Intense diurnal surface currents in the Bay of La Paz,Mexico

Currents in the northern Bay of La Paz were examined using an 8-month Acoustic Doppler Current Profiler (ADCP) record collected in the upper 185 m of the water column during 2007. Flow variability was dominated by tidal motions, which accounted for 43% (33% diurnal, 10% semidiurnal) of the total kinetic energy. The tidal motions had a pronounced vertical structure dominated within a shallow (∼30 m thick) surface layer by intense counterclockwise (CCW) rotary S₁ diurnal radiational currents that were highly coherent with the counterclockwise seabreeze. Motions within the semidiurnal frequency band were primarily associated with significant counterclockwise S₂ radiational tidal currents, which were also coherent with the seabreeze. Both S₁ and S₂ tidal ellipses in the upper layer were aligned perpendicular to the bay entrance with mean semi-major axes of 55 and 20 cm/s, respectively. Below the surface layer, tidal currents decayed rapidly to relatively weak, clockwise rotary barotropic motions. In contrast to those for radiational harmonics, tidal ellipses of the gravitational constituents (M₂, K₁ and O₁) were oriented cross-bay. Energy within the diurnal frequency band in the surface layer was dominated by a coherent component (barotropic, phase-locked baroclinic and radiational), which accounted for roughly 65% (59% from S₁ alone) of the total diurnal kinetic energy. Of the remaining diurnal band energy, 18% was associated with an incoherent baroclinic component and 17% with a background noise component. Below 30 m depth, the corresponding estimates are 40%, 32% and 28%, respectively. The persistent, surface-intensified CCW rotary currents observed at the mooring site are assumed to be forced by strong CCW seabreeze winds in the presence of a “slippery” low-density surface layer. This response may be further augmented by topographic narrowing at the bay entrance and by the close proximity of the diurnal and inertial frequency bands in the region.     

Relative effects of local and landscape factors on wetland algal biomass over a salinity gradient

Wetlands in south-eastern Australia and other arid regions of the world are experiencing increases in salinity due to dryland salinization and climate change. We investigated changes in wetland ecological function, measured as phytoplankton and benthic algal Chl a, over a large salinity gradient (0.047–226 mS cm⁻¹) and in relation to several local water chemistry variables that may be important predictors of algal biomass. We investigated the relative importance of landscape variables that may affect input pollution and hydrology of wetlands at four spatial scales (100, 500, 1,000 and 5000 m). We explored the strength and form of the relationships between algal biomass and local and landscape predictors with emphasis on the effects of local and landscape salinity. We found local variables were more important than landscape variables in influencing algal biomass. We also found salinity of wetlands was not a good predictor of phytoplankton biomass but it did predict benthic algal biomass.     

An overview of Fiji's fisheries development

Development and societal changes in the twentieth century have transformed the nature of fishing in Fiji. This paper attempts to consolidate a large amount of decentralized work on the development of Fijian fisheries to address the long-term sustainability and economic viability of Fiji's marine resources. Taking a broad perspective, this paper provides an overview that connects the historic context of Fiji's fisheries development with economic policy to address overfishing. The analysis highlights the need for an overarching management approach that encompasses the integration of Fiji's offshore and inshore fisheries to ensure the achievement of long-term economic benefits.     

Research Note: Internal/external seismic source wavefield separation and cancellation

A compact representation is obtained for the separation of a scalar wavefield on a closed surface into parts due to internal and external sources. The formula assumes that the total field and its gradients are known on the surface, as is the exact Green function of the medium. The derivation involves four rather straightforward applications of Green’s theorem or the representation theorem, though it is a remarkable result in that waves from either source that traverse the boundary many times are appropriately separated. The intermediate results at the four steps of the derivation also shed light on the possibility of acoustic shielding from unwanted sources without knowledge of the Green function for the medium.     

Toward Bayesian uncertainty quantification for forestry models used in the United Kingdom Greenhouse Gas Inventory for land use, land use change, and forestry

The Greenhouse Gas Inventory for the United Kingdom currently uses a simple carbon-flow model, CFLOW, to calculate the emissions and removals associated with forest planting since 1920. Here, we aim to determine whether a more complex process-based model, the BASic FORest (BASFOR) simulator, could be used instead of CFLOW. The use of a more complex approach allows spatial heterogeneity in soils and weather to be accounted for, but places extra demands on uncertainty quantification. We show how Bayesian methods can be used to address this problem.     

Spatial patterns and correlates of mortality due to selected non-communicable diseases among adults in South Africa, 2011

South Africa has a high prevalence of non-communicable diseases (NCDs) compared to other African countries. Government has predicted that NCDs will be a major threat of health in the country in the next 20–30 years and recommended a significant reduction in NCDs. This research studies spatial patterns of deaths resulting from chronic lower respiratory diseases (CLRD), malignant neoplasms of digestive organs (MNDO), diabetes mellitus (DM) and cerebrovascular diseases (CVD) among adults aged 15–69 years in 2011 at municipality level. The study uses secondary data from the civil registration system; population census; and supplementary information from the Business Register and a database of public health facilities. Moran’s Index, hot spot analysis and geographically weighted regression were applied to measure spatial autocorrelation of age-standardised death rates; to identify municipalities of high risk of deaths due to selected NCDs; and associated socio-economic and demographic factors. Clusters of high risk of deaths from selected NCDs were identified, with those for CLRD and MNDO mainly in the urban municipalities around the mid and western parts of the country while for DM and CVD they occurred mostly in the urban and rural north-eastern part, as well as in the urban municipalities of Northern Cape for CVD. Hot spots showed differential socio-economic and demographic risk factors in NCDs, which included sex, urbanisation, density of public hospitals; death occurrence in health facilities; smoking; asbestos roofing; mining and quarrying businesses. Findings highlight the importance of community-specific interventions and the need for a neighbourhood-based approach in tackling NCDs.     

Trophic structure of mesopelagic fishes in the Gulf of Mexico revealed by gut content and stable isotope analyses

Mesopelagic fishes represent an important component of the marine food web due to their global distributions, high abundances and ability to transport organic material throughout a large part of the water column. This study combined stable isotope (SIAs) and gut content analyses (GCAs) to characterize the trophic structure of mesopelagic fishes in the North‐Central Gulf of Mexico. Additionally, this study examined whether mesopelagic fishes utilized chemosynthetic energy from cold seeps. Specimens were collected (9–25 August 2007) over three deep (>1,000 m) cold seeps at discrete depths (surface to 1,503 m) over the diurnal cycle. GCA classified 31 species (five families) of mesopelagic fishes into five feeding guilds: piscivores, large crustacean consumers, copepod consumers, generalists and mixed zooplanktivores. However, these guilds were less clearly defined based on stable isotope mixing model (MixSIAR) results, suggesting diets may be more mixed over longer time periods (weeks–months) and across co‐occurring species. Copepods were likely important for the majority of mesopelagic fishes, consistent with GCA (this study) and previous literature. MixSIAR results also identified non‐crustacean prey items, including salps and pteropods, as potentially important prey items for mesopelagic fishes, including those fishes not analysed in GCA (Sternoptyx spp. and Melamphaidae). Salps and other soft‐bodied species are often missed in GCAs. Mesopelagic fishes had δ¹³C results consistent with particulate organic matter serving as the baseline organic carbon source, fueling up to three trophic levels. Fishes that undergo diel vertical migration were depleted in ¹⁵N relative to weak migrators, consistent with depth‐specific isotope trends in sources and consumers, and assimilation of ¹⁵N‐depleted organic matter in surface waters. Linear correlations between fish size and δ¹⁵N values suggested ontogenetic changes in fish diets for several species. While there was no direct measure of mesopelagic fishes assimilating chemosynthetic material, detection of infrequent consumption of this food resource may be hindered by the assimilation of isotopically enriched photosynthetic organic matter. By utilizing multiple dietary metrics (e.g. GCA, δ¹³C, δ¹⁵N, MixSIAR), this study better defined the trophic structure of mesopelagic fishes and allowed for insights on feeding, ultimately providing useful baseline information from which to track mesopelagic trophodynamics over time and space.     

Host‐dependent differences in resource use associated with Anilocra spp. parasitism in two coral reef fishes,as revealed by stable carbon and nitrogen isotope analyses

The role of parasites in trophic ecology is poorly understood in marine ecosystems. Stable isotope analyses (SIA) have been widely used in studies of trophic ecology, but have rarely been applied to study the role of parasites. Considering that some parasites are associated with altered host foraging patterns, SIA can help elucidate whether parasitism influences host trophic interactions. French grunt (Haemulon flavolineatum), an abundant Caribbean coral reef fish, contributes greatly to trophic connectivity. They typically depart the reef at dusk, feed overnight in seagrass beds, and return to the reef at dawn. The large parasitic isopod Anilocra haemuli commonly infects French grunt, and infected fish are less likely to complete their diel migration, and are in poorer condition than uninfected conspecifics. Brown chromis (Chromis multilineata) are diurnally feeding planktivores and infection by Anilocra chromis does not influence host condition. To determine if Anilocra infection influences host diet and foraging locality, we conducted stable carbon and nitrogen isotope analyses on scale, muscle, heart and gill tissues of infected and uninfected French grunt and brown chromis. We determined that all French grunt had δ¹³C values representative of seagrass habitats, but infected French grunt were significantly enriched in ¹³C and ¹⁵N compared to uninfected conspecifics. This suggests that compared to uninfected conspecifics, infected French grunt forage in seagrass, but on isotopically enriched prey, and/or are in poorer condition, which can elevate δ¹³C and δ¹⁵N values. For brown chromis, infection did not significantly influence any δ¹³C and δ¹⁵N values; hence they all foraged in the same environment and on similar prey. This is the first study to use SIA to examine differences in resource use by Caribbean coral reef fishes associated with parasitism and to evaluate how closely related parasites might have host‐dependent effects on host trophic ecology.     

Observations of Diurnal Cycles Over a West African Meridional Transect: Pre-Monsoon and Full-Monsoon Seasons

We document and characterize the climatology of the diurnal cycles encountered along a West African transect during the pre-monsoon and full-monsoon periods. The meridional gradient in low-level properties is fundamental for the monsoon dynamics and here, for the first time, it is studied based on a large set of observations from the African Monsoon Multidisciplinary Analysis (AMMA) campaign. A detailed analysis of surface energy budget, boundary-layer structures and cloud occurrence is carried out to investigate the diurnal cycles of the low levels. A relatively weak meridional gradient of net radiation is observed during the pre-monsoon period, and a large gradient in sensible heat flux is found over the transect with values increasing from south to north. This, as well as the boundary-layer structures, partly explains the large contrasts in the diurnal amplitude of potential temperature and specific humidity along the transect. During the monsoon period, the atmospheric regimes drastically change involving strong interactions between the surface, atmosphere and clouds. The maximum in net radiation is shifted northwards, towards the Sahel, which potentially has a significant impact on the monsoon circulation. The sensible heat flux is considerably reduced and the diurnal amplitude is strongly damped, while the daytime boundary-layer growth decreases significantly in the Sahel related to changes in the balance of boundary-layer processes. These results highlight the contrasted diurnal cycle regimes encountered over West Africa under dry, moist and wet conditions. They provide observationally-based diagnostics to investigate the ability of models to handle the representation of the diurnal cycle over land.