Patterns of long-term dynamics of aquatic communities and water quality parameters in the Great Lakes: Are they synchronized?

Long time series data can provide insights into dynamics of large lakes. We use the USEPA-GLNPO biological monitoring dataset (phytoplankton, benthos, zooplankton and water quality), collected from 1996 through 2016, to identify whether there is evidence of concordant linear or non-linear trends in community composition, density/biomass/biovolume and major environmental parameters. We show changes in biotic assemblages and water quality variables, particularly in Lakes Michigan and Huron. These include changes in phytoplankton biovolume and zooplankton biomass, increasing invasive Dreissena abundance and decreasing densities of other benthos. Biotic changes are accompanied by pronounced changes in water quality and nutrient ratios. Species change-points, identified using threshold indicator taxon analysis, are often less abrupt, but there are clear shifts in a large proportion of species in each assemblage. The concordance of breakpoints among assemblages or lack thereof provides valuable insight into potential drivers of ecosystem change.     

Mercury distribution in a polluted marine area, ratio of total mercury, methyl mercury and selenium in sediments, mussels and fish

Total mercury, methyl mercury and selenium concentrations were determined in sediments and organisms from the Kaštela bay in the Central Adriatic, polluted with inorganic mercury by a chlor-alkali plant. Sediments and mussels (Mytilus galloprovincialis) contained high total mercury concentrations, especially in the vicinity of the source of pollution. The percentage of mercury in the methyl form increased from surface sediments (up to 1.37%) to the edible parts of mussels (0.1–27%, negatively correlated with total mercury concentrations) and to the fish, in which methyl mercury accounted for most of the mercury in the muscle tissue.     

The Effects of Zebra Mussels on the Lower Planktonic Foodweb in Lake Champlain

Selective grazing by zebra mussels has altered phytoplankton communities in many North American lakes, but the specific changes are not the same in each ecosystem. Because of this variation in response, we investigated the impacts of zebra mussels on the plankton community of Lake Champlain with two objectives: first to determine whether zebra mussels increased the dominance of potentially toxic cyanobacteria in the phytoplankton, and second to explore the impact of zebra mussels on protozoans, rotifers, copepod nauplii, and other microzooplankton in the lower food web. Experiments were conducted in 200-L mesocosms filled with Lake Champlain water filtered through a 150-μm sieve to remove macrozooplankton. Zebra mussels were added to half of the mesocosms while the others were maintained as controls. Over a 96-hour experimental period, we tracked nitrogen and phosphorus concentration, chlorophyll a, microcystin concentration, and both phytoplankton and microzooplankton composition and abundance. We found an increase in SRP and total nitrogen concentration and a decrease in the ratio of TN:TP in the zebra mussel treatments over time. Microcystin was undetectable throughout the experiment using the ELISA assay. Phytoplankton biovolume, including cyanobacteria biovolume, declined significantly in the zebra mussel treatments, as did rotifer, protozoan and nauplii abundance. By both direct (consumption) and indirect (altered nutrient availabilities and increased competition) means, zebra mussels clearly seem capable of strongly influencing the lower planktonic foodweb in the many shallow water habitats of Lake Champlain.     

Diarrheic shellfish poisoning due to toxic mussel consumption: The first recorded outbreak in Greece

During the week of 14-20 January 2000, 120 people visited the Emergency Departments of hospitals in Thessaloniki, northern Greece, complaining of acute gastrointestinal illness after eating mussels (Mytilus galloprovincialis). The symptoms indicated diarrhoeic shellfish poisoning, and the toxicity of mussels harvested from Thermaikos Gulf in Thessaloniki during the outbreak was investigated using mouse bioassays. The bioassays revealed toxicity to mice by the mussel samples; while high numbers of toxic algae Dinophysis acuminata were identified in water samples from Thermaikos Gulf. The harvesting of mussels was immediately suspended and a monitoring programme for algal blooms was established from then onwards. During a follow-up of the mussels' toxicity from January 2000 to January 2005, two more mussel samples were found positive for diarrheic shellfish poisoning: one harvested in March 2001 from the area of the outbreak (Thermaikos Gulf) and the other harvested in January 2001 from Amvrakikos Gulf in north-western Greece. However, no sporadic cases or outbreaks were reported during this period.     

Phytoplankton community composition of Saginaw Bay,Lake Huron,during the zebra mussel (Dreissena polymorpha) invasion: A multivariate analysis

The colonization of the zebra mussel (Dreissena polymorpha) in Saginaw Bay dramatically altered the phytoplankton community composition resulting in exclusion of light sensitive species and dominance of species with oligotrophic preferences and light resistance. In 1990, the NOAA Great Lakes Environmental Research Laboratory initiated a 7-year survey program to monitor changes in the lower food web of Saginaw Bay, where zebra mussels became established in the fall of 1991. To investigate shifts in the phytoplankton community composition over the 7-year period from 1990 to 1996 we searched for clusters of similar composition using multivariate principal component analysis (PCA) on proportions of 22 taxonomic groupings of the total phytoplankton density (cells per milliliter). We then used an agglomerative hierarchical clustering analysis of the PCA scores. We identified five characteristic phytoplankton communities in configurations that allowed recognizing four distinct periods in Saginaw Bay linked to the zebra mussel invasion. Significant changes were indicative of increased water clarity and eutrophic conditions being replaced by more oligotrophic conditions as clusters dominated by light sensitive species, such as the cyanobacteria Oscillatoria redekii, became immediately rare and clusters dominated by diatoms such as Cyclotella spp. became common. Microcystis spp., a light tolerant cyanobacteria not grazed by zebra mussel, dominated assemblages after 1994. The shifts in phytoplankton composition confirm that zebra mussels effects on phytoplankton communities are mediated by both direct (filtration) and indirect (nutrient cycling) mechanisms and also suggests that increased light penetration is an important mechanism behind some changes.     

贻贝热泵干制过程中的品质变化研究

为研究贻贝热泵干制过程中的品质变化,对其蛋白质变性、脂肪氧化程度和风味与色泽变化等进行了研究。研究表明贻贝在干制过程中蛋白质主要在55~60发生变性,蛋白纤维紧缩和氢键的形成使得组织弹性和硬度增加,电镜观察到其肌纤维间隙减小、蛋白凝聚程度增加,质构测试结果验证了其咀嚼性的提升;TBARS值表明其脂肪氧化随着干制进程呈现先加剧后减缓的趋势,伴随着蛋白质和脂肪发生的化学变化而进行的风味物质含量变化形成了其独特的风味,呈鲜的谷氨酸、天冬氨酸和呈甜的甘氨酸和丙氨酸等氨基酸游离程度增加,使得干制品具有较好的鲜味,GC-MS结果说明醛类与烃类等其他物质之间在干制过程中发生了相互转化,挥发性风味物质的含量变化消除了海腥味,形成干品独特的氧化烘香气味;贻贝经过干制后颜色加深,得到以棕褐色为主的干制品,热泵干制能够得到色、香、味等各方面品质较好的贻贝干品。     

Bio-optical properties and primary production of Lake Michigan: Insights from 13-years of SeaWiFS imagery

Thirteen years of SeaWiFS data (1998–2010) from the early spring isothermal period (March–April) were used to determine trends of water attenuation coefficient (K_dPAR), chlorophyll a (Chl a), Photosynthetic Available Radiation (PAR), and modeled primary production in southern Lake Michigan. Surface PAR values remained unchanged between 1998 and 2010, but there was an 18–22% drop in K_dPAR during the March/April isothermal period as water clarity increased. This transparency increase was accompanied by a 41–53% decline in Chl a concentration (μg · L^− 1) and a 42–46% decline in modeled primary production (Great Lakes Primary Production Model). These changes were most pronounced in 2001–2003 which coincided with the period of initial colonization of the quagga mussels. Statistically significant spatial differences were noted in Chl a (μg · L^− 1) concentrations between mid-depth (z = 30–90 m deep), and offshore (z > 90 m deep) waters. Chl a concentrations in the mid-depth region (30–90 m) decreased at a higher rate compared to offshore waters (> 90 m) likely as a result of filtration activities of quagga mussel.     

对发展我国超声波电动机技术的若干建议

简要地叙述了超声波电动机技术发展的国内外的概况,重点介绍了国外超声波电动机技术发展的特点。针对国内外超声波电动机技术研究的现状,提出加速发展我国超声波电动机技术的若干建议。     

Stable isotopes in zebra mussels as bioindicators of river–watershed linkages

Concerns about biodiversity and sustainability extend to many ecological systems, including large river systems that are highly modified by human activities. The Mississippi River is one such system that is currently regulated for navigational and flood control purposes, bears a large agricultural nutrient load, and has experienced rapid spread of the exotic zebra mussel, Dreissena polymorpha, since 1991. Human development of the extensive watershed system of the Mississippi River is ongoing and is expected to lead to further changes in river ecology. This study tested whether stable isotope compositions of the zebra mussel could help identify watershed and tributary loading of carbon (C), nitrogen (N), and sulphur (S) to the mainstem river. Zebra mussels were collected seasonally in the lower Mississippi River at Baton Rouge in 1997, and along most of the length of the river in a north–south transect from Minnesota to Louisiana during August 1998. Results showed substantial seasonal variations in C, N and S isotopic compositions of 2‰ or greater, but also that seasonal changes appeared regular and linked to changing watershed inputs and chemistry of the river water. Nitrate was the dominant N nutrient in the Mississippi River, but isotope analyses showed that food webs based on ammonium rather than nitrate were likely important for the zebra mussel. Results from the north–south transect followed expectations based on mixing of mainstem river water with tributaries that had different chemistries, so that local zones of influence were detectable in the combined CNS zebra mussel isotopes downstream of major tributary confluences for the Illinois, Missouri and Ohio Rivers. Overall, the study supports use of stable isotopes to help monitor watershed development and downstream effects on aquatic food webs. Copyright © 2003 John Wiley & Sons, Ltd.