Impact of dredging on the volute Cymbiolacca pulchra and its environment at Heron Island, Great Barrier Reef, Australia

The impact of dredging operations on the volute Gastropod (Cymbiolacca pulchra) population of a coral reef atoll (Heron Island, Great Barrier Reef, Australia) was investigated using data from annual surveys of the population and its environment Comparisons were made of pre-dredging (1984 to 1986), during-dredging (1987) and post-dredging (1988 and 1989) summer densities and size distributions of volutes at eight locations on the reef. There was significant variation among the sites in the pre-dredging years with volutes restricted to four sites characterised by a combination ofre1ative1y low bommie cover « 2%) and high sand cover (> 75%). All four sites were influenced by the dredge plume during dredging operations (September to November 1987 and February 1988). Volute densities declined significantly during dredging (1987) compared to the pre-dredging years. In the following year (1988) the difference was highly significant with zero densities recorded. By 1989 there had been a recovery with no significant difference in the overall density of volutes although the density of small volutes was greater and larger volutes smaller compared to pre-dredging densities. From June 1985 to May 1986 monthly counts were made at all sites to examine seasonal patterns of recruitment Recruitment into the population occurred over much of the year, though it tended to be higher in the autumn months (March to May), presumably following summer breeding. We suggest that the declines in volute densities were probably due to a failure of recruitment during dredging coupled with a loss of large volutes which may have resulted from natural mortality, emigration, or dredging. The recovery probably followed immigration of large volutes from less affected areas. The environmental factors of percent cover of sand, rock, rubble, coral, bommies and macroalgae were also monitored and there were significant changes in the cover of algae, coral, sand and rubble. These changes are interpreted as covariates rather than causes of observed changes in volute densities. Post-dredging increases in the cover of algae persisted beyond the termination of this study

Effects of fishing in the Great Barrier Reef Region : proceedings of a workshop held under the auspices of the Advisory Committee on Research on Fishing in the Great Barrier Reef Region : summary report, February 19-24, 1989, Magnetic Island, Townsville, Qld

A scientific workshop was held in 1989 on the auspices of of the Advisory committee on Research on Fishing in the Great Barrier Reef Region to discuss and recommend a research program of the effects of fishing, particularly trawling, in the Great Barrier Reef Region

Four Regional Marine Biodiversity Studies: Approaches and Contributions to Ecosystem-Based Management

We compare objectives and approaches of four regional studies of marine biodiversity: Gulf of Maine Area Census of Marine Life, Baltic Sea History of Marine Animal Populations, Great Barrier Reef Seabed Biodiversity Project, and Gulf of Mexico Biodiversity Project. Each program was designed as an "ecosystem" scale but was created independently and executed differently. Each lasted 8 to 10 years, including several years to refine program objectives, raise funding, and develop research networks. All resulted in improved baseline data and in new, or revised, data systems. Each contributed to the creation or evolution of interdisciplinary teams, and to regional, national, or international science-management linkages. To date, there have been differing extents of delivery and use of scientific information to and by management, with greatest integration by the program designed around specific management questions. We evaluate each research program's relative emphasis on three principal elements of biodiversity organization: composition, structure, and function. This approach is used to analyze existing ecosystem-wide biodiversity knowledge and to assess what is known and where gaps exist. In all four of these systems and studies, there is a relative paucity of investigation on functional elements of biodiversity, when compared with compositional and structural elements. This is symptomatic of the current state of the science. Substantial investment in understanding one or more biodiversity element(s) will allow issues to be addressed in a timely and more integrative fashion. Evaluating research needs and possible approaches across specific elements of biodiversity organization can facilitate planning of future studies and lead to more effective communication between scientists, managers, and stakeholders. Building a general approach that captures how various studies have focused on different biodiversity elements can also contribute to meta-analyses of worldwide experience in scientific research to support ecosystem-based management

Morphology, flowering and seed production of Zostera capricorni Aschers. in subtropical Australia

The vegetative morphology, flowering characteristics, seed production, and seed distribution in the sediment of the seagrass Zostera capricorni Aschers. were studied for 18 months by monthly sampling. Three seagrass zones were studied. In each of these zones there was a different morphological type of Z. capricorni: small, dense plants in the midshore zone; large, sparse plants in the offshore zone; medium size and medium density plants in the inshore zone. The distribution of seeds in the sediment was also studied in bare areas adjacent to these vegetated zones. Flowering lasted for 8 months, from September to April, with the highest percentage of shoots flowering in September and November. Flowering lasted longest in the midshore zone (7 months), compared with the inshore (3 months) and offshore (4 months) zones. The density of flowering shoots was also higher in the midshore zone (341 ± 14.0 flowering shoots m) than in the inshore (4 ± 1.0) or offshore (12 ± 4.0) zones. Both the mean number of spathes per shoot (3.1 ± 0.07), and the number of female flowers per spathe (4.8 ± 0.20) did not vary significantly between zones. However, there were more male flowers per spathe in the offshore (10.5 ± 1.55) than in the inshore (5.6 ± 1.60) or midshore (5.4 ± 0.88) zones. Although most seeds were found in the midshore zone during the flowering season (177m ± 28.4), some seeds remained in the sediment for 4 months after seed production had ceased. Few seeds were found outside the seagrass beds, of these most were in bare areas long-shore of the seagrass

Microbial biomass and productivity in seagrass beds

Different methods for measuring the rates of processes mediated by bacteria in sediments and the rates of bacterial cell production have been compared. In addition, net production of the seagrass Zostera capricorni and bacterial production have been compared and some interrelationships with the nitrogen cycle discussed. Seagrass productivity was estimated by measuring the plastochrone interval using a leaf stapling technique. The average productivity over four seasons was 1.28 ± 0.28 gCm day (mean ± standard deviation, n = 4). Bacterial productivity was measured five times throughout a year using the rate of tritiated thymidine incorporated into DNA. Average values were 33 ± 12 mg C m day for sediment and 23 ± 4 for water column (n = 5). Spatial variability between samples was greater than seasonal variation for both seagrass productivity and bacterial productivity. On one occasion, bacterial productivity was measured using the rate of P incorporated into phospholipid. The values were comparable to those obtained with tritiated thymidine. The rate of sulfate reduction was 10 mmol SO4 m day . The rate of methanogenesis was low, being 5.6 mg CH4 produced m day . A comparison of C flux measured using rates of sulfate reduction and DNA synthesis indicated that anaerobic processes were predominant in these sediments.An analysis of microbial biomass and community structure, using techniques of phospholipid analysis, showed that bacteria were predominant members of the microbial biomass and that of these, strictly anaerobic bacteria were the main components. Ammonia concentration in interstitial water varied from 23 to 71 μM. Estimates of the amount of ammonia required by seagrass showed that the ammonia would turn over about once per day. Rapid recycling of nitrogen by bacteria and bacterial grazers is probably important