With in situ and laboratory chamber incubations we demonstrate that coral mucus, an important component of particulate organic matter in reef ecosystems, is a valuable substrate for microbial communities in the water column and sandy sediments of coral reefs. The addition of coral mucus to the water of benthic chambers placed on lagoon sands in the coral cay Heron Island, Australia, resulted in a rapid and significant increase in both O 2 consumption and DIC production in the chambers. The permeable coral sands permitted the transport of mucus into the sediment with interfacial water flows, resulting in the mucus being mainly (> 90%) degraded in the sediment and not in the water column of the chambers. A low ratio of 0.48 (in situ) to 0.64 (laboratory) for O 2 consumption/DIC production after the addition of coral mucus, and high sulfate reduction rates (SRR) in natural sediments which were exposed to coral mucus, suggest a large contribution of anaerobic processes to the degradation of coral mucus. Oxygen penetrated less than 5 mm deep into these sediments. The microbial reaction to mucus addition was rapid, with a calculated in situ C turnover rate ranging from 7 to 18% h -1 . The degradation of coral mucus showed a dependency on the permeability of the carbonate sediments, with faster degradation and remineralization in coarse sands. This indicates the importance of permeable reef sediments for the trapping and degradation of organic matter. We suggest that coral mucus may have a function as a carrier of energy to the benthic microbial consumers.KEY WORDS: Coral mucus · POM · Degradation · Permeable carbonate sands · O 2 consumption · DIC production · C turnover Resale or republication not permitted without written consent of the publisher
BackgroundCiguatera is a type of fish poisoning that occurs throughout the tropics, particularly in vulnerable island communities such as the developing Pacific Island Countries and Territories (PICTs). After consuming ciguatoxin-contaminated fish, people report a range of acute neurologic, gastrointestinal, and cardiac symptoms, with some experiencing chronic neurologic symptoms lasting weeks to months. Unfortunately, the true extent of illness and its impact on human communities and ecosystem health are still poorly understood.MethodsA questionnaire was emailed to the Health and Fisheries Authorities of the PICTs to quantify the extent of ciguatera. The data were analyzed using t-test, incidence rate ratios, ranked correlation, and regression analysis.ResultsThere were 39,677 reported cases from 17 PICTs, with a mean annual incidence of 194 cases per 100,000 people across the region from 1998–2008 compared to the reported annual incidence of 104/100,000 from 1973–1983. There has been a 60% increase in the annual incidence of ciguatera between the two time periods based on PICTs that reported for both time periods. Taking into account under-reporting, in the last 35 years an estimated 500,000 Pacific islanders might have suffered from ciguatera.ConclusionsThis level of incidence exceeds prior ciguatera estimates locally and globally, and raises the status of ciguatera to an acute and chronic illness with major public health significance. To address this significant public health problem, which is expected to increase in parallel with environmental change, well-funded multidisciplinary research teams are needed to translate research advances into practical management solutions.
Extensive coral bleaching occurred intertidally in early August 2003 in the Capricorn Bunker group (Wistari Reef, Heron and One Tree Islands; southern Great Barrier Reef). The affected intertidal coral had been exposed to unusually cold (minimum ϭ 13.3ЊC; wet bulb temperature ϭ 9ЊC) and dry winds (44% relative humidity) for 2 d during predawn low tides. Coral bleached in the upper 10 cm of their branches and had less than 0.2 ϫ 10 6 cell cm Ϫ2 as compared with over 2.5 ϫ 10 6 cell cm Ϫ2 in nonbleached areas. Dark-adapted quantum yields did not differ between symbionts in bleached and nonbleached areas. Exposing symbionts to light, however, led to greater quenching of Photosystem II in symbionts in the bleached coral. Bleached areas of the affected colonies had died by September 2003, with areas that were essentially covered by more than 80% living coral decreasing to less than 10% visible living coral cover. By January 2004, coral began to recover, principally from areas of colonies that were not exposed during low tide (i.e., from below dead, upper regions). These data highlight the importance of understanding local weather patterns as well as the effects of longer term trends in global climate.
Experimental studies of intact cores from the Baltic Sea were conducted to determine the response of sediment nutrient recycling processes to varied inputs of organic matter. A 2 mo enrichment experiment was carried out in the laboratory on sediment cores held at 4°C using a flow-through system where overlying waters were continuously replaced at a rate of 1 d.' The experiments were designed to simulate the deposition of organic matter that occurs during a typical spring diatom bloom ( l x ) and under enriched conditions with eutrophicatlon at approximately 3 times (3x) a normal spring bloom utilizing added organic matter from a natural phytoplankton assemblage collected in a eutrophic coastal fjord during the spring diatom bloom. Low and constant sediment-water fluxes were observed throughout the duration of the experiment in control cores with no added organic matter. In all cases an immediate response was noted when a single pulsed addition of algal material was added to the sediment surface. Sediment-water fluxes of ammonium (NHdt), and dissolved inorganic phosphate (DIP) increased significantly (ANOVA, p < 0.01). For nitrite + nitrate (NO; + NO3-) and dissolved silicate (DSi) sediment-water fluxes, differences were initially observed; however, only the NO2-+ NO3-fluxes were significantly different over time (ANOVA, p < 0.01). Fluxes of NOz-+ NO3-were into the sediment for 3 to 10 d after addition of organic material, followed by small fluxes out of the sediment. The addition of algal material proportionate to a normal spring bloom ( l x ) had only a minor effect on porewater nutrient concentrations, whereas the 3x treatment substantially modified both the short-and long-term response of sediments. A greater proportion of anaerobic decomposition products, e.g. NH,' and DIP, were observed with an expansion of more reducing conditions resulting from the addition of organic matter. The percentage of Si remineralized decreased as the flux of n~aterial to the sediment increased. Deposition rates similar to a typical spring bloom did not have long-term effects on the nutrient recycling processes; however, increases in the present level of deposition (as simulated in this study), which are forecasted with further eutrophication in the Baltic Sea, may have a significant impact on nutrient biogeochernical cycles.
Shallow water coastal environments are very important from the biological, social and economic point of view. Wireless technologies -and in particular wireless sensor networks (WSN) -are critical for enabling their efficient and pervasive monitoring. Electromagnetic (EM) communication is considered as the physical layer because, in shallow water coastal environments, it presents distinct advantages with respect to acoustic and optical communication. The benefit of lateral wave EM propagation in shallow water environment is explained. A theoretical analysis of EM propagation in a typical shallow water environment is then conducted, where the maximum distance coverable for a given transmitter power is calculated. The results are then compared with simulations and measurements: their differences with respect to theoretical predictions are assessed. A prototype of underwater communication system constituted by an underwater sensor and a hub buoy that relays data to the mainland is finally presented. Conclusions are drawn in terms of its performance, also in comparison with existing underwater EM communication systems and solutions.
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