Lake Champlain offshore benthic invertebrate community before and after zebra mussel invasion

Benthic invertebrates are important bio-indicators of water quality and play a significant role in aquatic systems. Lake Champlain has limited benthic invertebrate data which hinders development of food web models, assessment of invasive species impacts, and evaluation of management actions. In June 2016, we assessed benthic invertebrates along three transects in the main basin of Lake Champlain ranging from 5 to 100?m, and then compared results to densities from a limited survey in 1991 prior to the zebra mussel (Dreissena polymorpha) invasion. In 2016, total biomass and density were 1–2 orders of magnitude greater at 5?m than at 20–100?m. Zebra mussels, chironomids, oligochaetes, and gastropods were dominant at 5?m, and oligochaetes and sphaeriids were dominant at 20–100?m. Total density at the 5-m site was 94% lower in 2016 compared to 1991, but similar at the 100-m site. Diporeia, while abundant in many freshwater bodies, is historically rare in Lake Champlain and was not detected in our sampling. Because Lake Champlain benthic invertebrate densities are low and display dissimilar distributions to the Great Lakes, we hypothesize the offshore fish community is likely much more reliant on pelagic rather than benthic production. Although the current composition and biomass suggest the benthic community in Lake Champlain may not be greatly impacted by an invasion of quagga mussel (D. rostriformis bugensis), the potential for quaggas to re-route energy from pelagic to benthic habitats, as it has in the Great Lakes, could limit the Lake Champlain offshore fish community.     

Additional deepwater sampling of prey fish in Lake Michigan annual bottom trawl survey reveals new insights for depth distribution dynamics

Beginning in 2013, sites at the 128-m bottom depth contour were added to the sampling design of the annual Lake Michigan bottom trawl survey for prey fish, which has been conducted by the U.S. Geological Survey Great Lakes Science Center (GLSC) each fall since 1973, to better assess fish depth distributions in a changing ecosystem. The standard sampling design included bottom depths from 9 to 110 m, although the GLSC also sporadically conducted bottom trawl tows at the 128-m bottom depth contour during 1973–1988. Enactment of this new sampling design in 2013 revealed that mean biomass density of deepwater sculpins (Myoxocephalus thompsonii) at the 128-m depth exceeded the sum of mean biomass densities at shallower depths, indicating that the bulk of the deepwater sculpin population is residing in waters deeper than 110 m. Thus, our findings supported the hypothesis that the depth distribution of the deepwater sculpin population had shifted to deeper waters beginning in 2007, thereby explaining, at least in part, the marked decline in deepwater sculpin abundance since 2006 based on the standard sampling design. In contrast, our results did not support the hypothesis that the slimy sculpin (Cottus cognatus) population had shifted to deeper waters sometime after 2000. A portion of the burbot (Lota lota) population may have also shifted in depth distribution to waters deeper than 110 m after 2007, based on our results. Our findings have served as an impetus to further expand the range of depths sampled in our bottom trawl survey.     

Dreissenid colonization during the initial invasion of the quagga mussel in the largest Central European shallow lake,Lake Balaton,Hungary

The colonization progress of the invasive bivalve dreissenids, the formerly dominant Dreissena polymorpha and the recently (2008) introduced Dreissena rostriformis bugensis was studied between 2009 and 2013 in the largest Central European shallow lake, Lake Balaton, Hungary. The density of dreissenid planktonic veligers, new settlers (post-veligers and early juveniles), and the population structure (density, length frequency, relative abundance) of the two species were monitored on experimentally introduced natural stone substrata, on different time scales. Dreissenids started dynamic settling following a sudden veliger bloom. As substratum saturation progressed, competition between species for places was suggested, which, after two years, led to an increased number of large individuals (> 20 mm) and also recruits of D. r. bugensis. By contrast, the population of D. polymorpha was confined to middle size (11–18 mm) individuals of the first settler generation. On local substrata, where the benthic community was already established, the replacement of D. polymorpha by D. r. bugensis took longer, but it happened in a similar way. The invasion speed of D. r. bugensis in Lake Balaton resembled the speed obtained in other European water bodies where D. r. bugensis, similar to Lake Balaton, was introduced much later than D. polymorpha. However, a longer replacement process was found in North America, where both species invaded new habitats at the same time. This suggests that the speed, and probably the success, of D. r. bugensis invasion depends on new surface availability, and whether the two dreissenid species are introduced together or at different times.     

A mesocosm investigation of the effects of quagga mussels (Dreissena rostriformis bugensis) on Lake Michigan zooplankton assemblages

Dreissenid mussels are known to disrupt the base of the food web by filter feeding on phytoplankton; however, they may also directly ingest zooplankton thereby complicating their effects on plankton communities. The objective of this study was to quantify the effects of quagga mussel feeding on the composition and size structure of Lake Michigan zooplankton assemblages. Two mesocosm (six 946 L tanks) experiments were conducted in summer 2013, using quagga mussels and zooplankton collected near Beaver Island, MI, to examine the response of zooplankton communities to the presence and absence of mussels (experiment 1) and varying mussel density (experiment 2). Mesocosms were sampled daily and zooplankton taxa were enumerated and sized using microscopy and FlowCAM® imaging. In experiment 1, the presence of quagga mussels had a rapid negative effect on veliger and copepod nauplii abundance, and a delayed negative effect on rotifer abundance. In experiment 2, mussel density had a negative effect on veliger, nauplii, and copepodite abundance within 24 h. Multivariate analyses revealed a change in zooplankton community composition with increasing mussel density. Ten zooplankton taxa decreased in abundance and frequency as quagga mussel density increased: except for the rotifer Trichocerca sp., treatments with higher mussel densities (i.e., 1327, 3585, and 5389 mussels/m²) had the greatest negative effect on small-bodied zooplankton (≤ 128 μm). This study confirms results from small-scale (≤ 1 L) experiments and demonstrates that quagga mussels can alter zooplankton communities at mesoscales (~ 1000 L), possibly through a combination of direct consumption and resource depletion.     

Long-term changes in hypolimnetic dissolved oxygen in a large lake: Effects of invasive mussels,eutrophication and climate change on Lake Simcoe, 1980–2012

Lake Simcoe has been influenced by multiple environmental drivers over the past decades, especially by reductions in phosphorus (P) loading, climate change, and invasive species such as dreissenid mussels (DM) which became firmly established in 1996. We examined the cumulative impact of these drivers on the volume-weighted hypolimnetic dissolved oxygen concentration (VWHDO) below 18?m at station K42 in Kempenfelt Bay during ice-free seasons from 1980 to 2012. Hypolimnetic DO depletion began in early spring when thermal stratification was observable but weak and continued throughout the ice-free season until cooling sufficiently lowered water column stability. In comparison to the pre-DM invasion period (1980–1995), mean annual VWHDO_init was 2.4?mg?L^?1 higher in the post-DM period (1996–2012), VWHDO_min was 1.54?mg?L^?1 higher and the mean duration of the depletion period (L) was 16?days longer. Mean DO depletion rate (DR) and temperature adjusted DO depletion rate (DR_adj) were slightly lower (7% and 5%, respectively) after 1996. P controls and DM had a positive effect on VWHDO, presumably by lowering productivity and diverting organic matter away from the hypolimnon. However, longer L apparently offset improvements in VWHDO_min. If lengthening of L associated with regional warming continues, then additional efforts to reduce P loads will be necessary to achieve the goal of maintaining VWHDO_min above the target of 7?mg?O₂?L^?1 throughout the summer and fall.     

Phytoplankton and benthic algal response to ecosystem engineers and multiple stressors in the nearshore of Lake Huron

Resurgence of nuisance benthic algae in the Great Lakes, despite substantial efforts to reduce phosphorus loading, has stimulated renewed interest in exploring the diverse drivers of near-shore water quality. Interestingly, broad similarity in the underlying causes of shore fouling by benthic algae in Lakes Ontario, Erie, and Michigan appear to contrast with Lake Huron where system productivity and dreissenid abundance are lower. While total phosphorus was the primary predictor of chlorophyll concentrations (70–90% of variation) in the water column, we identified a series of spatial patterns that underpin this relationship (up to 28% of variation) and which integrate catchment processes, tributary influences, shoreline complexity, and distance from shore. Dreissenid mussels were the most important predictors of benthic algae cover and biomass in our models, explaining between 20 and 52% of variation. Spatial patterns explained an additional 21–48% of the variation in benthic algae cover and biomass and highlight the importance of site-specific spatial heterogeneity in benthic algae growth. Our results are consistent with the nearshore shunt hypothesis, wherein higher algal cover and biomass coincided with higher mussel density and biomass, although correlative effects with lake depth and loss of algal and mussel biomass due to physical disturbance must also be considered. These results underscore the difficulty associated with identifying the potential drivers of nearshore water quality as the diverse processes of nutrient loading, changes in catchment land use, and ecosystem change associated with invasion by dreissenids all vary in relative influence over a range of spatial scales.     

Effects of habitat suitability on the survival of relocated freshwater mussels

Freshwater mussels are often relocated from existing beds for both conservation and management reasons. In this study, we empirically tested whether the habitat type at the destination site was important in predicting the success of mussel relocation. In 1993, four species of freshwater mussels were relocated in the Apalachicola River in Florida, into three distinct habitat types: stable sand, limestone/sand and cobble. The conditional probability of survival of relocated mussels varied by species and habitat. Two species were considered habitat specialists, one species was considered a habitat generalist and recovery rates for the fourth species were too low to assess habitat preferences. We show empirically that microhabitat is important in the survival of relocated mussels and that the habitat-specific criteria for relocation is species specific. These results suggest that survival of relocated mussels can be enhanced if species-specific site selection criteria are developed using quantitative information. © 1997 John Wiley & Sons, Ltd.     

Dreissenid mussels from the Great Lakes contain elevated thiaminase activity

We examined thiaminase activity in dreissenid mussels collected at different depths and seasons, and from various locations in Lakes Michigan, Ontario, and Huron. Here we present evidence that two dreissenid mussel species (Dreissena bugensis and D. polymorpha) contain thiaminase activity that is 5–100 fold greater than observed in Great Lakes fishes. Thiaminase activity in zebra mussels ranged from 10,600 to 47,900 pmol g^− 1·min^− 1 and activities in quagga mussels ranged from 19,500 to 223,800 pmol g^− 1·min^− 1. Activity in the mussels was greatest in spring, less in summer, and least in fall. Additionally, we observed greater thiaminase activity in dreissenid mussels collected at shallow depths compared to mussels collected at deeper depths. Dreissenids constitute a significant and previously unknown pool of thiaminase in the Great Lakes food web compared to other known sources of this thiamine (vitamin B₁)-degrading enzyme. Thiaminase in forage fish of the Great Lakes has been causally linked to thiamine deficiency in salmonines. We currently do not know whether linkages exist between thiaminase activities observed in dreissenids and the thiaminase activities in higher trophic levels of the Great Lakes food web. However, the extreme thiaminase activities observed in dreissenids from the Great Lakes may represent a serious unanticipated negative effect of these exotic species on Great Lakes ecosystems.     

复合生物保鲜剂在贻贝保鲜中的试验研究

本文介绍了新鲜贻贝经处理后用不同配方的复合生物保鲜剂进行保鲜冷藏,结果表明:溶菌酶、Nisin等复合生物保鲜剂保鲜效果良好。     

蒸煮贻贝冰温贮藏保鲜剂的筛选、优化及评价

目的 筛选用于改善冰温贮藏蒸煮贻贝品质、延长蒸煮贻贝保质期的生物保鲜剂,对复合保鲜剂的配方及保鲜工艺进行优化,并评价其保鲜效果。方法 通过测定保鲜剂作用于贻贝优势腐败菌的抑菌圈大小,筛选出抑菌效果较强的保鲜剂,运用响应面法优化复合保鲜剂配方,采用肉汤稀释法测定最小抑菌浓度(minimuminhibitoryconcentration,MIC);利用正交实验确定复合保鲜剂用于蒸煮贻贝保鲜的最佳工艺;通过测定蒸煮贻贝冰温贮藏8 d后的感官评分、pH、挥发性盐基氮(total volatile basic nitrogen, TVB-N)含量、菌落总数、汁液流失率来评价复合保鲜剂的效果。结果 筛选出的3种保鲜剂分别为溶酶菌、乳酸链球菌素和丁香酚,复合保鲜剂对枯草芽孢杆菌和假单胞菌的MIC分别为16、8μg/mL,复合保鲜剂的优化配方(质量分数)为溶菌酶4%、乳酸链球菌素2%和丁香酚0.75%,最佳保鲜工艺为保鲜剂溶液p H 5.5、料液比1:2.5 (m:V)、浸泡时间60 min,采用优化的配方和工艺用于蒸煮贻贝的冰温贮藏,贻贝品质的综合评分为空白样品的2倍。结论 复合保鲜剂可以有效改善蒸...