Do some deep‐sea,sediment‐dwelling species of harpacticoid copepods have 1000‐km‐scale range sizes?

The range sizes of sediment‐dwelling deep‐sea species are largely unknown. Such knowledge is important because a deep sea composed in large part of species with 100‐km‐scale ranges would be very different from one composed predominantly of species with 1000‐km‐scale ranges. For example, the total species richness would be much greater in the first case than in the second. As a step towards the determination of the distribution of species’ range sizes in the deep sea, we asked whether harpacticoid copepods (Crustacea) on the continental rise in the northeastern Pacific had 1000‐km‐scale range sizes. We chose harpacticoids because they occur widely in deep‐sea sediments and thus are a typical deep‐sea taxon. In addition, they have no pelagic stage in their life history, so they allow a conservative test of hypotheses about species’ range sizes. We used morphology and gene‐sequence data to assign individuals to species. At least 13.3% of the species we studied had 1000‐km‐scale ranges, raising the question of how these species maintain genetic continuity.     

Extremely low genetic diversity across mangrove taxa reflects past sea level changes and hints at poor future responses

The projected increases in sea levels are expected to affect coastal ecosystems. Tropical communities, anchored by mangrove trees and having experienced frequent past sea level changes, appear to be vibrant at present. However, any optimism about the resilience of these ecosystems is premature because the impact of past climate events may not be reflected in the current abundance. To assess the impact of historical sea level changes, we conducted an extensive genetic diversity survey on the Indo‐Malayan coast, a hotspot with a large global mangrove distribution. A survey of 26 populations in six species reveals extremely low genome‐wide nucleotide diversity and hence very small effective population sizes (N_e) in all populations. Whole‐genome sequencing of three mangrove species further shows the decline in N_e to be strongly associated with the speed of past changes in sea level. We also used a recent series of flooding events in Yalong Bay, southern China, to test the robustness of mangroves to sea level changes in relation to their genetic diversity. The events resulted in the death of half of the mangrove trees in this area. Significantly, less genetically diverse mangrove species suffered much greater destruction. The dieback was accompanied by a drastic reduction in local invertebrate biodiversity. We thus predict that tropical coastal communities will be seriously endangered as the global sea level rises. Well‐planned coastal development near mangrove forests will be essential to avert this crisis.     

A theoretical study on effect of the initial redox state of cytochrome b559 on maximal chlorophyll fluorescence level (F(M)): implications for photoinhibition of photosystem II

In this work, we extended the reversible radical pair model which describes energy utilization and electron transfer up to the first quinone electron acceptor (Q(A)) in photosystem II (PSII), by redox reactions involving cytochrome (cyt) b559. In the model, cyt b559 accepts electrons from the reduced primary electron acceptor in PSII, pheophytin, and donates electrons to the oxidized primary electron donor in PSII (P680+). Theoretical simulations of chlorophyll fluorescence rise based on the model show that the maximal fluorescence, F(M), increases with an increasing amount of initially reduced cyt b559. In this work we applied, the first to our knowledge, metabolic control analysis (MCA) to a model of reactions in PSII. The MCA was used to determine to what extent the reactions occurring in the model control the F(M) level and how this control depends on the initial redox state of cyt b559. The simulations also revealed that increasing the amount of initially reduced cyt b559 could protect PSII against photoinhibition. Also experimental data, which might be used to validate our theory, are presented and discussed.     

A Model of Holocene Mangrove Development and Relative Sea-level Changes on the Bragança Peninsula (Northern Brazil)

Based on the integration of geological information, the pollen record, radiocarbon data, and modern mangrove distribution, this paper proposes a model of evolutionary development for mangroves on the Brazilian Bragança Peninsula driven by relative sea-level changes from the middle to late Holocene. After a postglacial relative sea-level rise (RSL), the mangrove habitats on the Bragança Peninsula began to develop at about 5100 years BP close to the current RSL, originating in the middle of the peninsula. Between 1800 and 1400 years BP, this littoral area underwent a maximum RSL fall of 1 m below the current one, followed by a gradual RSL rise until 1000 years BP, when the modern RSL was reached. Between 5100 and 1000 years BP, the RSL of the Bragança coastline was probably never higher than 0.6 m above the present level. The first Holocene mangrove forest (5100 years BP) in this region disappeared from the plains due to RSL fall and was replaced by herbaceous vegetation (Cyperaceae and Poaceae).     

不同气温条件下旱柳(Salix matsudana Koidz)幼苗的水分和构型特征

利用小温棚升高气温,探讨气温升高对半干旱毛乌素沙地乡土沙生乔木如何缓冲气温升高所带来的不利影响。水分饱和亏缺和失水系数均表现出随气温升高而降低的趋势。组织密度的变化趋势恰好相反;气温长高显著影响枝茎截面积比、叶干重茎截面积比、叶面积茎截面积比、叶干重枝截面积比和叶面积枝截面积比;叶死亡率和叶周转随气温升高呈现出降低趋势,而叶出生率和叶面积的变化格局为“钟形”曲线,气温升高促进分枝产生、增加分枝长度和角度,这利于增大植冠郁闭度。     

Corrected western Atlantic sea-level curve for the last 11,000 years based on calibrated <Superscript>14</Superscript>C dates from<Emphasis Type="Italic"> Acropora palmata</Emphasis> framework and intertidal mangrove peat

A corrected western Atlantic Holocene sea-level curve was constructed from 145 calibrated ¹⁴C and TIMS U-Th dates from shallow Acropora palmata framework and intertidal Rhizopora mangle peat from the Florida Keys, Belize, and the wider Caribbean. Data include both previously published and newly reported coral and peat dates. With the elevations of corals restricted to positions below sea level and those of peats to intertidal and higher levels, a curve bracketed by corals below and peat above effectively delineates the positions of a rising Holocene sea. From 3–11 ka, the corrected curve shifts progressively to older calibrated ages, reaching an ~1-kyr increase at –21 m MSL (mean sea level). Elevations and calibrated ages of samples from each locality in the wider Caribbean region constitute an important database for future refinement with glacio-hydro-isostatic elevation corrections from 3-D Earth models. In future studies of the history of western Atlantic coral reefs, scientists will be able to relate calibrated radiocarbon dates to this sea-level curve to determine paleo water depths and rates of sea-level rise.     

Reductions in the mitochondrial DNA diversity of coral reef fish provide evidence of population bottlenecks resulting from Holocene sea-level change

This study investigated the influence of reproductive strategy (benthic or pelagic eggs) and habitat preferences (lagoon or outer slope) on both diversity and genetic differentiation using a set of populations of seven coral reef fish species over different geographic scales within French Polynesia. We hypothesized that a Holocene sea-level decrease contributed to severe reduction of population size for species inhabiting lagoons and a subsequent decrease of genetic diversity. Conversely, we proposed that species inhabiting stable environments, such as the outer slope, should demonstrate higher genetic diversity but also more structured populations because they have potentially reached a migration-genetic drift equilibrium. Sequences of the 5' end of the mitochondrial DNA (mtDNA) control region were compared among populations sampled in five isolated islands within two archipelagos of French Polynesia. For all the species, no significant divergences among populations were found. Significant differences in mtDNA diversity between lagoonal and outer-slope species were demonstrated both for haplotype diversity and sequence divergence but none were found between species with different egg types. Pairwise mismatch distributions suggested rapid population growth for all the seven species involved in this study, but they revealed different distributions, depending on the habitat preference of the species. Although several scenarios can explain the observed patterns, the hypothesis of population size reduction events relative to Holocene sea-level regression and its consequence on French Polynesia coral reefs is the most parsimonious. Outer-slope species have undergone a probable weak and/or old bottleneck (outer reefs persisted during low sea level, leading to reef area reductions), whereas lagoonal species suffered a strong and/or recent bottleneck since Holocene sea-level regression resulted in the drying out of all the atolls that are maximum 70 meters deep. Since present sea level was reached between 5000 and 6000 years ago, different demographic events (bottlenecks or founder events) have lead to the actual populations of lagoons in French Polynesia.     

Climatic change and hydrophyte-dominated communities in inland wetland ecosystems

Thoughts about the potential effects of climatic change due to greenhouse warming on hydrophytes and hydrophyte communities in inland still waters of Europe are presented. A distinction is made between permanent and temporary shallow aquatic ecosystems and between freshwater and brackish systems. Potential effects of greenhouse warming on the hydrology and salinity of isolated brackish waters are illustrated with a computer model, simulating several scenario's of climatic change and differently shaped waters.In permanent waters, greenhouse warming may result in an earlier onset of growth of those hydrophytes in which the germination of propagules and the resumption of growth is primarily controlled by temperature. This may occur at the cost of macrophytes that have dormancy mechanisms regulated by environmental cues other than temperature (e.g. photoperiod). In addition, it seems plausible that because of milder winters, some thermophilous aquatic plants spread to the north. Furthermore, in culturally eutrophicated waters, in which the sediment compartment is heavily loaded with organic matter and/or nutrients, a rise in temperature may accelerate nutrient turn-over for several years, resulting in algal blooms and shifts in quality and quantity of macrophyte vegetation.Effects of greenhouse warming on temporary shallow waters will be more complex. Changes in temperature, precipitation and evaporation may lead to larger seasonal fluctuations in the water table and a more frequent or more prolonged period of desiccation. Some hydrophytes can cope with these circumstances, while others withstand desiccation only for a short period. Macrophyte communities may also be affected in an indirect way by periodic desiccation of their habitats. In emerged bottoms the rate of mineralization is probably higher than when overlying water is present. When water returns, a pulse of mineral nutrients may temporarily result in algal blooms and a high turbidity of the water, thus hampering hydrophyte growth. In addition, in isolated brackish waters an increased evaporation may result in larger fluctuations in salinity. In such a harsh environment species diversity of aquatic macrophytes will most probably decline.     

Palaeoenvironmental research on diatoms in early and middle Holocene deposits in central North Holland (The Netherlands)

In the geological research of the Holocene coastal deposits of The Netherlands, diatoms are used to reconstruct the sedimentary facies, palaeo-tide levels and salinity gradients during the deposition of the sediments. In this paper, the results of diatom research from 4 borings, taken from the early and middle Holocene deposits of central North Holland are presented. The oldest marine influenced sediments in the area are the deposits of the ‘Velsen layer’, a clay layer rich in organic matter and deposited about 8000–7000¹⁴C years before present (BP) at a depth of 20–12 m below present mean sea-level. This clay layer was formed in a shallow, permanently submerged environment with a limited tidal influence (lagoonal or pond-like conditions). The salinity changed from brackish/freshwater to marine/brackish. The younger sandy and clayey sediments, formed about 7000–4500 BP at a depth of 16–3 m below present mean sea-level, are classified as ‘tidal channel’ and ‘interchannel’ deposits. It is argued, on the base of both diatom and non-diatom criteria, that the lower and middle parts of the interchannel deposits in the central area of the palaeo-tidal basin of North Holland were formed in a subtidal environment. The upper part of the interchannel deposits and the deposits at the fringe of the North Holland tidal basin were formed in the intertidal zone or, at the fringe of the basin, even in the supratidal zone. The salinity in the North Holland tidal basin during the sedimentation of the tidal channel and interchannel deposits was marine/brackish to marine. This study indicates that diatoms, besides their palaeoecological applications, have chronostratigraphical significance (on a regional scale). The diatomsCymatosira belgica andActinoptychus splendens appear to be a useful (eco)stratigraphical marker in the Holocene coastal deposits of The Netherlands and Belgium.     

Kinetics of the flash-induced electrochromic absorbance change in the presence of background illumination. Turnover rate of the electron transport. I. Isolated intact chloroplasts

We investigated the flash-induced electrochromic absorbance change, A ₅₁₅, of isolated intact chloroplasts in continuous monochromatic background light of different intensities and wavelengths. From the variation of the amplitude of A ₅₁₅ in background illumination the steady-state turnover time of electron transport was found to be around 100 msec and the slowest process could be assigned to a photosystem 1 driven cycle. The change of pH induced by nigericin, ATP, or ADP did not modify substantially the turnover time.In contrast to earlier observations the slow rise (10 msec) of A ₅₁₅ in untreated chloroplasts persists also at high-intensity background illumination exciting both photosystems. The proportion of the slow rise of A ₅₁₅ in nigericin-treated chloroplasts increases in the presence of background light. This result on the slow rise is discussed in terms of two different models existing in the literature.