The effect of a centenary storm on the long-lived seagrass Posidonia oceanica

We used the disturbance resulting from a once in a 100‐yr storm on the northwest Mediterranean coast to examine the extent of the disturbance, the tolerance thresholds to burial, and the medium‐term response of the long‐lived Posidonia oceanica seagrass. Sediment burial at 12 surveyed areas was particularly strong in shallow meadows, with 23% of their surfaces buried, on average, under more than 10 cm of sediment. In contrast, less than 5% of the meadow was affected at deeper locations. At three sites, we tracked short‐term mortality along a gradient of sediment burial. Survival response to burial was clearly nonlinear, with a significant threshold at 4-5 cm, beyond which shoot mortality was 100%. To track medium‐term potential recovery, we established permanent plots subject to three sediment burial levels (0-5, 5-10, and > 10 cm burial) in four meadows. Where the initial shoot mortality was 100%, we recorded no shoot recovery over the 4‐yr period. In the remaining plots, where some shoots remained alive, we detected either further mortality or shoot recovery of 7% per year on average. Extreme storm events can result in sudden catastrophic losses of seagrass cover in shallow P. oceanica meadows. In the long term and due to the long return time of such storms, the species may still be able to recover despite its low recovery potential. However, added anthropogenic stressors, including climate change, may seriously test the ability of long‐lived shallow seagrass ecosystems to resist high‐intensity natural disturbances and may be critical for its persistence

Detecting the impacts of harbour construction on a seagrass habitat and its subsequent recovery

Managing coastal development requires a set of tools to adequately detect ecosystem and water column degradation, but it also demands tools to detect any post-disturbance improvement. Structural seagrass indicators (such as shoot density or cover) are often used to detect or assess disturbances, but while they may be very sensitive to the impact itself, it is unclear if those indicators on their own can effectively reflect recovery at time scales relevant to managers. We used the construction of a harbour affecting a nearby Posidonia oceanica seagrass community to test the ability of a set of indicators (structural and others) to detect alterations and to evaluate their sensitivity to recovery of environmental quality after harbour construction was complete and the disturbance ceased. We used a Beyond Before After Control Impact (BBACI) design to evaluate effects on one impacted and three control meadows where we used structural, morphological, community and physiological indicators (26 in total) to asses disturbance impacts. Additionally, we measured some of the potential environmental factors that could be altered during and after the construction of the harbour and are critical to the survival of the seagrass meadow (light, sediment organic matter, sediment accrual). Harbour construction caused a clear increase in sediment organic matter and in sediment deposition rates, especially fine sand. Light availability was also reduced due to suspended sediments. Sediment and light conditions returned to normal levels 5 and 15 months after the construction began. As expected, seagrass structural indicators responded unequivocally to these environmental changes, with clear reductions in shoot density. Additionally, reduced light conditions quickly resulted in a decline in carbohydrate content in affected meadows. Unexpectedly, we also recorded a significant increase in metal content in plant tissues. No response was detected in the physiological indicators related to eutrophication (e.g. N and P content in tissues) and in morphological (shoot biomass) and community (epiphyte biomass) indicators. More than three years after the completion of the harbour, structural indicators did not show any sign of recovery. In contrast, physiological indicators, mainly heavy metal and carbohydrates content, were much better in detecting the improvement of the environmental conditions over the fairly short period of this study. These results indicate that while structural indicators are critical to evaluate the immediate effect of disturbances and the recovery on impacted systems, specific physiological indicators may be much better suited to determining the timing of environmental quality recovery. The design of impact and monitoring protocols in the wake of coastal developmental projects need to consider the differential effectiveness and time-response of measured indicators carefully

Fear of failure: a polynomial regression analysis of the joint impact of the perceived learning environment and personal achievement goal orientation

Background and Objectives: Alongside a strong emphasis on performance and achievement in the current higher educational system, researchers hav

When birds of the same feather fly together: the impact of achievement goal compatibility in collaborative learning

In their pursuit of student engagement and achievement, educational institutes have increasingly been implementing student-centred approaches to learning with collaborative learning. In this study, we assessed the (mis)match effects of personal and group members’ achievement goals on student engagement and performance. Students (N = 266) from 36 different groups rated their achievement goals, their group members’ achievement goals, and their engagement for a course. Their exam performance was also included in the analysis. The results of the polynomial regression analyses indicated that both the degree of the compatibility and the direction of the incompatibility in mastery goals related to engagement, while only the degree in incompatibility in mastery goals related to performance. Conversely, neither the compatibility nor the incompatibility in performance goals related to engagement or performance. The results show the importance of examining the interplay between students’ and their group members’ achievement goals for student outcomes in a collaborative learning environment

Burn after reading: A shadow stack with microsecond-level runtime rerandomization for protecting return addresses

Return-oriented programming (ROP) is an effective code-reuse attack in which short code sequences (i.e., gadgets) ending in a ret instruction are found within existing binaries and then executed by taking control of the call stack. The shadow stack, control flow integrity (CFI) and code (re)randomization are three popular techniques for protecting programs against return address overwrites. However, existing runtime rerandomization techniques operate on concrete return addresses, requiring expensive pointer tracking. By adding one level of indirection, we introduce BarRA, the first shadow stack mechanism that applies continuous runtime rerandomization to abstract return addresses for protecting their corresponding concrete return addresses (protected also by CFI), thus avoiding expensive pointer tracking. As a nice side-effect, BarRA naturally combines the shadow stack, CFI and runtime rerandomization in the same framework. The key novelty of BarRA, however, is that once some abstract return addresses are leaked, BarRA will enforce the burn-after-reading property by rerandomizing the mapping from the abstract to the concrete return address space in the order of microseconds instead of seconds required for rerandomizing a concrete return address space. As a result, BarRA can be used as a superior replacement for the shadow stack, as demonstrated by comparing both using the 19 C/C++ benchmarks in SPEC CPU2006 (totalling 2,047,447 LOC) and analyzing a proof-of-concept attack, provided that we can tolerate some slight binary code size increases (by an average of 29.44%) and are willing to use 8MB of dedicated memory for holding up to 220 return addresses (on a 64-bit platform). Under an information leakage attack (for some return addresses), the shadow stack is always vulnerable but BarRA is significantly more resilient (by reducing an attacker's success rate to 1 220 on average). In terms of the average performance overhead introduced, both are comparable: 6.09% (BarRA) vs. 5.38% (the shadow stack)

Experiential peer support and its effects on desistance from delinquent behavior: protocol paper for a systematic realist literature review

Background Experiential peers are increasingly involved in the development and delivery of interventions for individuals who are engaged in delinquent behavior. Experiential peer support, which is the provision of support to an individual engaged in delinquent behavior by someone who has previously also practiced such behavior, is one such application. Little is known, however, about its effects on desistance, or the mechanisms that explain these effects. On the basis of theoretical papers, program descriptions, and interviews with experts, we developed an initial program theory. We propose seven mechanisms that might play a role in the (potential) effects of support by experiential peers: (1) empathy and acceptance, (2) social learning, (3) social bonding, (4) social control, (5) narrative and identity formation, (6) hope and perspective, and (7) translation and connection. In addition, in this protocol paper, we describe the methods of a systematic realist literature review that will be conducted in order to investigate the evidence base for this program theory. Methods The study described in this protocol paper is a realist review, which is a suitable approach to study complex interventions and fits the explanatory purpose of the study. We outline the steps to be taken for the systematic realist review, including the selection and assessment of studies and the methods for synthesizing the findings. Discussion Investigating the effects and the underlying mechanisms of support by experiential peers for individuals with delinquent behavior is relevant because the forensic setting has some unique features, and the involvement of service users might create even more tension than in other settings due to stigma and perceived risks. The findings that will be reported in the realist review will contribute to the knowledge of the effects of support by experiential peers and will provide insight into which aspects remain to be studied. It might also provide formal care institutions with guidance on whether to involve experiential peers in the delivery of their services and the conditions under which these interventions are likely to lead to positive results