Elevated manganese concentrations at the cores of clupeid otoliths: possible environmental,physiological, or structural origins

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to investigate the distribution of manganese (Mn) in Atlantic herring (Clupea harengus L.) otoliths. An unusual pattern of Mn concentration, which has not previously been reported in fish otoliths, was observed. Time-resolved plots (time roughly equivalent to ablation depth) of the Mn signal recorded in the ICP-MS detector during ablation of otoliths contained a distinct peak, suggesting that elevated Mn concentrations were specific to certain regions. Ablation inside and outside of the otolith core revealed that the region of high Mn concentration coincided with the ablation of the core. It was initially suggested that Mn from the gravel substrate on which herring eggs are incubated is incorporated into the otolith core, producing elevated Mn concentrations in this region. It was hypothesised that otoliths from fish whose eggs are not incubated in gravel will not contain high Mn concentrations at the core. To test this, otoliths of sprat (Sprattus sprattus), which have a pelagic embryological stage, and from reared herring, which were incubated on glass plates, were analysed using LA-ICP-MS. Peaks in the Mn signal were observed during the ablation of cores from some sprat and reared herring otoliths, indicating that incubation on a gravel substrate is not necessary for the accumulation of Mn at the otolith core and that otoliths from both pelagic and demersally spawning fish species can contain elevated Mn concentrations. The results suggest that Mn concentrations at the otolith core do not reflect the external environment of the developing embryo. Two other hypotheses are considered. A dramatic increase in Mn concentrations in the egg, associated with embryological development, may produce elevated Mn levels at the otolith core. Alternatively, the high levels of Mn observed at the otolith core may reflect spatial variation in the crystal structure of the calcium carbonate portion of the otolith. The possible influence of physiological or structural factors on the chemical composition of the otolith core may confound the environmental signal in this region of the otolith. This has important implications for the interpretation of otolith chemistry data.Communicated by J.P. Thorpe, Port Erin     

Nitrogen removal and nitrate leaching for forage systems receiving dairy effluent

Florida dairies need year-round forage systems that prevent loss of N to ground water from waste effluent sprayfields. Our purpose was to quantify forage N removal and monitor nitrate N (NO3(-)-N) concentrations in soil water below the rooting zone for two forage systems during four 12-mo cycles (1996-2000). Soil in the sprayfield is an excessively drained Kershaw sand (thermic, uncoated Typic Quartzipsamment). Over four cycles, average loading rates of effluent N were 500, 690, and 910 kg ha(-1) per cycle. Nitrogen removed by the bermudagrass (Cynodon spp.)-rye (Secale cereale L.) system (BR) during the first three cycles was 465 kg ha(-1) per cycle for the low loading rate, 528 kg ha(-1) for the medium rate, and 585 kg ha(-1) for the high. For the corn (Zea mays L.)-forage sorghum [Sorghum bicolor (L.) Moench]-rye system (CSR), N removals were 320 kg ha(-1) per cycle for the low rate, 327 kg ha(-1) for the medium, and 378 kg ha(-1) for the high. The higher N removals for BR were attributed to higher N concentration in bermudagrass (18.1-24.2 g kg(-1)) than in corn and forage sorghum (10.3-14.7 g kg(-1)). Dry matter yield declined in the fourth cycle for bermudagrass but N removal continued to be higher for BR than CSR. The BR system was much more effective at preventing NO3(-)-N leaching. For CSR, NO3(-)-N levels in soil water (1.5 m below surface) increased steeply during the period between the harvest of one forage and canopy dosure of the next. Overall, the BR system was better than CSR at removing N from the soil and maintaining low NO3(-)-N concentrations below the rooting zone.     

Hydrology and grazing jointly control a large-river food web

Inputs of fresh water and grazing both can control aquatic food webs, but little is known about the relative strengths of and interactions between these controls. We use long-term data on the food web of the freshwater Hudson River estuary to investigate the importance of, and interactions between, inputs of fresh water and grazing by the invasive zebra mussel (Dreissena polymorpha). Both freshwater inputs and zebra mussel grazing have strong, pervasive effects on the Hudson River food web. High flow tended to reduce population size in most parts of the food web. High grazing also reduced populations in the planktonic food web, but increased populations in the littoral food web, probably as a result of increases in water clarity. The influences of flow and zebra mussel grazing were roughly equal (i.e., within a factor of 2) for many variables over the period of our study. Zebra mussel grazing made phytoplankton less sensitive to freshwater inputs, but water clarity and the littoral food web more sensitive to freshwater inputs, showing that interactions between these two controlling factors can be strong and varied.     

The theory behind,and the challenges of,conserving nature's stage in a time of rapid change

Most conservation planning to date has focused on protecting today's biodiversity with the assumption that it will be tomorrow's biodiversity. However, modern climate change has already resulted in distributional shifts of some species and is projected to result in many more shifts in the coming decades. As species redistribute and biotic communities reorganize, conservation plans based on current patterns of biodiversity may fail to adequately protect species in the future. One approach for addressing this issue is to focus on conserving a range of abiotic conditions in the conservation‐planning process. By doing so, it may be possible to conserve an abiotically diverse “stage” upon which evolution will play out and support many actors (biodiversity). We reviewed the fundamental underpinnings of the concept of conserving the abiotic stage, starting with the early observations of von Humboldt, who mapped the concordance of abiotic conditions and vegetation, and progressing to the concept of the ecological niche. We discuss challenges posed by issues of spatial and temporal scale, the role of biotic drivers of species distributions, and latitudinal and topographic variation in relationships between climate and landform. For example, abiotic conditions are not static, but change through time—albeit at different and often relatively slow rates. In some places, biotic interactions play a substantial role in structuring patterns of biodiversity, meaning that patterns of biodiversity may be less tightly linked to the abiotic stage. Furthermore, abiotic drivers of biodiversity can change with latitude and topographic position, meaning that the abiotic stage may need to be defined differently in different places. We conclude that protecting a diversity of abiotic conditions will likely best conserve biodiversity into the future in places where abiotic drivers of species distributions are strong relative to biotic drivers, where the diversity of abiotic settings will be conserved through time, and where connectivity allows for movement among areas providing different abiotic conditions.     

Directional changes in the species composition of a tropical forest

Long-term studies have revealed that the structure and dynamics of many tropical forests are changing, but the causes and consequences of these changes remain debated. To learn more about the forces driving changes within tropical forests, we investigated shifts in tree species composition over the past 25 years within the 50-ha Forest Dynamics Plot on Barro Colorado Island (BCI), Panama, and examined how observed patterns relate to predictions of (1) random population fluctuations, (2) carbon fertilization, (3) succession from past disturbance, (4) recovery from an extreme El Ni?o drought at the start of the study period, and (5) long-term climate change. We found that there have been consistent and directional changes in the tree species composition. These shifts have led to increased relative representations of drought-tolerant species as determined by the species' occurrence both across a gradient of soil moisture within BCI and across a wider precipitation gradient from a dry forest near the Pacific coast of Panama to a wet forest near its Caribbean coast. These nonrandom changes cannot be explained by stochastic fluctuations or carbon fertilization. They may be the legacy of the El Ni?o drought, or alternatively, potentially reflect increased aridity due to long-term climate change. By investigating compositional changes, we increased not only our understanding of the ecology of tropical forests and their responses to large-scale disturbances, but also our ability to predict how future global change will impact some of the critical services provided by these important ecosystems.     

Science-Driven Management of Protected Areas: A Philippine Case Study

The lack of scientific baseline information hinders appropriate design and management of protected areas. To illustrate the value of science to management, we consider five scenarios for the 202.0 km² Puerto Princesa Subterranean River National Park, Philippines: (1) closure to human activities, (2) and (3) two levels of increase in unplanned human activities, (4) creation of a forest corridor and (5) additional allocation of land for permanent or shifting agriculture. We then use habitat-specific bird density estimates to simulate the net effect of each scenario on 18 focal bird populations. Closure has significant benefits—populations of five species are predicted to increase by >50 % and nine by >25 %, but two secondary forest flycatchers, including the endemic and ‘Vulnerable’ Palawan flycatcher, decline dramatically, while the creation of a 4.0 km² forest corridor yields average increases across species of 2 ± 4 % (SD). In contrast, heavier unplanned park usage produces declines in all but a few species, while the negative effects of an extra 2.0 km² of shifting cultivation are 3–5 times higher than for a similar area of permanent agriculture and affect species whose densities are highest in primary habitats. Relatively small changes within the park, especially those associated with agricultural expansion, has serious predicted implications for local bird populations. Our models do not take into account the full complexities of bird ecology at a site, but they do provide park managers with an evidence base from which to make better decisions relating to biodiversity conservation obligations which their parks are intended to meet.     

An ecosystem approach to analyse the livelihood of fishers of the Old Brahmaputra River in Mymensingh region,Bangladesh

This paper applies an ecosystem approach to analyse the livelihood of fishers dependent on the Old Brahmaputra River in Mymensingh, Bangladesh. Results suggest that the livelihood of fishers is increasingly threatened because of the fragile river ecosystem and poor livelihood assets. Most fishers face a wide range of vulnerability including shocks, trends and seasonality. This is because the ecosystem of the resource base on which their livelihood depends (i.e. the Old Brahmaputra River) has been degraded severely resulting in a significant decline in fish catch due to a combination of factors, such as over-fishing, use of destructive fishing gears, water pollution, siltation, rapid urbanisation and environmental degradation. We propose an adoption of the socio-ecological system with active community participation in the management of the resource base and collaboration amongst key stakeholders to produce positive livelihood outcomes for the fishers.     

Resources policies in Australia

Developments in Australia's resource industries in recent years have raised policy issues not previously encountered, and their consideration has been superimposed onto traditional policies affecting resource production and use. This review of Australia's policies on resources - here meaning minerals and energy policies - looks at the objectives of these policies and their interrelationships. It considers issues such as management, development objectives, investment, taxation, environment and processing, and likely future developments.