Metabolic rate and lipofuscin accumulation in juvenile European lobster (Homarus gammarus ) in relation to simulated seasonal changes in temperature

 The accumulation of lipofuscin, which is an indictor of physiological age, in the brain of juvenile European lobster (Homarus gammarus L.) was monitored for 22 mo in three experimental temperature regimes that simulated seasonal variation in temperature in the geographic range of this species. Metabolic rate responses to changes in temperature were estimated by measuring the activity of the electron transport system (ETS) in muscle tissue and in vivo rates of oxygen consumption. Lipofuscin accumulation oscillated with simulated seasonal changes in temperature and was described by seasonalised von Bertalanffy growth functions. The incremental accumulation in lipofuscin between sampling dates was linearly related to the number of degree days that accumulated between dates, irrespective of the amplitude of temperature fluctuation that had occurred. ETS activity increased with acclimation temperature and was modelled using a polynomial function. This indicated a lower temperature sensitivity in the temperature mid-range (12 to 16 °C), although the Q₁₀ for this mid-range was 2.1. ETS activity in lobsters acclimated to 8 and 18 °C and assayed at 13 °C was similar, indicating no compensation for changes in environmental temperature. Oxygen consumption rate was significantly higher at 14 °C than at 10.5 °C and had a Q₁₀ of 3.6, again suggesting no compensation to temperature change. The absence of metabolic compensation in response to temperature change in H. gammarus is consistent with the predictability of changes in temperature and food availability in the sub-littoral environment of this species. As lipofuscin accumulates according to metabolic rate, and metabolic rate in H. gammarus is directly correlated with temperature, geographic differences and long-term temporal trends in temperature will need to be considered when converting physiological age indices, obtained from lipofuscin estimates, to a chronological scale. Received: 27 April 2000 / Accepted: 21 July 2000     

Investigations into the transport and pathways of scallop larvae--the use of numerical models for managing fish stocks

The scallop fisheries off the southeast coast of Ireland have historically been considered a valuable resource for coastal communities, and hence their management is important. The scallop fishing grounds consist of a number of scallop beds dispersed throughout the St George's Channel and the southern Irish Sea. The boundaries between stocks and the interconnection in populations of adult scallops, through larval transport, is generally unknown. Until the time of this research, the stocks of scallop in this region had not been assessed. A research project was undertaken to develop novel, spatially explicit and multi-disciplinary approaches to the assessment of the scallop fisheries in the region. The project supported research in three related areas under the broad objective of developing stock assessment protocols and methods in order to promote sustainable management of these fisheries. One of these areas was the development and application of numerical models. The objectives of this modelling research were: (a) to reconstruct the physical environment of the study area; (b) investigate how this environment affects the demographics and nature of scallop; and (c) determine migration-transport pathways of the scallop larvae. From these investigations, light is shed on how the spatial variability in certain parameters of the natural environment determine habitats and the scallop populations. Also, the investigations now enable determinations to be made on the interconnectivities of 'disparate' scallop beds and where larvae are, in general, likely to be found. Thus, through the use of complex computer models, important clues are deduced that enable us to now understand key behavioural components of scallop larvae and their transport pathways. The analysis of these clues is assisting the development of protocols for managing the fish stock in a sustainable manner.     

Perfluorinated chemicals in selected residents of the American continent

Perfluorinated chemicals (PFCs) are used in multiple consumer products. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), the most widely studied PFCs, may be potential developmental, reproductive, and systemic toxicants. Although PFCs seem to be ubiquitous contaminants found both in humans and animals, geographic differences may exist in human exposure patterns to PFCs. We measured 11 PFCs in 23 pooled serum samples collected in the United States from 1990 through 2002, and in serum samples collected in 2003 from 44 residents from Trujillo, Peru. PFOS and PFOA were detected in all the pooled samples; perfluorohexane sulfonic acid (PFHxS) was detected in 21. Median concentrations were 31.1 micrograms per liter (mug/l, PFOS), 11.6 microg/l (PFOA), and 2 microg/l (PFHxS). The 90th percentile concentrations of PFCs in the 44 Peruvian residents were 0.7 microg/l (PFOS), 0.1 microg/l (PFOA), and <0.3 microg/l (PFHxS). The frequencies of detection were 20% (PFOS), 25% (PFOA), and 9% (PFHxS). The frequent detection of selected PFCs in the pooled samples from the United States and the lack of clear concentration trends based on a year of collection suggest a sustained widespread exposure to these compounds among US residents, at least since the 1990s. By contrast, the much lower frequency of detection and concentration ranges of PFCs in Peru suggest a lower exposure of Peruvians to PFCs compared with North Americans. Genetic variability, diet, lifestyle, or a combination of all these may contribute to the different patterns of human exposure to PFCs in the United States and Peru.     

Canopy and leaf composition drive patterns of nutrient release from pruning residues in a coffee agroforest

In a coffee agroforest, the crop is cultivated under the shade of fruit-bearing and nitrogen (N)-fixing trees. These trees are periodically pruned to promote flowering and fruiting as well as to make nutrients stored in tree biomass available to plants. We investigated the effect of canopy composition and substrate quality on decomposition rates and patterns of nutrient release from pruning residues in a coffee agroforest located in Costa Rica's Central Valley. Initial phosphorus (P) release was enhanced under a canopy composed solely of N-fixing, Erythrina poeppigiana compared to a mixed canopy of Erythrina and Musa acuminata (banana). Both initial and final N release were similar under the two canopy types. However, after five months of decomposition, a higher proportion of initial N had been released under the single canopy. Although patterns of decomposition and nutrient release were not predicted by initial substrate quality, mass loss in leaf mixtures rates were well predicted by mean mass loss of their component species. This study identifies specific pruning regimes that may regulate N and P release during crucial growth periods, and it suggests that strategic pruning can enhance nutrient availability. For example, during the onset of rapid fruit growth, a two-species mixture may release more P than a three-species mixture. However, by the time of the harvest, the two- and three-species mixtures have released roughly the same amount of N and P. These nutrients do not always follow the same pattern, as N release can be maximized in single-species substrates, while P release is often facilitated in species mixtures. Our study indicates the importance of management practices in mediating patterns of nutrient release. Future research should investigate how canopy composition and farm management can also mediate on-farm nutrient losses.     

Accounting for carbon stocks in models of land-use change: an application to Southern Yucatan

To assess the impact of land-use change on carbon stocks, we apply a new methodology, linking ecological and economic modeling, to southern Yucatan, Mexico. A spatial econometric multinomial logit model of ten land-cover classes is estimated (four primary forest categories, three secondary growth categories, an invasive species, and two agricultural land-cover categories), using satellite data on land cover, linked with census socioeconomic data and other biophysical spatial data from 2000. The analysis is novel in that it is the first attempt to link detailed satellite data on land use, with on-the-ground estimates of carbon stocks in a spatial econometric model of land use. The estimated multinomial logit model is then used with two scenarios of future economic growth (“low growth” and “high growth” changes in population, agricultural land use, market access, and education levels) in the region to predict land-cover changes resulting from the economic growth. The per hectare carbon (C) stocks in each land-cover class are derived from previously published estimates of biomass from field sampling across the study region. We consider aboveground-only, aboveground plus soil, transient and non-transient pools of carbon. These estimates are scaled up to the total area in each class according to the predictions of the model baseline and the two development scenarios. Subsequently, the changes in carbon stocks resulting from the predicted land-cover changes are calculated. Under the low growth scenario, carbon stocks declined by 5%; under the high growth scenario, losses were 12%. Including soil C, the proportional losses were lower, but the absolute amount lost was more than double (to 6 Tg C under the low and almost 15 Tg C under the high-growth scenario). This methodology could be further developed for applications in global change policy, such as payments for environmental services (PES) or reduction in emissions from deforestation and degradation (REDD).     

The ichthyoneuston of Galway Bay (Ireland)

The ichthyofauna of the neustal (0 to 10 cm) and immediate subsurface water (12 to 48 cm) of Galway Bay was sampled during the day from June 1983 to September 1984 and at night from May to September 1984. Species diversity (H) and the number of species per sample were significantly higher at night. The density of larvae at night was higher only during May. Thirty-nine of the more common species were grouped by factor analysis resulting in 13 species groups with distinct spatial and temporal distributions. Three main time periods, February to April, May to July and July to September and three spatially defined station categories, each of which had distinct species groups, were also isolated by factor analysis. Station categories were contiguous and hydrographically and topographically distinct. Eight species groups showed evidence of vertical migration. Five groups were most abundant from July to September compared with three during May to June and one to two at other times. Eighty-one species or other taxomonic entity (genus or family) were recorded. The majority were pseudoneustonic and represented by early larvae and post-larvae. Euneustonic species (Ciliata mustela, Ciliata septentrionalis, Crenimugil labrosus, Gaidropsaurus mediterraneus, Gasterosteus aculeatus, Liza sp., Rhinonemus cimbrius, Scophthalmus maximus) were all present as late post-larvae or juveniles and all except Ciliata spp occurred during autumn. Facultatively neustonic species (Ammodytes marinus, Belone belone, Ctenolabrus rupestris, Entelurus aequoreus, Nerophis lumbriciformis, Sprattus sprattus, Trachinus vipera) were, except for Belone belone and Ctenolabrus rupestris, all represented by juveniles. All except Ammodytes marinus and Sprattus sprattus were common only in autumn.