Mark Huxham

The influence of Cryptocotyle lingua (Digenea:Platyhelminthes) infections on the survival and fecundity of Littorina littorea (Gastropoda:Prosobranchia); an ecological approach

Abstract This study considers the impact of digenean parasites, especially Cryptocotyle lingua (Creplin) on the survival, reproduction, growth rate and foot colour of Littorina littorea (Forbes and Hanley). An 18 month field experiment demonstrated decreased survivorship of infected snails. A laboratory experiment showed a drastic reduction, but not total cessation, of gamete production in infected females. Infection was found to retard growth and correlate with reduced shell height in some animals. A strong relationship was found between foot colour and infection. The relevance of infection to the population dynamics of L. littorea on the Ythan, and to the Ythan food web as a whole, is considered.

Learning in lectures Do ‘interactive windows’ help?

Many educational development resources recommend making conventional lectures more interactive. However, there is little firm evidence supporting either the acceptability (to students) or efficacy of doing so. This research examined the use of short ‘interactive windows’ (discussions and problem-solving exercises) in first year evolution lectures delivered to between 73 and 126 students over five years. Semi-structured evaluations of the teaching, involving more than 500 responses, identified the interactive nature of the lectures as the single most popular feature of the sessions. The division of the year class into two separate groups allowed the opportunistic testing of how interactive windows influenced learning about discrete problems within each lecture. Two short problem-solving or discussion sessions were devised for each lecture; one of these sessions was taught interactively to the first student group, the second was taught interactively to the second group. Comparing test scores achieved in questions addressing these paired problems showed strong evidence for a generally weak, positive influence of the interactive windows on recall and learning.

Predation: a causal mechanism for variability in intertidal bivalve populations

Two caging experiments were conducted on an intertidal mudflat to assess the impact of predation on two species of bivalves; Macoma balthica and Cerastoderma edule. The first caging experiment enclosed the shore crab, Carcinus maenas, carapace width 15–25 mm, in 1-m2 cages. The three treatments were zero Carcinus (control), five Carcinus (the highest natural densities found at this site) and 20 Carcinus (a raised density). The experiment ran for approximately 1 month in August 1996. An exclosure experiment was conducted at the same site the following year and ran for approximately 2 months during September and October. The three treatments were full cages, partial cages and an un-caged control. Results from the enclosure indicate that crab predation was responsible for a reduction of both species of bivalve even at high naturally occurring crab densities. Significant reductions were observed between all treatments for C. edule and between the control and 20 Carcinus treatment for M. balthica. Significant differences occurred in the exclosure experiment between all treatments for C. edule. Almost all of the C. edule were removed in the un-caged areas. Significant differences only occurred between the full cages and un-caged areas for M. balthica. In both experiments there was a preference for C. edule over M. balthica and for the larger size classes of both species. Previous work at the present study site showed Carcinus predation to be site-specific, with predation rates dependent on the sediment type. The density of Carcinus at this site is extremely variable; this together with sediment-specific consumption of bivalves may be one of the causal mechanisms for both the spatial and temporal variability shown in populations of M. balthica and C. edule at this site.

Fast and Effective Feedback: Are Model Answers the Answer?.

Feedback to students is essential for effective learning, but there is little empirical information on what kind of feedback is best. This study compares student responses and performance after receiving two types of feedback, that provided by model answers and that provided by personal comments. In 2004 and 2005, a total of 183 students in first and honours years biology courses were provided with both types of feedback, and their perceptions and preferences were explored using a questionnaire. The examination marks of 155 students were analysed, comparing scores in questions relating to personal and model feedback given earlier in the course. Questionnaire results showed that a majority of students wanted both kinds of feedback, but that there was a preference for personal over model feedback. However, there were highly significant differences between the mean marks achieved in examinations, with students performing better in model answer questions in both 2004 and 2005. These results suggest that the best approach might be a hybrid one, drawing on the strengths of both kinds of feedback.

Intra- and interspecific facilitation in mangroves may increase resilience to climate change threats

Mangroves are intertidal ecosystems that are particularly vulnerable to climate change. At the low tidal limits of their range, they face swamping by rising sea levels; at the high tidal limits, they face increasing stress from desiccation and high salinity. Facilitation theory may help guide mangrove management and restoration in the face of these threats by suggesting how and when positive intra- and interspecific effects may occur: such effects are predicted in stressed environments such as the intertidal, but have yet to be shown among mangroves. Here, we report the results of a series of experiments at low and high tidal sites examining the effects of mangrove density and species mix on seedling survival and recruitment, and on the ability of mangroves to trap sediment and cause surface elevation change. Increasing density significantly increased the survival of seedlings of two different species at both high and low tidal sites, and enhanced sediment accretion and elevation at the low tidal site. Including Avicennia marina in species mixes enhanced total biomass at a degraded high tidal site. Increasing biomass led to changed microenvironments that allowed the recruitment and survival of different mangrove species, particularly Ceriops tagal.

Assigning Students in Group Work Projects. Can We Do Better than Random

Group work projects are increasingly used in higher education, but there is little guidance on how best to allocate students to groups. If groups can be engineered to contain compatible people, then the process of group work may be easier and more productive. The Honey and Mumford learning styles questionnaire provides a quick and easy way in which students might be classified into purportedly complementary categories. This paper discusses a comparison of the performance of student groups formed randomly, with those formed using the learning styles questionnaire. We found no significant differences in the performances of these two sets of groups, and we discuss some possible reasons for this.

Predator caging experiments: a test of the importance of scale

Abstract The impact of predators is often relative to the spatial scale at which the study is conducted. In this paper we investigated how spatial scale might influence the importance of predation. In doing this we addressed the hypothesis of scale-dependency in predation experiments. The predator studied was the shore crab, Carcinus maenas (L.), and its impact on intertidal macrofauna communities was assessed using a caging experiment . Two different treatments, small and large enclosure cages (of, respectively, 0.25 and 1 m 2 ), were established in a completely randomised design on two different sites, mud and muddy sand, which differed physically but were very similar biologically. The density of crabs per square metre was 48, much larger than the ambient density but comparable with previously published work. The experiment ran for a month and the resulting data and summary statistics were analysed using univariate and multivariate methods. Results indicate that the impacts of crab predation were similar in the different cage sizes but different on the different sites. The present work demonstrates the importance of scale in interpreting the results of caging experiments, but not at the small-scale level of cage size.

Turning the Tide: How Blue Carbon and Payments for Ecosystem Services (PES) Might Help Save Mangrove Forests

In this review paper, we aim to describe the potential for, and the key challenges to, applying PES projects to mangroves. By adopting a “carbocentric approach,” we show that mangrove forests are strong candidates for PES projects. They are particularly well suited to the generation of carbon credits because of their unrivaled potential as carbon sinks, their resistance and resilience to natural hazards, and their extensive provision of Ecosystem Services other than carbon sequestration, primarily nursery areas for fish, water purification and coastal protection, to the benefit of local communities as well as to the global population. The voluntary carbon market provides opportunities for the development of appropriate protocols and good practice case studies for mangroves at a small scale, and these may influence larger compliance schemes in the future. Mangrove habitats are mostly located in developing countries on communally or state-owned land. This means that issues of national and local governance, land ownership and management, and environmental justice are the main challenges that require careful planning at the early stages of mangrove PES projects to ensure successful outcomes and equitable benefit sharing within local communities.

Oral versus Written Assessments: A Test of Student Performance and Attitudes.

Student performance in and attitudes towards oral and written assessments were compared using quantitative and qualitative methods. Two separate cohorts of students were examined. The first larger cohort of students (n = 99) was randomly divided into ‘oral’ and ‘written’ groups, and the marks that they achieved in the same biology questions were compared. Students in the second smaller cohort (n = 29) were all examined using both written and oral questions concerning both ‘scientific’ and ‘personal development’ topics. Both cohorts showed highly significant differences in the mean marks achieved, with better performance in the oral assessment. There was no evidence of particular groups of students being disadvantaged in the oral tests. These students and also an additional cohort were asked about their attitudes to the two different assessment approaches. Although they tended to be more nervous in the face of oral assessments, many students thought oral assessments were more useful than written assessments. An important theme involved the perceived authenticity or ‘professionalism’ of an oral examination. This study suggests that oral assessments may be more inclusive than written ones and that they can act as powerful tools in helping students establish a ‘professional identity’.

Rapid losses of surface elevation following tree girdling and cutting in tropical mangroves.

The importance of mangrove forests in carbon sequestration and coastal protection has been widely acknowledged. Large-scale damage of these forests, caused by hurricanes or clear felling, can enhance vulnerability to erosion, subsidence and rapid carbon losses. However, it is unclear how small-scale logging might impact on mangrove functions and services. We experimentally investigated the impact of small-scale tree removal on surface elevation and carbon dynamics in a mangrove forest at Gazi bay, Kenya. The trees in five plots of a Rhizophora mucronata (Lam.) forest were first girdled and then cut. Another set of five plots at the same site served as controls. Treatment induced significant, rapid subsidence (−32.1±8.4 mm yr−1 compared with surface elevation changes of +4.2±1.4 mm yr−1 in controls). Subsidence in treated plots was likely due to collapse and decomposition of dying roots and sediment compaction as evidenced from increased sediment bulk density. Sediment effluxes of CO2 and CH4 increased significantly, especially their heterotrophic component, suggesting enhanced organic matter decomposition. Estimates of total excess fluxes from treated compared with control plots were 25.3±7.4 tCO2 ha−1 yr−1 (using surface carbon efflux) and 35.6±76.9 tCO2 ha−1 yr−1 (using surface elevation losses and sediment properties). Whilst such losses might not be permanent (provided cut areas recover), observed rapid subsidence and enhanced decomposition of soil sediment organic matter caused by small-scale harvesting offers important lessons for mangrove management. In particular mangrove managers need to carefully consider the trade-offs between extracting mangrove wood and losing other mangrove services, particularly shoreline stabilization, coastal protection and carbon storage.