Changes in North Sea macrofauna communities and species distribution between 1986 and 2000

The North Sea Benthos Project 2000 was initiated as a follow-up to the 1986 ICES North Sea Benthos Survey with the major aim to identify changes in the macrofauna species distribution and community structure in the North Sea and their likely causes.The results showed that the large-scale spatial distribution of macrofauna communities in the North Sea hardly changed between 1986 and 2000, with the main divisions at the 50 m and 100 m depth contours. Water temperature and salinity as well as wave exposure, tidal stress and primary production were influential environmental factors on a large (North Sea-wide) spatial scale.The increase in abundance and regional changes in distribution of various species with a southern distribution in the North Sea in 2000 were largely associated with an increase in sea surface temperature, primary production and, thus, food supply. This can be most likely related to the North Sea hydro-climate change in the late 1980s influenced by the variability in the North Atlantic Oscillation (NAO). Only one cold-temperate species decreased in abundance in 2000 at most of the stations. Indications for newly established populations of offshore non-native species were not found.Differences in macrofauna community structure on localised spatial scales were predominantly found north of the 50 m depth contour off the British coast along the Flamborough Head Front towards the Dogger Bank, off the coast of Jutland and at the Frisian Front. These changes were most likely attributed to stronger frontal systems in 2000 caused by the increased inflow of Atlantic water masses in relation to the hydro-climate change in the late 1980s.     

东海陆架浙闽沿岸泥质区不同属种底栖有孔虫对14C测年的影响及其原因初探

底栖有孔虫是浅海陆架区钻孔岩芯¹⁴C测年的良好材料,但由于其个体细小,为了获得足够的样品量,常常采用不区分属种和大小的混合壳体样品,不利于高分辨率的古环境研究。本研究选择东海陆架浙闽沿岸泥质区的两个钻孔沉积物样品,对其中不同的底栖有孔虫属种壳体化石分别进行¹⁴C测年,结果显示同一沉积物样品中不同的底栖有孔虫属种壳体化石¹⁴C年龄值存在差异,以Quinqueloculina spp.壳体¹⁴C年龄最老,其次是Ammonia comperessiuscula壳体,最年轻的分别为Elphidium spp.壳体和Bolivina cochei壳体。从底栖有孔虫的生态习性和壳体的结构特征等方面分析推测,同层位不同底栖有孔虫属种壳体年龄差异,不能简单地用它们生活时壳体和所处的微生境水体同位素交换来解释;不同属种有孔虫壳壁构造不同可能是产生壳体化石¹⁴C年龄差异的原因。建议为地质钻孔建立高分辨率年代地层挑取底栖有孔虫AMS ¹⁴C测年样品时,尽量选择相同的属种,或微生境相同、个体大小相近、壳壁厚度和壁孔大小密度近一致的类别,以降低属种不同对测年结果产生的影响,为海岸带高分辨率的古环境研究提供高精度的测年数据。

     

Scale-dependent effects of nutrient loads and climatic conditions on benthic and pelagic communities in the Gulf of Finland

Eutrophication and climate change are ranked among the most serious threats to the stability of marine ecosystems worldwide. The effects of nutrient loads and climatic conditions vary in direction, magnitude and spatial extent. To date the factors that are behind the scale-specific spatial and temporal variability are poorly known. In this study we assessed how variability in nutrient loads and climatic conditions at local, gulf and regional scales explained the spatial patterns and temporal trends of zooplankton and benthic invertebrates in the Gulf of Finland. In general both local and gulf scale environmental variability had an important effect on benthic invertebrate species and the variability was mainly due to local nutrient loading, gulf scale temperature and salinity patterns. Zooplankton species were equally affected by environmental variability at all spatial scales, and all nutrient load and climatic condition variables contributed to the models. The combination of variables at all spatial scales did not explain the substantially larger proportion in invertebrate variability than variables at any individual scale. This suggests that large-scale pressures such as nutrient loads and change of climatic conditions may define broad patterns of distribution but within these patterns small-scale environmental variability significantly modifies the response of communities to these large-scale pressures.     

稀有OTU对海洋底栖纤毛虫群落异质性的影响研究

运用高通量测序技术分析微型生物多样性时,生物学重复间常表现出明显的异质性,这可能是高比例的稀有可操作分类单元(operated taxonomic unit, OTU)造成的“假象”。为明晰陆架海区站位间及同一站位重复间底栖纤毛虫群落的异质性水平,并探明稀有OTU与群落异质性的关系,给出去除稀有OTU阈值的科学建议。本研究在东海选取具有明显环境梯度的4个站位,每站位采集3个重复沉积物,采用高通量测序技术研究纤毛虫群落与分布。研究表明同一站位重复间群落不相似度在30%～34%,重复间群落的高差异性会掩盖地理距离较近的站位间差异(33%)。各个站位重复间共有OTU分别占该站位检获的总OTU数的34.4%, 31.9%, 39.5%和36.5%,而序列数基本占据94%以上。相对丰度小于0.1%的OTU占总OTU数的80%。依次去除相对丰度低于0.01%至0.1%的OTU,发现去除稀有OTU能够有效降低重复间差异,去除越稀有的OTU,降低效果越强;对站位之间的差异影响较小,且站位差异越大影响越小。稀有OTU的分布随机性极强,基本与站位无关。相对丰度低于0.015%的OTU是造成重复间群落异质性...     

Pleistocene oceanographie changes indicated by deep sea benthic foraminifera in the northern Indian Ocean

An attempt has been made to understand the Pleistocene bottom water history in response to the paleoclimatic changes in the northern Indian Ocean employing quantitative analyses of deep sea benthic foraminifera at the DSDP sites 219 and 238. Among the 150 benthic foraminifera recorded a few species show dominance with changing percent frequencies during most of the sequence. The dominant benthic foraminiferal assemblages suggest that most of the Pleistocene bottom waters at site 219 and Early Pleistocene bottom waters at site 238 are of North Indian Deep Water (NIDW) origin. However, Late Pleistocene assemblage at site 238 appears to be closely associated with a water mass intermediate between North Indian Deep Water (NIDW) and Antarctic Bottom Water (AABW). Uvigerina proboscidea is the most dominant benthic foraminiferal species present during the Pleistocene at both the sites. A marked increase in the relative abundance ofU. proboscidea along with less diverse and equitable fauna during Early Pleistocene suggests a relative cooling, an intensified oceanic circulation and upwelling of nutrient rich bottom waters resulting in high surface productivity. At the same time, low sediment accumulation rate during Early Pleistocene reveals increased winnowing of the sediments possibly due to more corrosive and cold bottom waters. The Late Pleistocene in general, is marked by relatively warm and stable bottom waters as reflected by low abundance ofU. proboscidea and more diverse and equitable benthic fauna. The lower depth range for the occurrence ofBulimina aculeate in the Indian Ocean is around 2300 m, similar to that of many other areas.B. aculeata also shows marked increase in its abundance near the Pliocene/Pleistocene boundary while a sudden decrease in the relative abundance ofStilostomella lepidula occurs close to the Early/Late Pleistocene boundary.     

Phytopigments and fatty acids as molecular markers for the quality of near-bottom particulate organic matter in the North Sea

In February, May and August 1994, four stations in the North Sea (viz. at the Broad Fourteens, Frisian Front, German Bight and Skagerrak) were visited to sample near-bottom particulate organic matter. Samples, taken by means of a pump, a sediment trap and a sediment recorder, were analysed on organic carbon, total nitrogen, phytopigments and fatty acids. These molecular markers were used to describe the nature and quality of the organic particles in the near-bottom water. Principal component analysis showed chlorophyll a, phaeopigments and fatty acids to be useful markers for the quality of organic matter and yield complementary information.The quality of the near-bottom particles appeared to be related to the local hydrography and depositional circumstances. The Broad Fourteens station, a non-depositional sandy site along the Dutch coast, showed organic particles to be relatively fresh, little influenced by resuspended sedimentary material. Near-bottom organic particles on this site contained relatively high shares of chlorophyll a and polyunsaturated fatty acids, characteristic of algal matter. On the other hand the particulate organic material on the two depositional locations, the Frisian Front and the German Bight stations, was influenced by resuspension of sedimentary organic particles poor in pigments and fatty acids. Amounts of carbon trapped in the near-bottom environment at the Skagerrak station were lower than expected from the literature.     

Decoupling of nutrient and grazer impacts on a benthic estuarine diatom assemblage

Strong interactions between top-down (consumptive) and bottom-up (resource supply) trophic factors occur in many aquatic communities, but these forces can act independently in some microphytobenthic communities. Within benthic estuarine diatom assemblages, the dynamics of these interactions and how they vary with abiotic environmental conditions are not well understood. We conducted a field experiment at two sites with varying habitat characteristics to investigate the interactive effects of grazers and nutrients on benthic estuarine diatoms. We crossed snail (Cerithidea californica) and nutrient (nitrogen and phosphorus) addition treatments in enclosures on a restored tidal sandflat and a reference tidal mudflat in Mugu Lagoon, southern California. We repeated the study in summer 2000 and spring 2001 to assess temporal variation in the interactions. Snails caused a large decrease in diatom relative abundance and biomass (estimated as surface area); nutrients increased diatom abundance but did not alter diatom biomass. Snails and nutrients both reduced average diatom length, although the nutrient effect was weaker and temporally variable, occurring in the reference mudflat in the spring. There were few interactions between snail and nutrient addition treatments, suggesting that links between top-down and bottom-up forces on the diatom community were weak. There were no consistent differences in diatom assemblage characteristics between the two study sites, despite marked differences in sediment grain size and other abiotic characteristics between the sites. The strong diatom response to herbivores and weaker responses to enrichment differed from the previous studies where cyanobacteria increased in response to nutrient enrichment, further dissolving the “black box” perception of microphytobenthic communities.     

Implications of Colorado river (Texas, USA) freshwater inflow to benthic ecosystem dynamics: A modeling study

Estuaries are defined by mixing of freshwater from rivers and saltwater from seas. Water resource development can reduce river flows to the coast, but it is difficult to predict effects on estuaries. The Lavaca-Colorado Estuary is a major estuarine system along the Texas coast that provides major economic benefit to the region by supporting a variety of agricultural, residential, industrial, and recreational functions. New water projects could divert freshwater from Matagorda Bay. So, what environmental effects could result from further changes to inflow patterns in the Matagorda Bay system? To answer this question, a bioenergetic model, calibrated using a long-term dataset of benthic biomass, was run to investigate dynamics of macrobenthic biomass related to salinity regimes in the estuary. The model simulation results were interpreted to assess the role of freshwater inflow in controlling benthic productivity. Simulations, based on calibrated parameters (1988–1999), were run for a long-term period from 1988 to 2005. The model performance was found to be promising with the best percent root mean square (RMS) difference being 63% and worst being 92%. Sensitivity tests for the benthic responses to changes in salinity show that, in general, when salinity increased with decreasing nutrient concentrations, deposit feeder biomass increased while suspension feeder biomass decreased. Estuary-wide comparison predicts that reducing freshwater inflow may cause the upper and lower bay communities to respond in different ways. Reduced inflow to Lavaca Bay would result in decreasing benthic biomass; whereas, in Matagorda Bay, biomass would increase. Also, functional diversity would decrease in both bays with decreasing inflow. These effects are probably due to the benthic community acclimating to different salinity regimes, or more (or less) salt tolerant species populating the area. It is concluded that freshwater inflow plays an important role in maintaining the observed character of estuarine productivity through the combined effects of the frequency, duration, timing, and magnitude of inflow, particularly during droughts or low-flow periods.     

Dissolved Fe2+ and ∑H2S Behavior in Sediments Seasonally Overlain by Hypoxic-to-anoxic Waters as Determined by CSV Microelectrodes

Variability of dissolved Fe²⁺ and ∑H₂S concentrations in porewaters were studied, using cathodic stripping voltammetry (CSV) microelectrodes, in sediments overlain by hypoxic waters in the summer from the southeastern region of Corpus Christi Bay, Texas (CCB) and the Mississippi River Bight (MRB), Louisiana. These measurements were complimented by sediment microcosm studies where oxygen concentrations in the overlying water were manipulated. Sulfate reduction rates, benthic oxygen demand, total reduced sulfide, porewater sulfate, and total organic carbon were also determined. Fe²⁺ and ∑H₂S were the major dissolved redox-reactive dissolved species in these sediments. During hypoxic conditions, an upward migration of porewater Fe²⁺ and ∑H₂S occurred, with Fe²⁺ reaching much higher maximum concentrations than ∑H₂S. Statistically significant (p < 0.05) differences in both Fe²⁺ and ∑H₂S occurred between sediments at the CCB and MRB study sites. Although both sites were Fe-dominated, reactive and dissolved iron were higher while ∑H₂S was lower at the MRB site. However, there were no statistically significant (p > 0.05) difference in regard to ∑H₂S between microcosm and field monitoring studies. Results indicated that, for Fe²⁺ and ∑H₂S, relatively large and rapid changes occurred in both the concentrations and distributions of these important porewater constituents in response to relatively short-term changes in overlying water oxygen content. Model calculations indicated that conditions in the sediments can be responsible for the induction of hypoxic conditions in the formation of hypoxic overlying waters in <6 days at CCB and ~20 days at MRB.