The source of the Great Dyke, Zimbabwe, and its tectonic significance: Evidence from Re-Os isotopes

Re-Os data for chromite separates from 10 massive chromitite seams sampled along the 550-km length of the 2.58-Ga Great Dyke layered igneous complex, Zimbabwe, record initial 187Os/188Os ratios in the relatively narrow range between 0.1106 and 0.1126. This range of initial 187Os/188Os values is only slightly higher than the value for the coeval primitive upper mantle (0.1107) as modeled from the Re-Os evolution of chondrites and data of modern mantle melts and mantle derived xenoliths. Analyses of Archean granitoid and gneiss samples from the Zimbabwe Craton show extremely low Os concentrations (3-9 ppt) with surprisingly unradiogenic present-day 187Os/188Os signatures between 0.167 and 0.297. Only one sample yields an elevated 187Os/188Os ratio of 1.008. Using these data, the range of crustal contamination of the Great Dyke magma would be minimally 0%-33% if the magma source was the primitive upper mantle, whereas the range estimated from Nd and Pb isotope systematics is 5%-25%. If it is assumed that the primary Great Dyke magma derived from an enriched deep mantle reservoir (via a plume), a better agreement can be obtained. A significant contribution from a long-lived subcontinental lithospheric mantle (SCLM) reservoir with subchondritic Re/Os to the Great Dyke melts cannot be reconciled with the Os isotope results at all. However, Os isotope data on pre-Great Dyke ultramafic complexes of the Zimbabwe Craton and thermal modeling show that such an SCLM existed below the Zimbabwe Craton at the time of the Great Dyke intrusion. It is therefore concluded that large melt volumes such as that giving rise to the Great Dyke were able to pass lithospheric mantle keels without significant contamination in the late Archean. Because the ultramafic-mafic melts forming the Great Dyke must have originated below the SCLM (which extends to at least a 200-km depth ), the absence of an SCLM signature precludes a subduction-related magma-generation process.

Feeding ecology of the fish ectoparasite Gnathia sp. (Crustacea: Isopoda) from the Great Barrier Reef, and its implications for fish cleaning behaviour

The feeding rate of a parasitic gnathiid isopod on fish was examined. Individual fish, Hemigymnus melapterus, were exposed to gnathiid larvae and sampled after 5, 10, 30, 60, and 240 min. I recorded whether larvae had an engorged gut, an engorged gut containing red material, or had dropped off the fish after having completed engorgement; variation among sampling times and larval stages was analyzed using generalized linear mixed model analyses. The likelihood that larvae had an engorged gut increased with time and varied with larval stage. First stage (1.45 mm) larvae. After 30 min, however, most (>93%) larvae had an engorged gut regardless of their larval stage. The likelihood of red material in the gut of third stage larvae increased over time (46% after 30 min, 70% after 60 min, and 86% after 240 min) while that of first and second stage larvae remained relatively low (

Nitrogen ecophysiology of Heron Island, a subtropical coral cay of the Great Barrier Reef, Australia

Coral cays form part of the Australian Great Barrier Reef. Coral cays with high densities of seabirds are areas of extreme nitrogen (N) enrichment with deposition rates of up to 1000 kg N ha(-1) y(-1). The ways in which N sources are utilised by coral cay plants, N is distributed within the cay, and whether or not seabird-derived N moves from cay to surrounding marine environments were investigated. We used N metabolite analysis, N-15 labelling and N-15 natural abundance (delta(15)N) techniques. Deposited guano-derived uric acid is hydrolysed to ammonium (NH4+) and gaseous ammonia (NH3). Ammonium undergoes nitrification, and nitrate (NO3-) and NH4+ were the main forms of soluble N in the soil. Plants from seabird rookeries have a high capacity to take up and assimilate NH4+, are able to metabolise uric acid, but have low rates of NO3- uptake and assimilation. We concluded that NH4+ is the principal source of N for plants growing at seabird rookeries, and that the presence of NH4+ in soil and gaseous NH3 in the atmosphere inhibits assimilation of NO3-, although NO3- is taken up and stored. Seabird guano, Pisonia forest soil and vegetation were similarly enriched in N-15 suggesting that the isotopic enrichment of guano (delta(15)N 9.9parts per thousand) carries through the forest ecosystem. Soil and plants from woodland and beach environments had lower delta(15)N (average 6.5parts per thousand) indicating a lower contribution of bird-derived N to the N nutrition of plants at these sites. The aquifer under the cay receives seabird-derived N leached from the cay and has high concentrations of N-15-enriched NO3- (delta(15)N 7.9parts per thousand). Macroalgae from reefs with and without seabirds had similar delta(15)N values of 2.0-3.9parts per thousand suggesting that reef macroalgae do not utilise N-15-enriched seabird-derived N as a main source of N. At a site beyond the Heron Reef Crest, macroalgae had elevated delta(15)N of 5.2parts per thousand, possibly indicating that there are locations where macroalgae access isotopically enriched aquifer-derived N. Nitrogen relations of Heron Island vegetation are compared with other reef islands and a conceptual model is presented.

Sustainable Management of the Great Artesian Basin: An Analysis Based on Law and Environmental Economics

Current policy issues surrounding management of the Great Artesian Basin - historical development of existing legislation and institutions - hydrological and historical background information - development of concerns over unsustainable use of resources and possible adverse environmental impacts - recent developments associated with the general reforms to water law and policy initiated by the Council of Australian Governments (COAG) - comparison of issues surrounding the Murray-Darling Basin and the Great Artesian Basin.

Water quality monitoring: A combined approach to investigate gradients of change in the Great Barrier Reef, Australia

For the managers of a region as large as the Great Barrier Reef, it is a challenge to develop a cost effective monitoring program, with appropriate temporal and spatial resolution to detect changes in water quality. The current study compares water quality data (phytoplankton abundance and water clarity) from remote sensing with field sampling (continuous underway profiles of water quality and fixed site sampling) at different spatial scales in the Great Barrier Reef north of Mackay (20 degrees S). Five transects (20-30 km long) were conducted from clean oceanic water to the turbid waters adjacent to the mainland. The different data sources demonstrated high correlations when compared on a similar spatial scale (18 fixed sites). However, each data source also contributed unique information that could not be obtained by the other techniques. A combination of remote sensing, underway sampling and fixed stations will deliver the best spatial and temporal monitoring of water quality in the Great Barrier Reef. (c) 2004 Elsevier Ltd. All rights reserved.

Revision of Telotrema Ozaki, 1933 (Digenea : Gyliauchenidae Fukui, 1929), including the description of a new species from an acanthurid fish from the Great Barrier Reef, Queensland, Australia

We describe one new species of Telotrema Ozaki, 1933 from the intestine of an acanthurid fish of the Great Barrier Reef. Telotrema brevicaudatum n. sp. is described from 2 mature specimens from the yellowfin surgeonfish, Acanthurus xanthopterus Valenciennes, 1835 ( Acanthuridae), from waters off Lizard Island, Queensland, Australia. This species is distinguished from the type-species, Telotrema caudatum Ozaki, 1933, by the smaller excretory papilla, the massive pars prostatica, the unipartite, globular seminal vesicle, and the intertesticular position of the ovary. The proposal of a new species of Telotrema necessitates re-examination of the generic diagnosis, and the genus is here redefined in light of the morphology of T. brevicaudatum. Telotrema is distinguished from Gyliauchen Nicoll, 1915 by the possession of a ventral sucker which is larger than the pharynx, a straight or sigmoid oesophagus, an extensive and dense vitellarium, and a distinct excretory papilla. We here recognise 3 species and distinguish them in a key. The biogeographical range for species of Telotrema now includes acanthurid and pomacentrid fishes of the western Pacific Ocean.

Prosorhynchoides lamprelli n. sp (Digenea : Bucephalidae) from the brassy trevally, Caranx papuensis (Teleostei : Carangidae), from off Lizard Island on the Great Barrier Reef, Australia

Prosorhynchoides lamprelli n. sp. ( Digenea: Bucephalidae) is described from the intestine of the brassy trevally, Caranx papuensis (Carangidae) from off Lizard Island, Great Barrier Reef, Australia. The new species is differentiated from other species of Prosorhynchoides Dollfus, 1929 by the shape and distribution of its vitelline follicles, the shape and extent of its uterus and the configuration of its digestive system. This is the first bucephalid to be described from Caranx papuensis; we have not encountered this species from other carangids or from over 1,500 individuals of other teleosts species we have found to be infected with bucephalids from the Great Barrier Reef.

Grammatorcynicola n. g. (Bucephalidae : Dolichoenterinae) from Grammatorcynus spp. (Scombridae) on the Great Barrier Reef, Australia

A new trematode genus, Grammatorcynicola n. g. (Bucephalidae: Dolichoenterinae), and two new species, G. brayi n. sp. and G. nolani n. sp. from the intestines of the scombrids, Grammatorcynus bicarinatus and Gr. bilineatus respectively, are reported from the Great Barrier Reef, Australia. Grammatorcynicola n. g. is placed in the Dolichoenterinae, as the pharynx is in the anterior quarter of the body, the caecum is tube-like and extends to the posterior quarter of the body, the cirrus-sac is small relative to the size of the worm when compared with other bucephalids and the pars prostatica is curved. Grammatorcynicola n. g. differs from other dolichoenterine genera in having a simple sucker-like rhynchus, the ovary anterior to the testes and by not having a particularly thick cirrus-sac wall.

Patterns of digenean parasitism of bivalves from the Great Barrier Reef and associated waters

Digenean parasites of marine bivalves are relatively poorly known, particularly in Australia. We surveyed 2256 bivalve individuals ( 47 species, 17 families) from Queensland marine waters incorporating south-east Queensland, Heron Island ( southern Great Barrier Reef) and Lizard Island ( northern Great Barrier Reef). Infections of trematode species from three families, Bucephalidae, Gorgoderidae and Monorchiidae, were found. Overall prevalence of infection was 2.3%. The Bucephalidae was the most commonly found family; 11 species were found in Tellinidae, Ostreidae, Isognomonidae and Spondylidae - the latter two previously unknown as hosts for bucephalids. A single gorgoderid infection was found in a venerid, Lioconcha castrensis. Five species of monorchiids were found from Tellinidae and Lucinidae. All infections are new host/parasite records. No infections were found in 35 of the 47 bivalve species sampled. The generally low prevalence of infection by digeneans of bivalves suggests that it is unlikely that any of the species reported here are seriously damaging to bivalve populations in these waters. We deduce that, at best, we have some life-cycle information but no actual identifications for 10% of the species of trematodes that infect bivalves of Queensland marine waters.