Development of blooms of <Emphasis Type="Italic">Cyclotella meneghiniana</Emphasis> and <Emphasis Type="Italic">Nitzschia</Emphasis> spp. (Bacillariophyceae) in a shallow river and estimation of effective suppression flows

Diatom blooms in the middle reaches of the shallow, freshwater, Hunter River, Australia, are a frequent nuisance to river users. During a 4-year study, blooms of Cyclotella meneghiniana and Nitzschia spp. coincided with water temperatures above 23°C and flows below 400 Ml d⁻¹ that lasted for more than 12 days. Redundancy analysis showed that water temperature was positively related, and antecedent flow was negatively related, to the abundance of both taxa. Addition experiments indicated that nutrients are seldom limiting to growth. It is suggested that a combination of faster growth rates at higher temperatures and longer retention times at low flows allows bloom populations to develop. Simulation modelling showed that flow regulation and water extraction have decreased flows in the river during summer, and consequently have probably increased the number of diatom blooms. Environmental flows have been provided to the river, but are not sufficient to prevent blooms. Discharges required for bloom suppression are described.     

Adaptations to Stochastic Environmental Variations: The Effects of Seasonal Temperatures on the Migratory Window of Svalbard Arctic Charr

The circumpolar Arctic charr, Salvelinus alpinus, is ideal for studying how environmental factors affect life history in fishes. Charr populations demonstrate a tremendous ecological plasticity and adaptations to harsh environments. Arctic charr is the only freshwater fish on Svalbard, including anadromous, resident, and landlocked stocks. Freshwater lake systems on Svalbard are characterized by very low water temperatures, long-term or even permanent ice cover, and low levels of nutrients. Food is thus limited and may lead to growth stagnation and early maturity in Arctic charr. The individual growth pattern may alternatively follow a sigmoid-shaped curve, caused by a shift to either cannibalistic or anadromous (migration to sea) behaviour. In lake systems that include migratory charr, the population may consist of a mixture of parr, postsmolt, and adult migratory individuals, as well as small-sized resident, large-sized resident (cannibals), and large formerly resident individuals transformed to anadromy. Our study in the Lake Dieset watercourse (79°N), Svalbard, demonstrates that the annual water flow in the outlet river is strongly correlated to air temperatures and provides a passage to the sea, allowing the charr access to the nutrient-rich seawater environment, during at most two months each year. During one of the years studied, the youngest and small-sized part of the sea-going stock was prevented from ascending the river and probably suffered mortality during winter. The migratory window of the Arctic charr in Lake Dieset is therefore highly variable among years and thus unpredictable. We hypothesize that in worst case scenarios (cold years, low water discharge), climatic variations may occasionally prevent charr from migrating upstream in Svalbard lake systems in late autumn, resulting in high mortality in the population.     

Seasonal changes in the microbial population of the water column and sediments of the Ongagawa River,northern Kyushu,Japan

The total viable count, population density of Escherichia coli and coliform bacteria, and nitrogen in the microbiomass (microbiomass-N) in sediments were monitored monthly at 12 points in the Ongagawa River basin from June 2002 to May 2006. The measurement of the sediment microbiomass-N was used for evaluation of the sediment’s microbial population in the river ecosystem. An extraordinarily high population of E. coli was observed during the season when there was stagnant water in the basin, with a high population and an insufficient drain diffusion system, and, thus hydrological water control is indispensable to prevent rapid E. coli growth. Microbiomass-N in sediments showed a negative correlation or independent fluctuation in relation to the bacterial population in the water column of the river. Seasonal changes in extracted nitrogen (N) in river sediments did not show correspondence with microbiomass-N in sediments. The microbiomass-N in sediments changed independently of the bacterial population in the river water, indicating that the high population of bacteria in the water does not lead to a high microbial population in river sediments. Ordination of the microbial parameters by canonical correspondence analysis (CCA) showed that microbiomass-N in sediments was quite different from other parameters. Relatively higher H⁺ (lower pH), PO₄ ³⁻ concentration and dissolved oxygen (DO) were the determinant parameters of higher microbiomass-N in sediments. A relative microbial abundance between the water column and sediments as well as each of the microbial populations in the water column and sediments could be a quantitative parameter for evaluating the biochemical processes of stream water.     

Freshwater bryozoans (Bryozoa) of Norway II: distribution and ecology of two species of Fredericella

Freshwater bryozoans were investigated during field studies of 601 lakes and other surface water bodies throughout Norway from 1960 to 1978. The frequency of occurrence of the two Fredericella species was evaluated in relation to 12 environmental variables. Statistically significant deviations from the frequencies expected on the basis of random distribution were described using the categories preference, avoidance and absence. The typical European Fredericella sultana (with glossy statoblasts) occurred at 72 localities, north to 70° 25 N (the northernmost record on a global scale). Its frequency dropped towards the north. Maximum elevation above sea level was 1097 m (maximum recorded for Northern Europe). Another species with pitted statoblasts, tentatively considered to be Fredericella indica, occurred at 50 localities, north to 71° 09 N (the northernmost record reported to date). The geographical distribution reflected a typical northern cold-water species. One third of the 50 records were from lakes situated north of the Arctic Circle, and rich colonies were found on the North Cape plateau, as far north as possible on the European mainland. The few records from southeastern Norway were from high mountain lakes, up to 1397 m above sea level (highest record for Europe). This species was not found in any of the numerous lowland lakes investigated in southeastern Norway where F. sultana was common. Both species tolerated a cold climate, especially Fredericella indica, and they occurred in a wide range of environments. F. sultana preferred lakes with rather low elevation above sea level, rich vegetation with plant species typical for eutrophic environments, gyttja sediments and stony "hard" shores, some wave action, high content of calcium, and slightly coloured water. This species avoided ponds and was absent from ditches and mires, avoided dystrophic lakes surrounded by Sphagnum bog, with dy sediments and strongly coloured water, avoided sites with small wave action, was indifferent to magnesium and low concentrations of calcium, and was absent from lakes with pH below 5.4. F. indica was only recorded from lakes. It preferred rather low temperatures, oligotrophic conditions with poor aquatic vegetation and stony shores, some wave action, pH above 7.0, and low water colour (below 11 mg Pt l^–1). This species avoided lakes with high temperatures and was absent above 20 °C, was absent where aquatic vegetation was rich or consisted of Sphagnum bog, avoided lakes with soft sediments of dygyttja and dy, places with small wave action, acid lakes, was absent at pH below 5.9, tended to avoid water with colour above 10 mg Pt l^–1 and was absent in lakes with colour above 40 mg Pt l^–1. F. sultana and F. indica occurred together in only six lakes, four in the north, and two in the southern mountain areas. The opposite sensitivity and reactions of the two species towards several environmental variables were supported by a logistic regression analysis. The main ecological difference between the two species is that F. indica appears to be more strongly dependent on climatic factors.     

Bacterial phylotypes associated with the digestive tract of the sea urchin Paracentrotus lividus and the ascidian <Emphasis Type="Italic">Microcosmus</Emphasis> sp.

We used sequencing and phylogenetic analysis of PCR-amplified 16S rRNA genes from bacteria that are associated with the esophagus/pharynx, stomach and intestine of two marine sympatric invertebrates but with different feeding mechanisms, namely the sea urchin Paracentrotus lividus (grazer) and the ascidian Microcomus sp. (suspension feeder). Amplifiable DNA was retrieved from all sections except the pharynx of the ascidian. Based on the inferred phylogeny of the retrieved sequences, the sea urchin’s esophagus is mainly characterized mostly by bacteria belonging to α-, γ-Proteobacteria and Bacteriodetes, most probably originating from the surrounding environment. The stomach revealed phylotypes that belonged to γ- and δ-Proteobacteria, Verrucomicrobia and Fusobacteria. Since the majority of their closest relatives are anaerobic species and they could be putative symbionts of the P. lividus stomach, in which anaerobic conditions also prevail. Seven out of eight phylotypes found in the sea urchin’s intestine belonged to sulfate reducing δ-Proteobacteria, and one to γ-Proteobacteria, with possible nutritional activities, i.e. degradation of complex organic compounds which is beneficial for the animal. The bacterial phylotypes of the ascidian digestive tract belonged only to the phyla of Actinobacteria and Proteobacteria. The stomach phylotypes of the ascidian were related to pathogenic bacteria possibly originating from the water column, while the intestine seemed to harbour putative symbiotic bacteria that are involved in the degradation of nitrogenous and other organic compounds, thus assisting ascidian nutrition. The text was submitted by the authors in English.     

洮河上游不同海拔紫果云杉根际与非根际土壤细菌多样性及影响因子

【背景】紫果云杉天然林在维护洮河上游生态环境安全方面发挥着重要作用,不同海拔梯度如何影响紫果云杉根际与非根际细菌多样性、土壤养分因子及三者之间的相关性尚不清楚。【目的】深入探索紫果云杉根际与非根际土壤细菌群落结构组成及受控因子。【方法】采用Illumina Miseq平台对洮河上游不同海拔紫果云杉天然林根际与非根际土壤细菌进行测序分析,分析土壤理化因子与细菌多样性随海拔的变化趋势,并通过相关性与冗余分析探究环境因子对细菌群落的影响。【结果】土壤养分因子随海拔升高呈先增加后降低趋势;根际土养分因子组间差异显著(P<0.05),非根际组间差异不显著(P>0.05)。随海拔升高根际微生物物种多样性指数(H)、均匀度指数(E)、丰富度指数(Chao1/ACE)和OTU数目呈单峰型变化趋势;非根际多样性指数随海拔升高呈双峰型变化趋势。土壤细菌多样性与养分因子密切相关,其中有机质、全氮和碱解氮呈显著正相关(P<0.05),而土壤pH和有效磷与细菌多样性呈负相关但不显著(P>0.05)。不同海拔梯度下紫果云杉天然林细菌群落结构一致性较高,从30个样本中获得7 159个细菌OTU,注释到37个门;细菌优势类群为放线菌门、变形菌门、酸杆菌门和绿弯菌门。不同细菌门对土壤养分因子的响应各不相同,有机质、全氮和碱解氮与变形菌门呈显著正相关(P<0.05)。【结论】土壤理化因子能够显著影响紫果云杉根际与非根际细菌多样性和组成,海拔和水热条件等环境因子对植物和土壤的驱动影响是细菌群落结构稳定组成的重要原因。本研究有助于深入理解紫果云杉天然林土壤细菌多样性的变化和驱动机制,为洮河上游天然林恢复与生态恢复提供借鉴。     

Moulting diving ducks and their food supply

Numbers of moulting diving ducks at Myvatn, north Iceland, were monitored over a period of 25 years; aquatic insects (Chironomidae and Simuliidae), a major food resource, were monitored with window traps for 23 years. The response of the duck populations to changes in the food situation during the moulting period varied between species. Histrionicus histrionicus and Melanitta nigra invariably go to the sea to moult. Three species (Aythya fuligula, Clangula hyemalis and Mergus serrator) have shown long term variation in moult migration habits. Aythya marila and Bucephala islandica stay for moulting, their numbers supplemented by birds from elsewhere. A. marila is a generalist feeder and therefore at low risk of starving, the strategy of Bucephala islandica is to move within the water system where the food situation tends to alternate between the lake and the river. Numbers of Bucephala islandica males moulting on Lake Myvatn were strongly and positively correlated with chironomid numbers and those moulting on the river Laxá with Simulium vittatum, the main food resource there. We did not find convincing evidence that numbers of moulting A. marila and C. hyemalis responded to variation in the food supply during the study period. This applied also to A. fuligula in the South Basin of Myvatn, but numbers in the North Basin were positively associated with chironomid numbers. M. serrator moulting on Myvatn showed negative correlations with the chironomids, perhaps reflecting a negative association between chironomids and its main food, Gasterosteus aculeatus. Apart from safety considerations for a flightless bird, the choice of a moulting site is apparently influenced by the local food conditions on one hand and by the opportunities and risks involved in migrating to distant moulting sites with an unknown food situation on the other hand.     

Advances in cultivation of Gelidiales

Currently, Gelidium and Pterocladia (Gelidiales) are collected or harvested only from the sea. Despite several attempts to develop a cultivation technology for Gelidium, no successful methodology has yet been developed. Initial steps towards developmental efforts in Portugal, Spain, South Africa and Israel have been published. More developments have probably been performed but have not been published. Two different technological concepts have been tested for Gelidium cultivation: (1) the attachment of Gelidium fragments to concrete cylinders floating in the sea, and (2) free-floating pond cultivation technology. These vegetative cultivation technologies might be partially optimized by controlling physical, chemical and biological growth factors. The pond cultivation technology is the much more controllable option. The effects of all factors are discussed in detail in this review. It seems that the main difficulty with cultivation of Gelidium is its low growth rate. The claimed yields of the two technologies are far from being economically attractive at this stage of their development. It seems that in order to introduce Gelidium into commercial cultivation, major efforts in genetic improvement through selection or genetic engineering will be required. Only high yield strains will have the potential to compete economically with the present harvesting tradition. However, accumulated experience with genetic improvement of other useful seaweed species suggests that this is possible.     

Comparison of the life cycles of two sympatric estuarine polychaetes, Hediste diadroma and H. atoka (Polychaeta: Nereididae), in the Nanakita River estuary, northeastern Japan

The life cycles of two species of estuarine polychaetes, Hediste diadroma and H. atoka, were investigated using field surveys and colonization experiments in the Nanakita River estuary, Japan. Lactate dehydrogenase (LDH) allozyme banding patterns in starch gel electrophoresis were used to distinguish between the species. We found differences in the life cycle, reproductive ecology, and distribution of the two polychaetes. H. diadroma exhibited conspicuous reproductive swarming behavior during the spring tide in April to early May. After hatching, the trochophore larvae may be transported out to sea and return to the river estuary at the =3-setiger stage. By late July, juveniles settled into brackish water, where they completed the 1-year life span. In contrast, H. atoka never exhibited this conspicuous reproductive swarming behavior. The reproductive period of this species spanned most of the year, except winter. H. atoka juveniles hatched mainly as 3-setiger nectochaetes, which immediately became benthic. The juveniles actively dispersed during the 4-to 7-setiger stage, although they could also do so at any later stage. The life span of H. atoka was about 6 months. In small river estuaries, river flooding may flush sediment and benthic animals out to sea and create vacant habitats for colonization by polychaetes. In the Nanakita River estuary, H. atoka maintained a large and stable population in Gamo Lagoon, located 250m upstream from the river mouth, whereas H. diadroma was rarely found there. Swimming excursions of juvenile H. atoka at any stage in the life cycle may ensure its distribution to new vacant habitats, and its life-cycle characteristics may allow large populations to build rapidly. As a result, H. atoka was able to maintain dominance in both the river and the lagoon in the Nanakita River estuary.     

The distributions of autumn picoplankton in relation to environmental factors in the reservoirs along the Wujiang River in Guizhou Province,SW China

Autumn picoplankton (Synechococcus, picoeukaryotes and heterotrophic bacteria) and environmental factors have been investigated in a series of reservoirs along the Wujiang River in Guizhou Province, SW China. The average abundances of Synechococcus, picoeukaryotes and heterotrophic bacteria was 10⁴, 10² and 10⁶ cells ml⁻¹, respectively. In autumn meso-eutrophic reservoirs, thermal stratification was clear and abundances of different picoplankton groups in release water was low; whereas these phenomena were not obvious in autumn hypereutrophic reservoir. Picoplankton numbers decreased with increasing water depth and showed a positive correlation with water temperature, which reflected the importance of light and temperature on the picoplankton growth. Contribution of Synechococcus to total phytoplankton production and contribution of picoeukaryotes to total phytoplankton production asynchronous changed with varying trophic states. Synechococcus preferred meso-eutrophic reservoirs over hypereutrophic reservoir and picoeukaryotes showed no preference for the investigated reservoirs in autumn. Handling editor: L. Naselli-Flores     

Germination characteristics of native Japanese dandelion autopolyploids and their putative diploid parent species

Germination characteristics of native Japanese Taraxacum lineages of Taraxacum platycarpum (diploid), T. venustum (triploid and tetraploid), and T. albidum (pentaploid) have been studied at different temperatures. Taraxacum platycarpum ssp. hondoense is the putative diploid parent of T. venustum. Diploid T. platycarpum ssp. hondoense and the polyploids T. venustum and T. albidum are found in different areas of Japan, and distribution differences may reflect divergent ecological and physiological traits among ploidy levels. In this study, to prevent mixing of seeds of different polyploidy we used flow cytometry to examine the ploidy level of the plants from which seeds were collected. Results from seed-germination experiments showed that dependence on temperature of final percentage germination was qualitatively similar for both autopolyploids T. venustum and diploids T. platycarpum—germination was suppressed at high and low temperatures. It was also shown that seed germination of autopolyploids was suppressed more than that of the ancestral diploid at low temperatures and that seed germination for polyploids was higher than for the diploid. Threshold variations at low temperatures might affect the distribution of native dandelions. Taraxacum venustum, which occurs in cool climates, might have developed a distinctly lower germination threshold at low temperatures whereas T. albidum, which is native to warm climates, might have developed an adaptive threshold at high temperatures.     

The effects of northern italian rivers and Eastern Mediterranean ingressions on the phytoplankton of the Adriatic Sea

An analysis of the distribution of the phytoplankton standing crop during a period of high stability characterized the relative influence of northern Italian rivers and Mediterranean waters on the Adriatic Sea. The region influenced by northern Italian rivers was marked by low community diversities, relatively high chlorophyll a standing crops and cell densities, high microplankton to nannoplankton community volume ratios, and the dominance of Nitzschia seriata. To the contrary, the region influenced by Mediterranean waters exhibited high community diversities with prominent oceanic and warm water elements, low chlorophyll a standing crops and microplankton cell densities, low microplankton to nannoplankton ratios, and a relatively conspicuous coccolithophore flora.Nannoplankton populations remained relatively constant throughout the Adriatic. However eutrophication resulted in a marked increase in the microplankton component of the community, with the diatom Nitzschia seriata serving as a prime indicator of the process, even in regions several hundred kilometers downstream from nutrient sources.Even under relatively low rates of river discharge, the influence of northern Italian rivers could be traced along the entire western sode of the sea to the Otranto Strait, with low north to south and high west to east gradients resulting from the effect of a cyclonic surface circulation pattern on inflowing Mediterranean waters in the south and river discharge in the north.     

Freshwater bryozoans (Bryozoa) of Norway IV: Distribution and ecology of four species of Plumatella with notes on Hyalinella punctata

Bryozoans were investigated during field studies of 601 lakes and other surface water bodies throughout Norway from 1960 to 1978. The frequency of occurrence of Plumatella repens was evaluated in relation to 12 environmental variables. Statistically significant deviations from the frequencies expected on the basis of random distribution were described using the categories preference, avoidance and absence. P. repens is one of the most common bryozoan species in Norway. It is represented at 227 localities in our material and by 29 additional records. The species occurred frequently all over the country, north to 71°09N (the northernmost record on the European mainland). Maximum elevation above sea level was 1052 m (maximum for Northern Europe). P. repens preferred lakes, avoided rivers, and was absent from the smallest water bodies. The species preferred (1) low elevation (2–200 m above sea level), (2) medium water temperature, (3) rich aquatic vegetation (eutrophic conditions), (4) small wave action, (5) high content of calcium and magnesium, (6) pH 6.4–9.6, and (7) rather high water colour. Otherwise P. repens avoided (1) habitats above 500 m but occurred up to 1052 m, (2) the lowest water temperature intervals, (3) sites with poor aquatic vegetation and stony shores, (4) medium wave action, (5) sites with a low calcium and magnesium content, (6) lakes of low water colour, and (7) lakes with pH below 6.6: it was absent from lakes with pH below 5.2. For many environmental variables, the species had a wider tolerance range than reported from elsewhere. P. fungosa, P. casmiana, and P. emarginata are all rare in Norway. The total numbers of known localities, with our records in (), are 18 (11), 7 (7), and 7 (5), respectively. These sites are all from lowland areas up to 133 m above sea level. Environmental variables in the habitats are described. P. fungosa was represented by a single floatoblast in each of the four northernmost lakes where it was recorded. One of these lakes was in North Norway some 1000 km away from the nearest known sites with living colonies. The presence of large colonies of P. fungosa in some parts of southern Norway and only `single floatoblast lakes' further north is discussed in relation to the equilibrium theory of island biogeography: birds facilitate immigration by carrying floatoblasts and environmental conditions prevent their germination and the development of living colonies. All records of P. casmiana and P. emarginata were from South Norway. Results for P. fruticosa have been published previously. Notes are given on an old and now missing sample from ca. 1900, identified by Lacourt (1968) as Hyalinella punctata – the only record of this species from Norway.     

Water temperature and upstream migration of glass eels in New Zealand: implications of climate change

Glass eels migrating upstream in a New Zealand river showed a clear preference for water temperatures between 12 and 20°C, with an optimum of 16.5°C. Water temperatures <12°C and >22°C almost completely inhibited migration, which implies that warmer temperatures associated with global climate change might have a detrimental impact on glass eel recruitment in their current ranges. We established this by trapping glass eels of shortfin, Anguilla australis, and longfin, A. dieffenbachii, eels nightly from September to November. Eels caught in 2001 (50,287) outnumbered those caught in 2002 (19,954); shortfin glass eels dominated catches in both years, comprising 91–93% of the catch. Longfins were larger than shortfins, and size and pigmentation in both species increased as the seasons progressed. Temperatures within the migratory season in 2001 showed ∼14-day intervals between maxima that appeared to be associated with the new and full moons.     

The response of three chydorid species to temperature, pH and food

The responses of three chydorid species, Chydorus sphaericus(O.F. Müller), Alona affinis (Leydig) and Alonopsis elongata (Sars) to temperature, pH and food type were examined. Egg development time of all species decreased with increasing temperature, although the degree of change was different for each species. C. sphaericus had the fastest development time at all temperatures, and A. elongata the slowest. pH also affected the egg development time of each species differently. A. elongata failed to reproduce at low and medium pH, the egg development time of C. sphaericus was fastest at high pH while that of A. affinis was fastest at low pH. Food type was found to have significant effects on the population growth of individual species. C. sphaericus populations grew equally well in all three food types provided, and grew more than the other two species when fed on an algae culture, and filtered pond water. A. affinisand A. elongata populations grew best when fed on a detritus food source. The responses of each species to the different variables tested are discussed in relation to field observations of their distribution and abundance.     

Conjugative transfer of the IncP-7 carbazole degradative plasmid, pCAR1, in river water samples

The transfer of the IncP-7 carbazole degradative plasmid pCAR1 from Pseudomonas putida SM1443 (derived from strain KT2440) into bacteria of river water samples was monitored using a reporter gene encoding red fluorescent protein (RFP). The number of transconjugants drastically increased in the presence of carbazole, and most appeared to belong to the genus Pseudomonas. The results suggest that the presence of carbazole benefits the appearance of transconjugants belonging to the genus Pseudomonas. Intriguingly, we also detected the transfer of pCAR1 into non-Pseudomonas, Stenotrophomonas-like bacteria.     

Impact of warm water advection on the winter zooplankton community in an Arctic fjord

The west coast of Spitsbergen is influenced by water masses of Atlantic and Arctic origin. During the winter of January–April 2006, water temperatures on the West Spitsbergen Shelf were ∼3°C warmer than typical winter conditions, leading to a coastal sea ice cover of reduced thickness, extent and duration. A sediment trap deployed from September 2005 to May 2006 in the outer basin of Kongsfjorden (NW Spitsbergen) at a depth of 115 m has provided a continuous winter time-series of zooplankton during a period of rapid increase in water temperatures. Prior to an anomalous and prolonged influx of warm Atlantic water (AW) starting at the end of January, the trap samples were dominated by the boreo-Arctic copepod Metridia longa. Species that increased in abundance during the influx included late stages of Calanus finmarchicus, C. glacialis, C. hyperboreus and Paraeuchaeta norvegica. The early introduction of shelf populations into the fjord, and thus increased copepod biomass relative to typical winter conditions with little advection, has implications for the marine pelagic food web and pelagic-benthic coupling.     

Seasonal variation of chromophore composition in the eye of the Japanese dace, <Emphasis Type="Italic">Tribolodon hakonensis</Emphasis>

The relationship between seasonal variation and the effect of several different environmental factors on chromophore composition was investigated in the eye of the Japanese dace, Tribolodon hakonensis which lives either in rivers or in the sea. Eyes obtained from river and sea populations had both retinal (A1) and 3,4-didehydroretinal (A2) all through the year but the ratio of these chromophores showed seasonal variation the relative amount of A2 was higher in winter and lower in summer. Besides seasonal variation, A2 showed marked differences depending on habitat: the highest proportion of A2 was 67% in January and the lowest 13% in July, in the river population, whereas in the sea population the highest and the lowest values were only 30 and 6%, respectively, during the same months. The seasonal variation in gonadosomatic index showed no correlation to variations in A2 proportion, and the maximum difference in water temperature between summer and winter was ca. 15°C for both habitats. Because spectral conditions at the locations of capture of both river and sea populations were similar, we conclude that Japanese dace eyes are affected by exogenous factors related to differences between freshwater and seawater environments.     

Occurrence ofDinophysis spp. and toxic shellfish in the Northern Adriatic

The dynamics of the toxicity of the musselMytilus galloprovincialis was compared between two different shellfish farms, 5 km apart, but using the same cultivation technique. The main differences concerned the freshwater influx and the open aspect to the Gulf of Trieste. It is suggested that a deep closed bay and abundant fresh water inflow are the two main conditions for the low toxicity levels in mussels and for shorter periods of danger. A detailed study of the phytoplankton samples revealed the presence of eight species ofDinophysis in the area of both shellfish farms. During the period of the DSP outbreak in Slovenia (autumn and winter 1989).D. fortii andD. acuminata were the most frequentDinophysis species. There was a high positive correlation between the onset of mussel toxicity and the appearance ofDinophysis spp.     

In situ measured seasonal variations in F v/F m of two common Red Sea corals

Pulse amplitude modulated (PAM) fluorometry has been suggested as a tool for estimating environmental stresses on corals. However, information regarding natural changes in maximal quantum yields (F _v/F _m) of corals during “normal” (i.e. non-bleaching) years has been limited. In this study, seasonal variations in F _v/F _m for Stylophora pistillata and Favia favus, measured in situ, correlated with seasonal changes in solar irradiance but not in sea temperature. Interactions between sea temperature and irradiance were further studied by growing these corals and Pocillopora damicornis under controlled conditions. Exposure to high light with normal or high temperatures resulted in lower F _v/F _m values than exposure to low light at both temperatures. Thus, high irradiances may cause decreased F _v/F _m values in corals at least as much as, if not more than, high temperatures. Such seasonal variations should be taken into account when using PAM fluorometry as a diagnostic tool for predicting coral bleaching.