Sea level and diagenesis: a case study on Pleistocene beaches,Whalebone Bay,Bermuda

Pleistocene fluctuations of sea level have left marine and aeolian limestones intercalated with glacial red soils on the Bermuda Carbonate Platform (Atlantic, 64°50W, 32°20N). Successive eustatic highstands of similar amplitude drowned the tectonically stable platform and piled up similar sets of sediments. Up to three Pleistocene beaches are stacked in shorelines sections. Post-depositional diagenetic histories of these beaches can be linked to repeated changes in sea level and pore waters.This paper presents field evidence and petrographic results (microscope, X-ray, cathodoluminescence, SEMEDAX) for the diagenetic histories of two superimposed Pleistocene beaches in Whalebone Bay, Bermuda North Shore. The younger beach was deposited during isotopic stage 5e, about 120 ka ago. The age of the older beach may be isotopic stage 9 or older.Diagenesis drastically altered the older beach before the stage 5e transgression. Primary high-Mg calcite (HMC) and aragonite were no longer present. Marine skeletal grains were instead leached or recrystallized to low-Mg calcite (LMC). Primary and secondary pore space were largely reduced by LMC cement. Lines of needle relics reminiscent of marine aragonite cement occur as inclusions within syntaxial rim cements around echinoderm grains, indicating that a marine influence had at least once interrupted this period of freshwater alteration. Finally, before the rocks became buried by the sediments of the younger beach, a crust of marine, bladed HMC cement was precipitated throughout the pore space.The younger beach consists of skeletal grains that are, apart from the effects of non-selective dissolution, essentially unaltered. The sediments are only weakly lithified by cryptocrystalline LMC showing an alveolar texture, tangential fibres and other features characteristic of calichification. A younger post-depositional marine influence is not recorded.These results suggest that, under favourable conditions, diagenetic processes can document sea-level fluctuations. The recorded fluctuations, however, are difficult to assess because even major sea-level highstands may not produce a diagenetic imprint. Correspondence to: R. Vollbrecht     

Transformative tans? Gendered and raced bodies on beaches

Abstract: In this paper I examine the intentional act of transforming the colour of one's skin – sun‐tanning – by Pākehā at three New Zealand beaches: Papamoa, Mount Maunganui, and Takapuna. Recent debates about the construction of whiteness are outlined before discussing the historical significance of beaches and sun to New Zealand's leisure culture. This paper seeks to de‐naturalize whiteness through the disclosure of gendered leisure practices of tanning. Empirical material reveals that Pākehā, who actively seek brown skin, negotiate a number of racialized and gendered ‘truths’ as their sun‐tan transforms their bodies. I conclude by arguing that geographers need to be more attentive to the ways in which place constructs particular forms of gendered whiteness.     

The effect of human use of sandy beaches on developmental stability of Talitrus saltator (Montagu, 1808) (Crustacea, Amphipoda). A study on fluctuating asymmetry

In recent years, there has been an increasing intensity of human use of coastal areas in Galicia (NW Spain). Actually, there is great concern about rapid and unplanned urban and industrial development on certain locations, as this can generate adverse impacts on those areas. In this study, we selected three sandy beaches along the Galician coast (Chanteiro, Insuela and Valieros) facing different levels of anthropic pressure, and we analysed Talitrus saltator individuals with the aim of elucidating whether anthropogenic pressures on beaches such as tourism or pollution have an influence on the incidence of morphological developmental alterations in sandhoppers in the field. Specifically, levels of fluctuating asymmetry were selected as indicators of environmental stress. Results of two sampling dates (May and September) show that individuals collected at the most touristy and polluted beach were those showing the highest asymmetry values, although results were only statistically significant for samples collected during spring. Results are in accordance with the hypothesis that beach management and pollution reduce symmetry in sandhoppers living in altered beaches.     

Measuring species richness on sandy beach transects: extrapolative estimators and their implications for sampling effort

Species richness is a measure that is fundamental to many studies in ecology, and it is particularly important on sandy beaches, where it underlies patterns described by the broadly accepted swash exclusion hypothesis. However, its estimation in practice is problematic. This has led ecologists in other fields to adopt extrapolative estimators of species richness, which project the total number of species present in a habitat by adjusting upward the number of species observed by an amount related to the number of rare species encountered in the samples. In so doing, the species richness can be estimated, with confidence intervals, at any level of sampling effort. Despite the availability and advantages of these methods, beach ecologists have continued to use the observed species richness as a point estimate of biodiversity for beaches. Here, we employ a Monte Carlo resampling approach over a range of routine transect designs used to sample sandy beaches, and evaluate the performance of seven non-parametric extrapolative estimators for species richness relative to that of the more conventionally used observed species richness. We find that the first-order Jackknife estimator (Jack 1) is the least biased, most accurate and most consistent across sites. Employing this estimator would allow accurate estimation of species richness on short (tens of metres) stretches of beach without exceeding the acceptable levels of sampling effort (4–5 m²). Spreading this effort evenly over three across-shore transects, each with a minimum of 13 equally spaced levels seems appropriately efficient. Although a greater number of research studies is required to ascertain the generality of these results beyond the beaches we sampled, we tentatively recommend the application of our results in biodiversity surveys on sandy beaches.     

Sun and landscape orientation in adult and juvenile sandhoppers Orchestoidea tuberculata (Amphipoda, Talitridae) from two beaches in south central Chile

The behaviour of a talitrid amphipod, Orchestoidea tuberculata Nicolet 1849, was investigated for populations inhabiting two exposed sandy beaches in south central Chile to evaluate orientation capabilities with respect to sun azimuthal changes and landscape. The study beaches (Calfuco and La Misión) were backed by high cliffs but differed in shoreline orientation. Under test conditions of dry substrate, both populations oriented seawards using celestial cues when landscape vision was screened off and showed a higher concentration seawards when they could see the landscape suggesting additive effects of these cues. The absence of a phototactic response to the sun implies the involvement of an inner circadian clock, as the experiments were conducted at different times of the day. The distribution of juveniles was more concentrated than adults in the trials, a result in accordance with their tendency to occupy a zone located closer to the water than adults. Our results suggest that the Calfuco population was oriented to its shoreline, while animals at La Misión tended to deviate from the expected direction and their distribution was more scattered. This observed difference between the populations may be related to the higher human impact on the latter beach, which was more intensively used for recreation and periodically cleaned, removing the wrack. The comparison of results on orientation of O. tuberculata with those of different sandhopper species contributes new phylogenetic insight concerning this important adaptation. This study not only represents an extension of contemporary knowledge of behavioural adaptations of beach amphipods to coasts differing geographically and ecologically, but also analyses orientation in a southern Pacific species of talitrid amphipod for the first time.     

The effects of beach nourishment on the sandy-beach amphipod Exoediceros fossor: impact and recovery in Botany Bay, New South Wales, Australia

Beach nourishment is increasingly being implemented to address problems of erosion. However, the ecological consequences of nourishment are poorly understood, especially in Australia. In Botany Bay, sand was piped from an intertidal borrow area at Elephant's Trunk to nourish the nearby eroding beach at Towra Point. The effects on an intertidal exoedicerotid amphipod, Exoediceros fossor (Stimpson, 1856), were examined using a beyond-BACI (Before–After, Control–Impact) sampling design. Sampling was conducted before and after engineering operations at sites within the borrow and nourishment locations and multiple control locations. Hypotheses concerning impact and recovery were tested using asymmetrical ANOVAs and two-tailed F-tests. These examined the effects on abundance and spatial variability, respectively. The impact of the engineering operations on abundance was very large at both borrow and nourishment locations. However, recovery started within several weeks and, using space × time interactions as a criterion, appeared to be complete within a year. This conclusion is made cautiously because of low statistical power and because other criteria for recovery suggest that it was not complete at some sites. As beach erosion is likely to increase in severity with rising sea levels and greater storm surges associated with climate change, management authorities will need a better understanding of the ecological effects of beach nourishment.     

Variable orientation within a natural population of the sandhopper Talitrus saltator (Crustacea: Amphipoda) as a response to a variable environment: The case-study of Berkoukesh beach,Tunisia

Sandy beaches are harsh environments, driving resident arthropod populations to various typical adaptations, particularly behavioural ones. Here we evaluated the effects of seasonal meteorological variability on the behaviour of Talitrus saltator on Berkoukesh beach (N-W Tunisia). The site is characterised by a Mediterranean climate, but is particularly exposed to seasonal winds and storms. The shoreline is in morphodynamic equilibrium. We tested sandhopper Talitrus saltator orientation in April, when sudden rainfall and storms are common, and in June, when as a rule the weather is warm and dry. The results were analysed with circular statistics and multiple regression models adapted to angular distributions, in order to highlight differences in orientation under the various conditions. Depending on the environmental conditions, amphipods from the same population appeared to utilise various orientation strategies as a response to different environmental constraints. The use of a range of behavioural mechanisms (sun-orientation seaward, sun-orientation landward, and phototaxis) resulted in links to the local landscape and to the animals’ life cycle. As a general conclusion, we can infer that the behavioural variability found within the same population represents a response to seasonal environmental fluctuation. Such an increase in variability is likely to develop on a beach in dynamic equilibrium, where landscape references are stable, and a variable behaviour represents a strategy for dealing with environmental fluctuations.     

深圳市浴场用海定级研究

海域分等定级是制定海域使用金征收标准和开展海域资产价格评估的前提和依据。借鉴《海域定级技术指引(试行)》,遵循资源禀赋差异、收益差异、节约利用和生态用海的原则选取海域自然条件和海域区位条件2个定级因素及海水质量、海洋自然灾害等10个评价因子,构建深圳市浴场用海定级的评价指标体系。采用综合指数评价法计算出207个评价单元的得分情况,通过聚类分析方法和变异系数(CV)来校核级别,最终将浴场用海的海域划分为Ⅰ级(22.22%)、Ⅱ级(33.82%)和Ⅲ级(43.96%)3个级别。研究成果为海洋管理部门制定浴场用海不同级别的基准价格提供了依据。     

厦门岛东海岸的蚀退与防护

根据波浪输沙和地形对比，对厦门岛东部海岸的岸滩侵蚀动态及演变趋势进行探讨，并根据其海岸特点提出相应的防护对策。