P. lobata) were also investigated to assess possible 'stress' factors on the reefs. </p> <p> Average coral cover at the 'affected' site was very low (14 %), compared to the other sites: Samalona (44.3 %), B. Lompo {47.2 %) and Kapoposan {66.6 %). Also, the lowest total number ofspecies occurred at Kayangan (42 spp.), compared to the other sites: Samalona {62 spp.), B. Lompo {71·spp.) and Kapoposan (80 spp.) </p> <p> Environmental parameters indicated that sedimentation and eutrophication (sewage) were the main 'stress' factors at Kayangan reef: while human disturbances such as fish bombing. anchoring. coral collection, and other activities affected Samalona and B. Lompo more. High coral cover and number of species at Kapoposan reef indicated fewer 'stress' factors. </p> <p> Coral growth rates showed a different trend from coral cover and total number of species. The highest coral growth rates occurred at B. Lompo (15.9 ± 0.8 mm yr-1) followed by Kayangan, Samalona and Kapoposan. Based on environmental parameters, it seemed that coral growth rates were higher at more eutrophic reefs, but slower at certain maximum critical nutrient values. </p> <p> δ^15 values of coral tissue found in this study are positively correlated with chlorophyll a, dissolved nutrients, and sedimentation rates. The high δ^(15)N values at Kayangan (8.03 ± 0.62 %) support the idea that this site was affected by human waste and sewage. </p> / Thesis / Master of Science (MSc)

No description available.

No description available.

Synthetic marine habitats such as artificial reefs (ARs) are deployed to offset marine habitat losses and aid conservation of marine communities, including species at risk. Though environmental benefit is often assumed, AR’s ability to support northern temperate marine fish communities has rarely been tested. The structural orientation and location of a reef can strongly influence biodiversity and productivity of faunal communities inhabiting it. For ARs, understanding how reef characteristics affect species and community composition are key in optimizing their use in conservation initiatives. I used ROV and sonar to survey threatened rockfish (Sebastes spp.) and other groundfish species associated with 18 ARs and natural reefs (NRs) along the northeast Pacific coastal shelf, along the coast of BC, Canada. In my second chapter, I investigate how ARs compare to NRs in achieving conservation objectives as measured by fish abundance and species richness. I found that community composition significantly differed between NRs and ARs. ARs had high variability in rockfish abundance, while NRs consistently supported intermediate rockfish abundances. Groundfish diversity was markedly greater on NRs. Depth and relief significantly explained variability in abundance and species richness. Interestingly, rockfish abundance was negatively associated with proximity to nearest rockfish conservation area. In my third chapter, I assess variation between AR fish communities on six reefs to better understand efficacy of meeting conservation objectives. I quantified structural characteristics of each reef using high-definition sonar data to create three-dimensional models and calculate measurements of reef structure. I also examined the effects of surrounding habitat associated with reef locations. I found that depth, conservation status, rugosity, and reef age significantly explained rockfish abundance. Groundfish species richness was significantly associated with conservation status, relief, reef size, and an interaction between depth and reef age. This research is a first step in proposing underlying mechanisms for differences between fish communities on ARs in BC, and which reef attributes facilitate successful contributions to conservation. Though ARs show promise in the conservation of some threatened species, the maintenance of diverse fish communities may depend on protection of heterogeneous natural reef communities. Given that a critical component of AR success is structure, using three-dimensional technologies can be used as a tool to understand species-habitat association on existing reefs and help predict the success of future reefs. / Graduate