Persistent “upwelling shadows” and their influence on zooplankton distributions

Physical (temperature and salinity) and biological (zooplankton) properties were sampled over a 15 mo period in 1988 and 1989 to monitor nearshore environmental variability in northern Monterey Bay, California, USA. During the upwelling seasons of 1988 and 1989, there were two distinct bodies of water along the sampling transect. The offshore water body was characterized by recently upwelled water (typically <12°C) while the nearshore body was significantly warmer (approaching 16°C). A sharp thermal gradient (=front) separated the two water bodies. This front persisted 6.5 km from shore throughout the upwelling season of 1988 and was present again in 1989. Zooplankton-assemblage analysis confirmed the presence of two distinct regions in northern Monterey Bay. We refer to this phenomenon as an upwelling shadow, which is the result of the advection of recently upwelled water bearing nutrients and larvae past coastal recesses which are equatorward of upwelling centers.     

Comparative feeding preference of Strongylocentrotus droebachiensis (Echinoidea) for the invasive seaweed Codium fragile ssp. tomentosoides (Chlorophyceae) and four other seaweeds

Laboratory experiments conducted during 1987 on Appledore Island, Maine, USA, tested whether feeding preference or the absence of an attractant was the cause for the occurrence of beds of Codium fragile ssp. tomentosoides (herein referred to as Codium fragile) within rocky barrens grazed clear of kelp by the sea urchin Strongylocentrotus droebachiensis. Consumption of C. fragile in single-diet experiments (1 seaweed/sea urchin) was highly variable and was not significantly different from that for several other seaweeds (Agarum cribrosum, Ascophyllum nodosum, Chondrus crispus, and Laminana saccharina) important in the field diet of the green sea urchin. In multiple-diet experiments (5 seaweeds/sea urchin) significantly less Codium fragile was eaten than Chondrus crispus, but significantly more Codium fragile was eaten than A. cribrosum. Chemosensory experiments suggest that C. fragile does not attract the sea urchin. Sea urchins are unable to detect C. fragile but will eat it when they come in contact with it.     

The effect of nitrogen deficiency,methionine and inhibitors of methionine metabolism on the DMSP contents of Tetraselmis subcordiformis (Stein)

The unicellular alga Tetraselmis (Platymonas) subcordiformis (Prasinophyceae) displayed a two-phase increase in DMSP (dimethylsulfoniopropionate) contents in response to nitrogen deficiency. In the first phase, DMSP pools increased by 75% within 24 h. The second increase in DMSP was observed after 14 d and was accompanied by cyst formation. Methionine metabolism was involved in DMSP accumulation. A 2.6-fold increase of the DMSP pool could be induced by supplementing a complete ASP (artifical seawater Provasoli) medium with 100 M L-methionine. Inhibition of methionine utilization by T. subcordiformis caused by the addition of S-adenosylhomocystein, a competitive inhibitor of S-adenosylmethionine-dependent transmethylases, resulted in a 24% increase of DMSP contents after 7 h. DMSP accumulation after hyperosmotic shock was significantly delayed when methionine liberation from proteins was inhibited by a set of protease inhibitors. A model for the mechanism of DMSP accumulation is presented on the basis of these data and additional information from the literature. It is proposed that methionine availability in T. subcordiformis determines the rate of DMSP synthesis.     

Ultrastructure of sperm and spermathecae in Micromaldane spp. (Polychaeta: Capitellida: Maldanidae)

Assessing the possibility that external fertilization has re-evolved requires the study of monophyletic groups that exhibit various reproductive methods. Maldanid polychaetes show a range of reproductive mechanisms, though previous studies of reproduction have hitherto been restricted to larger species with external fertilization. Micromaldane pamelae Rouse and M. nutricula Rouse are small, gonochoristic maldanids that brood directly developing larvae. Both species have sperm with elongate nuclei and an acrosome extending down each side of the anterior end of the nucleus. A true midpiece is absent; two mitochondria extend along the posterior region of the nucleus. Spermatids develop synchronously in large clusters connected by a cytophore. In M. pamelae sperm are released into the water as spermatozeugmata. These are comprised of clusters of sperm with their tails oriented to the centre and the sperm heads facing outwards. Females of M. pamelae and M. nutricula bear pairs of spermathecae ventrally (M. pamelae three pairs, between setigers 10 and 11, 11 and 12 and 12 and 13 and M. nutricula two pairs, between setigers 10 and 11 and setigers 11 and 12). The blind sacs are epidermal invaginations bound closely together. The entrance to each spermatheca may only be 1 to 2 m across with each spermatheca holding several hundred sperm. This represents the first detailed study of spermathecae in the Capitellida. The occurrence and structure of spermathecae and spermatozeugmata in other groups are discussed and compared with Micromaldane spp. Comparisons are made with non-polychaetes with the purpose of discussing functional aspects of reproductive mechanisms in marine metazoans in general. Elongate sperm nuclei are associated with sperm storage and/or large egg size. The lack of an elongate sperm midpiece may be an indicator of having to swim in water but does not contraindicate sperm storage. Spermatozeugmata may serve as an indication of sperm storage and brooding of larvae. Speculations on the phylogenetic significance of these reproductive features are limited by the fact that supposedly modified (i.e., derived) states may reflect functional/structura, constraints of small body size.     

Loch fleet: liming to restore a brown trout fishery

This project has been successful in meeting its objectives in terms of demonstrating that catchment liming techniques can restore acidified waters to conditions suitable for fish populations for relatively long periods. This improvement in conditions has extended to the inlet stream, which provides vital fish spawning and nursery areas, which are difficult to treat effectively be other means in remote locations. The project has also provided an assessment of the effectiveness of differing rates and modes of lime application, which suggest that only quite restricted parts of a catchment require treatment. This not only maximizes the cost-effectiveness of the treatments, but also helps to minimize any side-effects on, for example, moorland vegetation. The biological monitoring programme at Loch Fleet has also provided an assessment of the overall ecological consequences of adding limestone to naturally acidic and calcium-deficient ecosystems.     

Measurement of dry deposition of ammonia on a forest

Ammonia concentration gradients above a Douglas fir canopy were measured from 16 August to 31 December 1989 by two automated high-precision thermodenuders at the location Speulderbos in The Netherlands. Concentration gradients were used to calculate the dry deposition flux of ammonia via flux-gradient theory. Meteorological data were obtained from a nearby tower. Ammonia concentrations were highly variable with highest values during the night. Concentration gradients were very small during daytime and quite large at night. Median values of the calculated deposition flux and deposition velocity were 0.1 microg m(-2) s(-1) and 3.2 cm s(-1) respectively (N=1624).     

Critical loads for Finnish lakes: comparison of three steady-state models

Three simple steady-state water-chemistry models are used to calculate critical loads of sulfur for lakes in Finland. Because of the high concentrations of organic matter in Finnish lakes, the influence of organic anions on the calculation of critical loads has been given special attention. The first two methods are well known ion-balance methods which have been used in many previous lake-acidification studies. The third method, developed for this study, includes the numerical solution of equilibrium equations for organic anions, inorganic carbon species and inorganic monomeric aluminum. The original pH and aluminum concentration of the lakes are estimated with this model, and a method to estimate the original acid neutralizing capacity (ANC) by simulating a Gran-titration is also tested on the lake data. Uncertainty in the predictions is estimated by varying the most critical model parameters.     

The aggregation pheromone ofIps duplicatus and its role in competitive interactions withI. typographus (Coleoptera: Scolytidae)

Summary Ips duplicatus withI. typographus co-inhabiting Norway spruce (Picea abies (L.) Karst.) would benefit from a pheromone blend distinct from that of the larger competitorI. typographus. GC-MS analysis showed thatI. duplicatus males feeding in the host produced ipsdienol (Id),cis-verbenol (cV),trans-verbenol (tV), myrtenol (Mt), andE-myrcenol (EM) and traces of 2-methyl-3-buten-2-ol (MB).I. duplicatus produced Id in approximately racemic form (48.9-54.5% (+)-(S)-isomer). The amounts of Id and EM released over a 9 day period had a maximum of 250 and 5 ng/h/male, respectively, on day 2. Exposure ofI. duplicatus males to myrcene and -pinene resulted in the production of small amounts of Id, cV, tV, Mt, andtrans-pinocarveol, but not of EM. In laboratory bioassays with walking beetles, the pheromone component Id alone was weakly attractive while EM was inactive, but in binary combination with Id strongly synergized attraction. A combination of EM and Id at a release rate equivalent to 100–200 males was more attractive in the field than 70 unmated males in a spruce log. The addition of myrcene ( a suggested pheromone precursor of Id) to Id did not enhance trap caches, while addition of EM increased catches > 10-fold. Subtracting EM from a blend of Id, EM, cV and MB drastically reduced trap catches while subtraction of cV or MB or both had no significant effect. Addition of EM over a wide concentration range to the synthetic pheromone ofI. typographus did not reduce the attraction of females of this species in the laboratory. A two-species pheromone interaction field test releasingI. typographus pheromone components (MB + cV) at 10–1000 male equivalents (ME) andI. duplicatus pheromone (Id + EM) at 0, 10–1000 ME in all possible combinations showed both positive intraspecific dose-response effects and an interspecific inhibition. Higher release rates of EM appeared to inhibitI. typographus, especially males. In a tree colonization model, the response of the two competing species to their respective pheromones show a good separation during the mass-attack with a small initial cross-attraction. It remains to be shown whether either of the two pheromone systems have in fact evolved in the present sympatry, or if they are an incidental effect of ancestry of these phylogenetically distantIps.     

Ozone in the urban southeastern United States

Ozone measurements (daily maximum values) from the Aerometric Information Retrieval System database are analyzed for selected sites, during 1980 to 1988, in southeastern USA. Frequency distributions, for most sites during most years, show a typical bell-shaped curve with the higher frequency around the yearly daily maximum ozone mean of about 100 to about 110 microg m(-3) (50-55 ppbv). Abnormal years in ozone concentration may skew the distribution as the mean shifts. A correlation of daily maximum ozone concentrations above 140 microg m(-3) (70 ppbv) between sites shows a division between the sites in the northern protion of the region and those in the southern portion of the region. Variations in ozone levels are well correlated over distances of several hundred kilometers, suggesting that high values are associated with synoptic scale episodes. An ozone exposure analysis also shows higher ozone exposures (250-300 ppm days) in the northerly sites as compared to the southerly sites (150-170 ppm days).     

The response of stream-dwelling fish to liming

The fish fauna in 22 limed and seven unlimed small streams was monitored using yearly electrofishing to assess the effects of liming on species occurrence and abundance. The liming techniques were divided into three main methods, lake liming, doser liming and wetland liming, to evaluate whether different strategies had different effects on the fish fauna. The predominant species at the investigated stations were salmonids, mainly brown trout (Salmo trutta) and Atlantic salmon (Salmo salar). Other species generally occurred in low numbers. The average number of fish species did not increase significantly after liming, which was probably due to recolonization difficulties caused by the frequent occurrence of migration obstacles in the streams. After liming the density of salmonids increased significantly, irrespective of the liming method. Other fish species showed no general increase, but in individual streams significant increases of European minnow (Phoxinus phoxinus) and bullhead (Cottus gobio) occurred. Some unlimed streams had acid spates with a pH below 6, which immediately lowered the numbers of salmonid parr. Other unlimed streams lost fish species progressively due to increasing acidification. pH, and probably increased levels of metals, were the major factors regulating the fish fauna. Few examples of biotic interactions were observed, but with an increase of Atlantic salmon parr after liming, brown trout abundances decreased in three streams.