Spatial and temporal variations in turbidity on two inshore turbid reefs on the Great Barrier Reef, Australia

This study describes the natural turbidity regimes at two inshore turbid reefs on the central Great Barrier Reef where wind-driven waves are the main agent of sediment resuspension. Many corals on inshore turbid reefs have adapted to high and fluctuating turbidity, however, anthropogenic activities such as dredging are speculated to produce larger and more prolonged turbidity events that may exceed the environmental tolerance and adaptive capacity of corals on these reefs. Natural turbidity regimes must be described and understood to determine whether and when coral communities on inshore turbid reefs are at risk from anthropogenically elevated turbidity, but at present few baseline studies exist. Here, we present turbidity data from (a) Middle Reef, a semi-protected reef located between Magnetic Island and Townsville and (b) Paluma Shoals, a reef exposed to higher energy wind and waves located in Halifax Bay. Instruments were deployed on both reefs for 16 days to measure spatial and temporal variations in turbidity and its driving forces (waves, currents, tides). Locally driven wind waves were the key driver of turbidity, but the strength of the relationship was dependent on wave exposure. Turbidity regimes thus vary markedly over individual reefs and this is reflected in community assemblage distributions, with a high abundance of heterotrophic corals (e.g. Goniopora) in reef habitats subjected to large fluctuations in turbidity (>100 NTU). A turbidity model developed using local wind speed data explained up to 75 % and up to 46 % of the variance in turbidity at Paluma Shoals and Middle Reef, respectively. Although the model was based on a brief two-week observational period, it reliably predicted variations in 24-h averaged turbidity and identified periods when turbidity rose above ambient baseline levels, offering reef managers insights into turbidity responses to modified climate and coastal sediment delivery regimes.     

Sequence and embryonic expression of deltaC in the zebrafish

Four genes - deltaA, deltaB, deltaC and deltaD - coding for homologues of the Notch ligand Delta have been discovered in zebrafish (Haddon et al., 1998b). We report here the cDNA sequence and expression pattern of deltaC. Its closest relatives are deltaB and Xenopus X-Delta-2. Unlike deltaA, deltaB, and deltaD, deltaC is not expressed in the majority of nascent primary neurons; but it is strongly expressed in the early retina, where it precedes other delta genes. It is also expressed in cranial ganglia, in sensory epithelia including ear and lateral line, and in scattered epidermal cells. In the mesoderm, expression is visible by 50% epiboly; it is seen subsequently in the tail bud, in stripes in the presomitic mesoderm and in the posterior half of each somite. There is expression also in notochord, blood vessels and pronephros.     

Holocene sea level instability in the southern Great Barrier Reef,Australia: high-precision U–Th dating of fossil microatolls

Three emergent subfossil reef flats from the inshore Keppel Islands, Great Barrier Reef (GBR), Australia, were used to reconstruct relative sea level (RSL). Forty-two high-precision uranium–thorium (U–Th) dates obtained from coral microatolls and coral colonies (2σ age errors from ±8 to 37 yr) in conjunction with elevation surveys provide evidence in support of a nonlinear RSL regression throughout the Holocene. RSL was as least 0.75 m above present from ~6500 to 5500 yr before present (yr BP; where “present” is 1950). Following this highstand, two sites indicated a coeval lowering of RSL of at least 0.4 m from 5500 to 5300 yr BP which was maintained for ~200 yr. After the lowstand, RSL returned to higher levels before a 2000-yr hiatus in reef flat corals after 4600 yr BP at all three sites. A second possible RSL lowering event of ~0.3 m from ~2800 to 1600 yr BP was detected before RSL stabilised ~0.2 m above present levels by 900 yr BP. While the mechanism of the RSL instability is still uncertain, the alignment with previously reported RSL oscillations, rapid global climate changes and mid-Holocene reef “turn-off” on the GBR are discussed.

     

Predicting a change in the order of spring phenology in temperate forests

The rise in spring temperatures over the past half‐century has led to advances in the phenology of many nontropical plants and animals. As species and populations differ in their phenological responses to temperature, an increase in temperatures has the potential to alter timing‐dependent species interactions. One species‐interaction that may be affected is the competition for light in deciduous forests, where early vernal species have a narrow window of opportunity for growth before late spring species cast shade. Here we consider the Marsham phenology time series of first leafing dates of thirteen tree species and flowering dates of one ground flora species, which spans two centuries. The exceptional length of this time series permits a rare comparison of the statistical support for parameter‐rich regression and mechanistic thermal sensitivity phenology models. While mechanistic models perform best in the majority of cases, both they and the regression models provide remarkably consistent insights into the relative sensitivity of each species to forcing and chilling effects. All species are sensitive to spring forcing, but we also find that vernal and northern European species are responsive to cold temperatures in the previous autumn. Whether this sensitivity reflects a chilling requirement or a delaying of dormancy remains to be tested. We then apply the models to projected future temperature data under a fossil fuel intensive emissions scenario and predict that while some species will advance substantially others will advance by less and may even be delayed due to a rise in autumn and winter temperatures. Considering the projected responses of all fourteen species, we anticipate a change in the order of spring events, which may lead to changes in competitive advantage for light with potential implications for the composition of temperate forests.     

Regional‐scale dominance of non‐framework building corals on Caribbean reefs affects carbonate production and future reef growth

Coral cover on Caribbean reefs has declined rapidly since the early 1980's. Diseases have been a major driver, decimating communities of framework building Acropora and Orbicella coral species, and reportedly leading to the emergence of novel coral assemblages often dominated by domed and plating species of the genera Agaricia, Porites and Siderastrea. These corals were not historically important Caribbean framework builders, and typically have much smaller stature and lower calcification rates, fuelling concerns over reef carbonate production and growth potential. Using data from 75 reefs from across the Caribbean we quantify: (i) the magnitude of non‐framework building coral dominance throughout the region and (ii) the contribution of these corals to contemporary carbonate production. Our data show that live coral cover averages 18.2% across our sites and coral carbonate production 4.1 kg CaCO₃ m^?2 yr^?1. However, non‐framework building coral species dominate and are major carbonate producers at a high proportion of sites; they are more abundant than Acropora and Orbicella at 73% of sites; contribute an average 68% of the carbonate produced; and produce more than half the carbonate at 79% of sites. Coral cover and carbonate production rate are strongly correlated but, as relative abundance of non‐framework building corals increases, average carbonate production rates decline. Consequently, the use of coral cover as a predictor of carbonate budget status, without species level production rate data, needs to be treated with caution. Our findings provide compelling evidence for the Caribbean‐wide dominance of non‐framework building coral taxa, and that these species are now major regional carbonate producers. However, because these species typically have lower calcification rates, continued transitions to states dominated by non‐framework building coral species will further reduce carbonate production rates below ‘predecline’ levels, resulting in shifts towards negative carbonate budget states and reducing reef growth potential.     

The presence of antibody in mice chronically infected with Schistosoma mansoni which blocks in vitro killing of schistosomula

We have previously reported that IgM monoclonal antibodies (mAb) that recognize surface carbohydrate determinants shared between schistosomula, cercariae, and miracidia block antibody/complement dependent killing of schistosomula in vitro. Binding assays that make use of one of the IgM mAb labeled with 125I demonstrated that serum from chronically infected mice (CMS) contained high levels of competing antibody, whereas serum from mice vaccinated with irradiated cercariae (VMS) contained little antibody of this specificity. Absorption of CMS with cercariae that removed antibodies to schistosomulum surface carbohydrate determinants increased its ability to kill schistosomula in vitro; absorption of VMS with cercariae failed to alter the lethal activity of the serum. Furthermore, fractionation of CMS by protein A Sepharose chromatography demonstrated that the IgG fraction had an increased lethal activity compared with unfractionated serum; this result was not seen with VMS. Finally, the IgM fraction of CMS was shown to block in vitro killing of the IgG fractions of both CMS and VMS. These data suggest that the blocking activities observed with the IgM mAb are contained within the serum of chronically infected mice but not in the serum of mice vaccinated with irradiated cercariae.     

Analysis of the anti-Schistosoma mansoni surface antibody response during murine infection and its potential contribution to protective immunity

Absorption of serum from chronically infected mice with homogenized schistosome eggs reduced antibody binding to the schistosomulum surface by 94%, indicating that almost all schistosomulum surface recognition during chronic infection is due to epitopes shared with the egg. Absorption of the serum with egg homogenate from which protein antigens had been removed by boiling and digestion with proteinase K resulted in a similar reduction of antisurface antibody demonstrating that all the shared epitopes that are recognized are carbohydrate in nature. Analysis of the time course of anticarbohydrate antibody production and the levels of antibody in mice infected with a single sex of schistosome indicated that eggs directly stimulated this response. Mouse mAb were identified that bound at very high levels to the schistosomulum surface and that recognized carbohydrate epitopes shared with the egg. Three of these had previously been demonstrated to passively transfer resistance, indicating that these surface carbohydrates are potential targets of protective immunity in the mouse. All the anticarbohydrate mAb also bound to the surface of schistosomula of other schistosome species. Thus, the strong immune response against these epitopes in chronic infection could account for the cross-specific immunity observed. Mice vaccinated with irradiated cercariae lacked high levels of anticarbohydrate antibodies and their recognition of the surface was largely due to antibody to species-specific polypeptide epitopes. With respect to the Mr greater than 200,000 and 38,000 antigens, it was demonstrated that these epitopes were present on the same antigens that bear the carbohydrate moieties recognized by antibodies from chronically infected mice. This specific polypeptide recognition is also reflected in the immunity generated by exposure to irradiated cercariae.     

Gene-Enzyme Relations of Tryptophan Mutants in STREPTOMYCES COELICOLOR A3(2)

Mutations in twenty-eight tryptophan mutants of S. coelicolor A3(2) were mapped relative to the nearest flanking markers. Mutants lacking single enzymatic activities for phosphoribosyltransferase, phosphoribosylanthranilate isomerase, indodeglycerol phosphate synthase, tryptophan synthase A and tryptophan synthase B were identified.     

Changing dynamics of Caribbean reef carbonate budgets: emergence of reef bioeroders as critical controls on present and future reef growth potential

Coral cover has declined rapidly on Caribbean reefs since the early 1980s, reducing carbonate production and reef growth. Using a cross-regional dataset, we show that widespread reductions in bioerosion rates—a key carbonate cycling process—have accompanied carbonate production declines. Bioerosion by parrotfish, urchins, endolithic sponges and microendoliths collectively averages 2 G (where G = kg CaCO₃ m⁻² yr⁻¹) (range 0.96–3.67 G). This rate is at least 75% lower than that reported from Caribbean reefs prior to their shift towards their present degraded state. Despite chronic overfishing, parrotfish are the dominant bioeroders, but erosion rates are reduced from averages of approximately 4 to 1.6 G. Urchin erosion rates have declined further and are functionally irrelevant to bioerosion on most reefs. These changes demonstrate a fundamental shift in Caribbean reef carbonate budget dynamics. To-date, reduced bioerosion rates have partially offset carbonate production declines, limiting the extent to which more widespread transitions to negative budget states have occurred. However, given the poor prognosis for coral recovery in the Caribbean and reported shifts to coral community states dominated by slower calcifying taxa, a continued transition from production to bioerosion-controlled budget states, which will increasingly threaten reef growth, is predicted.     

Hypoxanthine phosphoribosyltransferase: radiochemical assay procedures for the forward and reverse reactions

Simple and rapid radiochemical assay procedures for the forward (IMP synthesis) and reverse (IMP pyrophosphorolysis) reactions catalyzed by hypoxanthine phosphoribosyltransferase have been developed. Enzyme activity in the forward direction was assessed by measuring the amount of [8-14C]IMP formed from [8-14C]hypoxanthine following their separation by polyethyleneimine-cellulose TLC in methanol:water (1:1, v/v). [8-14C]IMP has been synthesized from [8-14C]hypoxanthine, using hypoxanthine phosphoribosyltransferase derived from human brain, with subsequent purification by elution from phenyl boronate-agarose. Enzyme activity in the reverse direction was assessed by measuring the amount of [8-14C]uric acid formed from the labeled IMP following their separation by polyethyleneimine-cellulose TLC in 0.2 M LiCl saturated with boric acid (pH 4.5):95% ethanol (1:1, v/v), the transferase reaction being coupled with excess xanthine oxidase and catalase to overcome the unfavorable equilibrium.