Structural complexity strongly influences biodiversity and ecosystem productivity. On coral reefs, structural complexity is typically measured using a single and small-scale metric ('rugosity') that ...represents multiple spatial attributes differentially exploited by species, thus limiting a complete understanding of how fish associate with reef structure. We used a novel approach to compare relationships between fishes and previously unavailable components of reef complexity, and contrasted the results against the traditional rugosity index. This study focused on damselfish to explore relationships between fishes and reef structure. Three territorial species, with contrasting trophic habits and expected use of the reef structure, were examined to infer the potential species-specific mechanisms associated with how complexity influences habitat selection. Three-dimensional reef reconstructions from photogrammetry quantified the following metrics of habitat quality: 1) visual exposure to predators and competitors, 2) density of predation refuges and 3) substrate-related food availability. These metrics explained the species distribution better than the traditional measure of rugosity, and each species responded to different complexity components. Given that a critical effect of reef degradation is loss of structure, adopting three-dimensional technologies potentially offers a new tool to both understand species-habitat association and help forecast how fishes will be affected by the flattening of reefs.
Coral reefs are likely to be exposed to more intense cyclones under climate change. Cyclone impacts are spatially highly variable given complex hydrodynamics, and coral-specific sensitivity to wave ...impacts. Predicting reef vulnerability to cyclones is critical to management but requires high resolution environmental data that are difficult to obtain over broad spatial scales. Using 30m-resolution wave modelling, we tested cyclonic and non-cyclonic wave metrics as predictors of coral damage on 22 reefs after severe cyclone Ita impacted the northern Great Barrier Reef, Australia in 2014. Analyses of coral cover change accounting for the type of coral along a gradient of vulnerability to wave damage (e.g., massive, branching, Acroporids) excluded cyclone-generated surface wave metrics (derived from wave height) as important predictors. Increased bottom stress wave environment (near-bed wave orbital velocity) due to Ita (Ita-Ub) explained spatial patterns of 17% to 46% total coral cover loss only when the initial abundance of Acroporids was accounted for, and only when exceeding 35% cover. Greater coral losses occurred closer to the cyclone path irrespective of coral type. Massive and encrusting corals, however, had losses exacerbated in higher non-cyclonic bottom-wave energy environments (nc-Ub). The effect of community composition on structural vulnerability to wave damage was more important predicting damage that the magnitude of the cyclone-generated waves, especially when reefs are surveyed well beyond where damaging waves are expected to occur. Exposure to Ita-Ub was greater in typically high nc-Ub environments with relatively low cover of the most fragile morphologies explaining why these were the least affected overall. We reveal that the common surface-wave metrics of cyclone intensity may not always be able to predict spatial impacts and conclude that reef vulnerability assessments need to account for chronic wave patterns and differences in community composition in order to provide predictive tools for future conservation and restoration.
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•We used high spatial resolution wave modelling to assess reef exposure to cyclones.•Bottom-wave metrics explained better coral damage than surface-wave metrics.•Coral composition influence on structural vulnerability to waves explained damage.•Chronic wave patterns influenced the spatial variability of cyclone impacts.•Reef vulnerability assessments need chronic wave patterns and coral community data.
From January 2011 to December 2013, we constructed a comprehensive pCO2 data set based on voluntary observing ship (VOS) measurements in the western English Channel (WEC). We subsequently estimated ...surface pCO2 and air–sea CO2 fluxes in northwestern European continental shelf waters using multiple linear regressions (MLRs) from remotely sensed sea surface temperature (SST), chlorophyll a concentration (Chl a), wind speed (WND), photosynthetically active radiation (PAR) and modeled mixed layer depth (MLD). We developed specific MLRs for the seasonally stratified northern WEC (nWEC) and the permanently well-mixed southern WEC (sWEC) and calculated surface pCO2 with uncertainties of 17 and 16 µatm, respectively. We extrapolated the relationships obtained for the WEC based on the 2011–2013 data set (1) temporally over a decade and (2) spatially in the adjacent Celtic and Irish seas (CS and IS), two regions which exhibit hydrographical and biogeochemical characteristics similar to those of WEC waters. We validated these extrapolations with pCO2 data from the SOCAT and LDEO databases and obtained good agreement between modeled and observed data. On an annual scale, seasonally stratified systems acted as a sink of CO2 from the atmosphere of -0.6 ± 0.3, -0.9 ± 0.3 and -0.5 ± 0.3 mol C m-2 yr-1 in the northern Celtic Sea, southern Celtic sea and nWEC, respectively, whereas permanently well-mixed systems acted as source of CO2 to the atmosphere of 0.2 ± 0.2 and 0.3 ± 0.2 mol C m-2 yr-1 in the sWEC and IS, respectively. Air–sea CO2 fluxes showed important inter-annual variability resulting in significant differences in the intensity and/or direction of annual fluxes. We scaled the mean annual fluxes over these provinces for the last decade and obtained the first annual average uptake of -1.11 ± 0.32 Tg C yr-1 for this part of the northwestern European continental shelf. Our study showed that combining VOS data with satellite observations can be a powerful tool to estimate and extrapolate air–sea CO2 fluxes in sparsely sampled area.
A concordance analysis was used to study the simultaneous influence of several environmental data sets on chaetodontid (butterflyfish) distributions. This multivariate and multitable method enabled ...the correlation of three types of benthic characteristics (mineral substratum, coverage of structural species and large echinoderms) with butterflyfish abundances in two bays of the urban centre of Nouméa (New Caledonia). The first concordance axis was related to a gradient in the coverage of branching corals. This disturbance gradient compared damaged reef areas dominated by long‐spined sea urchins to areas with an extensive coverage of branching corals. The abundance of corallivorous chaetodontids was related to this gradient, supporting the view of corals as a food and shelter source for these fishes. The second concordance axis was interpreted as a gradient of heterogeneity in the coverage of benthic life‐forms. The abundance of omnivorous chaetodontids was related to this gradient. Thus, the concordance axes defined two key components of habitat structure that were related to the entire fish community structure.
Expert opinion was canvassed to identify crucial knowledge gaps in current understanding of climate change impacts on coral reef fishes. Scientists that had published three or more papers on the ...effects of climate and environmental factors on reef fishes were invited to submit five questions that, if addressed, would improve our understanding of climate change effects on coral reef fishes. Thirty-three scientists provided 155 questions, and 32 scientists scored these questions in terms of: (i) identifying a knowledge gap, (ii) achievability, (iii) applicability to a broad spectrum of species and reef habitats, and (iv) priority. Forty-two per cent of the questions related to habitat associations and community dynamics of fish, reflecting the established effects and immediate concern relating to climate-induced coral loss and habitat degradation. However, there were also questions on fish demographics, physiology, behaviour and management, all of which could be potentially affected by climate change. Irrespective of their individual expertise and background, scientists scored questions from different topics similarly, suggesting limited bias and recognition of a need for greater interdisciplinary and collaborative research. Presented here are the 53 highest-scoring unique questions. These questions should act as a guide for future research, providing a basis for better assessment and management of climate change impacts on coral reefs and associated fish communities.
From January 2011 to January 2013, a FerryBox system was installed on a Voluntary Observing Ship (VOS), which crossed the Western English Channel (WEC) between Roscoff (France) and Plymouth (UK) up ...to 3 times a day. The FerryBox continuously measured sea surface temperature (SST), sea surface salinity (SSS), dissolved oxygen (DO), fluorescence and partial pressure of CO2 (from April 2012) along the ferry track. Sensors were calibrated based on 714 bimonthly surface samplings with precisions of 0.016 for SSS, 3.3μM for DO, 0.40μgL−1 for Chlorophyll-a (Chl-a) (based on fluorescence measurements) and 5.2μatm for pCO2. Over the 2years of deployment (900 crossings), we reported 9% of data lost due to technical issues and quality checked data was obtained to allow investigation of the dynamics of biogeochemical processes related to air–sea CO2 fluxes in the WEC. Based on this unprecedented high-frequency dataset, the physical structure of the WEC was assessed using SST anomalies and the presence of a thermal front was observed around the latitude 49.5°N, which divided the WEC in two main provinces: the seasonally stratified northern WEC (nWEC) and the all-year well-mixed southern WEC (sWEC). These hydrographical properties strongly influenced the spatial and inter-annual distributions of phytoplankton blooms, which were mainly limited by nutrients and light availability in the nWEC and the sWEC, respectively. Air–sea CO2 fluxes were also highly related to hydrographical properties of the WEC between late April and early September 2012, with the sWEC a weak source of CO2 to the atmosphere of 0.9mmolm−2d−1, whereas the nWEC acted as a sink for atmospheric CO2 of 6.9mmolm−2d−1. The study of short time-scale dynamics of air–sea CO2 fluxes revealed that an intense and short (less than 10days) summer bloom in the nWEC contributed to 29% of the CO2 sink during the productive period, highlighting the necessity for high frequency observations in coastal ecosystems. During the same period in the sWEC, the tidal cycle was the main driver of air–sea CO2 fluxes with a mean difference in pCO2 values between spring and neap tides of +50μatm. An extraction of day/night data at 49.90°N showed that the mean day–night differences accounted for 16% of the mean CO2 sink during the 5months of the study period implying that the diel biological cycle was also significant for air–sea CO2 flux computations. The 2years of deployment of our FerryBox allowed an excellent survey of the variability of biogeochemical parameters from inter-annual to diurnal time scales and provided new insights into the dynamics of air–sea CO2 fluxes in the contrasted ecosystems of the WEC.
•We recorded and calibrated high-frequency FerryBox data during 2years in the WEC.•We successfully deployed for the first time on a FerryBox an HYDROC CO2/FT sensor.•Phytoplankton bloom dynamics showed important variability in the 2 WEC provinces.•The physical structure of the water column strongly influenced air–sea CO2 fluxes.•Significant daily to inter-annual variability of air–sea CO2 fluxes occur in the WEC.
From 2008 to 2014, the MAREL-Iroise buoy, located in the Bay of Brest, collected high-frequency measurements of partial pressure of CO2 (pCO2) and ancillary hydrographic parameters, in conjunction ...with a comprehensive sampling regime of two additional carbonate system variables total alkalinity (AT), and dissolved inorganic carbon (DIC). Biological processes drive variations in AT and DIC throughout the year, except in winter, when primary production is negligible and large freshwater inputs occur. Annually, the Bay of Brest generally behaves as a source of CO2 to the atmosphere (0.14±0.20molCm−2yr−1), showing inter-annual variability significantly linked to annual net community production (NCP). The presence of a large community of benthic filter feeders leads to high levels of particulate organic matter (POM) and opal deposition during the spring diatom bloom. Over the following few months, benthic POM remineralisation reduces the spring CO2 deficit relative to the atmosphere, and remineralisation of biogenic silica supplies further late spring primary production. The result is an inverse spring NCP – air-sea CO2 flux relationship, whereby greater NCP in early spring results in lower fluxes of CO2 into the Bay in late spring. This recycling mechanism, or silicic acid pump, also links the spring and summer NCP values, which are both determined by the peak wintertime nutrient concentrations. The carbonate system is further affected by the benthic community in winter, when CaCO3 dissolution is evident from notable deviations in the ΔAT:ΔDIC ratio. This study highlights the necessity of individual study of coastal, temperate ecosystems and contributes to a better understanding of what determines coastal areas as sinks or sources of CO2 to the atmosphere.
•The Bay of Brest generally behaves as a source of CO2 to the atmosphere.•Inter-annual variability in air-sea CO2 exchange is linked to net community production.•Springtime net community production is determined by the winter, river dissolved silica supply.•Total alkalinity and dissolved inorganic carbon variability is driven by biology.
Seawater concentrations of the four brominated trace gases, dibromomethane (CH2Br2), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3) were measured at different ...depths of the water column in the Iberian upwelling off Portugal during summer 2007. Statistical analysis of the data set revealed three distinct clusters, caused by different sea surface temperature. Bromocarbon concentrations were elevated in recently upwelled and aged upwelled waters (mean values of 30 pmol l−1 for CHBr3), while concentrations in the open ocean were significantly lower (7.4 pmol l−1 for CHBr3). Comparison with other productive marine areas revealed that the Iberian upwelling had higher halocarbon concentrations than the Mauritanian upwelling. However, the concentrations off the Iberian Peninsula were still much lower than those of coastal macroalgal-influenced waters or those of Polar regions dominated by cold water adapted diatoms. Correlations with biological variables and marker pigments indicated that phytoplankton was a source of bromocarbon in the open ocean. By contrast, in upwelled water masses along the coast, halocarbons showed weaker correlations to marker pigments but were significantly influenced by the tidal frequency. Our results indicate a strong intertidal coastal source of bromocarbon and transport by surface currents of these enriched waters towards the upwelling region.
The carbon budget of the North Sea Thomas, H.; Bozec, Y.; de Baar, H. J. W. ...
Biogeosciences,
01/2005, Letnik:
2, Številka:
1
Journal Article, Web Resource
Recenzirano
Odprti dostop
A carbon budget has been established for the North Sea, a shelf sea on the NW European continental shelf. The carbon exchange fluxes with the North Atlantic Ocean dominate the gross carbon budget. ...The net carbon budget – more relevant to the issue of the contribution of the coastal ocean to the marine carbon cycle – is dominated by the carbon inputs from rivers, the Baltic Sea and the atmosphere. The North Sea acts as a sink for organic carbon and thus can be characterised as a heterotrophic system. The dominant carbon sink is the final export to the North Atlantic Ocean. More than 90% of the CO2 taken up from the atmosphere is exported to the North Atlantic Ocean making the North Sea a highly efficient continental shelf pump for carbon.
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