The Bering Strait connection: dispersal and speciation in boreal macroalgae

A large number of boreal seaweeds have either sibling species or conspecific populations of a single species in the North Pacific and North Atlantic Oceans. This pattern is thought to have arisen from the dispersal between the two oceans through the Arctic Ocean after the opening of the Bering Strait in the mid-to-late Miocene or earliest Pliocene and from subsequent vicariant speciation as the Arctic Ocean froze and Bering Strait closed intermittently during glacial periods. Recent molecular studies of species in all three major seaweed phyla reveal patterns of vicariance. However, a number of lines of evidence point to differences in origins of these clades; some appear to be Pacific in origin whereas others appear to be derived from Atlantic stock. Different origins can be explained by recent stratigraphic finds that push the first Cenozoic opening of the Bering Strait back from 3.1–4.1 to 4.8–7.4 Ma (million years ago). Northern hemisphere ocean circulation models suggest that water flow would have been from the North Atlantic–Arctic south through the Bering Strait prior to the closure of the Panamanian Isthmus c. 3.5 Ma in contrast to the northward flow from the Pacific into the Arctic and North Atlantic, which developed after the closing of the Isthmus. Despite these differences in timing of the two invasions, there are no significant differences in levels of relationships among species with a North Atlantic origin compared with species with a North Pacific origin based on currently available data. More work is required to understand vicariance in seaweeds, especially in deciphering when a speciation event has occurred.     

An integrated study of the temporal and spatial variation in the supply of propagules, recruitment and assemblages of intertidal macroalgae on a wave-exposed rocky coast, Victoria, Australia

Recruitment is known to influence distributions and abundances of benthic marine organisms. It is therefore important to document patterns of variability in recruitment and how these relate to patterns in established assemblages. This study provides an integrated assessment of the temporal and spatial variation in supply and recruitment of propagules and established populations of several macroalgae. Propagules in water samples from two stages of the incoming tide, recruitment to artificial substrata and percentage cover of species established on the shore were recorded every 2 months from December 1994 to October 1995, in two zones of an intertidal, wave-exposed rocky shore. Variability in recruitment was measured at three spatial scales: 10s cm, 100s cm and 100s m. Availability and recruitment of most taxa were greatest between April and August, although many species had available propagules and recruited throughout the year. Temporal variation in the established assemblages was, however, more species-specific. Differences in established assemblages between zones were reflected in differences in availability and recruitment of propagules between zones. Recruitment could not be predicted directly from supply of propagules, but the two processes were linked. For most species, the greatest variation in recruitment occurred at the smallest spatial scale of 10s cm, although there was also considerable large-scale (between site) variation in recruitment of several species. Results indicate that while pre-and post-settlement mortality are likely to influence macroalgal distribution and abundance, the temporal and spatial variability in supply and recruitment of propagules can explain much of the patchiness in macroalgal assemblages.     

Effects of wave energy on the residence times of a fluorescent tracer in the canopy of the intertidal marine macroalgae,Sargassum fusiforme (Phaeophyceae)

We determined the relationship between the residence times of water within the canopy of the intertidal macroalgae, Sargassum fusiforme (Harvey) Setchell to the energy caused by hydrodynamic mixing. We measured the residence times (t) of fluorescein dye injected into the canopy (31 ± 9 ind/quadrat; canopy plan form area 6 × 1 m²) to estimate the length of time gametes persist within the canopy. The total kinetic energy (TKE) and wave energy (WE) was measured during dye dispersal, which ranged from 0.002 to 0.009 m²/s² and 0.001 to 0.016 m²/s², respectively. The experiments revealed that the canopy significantly (P < 0.0001) increased t, which was 56 ± 35 s inside of the canopy compared with 14 ± 4 s outside. Moreover, the relationship between t and energy could be statistically modeled with a power function, and for the results inside of the canopy, t = 3.67 TKE^?0.50 for turbulent kinetic energy and t = 1.83 WE^?0.38 for wave energy. Outside of the canopy, t = 0.98 TKE^?0.50 and t = 1.83 WE^?0.38 Based on the values of t determined for within the canopy, we developed a dispersion model to explore how gametes dispersed within the canopy. The estimated dispersion coefficient (D) with respect to WE, could be modeled as D = 403 WE^0.55 and ranged from 10 to 42 cm²/s for the WE examined in the study. Areal gamete densities modeled in the canopy increased in density for increasing WE at short (0.5 h) durations of gamete discharge; however, the relationship reversed above 2 h of discharge.     

大亚湾潮间带软体运动的物种多样性初步研究

1999年7月在大亚湾潮间带4种不同生境（岩石岸、砾石滩、泥沙滩、沙滩）10个样方采集软体动物38种,隶属于23个科。采用丰富度指数和多样性指数对不同生境软体动物的多样性进行研究。研究结果表明,大亚湾软体动物物种丰富度指数砾石滩、岩石岸(D=4.328～9.378)>泥沙滩(D=4.328～6.493)>沙滩(D=2.886)。多样性指数也显示砾石滩、岩石岸(H′=0.429～0.842)>泥沙滩(H′=0.315～0.450)>沙滩(H′=0.182)。对上述样方聚类结果表明,软体动物种类分布及数量受底质、浪击和污染的影响。     

上川岛潮间带不同生境底栖软体动物物种多样性初步研究

目的:研究上川岛潮间带不同生境底栖软体动物物种多样性。方法:对上川岛潮间带(沙滩、泥沙滩、红树林泥滩、岩石滩) 4种不同生境的7个样方的底栖软体动物进行了生物多样性的初步调查。结果:共鉴定底栖软体动物14科30种,上川岛潮间带底栖软体动物物种丰富度指数为岩石滩(平均为1.784 ) >泥沙滩(平均为1.5 2 1) >红树林泥滩(平均为1.2 35 ) >沙滩(平均为0 .6 92 ) ;多样性指数岩石滩(平均为1.5 5 1) >红树林泥滩(平均为1.30 4 ) >泥沙滩(平均为1.16 2 ) >沙滩(平均为0 .4 0 3)。结论:底栖软体动物的种类及数量分布受底质、浪击等因素的影响。     

High diversity of tropical intertidal zone sponges in temperature, salinity and current extremes

The wide intertidal zone of the Quirimba Archipelago (Mozambique, East Africa) encompasses many different habitats, which all experience wide environmental variation. Large daily fluctuations in temperature occur when standing water is heated up at low tide to >10°C above ambient. Salinity may be high in the dry season and periodically almost fresh in the wet season. Very high current velocities (≈3 ms⁻¹) may occur and the direction of water flow is often complex. Sponges were a major component of the fauna (and dominate the sessile forms) in most of the eight habitats studied: exposed reef, sheltered reef, sand-rock, cave, reef boulders, boulders on sand, mangrove swamp and seagrass meadows. The highest number of sponge species occurred in the two reef habitats: from mean values of between ≈2.5 and ≈0.5 species/m² (upper and lower shore, respectively). The diversity of species present yielded a high Shannon index value of H=2.95 for the total of 33 species. A rank-abundance plot of the data showed a high level of equitability (J=0.84). Community similarity measurement using Bray–Curtis index showed two clusters; the exposed habitats of the reefs and sand-rock and the refugia of cave, reef and sand boulders.     

'Prepackaged symbioses': propagules on roots of the myco-heterotrophic plant Arachnitis uniflora

Arachnitis uniflora, a myco-heterotrophic plant species, has fleshy tuberous roots colonized by the arbuscular mycorrhizal fungal genus Glomus (Phylum Glomeromycota). These roots produce apical and lateral propagules, both reported here for the first time. The objective of the study was to characterize the ontogeny and structure of the propagules, and to determine their function. Scanning electron microscopy, laser scanning confocal microscopy and light microscopy were used to study the ontogeny and structure of the propagules. Propagules developed either from cortical parenchyma cells or from cells immediately beneath the root cap; they developed a shoot meristem and cells in the basal region which were colonized by various fungal structures including hyphae and vesicles. These propagules may detach from the roots, establishing new plants.     

Geographical variation in the distributions of macroalgae in estuaries

Assemblages of macroalgal species present in the upper reaches of estuaries were compared using published species lists for the North Atlantic, covering a north-south gradient in Europe from Iceland to northern Spain, and in North America between the St. Lawrence and Virginia. Patterns were sought using cluster analysis and ordination. Three groupings of estuaries were noted: Icelandic, mainland European and American. There was a slight trend of increase in the ratio of red to brown algae with decreasing latitude in Europe, though not as marked as for open coastal algae. This might be associated with the effect of temperature on salinity tolerance. Despite this biogeographic trend, some of the commonest species appear to be widely spread through estuaries, possibly including southern Atlantic and Pacific locations. Confirmation of the trends suggested requires further data from southern European estuaries.     

嵊泗列岛潮间带大型海藻群落结构的季节变化

于2010年8月-2011年8月对嵊泗列岛潮间带大型海藻进行调查.结果表明:共有大型海藻114种,隶属3门53属,其中红藻门33属75种,占总数的65.8％,褐藻门13属21种,占18.4％,绿藻门7属18种,占15.8％;枸杞最多(87种),金平其次(42种),马关最少(26种);79.8％海藻分布在低潮带,62.3％分布在中潮带,种类组成相似性指数中、低潮带为0.57,高、中潮带为0.15,高、低潮带为0.06;种类组成夏季(57种)＞冬季(55种)＞春季(52种)＞秋季(46种),春季优势种有裙带菜、孔石莼、长石莼和厚膜藻等,夏季优势种为瓦氏马尾藻、粗枝软骨藻、鼠尾藻和麒麟菜等,秋季优势种为江蓠、小杉藻、鼠尾藻和石莼等,冬季优势种为萱藻、圆紫菜、鼠尾藻和日本多管藻等.     

Vertical distribution of chitons (Mollusca: Polyplacophora) in the rocky intertidal zone of central Chile

The patterns of vertical distribution of chitons in various exposed rocky shore habitats of central Chile are described. The density and size of the individuals were determined at different levels on intertidal rock walls, in pools and on boulders. A group of four species was found on rock walls while another group of four species was found in tidal pools and on boulders. The species showed vertical separation on rock walls and segregation according to a range of increasing frequency of water movement in pools and on boulders. Only the two species with largest adult individuals (Acanthopleura echinata (Barnes) and Chitonlatus Sowerby) showed vertical segregation in size. Small-sized species and small individuals of large-sized species were found higher on rock walls or in zones where water movement is less; large chitons occur in zones of greatest water impact. This suggests that water movement may be a significant factor in setting the lower limits of distribution of these herbivores. Some of the species examined were extremely abundant (600·m^-2) with densities of one to two orders of magnitude greater than for other chiton species elsewhere.     

浙江渔山列岛岩礁潮间带大型底栖动物次级生产力

为揭示渔山列岛潮间带大型底栖动物现状,2009年3月至2010年1月在渔山列岛潮间带布设5条断面进行了4个季节的调查取样.利用Brey的经验公式计算了调查海区大型底栖动物栖息密度、生物量、次级生产力和P/B值.结果表明:该潮间带大型底栖动物平均栖息密度为1419.5ind.m-2,以去灰干质量(AFDM)计,平均生物量为565.53g.m-2,平均次级生产力为285.58g.m-2.a-1,P/B值为0.51.潮间带次级生产力受大型软体动物和甲壳类影响明显,5个关键生物种(条纹隔贻贝、偏顶蛤、覆瓦小蛇螺、日本笠藤壶和鳞笠藤壶)对次级生产力的贡献为84.0%.研究海域P/B值低于其他海域,说明该海域大型底栖动物世代更替速度较慢,群落结构较稳定.     

A comparison of ecological responses among aclonal (unitary), clonal and coalescing macroalgae

Based on growth patterns, regeneration capabilities and genetic make up, benthic macroalgae include three groups of species. Similar to land plants, they include clonal and aclonal species, and, similar to colonial aquatic animals, seaweeds also include coalescing species, that have the capacity to fuse forming composite (chimeric) entities. Since the awareness of the differences between these three kinds of seaweeds is rather recent, most ecological studies have not discriminated among them. However, ecological models based on one kind of seaweeds will not necessarily apply to all kinds of seaweeds. This study reviews ecological responses of algae at the individual and community levels, and describes similarities and differences among both the three algal groups and with parallel groups in land plants and chimeric marine animals. The ecological responses reviewed are plant sizes and shapes; patterns of resource acquisition; algal life phases, reproduction and dispersal; genetic variability, intraspecific and interspecific competition and herbivory. Analysis of these responses supports the idea in distinguishing among the above three algal group, reveals the need for numerous additional ecological studies and advices on incorporating concepts from the biology of chimeric aquatic animals and from clonal theory of land plants into the study of benthic macroalgae.     

Variations in the dispersal curves of macroalgal propagules from a source

The process of dispersal is critical to marine benthic species (i.e. invertebrates and algae) as a fundamental element of population ecology and a crucial ecological process that maintains the diversity in communities. We simultaneously sampled the abundance of spores inhabiting the water column at different distances from known parent sources at 3 sites along the coast of central Chile. From these data we constructed 258 dispersal curves for common rocky intertidal macroalgae. Only 43.8% of these curves could be predicted by the expected model, which describes the spatial distribution of propagules to be dominated by a larger concentration near the parent individual or “source site”, followed by a marked decrease in abundance with increasing distance. The curves that departed from the expected model (56.2%) were grouped into three curve types, according to the number of propagule abundance maxima observed in space. This work suggests that macroalgal propagule dispersal patterns are more variable than previously thought. The existence of several alternative curves to the expected model, as well as the presence of one to several abundance maxima associated with the differential distribution of propagule patches in the water column, suggests the idea that propagules are released in pulses which can be transported variable distances from the source site.     

The influence of aqueous extracts of burnt or heated soil on the activity of vesicular-arbuscular mycorrhizal fungi propagules

Summary Aqueous extracts of burnt soil, unburnt soil and oven-heated unburnt soil were tested as to their effects on vesicular-arbuscular mycorrhizal (VAM) fungi (spore germination, mycelial propagule activity and root colonization). The extracts of burnt or heated soil inhibited VAM spore germination and extrarrhizal mycelium activity.     

The soil environment of the intertidal area in the Westerschelde

Hydrodynamic forces and sediment discharges determine the sedimentary environment and surface morphology of the intertidal area in the Westerschelde estuary in the S.W. Netherlands. Sandflats (clay content <8%) are found in the central part, mudflats (>8% clay) and especially salt marshes (>15% clay) occur in sheltered places.The semi-terrestrial soil of the intertidal area is a complex environment where hydrosphere, biosphere, lithosphere, and atmosphere interact. Surface morphology and the semi-diurnal tide may significantly modify this interaction pattern. Organic matter and constituents of the clay-size fraction are the most reactive compounds in the soil.The pathway and rate of organic matter decomposition determines the nature of many biogeochemical processes. Sulfur transformations are dominant processes in the sulfidic grey-black coloured horizons underneath the generally thin yellow-brown surface layer. The sulfur geochemistry also affects the sorption-behaviour of metals. Oxygen intrusion by diffusion, burrowing fauna and plant roots cause a local and sometimes temporary oxidation of reduced inorganic compounds. Thus, in the surface layers, and in and around tubes and roots at greater depth in the soil, a dynamic cycling occurs of redox active compounds, which affects the sorption mechanism ofe.g. metals-ions.     

Indole alkaloids in clonal propagules of Rauwolfia serpentina benthe ex kurz

Plantlets were succesfully regenerated from shoot cultures of Rauwolfia serpentina initiated from auxillary meristems on medium containing BA (4.44 M) + NAA (0.54 M). Rooting was initiated in White's basal medium supplemented with NAA (0.54 M). Tissue culture derived piants of R. serpentina (RSTC) were similar to normal plants (RS) in their morphological characteristics and chemical consitution. The biomass of the RSTC plants was higher (47.11 gms) than the normal plant (18.23 gms) on a dry weight basis. Five RSTC plants were cloned and the cloned plants were similar in biomass and alkaloid content to the normal plant.Abbreviations BA benzyl adenine - NAA naphthalene acetic acid - MS Murashige and Skoog - TLC thin layer chromatography - HPLC high performance liquid chromatography - F.W. fresh weight - D.W. dry weight - RS normal field grown plant established from stem cuttings - RSTC tissue culture plants established from shoot cultures - R reserpine - Aj ajmalicine - A ajmaline - S serpentine     

廉州湾滨海湿地潮间带大型底栖动物群落次级生产力

于2011年1月、4月、7月和10月开展广西廉州湾的裸滩、红树林和茳芏(Cyperus malaccensis)盐沼3种湿地生境类型的潮间带大型底栖动物群落季节动态调查,采用Brey 经验公式估算各生境次级生产力.结果表明:共采集到潮间带大型底栖动物8门156种,其中裸滩生境有136种,红树林生境85种,盐沼生境29种;站位平均种数为裸滩9.5±4.8种,红树林9.5±3.9种,盐沼5.9±1.9种,同时,各类群占总种数比例大小规律一致,为软体动物门＞节肢动物门＞环节动物门＞脊索动物门＞其他;盐沼生境大型底栖动物群落结构变化较小,宁波泥蟹(Ilyoplax ningpoensis)优势很明显,随着水体盐度上升,红树林和裸滩优势种由适应低盐环境向适应高盐环境的种类变化;廉州湾潮间带大型底栖动物群落的次级生产力平均为15.88 g·m-2·a-1,裸滩、红树林和盐沼生境分别为16.16、9.97、3.88g·m-2 ·a-1;P/B值平均为0.70,3种生境分别为盐沼1.02,裸滩0.70,红树林0.65;廉州湾潮间带大型底栖动物年湿质量生产量为14623 t.水体盐度和植被类型是影响廉州湾潮间带大型底栖动物群落结构的优势种群以致次级生产力的空间分布变化的主要因素.