THE TROPHIC ROLE OF MARINE MAMMALS IN THE NORTHERN GULF OF ST. LAWRENCE

The trophic role of apex predators was evaluated in the northern Gulf of St. Lawrence ecosystem. An Ecopath model was developed for the period 1985–1987 prior to the collapse of commercially exploited demersal fish stocks in this area. Marine mammal trophic levels were estimated by the model at 4.1 for cetaceans, 4.4 for harp seals (Pagophilus groenlandicus), 4.7 for hooded seals (Cystophora cristata), 4.5 for gray seals (Halichoerus grypus), and 4.3 for harbor seals (Phoca vitulina). Harp seals were the third most important predator on vertebrate prey following large Atlantic cod (Gadus morhua) and redfish (Sebastes spp.). Different seal species preyed on different levels of the food chain. Harp seals preyed on most trophic groups, whereas larger seals, such as gray seals and hooded seals, mainly consumed higher trophic levels. The model suggested that apex predators had a negative effect on their dominant prey, the higher trophic level fish, but an indirect positive feedback on the prey of their preferred prey, mainly American plaice (Hippoglossoides platessoides), flounders, skates, and benthic invertebrates. Our results suggest that both marine mammals and fisheries had an impact on the trophic structure.     

CONTROL OF GERMINATION OF ALEXANDRIUM TAMARENSE (DINOPHYCEAE) CYSTS FROM THE LOWER ST. LAWRENCE ESTUARY (CANADA)

Cysts of the toxic dinoflagellate Alexandrium tamarense (Lebour) Balech 1992 from the lower St. Lawrence estuary were used in a test of the following hypotheses: (1) cyst germination is triggered by a change in temperature, and (2) germination rate varies throughout the year and is controlled by a circannual internal biological clock. Results show that cyst germination was not affected significantly by temperature of incubation over the range 1°–16° C, and light showed no significant stimulation of germination. This is supported by the lack of effect of cyst incubation conditions during evaluation of the seasonal changes in germination rate (two temperatures: 4° and 15° C, and two light conditions: darkness and 150 μmol photons·m^?2·s^?1). Thus, direct environmental control through short-term increases in temperature and exposure to light has no effect on the germination of the cysts tested. The rate of germination, observed monthly over a 16-month period, showed low germination (<20%) over most of the period tested, except for a maximum reaching more than 50% germination in August to October of the second year of the experiment. This pattern was observed for cysts both from monthly field collections and from laboratory-stored cysts kept under constant environmental conditions (4° C, in the dark). The peak in germination observed under constant environmental conditions (in the laboratory), the almost coincidental increase in cyst germination observed for the field-collected cysts, and the absence of effects of temperature and light during incubation could be explained either by a temperature-controlled cyst maturation period (the time-temperature hypothesis of Huber and Nipkow 1923) or by the presence of an internal biological clock. However, the large decline in the rate of germination 2 months after the maximum provides strong support for the biological clock hypothesis. The ca. 12-month maturation (dormancy) period observed for the laboratory-stored cysts is the longest reported for this species to our knowledge; this might be related to the low storage temperature (4° C), which is close to bottom temperatures generally encountered in this environment (0° to 6° C). Similar field and laboratory storage temperatures could explain the coincidental increase in germination rate in the fall of the second year if cyst maturation is controlled by temperature. A fraction of the laboratory-stored cysts did not follow a rhythmic pattern: A rather constant germination rate of about 20% was observed throughout the year. This continuous germination of likely mature cysts may supplement the local blooms of this toxic dinoflagellate, as these often occur earlier than peak germination observed in late summer. It seems that two cyst germination strategies are present in the St. Lawrence: continuous germination after cyst maturation, with temperature controlling the length of the maturation period, and germination controlled by a circannual internal rhythm.     

DIATOM PALEOLIMNOLOGY OF TWO FLUVIAL LAKES IN THE ST. LAWRENCE RIVER: A RECONSTRUCTION OF ENVIRONMENTAL CHANGES DURING THE LAST CENTURY

Water quality degradation is a serious concern for the St. Lawrence River. While some environmental data are available for the St. Lawrence ecosystem, long-term monitoring data are generally lacking. To infer past environmental changes, we undertook a paleolimnological assessment of diatom assemblages preserved in four ²¹⁰Pb- and ¹³⁷Cs-dated sediment cores from two fluvial lakes in the river, and used diatom transfer functions to infer past shoreline habitat characteristics. At sites in Lake Saint-François, a fluvial lake downstream from Cornwall, water quality decreased this century in response to human impacts (e.g. macrophyte density and nutrient levels increased). These trends were apparent from an increase in epiphytic diatom taxa, followed by an increase in eutrophic planktonic taxa. Water quality, however, appears to have improved somewhat in response to rehabilitation measures during the last two decades. From a sediment core near Montréal (Lake Saint-Louis), we also noted a large proportion of eutrophic and epiphytic taxa, but less evidence was recorded of a recent improvement in water quality. The diatom-based inference model for habitat characteristics appeared to reconstruct environmental conditions in the St. Lawrence River during the last century. The most notable shift has been an increase in diatom taxa commonly associated with macrophyte substrates. Trends in some of the planktonic diatoms were similar to those recorded in paleolimnological investigations from Lake Ontario, but cores from the river also may be reflecting local environments. This study shows that diatom-based paleolimnological studies are possible in large river systems, if coring sites (e.g. fluvial lakes) are carefully selected.     

WEIGHTS AND ANATOMICAL MEASUREMENTS OF NORTHEASTERN ATLANTIC FIN (BALAENOPTERA PHYSALUS, LINNAEUS) AND SEI (B. BOREALIS, LESSON) WHALES

Piecemeal body weights of eleven fin and four sei whales and intact weights of three foetuses, obtained from Iceland, are compared with published weight data. The Icelandic fin are similar to other northern hemisphere animals but are significantly leaner than their Antarctic counterparts. The Icelandic sei appear heavier than the North Pacific sei whales. Their weights cannot be predicted from a North Pacific sei whale weight/length formula. Length, girth and blubber thickness measurements indicate changes in relative body dimensions in the early fin whale foetus compared with juveniles and adults; however, the midterm sei whale foetus is similar to the adult and juvenile sei whales. The blubber appears to form a major component even in the foetal body. The integration of a standard series of lengths, girths and blubber thicknesses in juveniles and adults can provide an estimate of the blubber component. Both girth and length are significant parameters in estimating body weight, a simple weight/length formula being found to be inadequate to allow for variability in body fatness. Evaluation of such a multiple parameter formula for calculating weight appears satisfactory for both fin and sei whales. Apparent weight/length differences between species and stocks may thus be partly due to variations in body fatness.     

DISTRIBUTION OF DIATOMS IN THE PLANKTON OF YAQUINA ESTUARY,OREGON1

The distributional patterns of diatoms in the plankton of the Yaqnina Estuary, Oregon, were, investigated and related to selected climatic and hydrographic factors. Distribution was strongly influenced by seasonal patterns of rainfall resulting in the introduction of a large volume of fresh water into the estuary during fall and winter. Plankton assemblages in spring, summer and fall had fewer diatom species and exhibited a more rapid rate of change in species composition than in winter. Winter assemblages were further characterized by many pennate diatoms, apparently dislodged from the benthos during periods of high freshwater discharge and silt loads. A statistical measure of community difference indicated an increase in taxonomic homogeneity among assemblages throughout the estuary with the onset of the rainy season in late fall and a gradual transition to a more heterogeneous system again during late spring. Canonical correlation ordered 20 prominent diatom taxa along the salinity gradient and identified possible relationships among certain taxa and selected environmental variables, namely visible light energy and temperature. Redundancy in the species data given the environmental data was only 40%, emphasizing the difficulty in demonstrating a quantitive relationship between plankton dynamics in the field and concurrent measurements of chemical and physical variables.     

VENTILATORY RATE DIFFERENCES BETWEEN SURFACE-FEEDING AND NON-SURFACE-FEEDING FIN WHALES (BALAENOPTERA PHYSALUS) IN THE WATERS OFF EASTERN LONG ISLAND, NEW YORK, U.S.A., 1981–1987

Observations of feeding and ventilatory behavior of individual fin whales ( Balaenoptera physalus )were made from various vessels during the months of May–September, 1981–1987, in the waters off eastern Long Island, N.Y., U.S.A. Intervals between blows were measured and recorded to the nearest second. Information about behavior was recorded, as were location, depth, and surface temperature at sounding dives. Animals observed feeding at the surface were noted as such, ail others were considered non-surface-feeding animals. Data were compiled by individual, month, year, and analyzed for mean interblow interval during surface activity bouts; mean dive duration; and overall mean blow interval.
Overall mean blow intervals (±SE) of 47.89 ± 0.81 set for surface-feeding ( n = 10,411), and 57.92 ±0.97 sec for non-surface-feeding animals ( n = 11,024), differed significantly (Mann-Whitney U, P < 0.001). Interblow intervals for surface activity bouts (±SE) of 12.29 ± 0.05 set for surface-feeding ( n = 7,894), and 13.58 ± 0.06 set, for non-surface-feeding animals (n = 8,187), also differed significantly (Mann-Whitney U, P < 0.001), as did mean dive duration (159.53 ± 2.16 sec, n = 2,517, for surface-feeding animals; 185.86 ± 2.53 set, n = 2,837, for non-surface-feeding animals). Yearly comparisons of blow intervals between surface-feeding and non-surface-feeding animals during surface activity bouts yielded significant differences for each year except 1981, while comparisons of dive durations yielded significant differences for all years except 1981, 1982, and 1985.     

猫背外侧索中上行纤维的电生理学特征的初步观察

在麻醉猫的脊髓的背外侧索中用显微解剖法剥制出神经纤维细束,研究其传入的单位放电活动。根据对自然刺激的反应共记录到五类性质的不同的单位:肌梭传入单位(n=111),对轻压刺激敏感的低阈值机械感受单位(n=85),对触毛十分敏感的毛单位(n=65),毛—低阈值机械感受性混合单位(n=17),以及仅对伤害性刺激有反应的高阈值机械感受性单位(n=11)。其中肌梭单位最易观察到,可能是肌梭的传入纤维的直径较粗,因而较易完整无损地被分离到。值得指出,所有传递躯体感受信息的脊髓上行纤维均位于背外侧索的外侧三分之一处,而其他纤维则主要分布于背外侧索的内侧三分之二的区域。     

正常猫膈神经单纤维电活动特征

在麻醉猫和麻痹的切断迷走神经的清醒猫,观察了膈神经单纤维电活动特征。1.电活动类型:按膈神经单纤维放电与其总干放电的相位关系分为三种类型。(1)完全同步型,即单纤维放电与总干放电同时开始并同时停止,占76.9％。(2)部分同步型占15.4％,其中早期同步,即单纤维放电与总干放电同时开始,但提前终止,占1.9％,中期同步,即单纤维放电较总干放电开始晚,又提前终止,占5.8％,晚期同步,即单纤维放电较总干放电开始晚,但两者同时终止,占7.7％。(8)非同步型,即吸气相和呼气相都有放电,但呼气相时冲动频率较低,占7.7％。前两型为单纯的吸气性放电,共占92.3％。2.单纤维放电平均参数值:麻醉猫每次吸气发放11个冲动,其频率为21次/秒,清醒猫每次吸气发放18个冲动,其频率为34次/秒。结果表明:猫膈神经单纤维放电类型和文献上报导的直接记录膈神经运动神经元放电一致,即以单纯的吸气性放电为最多。     

大鼠背外侧索中各类上行纤维的电生理学特征

在大鼠胸髓下段,用分离纤维细束法观察背外侧索(dorsolateral funiculus,DLF)中各类上行纤维的电生理学特征。在记录的251个单位中,144个主要接受A_β类纤维输入的单位对触毛和/或轻压皮肤反应,26个伤害性单位和毛压-伤害性会聚单位接受A_δ和C纤维的传入;这两类纤维主要沿DLF的中、浅层上行,且具有明显的会聚特点;提示其中部分单位可能属于脊颈束(spinocervicaltract,SCT)。在DLF的深、中层分离到61个对关节运动敏感的单位,它们可能属于脊髓小脑背束(dorsal spinocerebellar tract,DSST)。另有20个对各类自然刺激均无反应的自发单位。在DLF的浅层近背根处,还记录到38条来自对侧的交叉上行纤维,它们与同侧的非交叉上行纤维相混杂,其生理学特性与同侧上行纤维相似,本文结果提供了大鼠DLF中存在部分交叉上行纤维的生理学证据。     

视觉系统皮层下细胞的方位和方向敏感性

视觉方位、方向选择性曾被认为是高等哺乳动物视皮层细胞的特有功能。近年来大量的实验结果表明,视皮层下的外膝体神经元和视网膜神经节细胞都具一定程度的方位和方向敏感性,这些性质是遗传决定的,不受后天环境的影响。在外膝体内,已为视皮层细胞高度的方位、方向选择性和功能柱的形成做出了初步的分类与编组,提供了前级安排。这种皮层下的方位、方向敏感性细胞在发育过程中传递和加工了环境视觉信息,促进了视皮层更强的方位、方向选择性机制和方位功能柱的形成。外膝体在视觉信息平行处理通道的形成上起着分类集聚的重要作用。     

西菲律宾海盆表层沉积硅藻分布特征

本文对西菲律宾海盆186个表层沉积硅藻样品进行分析,共鉴定出硅藻68个种和变种,隶属于26个属。西菲律宾海盆硅藻总平均丰度为1 111.5粒/g。硅藻属种主要以外洋暖水种和广温种为主,其中Azpeitia nodulifera的百分含量最高,其次是Hemidiscus cuneiformis,Coscinodiscus africanus,Thalasiosira excentrica和Nitzschia marina,以上5种硅藻占所有硅藻百分含量的88%以上。西菲律宾海盆大部分站位热带远洋种含量均高于20%,这与现今黑潮暖流流经该区相吻合。通过主成分分析,该海域表层沉积硅藻可分划为3个区域。此外,整个菲律宾海盆大部分海域都分布有Ethmodiscus rex,但西菲律宾海盆的分布范围更广。     

培养的下丘脑神经细胞电生理特征的衰老性变化

本文采用玻璃微电极细胞内记录技术,研究了培齿０－１４０ｄ新生ＳＤ大鼠下丘脑神经细胞电生理学特征的增龄性变化。以神经突起的生长速度为指标,将细胞体外存活过程分为三期,即恢复期、生长期、衰老期。发现,神经细胞膜时间常数及膜电容于生长期达最大值,而在衰老期显著减小。恢复期膜阻抗最高,生长期显著下降,但衰老期变化不显著。神经细胞可产生单个或多个诱发放电,其静息电位约－３０－－６０ｍＶ,并呈增龄性增高。可见     

鱼体微量元素的生态化学特征研究

本文以１６种鱼的１６个元素含量和相应水环境中的元素含量的大量分析数据为基础,分析了鱼体内微量元素的生态化学特征。结果表明,鱼体内一些元素之间存在显著相关性,且一种元素的含量能较好地用几种其它元素的回归方移表示。鱼体对微量元素有很强的富集作用,１２种微量元素在１２种鱼体的个均富集系数（鱼体／过滤水）在７９２－２１２０６之间,文中比较了不同元素的富集水平,以及不同鱼种的富集能力。鱼体和水中的徽量元素之间存在显著相关性,相关系数为０．９８００。     

江苏沿岸海域浮游病毒的时空分布

在2006.7—2007.12期间,采用SYBR Green I染色-荧光显微直接计数法,对江苏沿海海域浮游病毒丰度进行了四个季度的调查,同时调查还包括细菌丰度、叶绿素a浓度。浮游病毒水平分布呈现中间高,两侧低。苏北浅滩海域病毒含量最高,最高值为47.90×106个/mL;吕泗海域最低,最低值为0.03×106个/mL。季节变化表现为冬季最高,夏季次之,春秋季相当。垂直分布也变现为明显的季节变化,除秋季外,表层浮游病毒丰度高于底层水体。浮游病毒与细菌丰度比(VBR)为0.30—180.08,平均为18.35。春季浮游病毒与叶绿素a、细菌之间均存在较强的相关性,相关系数分别为0.79和0.74(P<0.01);而在秋季,浮游病毒只与细菌有较强的相关性(r=0.79,P<0.01),这说明不同季节,浮游病毒的主要宿主会发生变化。     

银合欢生态特性及人工林地上部生物量

五个银合欢品种K8、K28、K29、K67和K132的盆栽苗经人工气候箱冻害试验表明,-3℃时各品种未发生冻害现象,至-4℃时叶片冻萎而脱落,转入常温下茎梢可以恢复生长;-5℃时茎,根全冻死,皮层坏死。K28萎蔫系数,沙壤土为5.1％～5.3％,粘红壤土为5.6％～5.8％。pH值最适范围5.2～7.5,pH<5.0或>8.0时生长受阻。5年生各品种根瘤固氮酶活性分别为34.600、22.764、20.840、31.750和121.240μgN_2·gFw~(-1)·h~(-1)。生长季高度生长量分别为2.24、1.06、1.24、1.08和2.42cm·d~(-1),年平均生长量(高/朐径)分另11为2.0/1.4、1.9/1.3、1.6/1.4、1.6/1.4和1.9/1.2m·cm~(-1)。3年生人工林地上邯生物量分别达30.53、35.86、30.71、42.80和43.66t·ha~(-1),凋落物量分别为4.30、4.49、8.30、10.87和12.05t·ha~(-1)·a~(-1)。K28萌蘖条1年生物量达21.75t·ha~(-1)(丘陵旱地)和25.23t·ha~(-1)(池边湿地)。