Lag effects in the impacts of mass coral bleaching on coral reef fish, fisheries, and ecosystems

Recent episodes of coral bleaching have led to wide-scale loss of reef corals and raised concerns over the effectiveness of existing conservation and management efforts. The 1998 bleaching event was most severe in the western Indian Ocean, where coral declined by up to 90% in some locations. Using fisheries-independent data, we assessed the long-term impacts of this event on fishery target species in the Seychelles, the overall size structure of the fish assemblage, and the effectiveness of two marine protected areas (MPAs) in protecting fish communities. The biomass of fished species above the size retained in fish traps changed little between 1994 and 2005, indicating no current effect on fishery yields. Biomass remained higher in MPAs, indicating they were effective in protecting fish stocks. Nevertheless, the size structure of the fish communities, as described with size-spectra analysis, changed in both fished areas and MPAs, with a decline in smaller fish (<30 cm) and an increase in larger fish (>45 cm). We believe this represents a time-lag response to a reduction in reef structural complexity brought about because fishes are being lost through natural mortality and fishing, and are not being replaced by juveniles. This effect is expected to be greater in terms of fisheries productivity and, because congruent patterns are observed for herbivores, suggests that MPAs do not offer coral reefs long-term resilience to bleaching events. Corallivores and planktivores declined strikingly in abundance, particularly in MPAs, and this decline was associated with a similar pattern of decline in their preferred corals. We suggest that climate-mediated disturbances, such as coral bleaching, be at the fore of conservation planning for coral reefs.\u

Cluster-induced crater formation

Using molecular-dynamics simulation, we study the crater volumes induced by energetic impacts ($v= 1- 250$ km/s) of projectiles containing up to N=1000 atoms. We find that for Lennard-Jones bonded material the crater volume depends solely on the total impact energy $E$. Above a threshold \Eth, the volume rises linearly with $E$. Similar results are obtained for metallic materials. By scaling the impact energy $E$ to the target cohesive energy $U$, the crater volumes become independent of the target material. To a first approximation, the crater volume increases in proportion with the available scaled energy, $V=aE/U$. The proportionality factor $a$ is termed the cratering efficiency and assumes values of around 0.5.Comment: 9 page

Improved Calculation of Vibrational Mode Lifetimes in Anharmonic Solids - Part I: Theory

We propose here a formal foundation for practical calculations of vibrational mode lifetimes in solids. The approach is based on a recursion method analysis of the Liouvillian. From this we derive the lifetime of a vibrational mode in terms of moments of the power spectrum of the Liouvillian as projected onto the relevant subspace of phase space. In practical terms, the moments are evaluated as ensemble averages of well-defined operators, meaning that the entire calculation is to be done with Monte Carlo. These insights should lead to significantly shorter calculations compared to current methods. A companion piece presents numerical results.Comment: 18 pages, 3 figure

New cod war of words:'Cod is God' versus 'sod the cod'—Two opposed discourses on the North Sea Cod Recovery Programme

New insights into the North Sea Cod Recovery Programme (CRP), initiated in 2003 by the European Commission to reverse the long-term decline in cod stocks, are presented using discourse analysis. The main conservation measures taken under the CRP have been to reduce catch limits drastically and to increase control over vessels' fishing activities. There has been considerable controversy over the programme from its inception, with protagonists broadly divided into two discourses: (1) 'cod is God'-in which cod has assumed the status of the defining test of the European Union's (EU) resolve to manage fish stocks sustainably in EU waters; (2) 'sod the cod'-in which cod is regarded as one of a number of target commercial fish species, with no special status. Drawing on Frank Fischer's distinction between hegemonic and challenging discourses, we analyse the conflict between them at three levels: empirical; conceptual; and political. We consider moves to reconcile the two discourses in a policy consensus on a revised CRP, which suggest that the challenging discourse (sod-the-cod) has had some success in modifying the impact of the hegemonic discourse (cod-is-God

Electronic and structural properties of vacancies on and below the GaP(110) surface

We have performed total-energy density-functional calculations using first-principles pseudopotentials to determine the atomic and electronic structure of neutral surface and subsurface vacancies at the GaP(110) surface. The cation as well as the anion surface vacancy show a pronounced inward relaxation of the three nearest neighbor atoms towards the vacancy while the surface point-group symmetry is maintained. For both types of vacancies we find a singly occupied level at mid gap. Subsurface vacancies below the second layer display essentially the same properties as bulk defects. Our results for vacancies in the second layer show features not observed for either surface or bulk vacancies: Large relaxations occur and both defects are unstable against the formation of antisite vacancy complexes. Simulating scanning tunneling microscope pictures of the different vacancies we find excellent agreement with experimental data for the surface vacancies and predict the signatures of subsurface vacancies.Comment: 10 pages, 6 figures, Submitted to Phys. Rev. B, Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Measuring kinetic coefficients by molecular dynamics simulation of zone melting

Molecular dynamics simulations are performed to measure the kinetic coefficient at the solid-liquid interface in pure gold. Results are obtained for the (111), (100) and (110) orientations. Both Au(100) and Au(110) are in reasonable agreement with the law proposed for collision-limited growth. For Au(111), stacking fault domains form, as first reported by Burke, Broughton and Gilmer [J. Chem. Phys. {\bf 89}, 1030 (1988)]. The consequence on the kinetics of this interface is dramatic: the measured kinetic coefficient is three times smaller than that predicted by collision-limited growth. Finally, crystallization and melting are found to be always asymmetrical but here again the effect is much more pronounced for the (111) orientation.Comment: 8 pages, 9 figures (for fig. 8 : [email protected]). Accepted for publication in Phys. Rev.

Boredom, Information-Seeking and Exploration

Any adaptive organism faces the choice between taking actions with known benefits (exploitation), and sampling new actions to check for other, more valuable opportunities available (exploration). The latter involves information- seeking, a drive so fundamental to learning and long-term reward that it can reasonably be considered, through evolution or development, to have acquired its own value, independent of immediate reward. Similarly, behaviors that fail to yield information may have come to be associated with aversive experiences such as boredom, demotivation, and task disengagement. In accord with these suppositions, we propose that boredom reflects an adaptive signal for managing the exploration-exploitation tradeoff, in the service of optimizing information acquisition and long-term reward. We tested participants in three experiments, manipulating the information content in their immediate task environment, and showed that increased perceptions of boredom arise in environments in which there is little useful information, and that higher boredom correlates with higher exploration. These findings are the first step toward a model formalizing the relationship between exploration, exploitation and boredom

Detector Description and Performance for the First Coincidence Observations between LIGO and GEO

For 17 days in August and September 2002, the LIGO and GEO interferometer gravitational wave detectors were operated in coincidence to produce their first data for scientific analysis. Although the detectors were still far from their design sensitivity levels, the data can be used to place better upper limits on the flux of gravitational waves incident on the earth than previous direct measurements. This paper describes the instruments and the data in some detail, as a companion to analysis papers based on the first data.Comment: 41 pages, 9 figures 17 Sept 03: author list amended, minor editorial change