Timing and size of blooms of the ctenophore Mnemiopsis leidyi in relation to temperature in Narragansett Bay, RI

The ctenophore Mnemiopsis leidyi is at the northern extreme of its geographic range in Narragansett Bay, an estuary on the northeast coast of the United States. Blooms have typically been observed in late summer and fall according to records from 1950 to 1979. We document an expansion of the seasonal range of this important planktonic predator to include springtime blooms during the 1980s and 1990s. This shift to an earlier seasonal maximum is associated with increasing water temperature in Narragansett Bay. Temperatures in spring have risen, on average, 2 °C from 1950 to 1999 with warm years being associated with the positive phase of the North Atlantic Oscillation. During 1999, M. leidyi appeared earlier in spring and was more abundant than during any previous year for which records are available. Changes in the seasonal pattern and abundance of this predator are likely to have important effects on planktonic ecosystem dynamics of Narragansett Bay. These include reduction of zooplankton abundance in spring followed by increases in size and frequency of summer phytoplankton blooms. Earlier blooms of M. leidyi may also reduce survival of eggs and larvae of fish because, as in 1999, they coincide with the period of peak spawning.     

Seasonal growth,density, reproductive phenology and agar quality of Gracilaria sordida (Gracilariales,Rhodophyta) at Mokomoko Inlet,New Zealand

Growth of mesh-enclosed Gracilaria sordida plants was determined monthly for one year at the Mokomoko mudflat, South Island, New Zealand. Growth of plants with permanent water cover was correlated with water temperature and was most rapid during summer months. Plants exposed at low tide grew only during early spring and late autumn. Bimonthly quadrat sampling of a mudflat population showed that all stages of the life cycle were present throughout the year. Spermatangial plant length and biomass were greatest in early spring; cystocarpic and tetrasporic plants were greatest in midsummer. Sterile plants were most numerous in the late summer. Agar yield showed little variation either seasonally or between different stages of the life cycle. Agar gel strengths for all life cycle stages were greatest at the time of peak plant size and abundance. Gels from spermatangial plants generally were weaker than those from other stages.     

Meiofaunal prominence and benthic seasonality in a coastal marine ecosystem

Summary The muds of a shallow (7 m) site in Narragansett Bay, Rhode Island contained higher abundances of meiofauna (averaging 17×10⁶ individuals per m² and ash free dry weight of 2.9 g/m² during a 3 year period) than have been found in any other sediment. The majority of sublittoral muds, worldwide, have been reported to contain about 10⁶ individuals per m². This difference is attributed primarily to differences in sampling techniques and laboratory processing.Extremely high meiofaunal abundances may have also occurred because Narragansett Bay sediments were a foodrich environment. While the quantity of organic deposition in the bay is not unusually high for coastal waters, this input, primarily composed of diatom detritus, may contain an unusually high proportion of labile organics. Furthermore, meiofauna could have thrived because of spatial segregation of meiofauna and macrofauna. While meiofauna were concentrated at the sediment-water interface, most macrofauna were subsurface deposit feeders. Macrofaunal competition with, and ingestion of meiofauna may thus have been minimized.The seasonal cycles of meiofauna and macrofauna were similar. Highest abundances and biomass were observed in May and June and lowest values in the late summer and fall. Springtime increases of meiofaunal abundance were observed in all depth horizons, to 10 cm. We hypothesize that phytoplankton detritus accumulated in the sediment during the winter and early spring, and that the benthos responded to this store of food when temperatures rose rapidly in the late spring. By late summer, the stored detritus was exhausted and the benthos declined.     

Relative effects of nutrient enrichment and grazing on epiphyte-macrophyte (Zostera marina L.) dynamics

The independent and interactive effects of nutrient concentration and epiphyte grazers on epiphyte biomass and macrophyte growth and production were examined in Zostera marina L. (eelgrass) microcosms. Experiments were conducted during early summer, late summer, fall, and spring in a greenhouse on the York River estuary of Chesapeake Bay. Nutrient treatments consisted of ambient or enriched (3× ambient) concentrations of inorganic nitrogen (ammonium nitrate) and phosphate. Grazer treatments consisted of the presence or absence of field densities of isopods, amphipods, and gastropods. epiphyte biomass increased with both grazer removal and nutrient enrichment during summer and spring experiments. The effect of grazers was stronger than that of nutrients. There was little epiphyte response to treatment during the fall, a result possibly of high ambient nutrient concentrations and low grazing pressure. Under low grazer densities of early summer, macrophyte production (g m^–2 d^–1) was reduced by grazer removal and nutrient enrichment independently. Under high grazer densities of late summer, macrophyte production was reduced by enrichment only with grazers absent. During spring and fall there were no macrophyte responses to treatment. The relative influence of epiphytes on macrophyte production may have been related to seasonally changing water temperature and macrophyte requirements for light and inorganic carbon.     

Growth of larval Pacific anchovy Engraulis japonicus in the Yellow Sea as indicated by otolith microstructure analysis

Larval Pacific anchovy Engraulis japonicus were sampled from coastal waters off the central west coast of Korea from June to November 1996. Using otolith microstructure analysis (daily growth increments), three cohorts (spring, early summer and late summer) were distinguished based on backcalculated spawning dates. Growth rates differed between cohorts, with higher growth rates for late-summer cohorts than either the spring or early-summer cohorts. Growth rate was positively related to surface water temperature, with an optimum temperature range of between 20 and 26° C occurring during the late summer (late July through to mid-September). The study highlights that early growth rates of Pacific anchovy are dependent on ecosystem (particularly water temperature) attributes during early life.     

LIFE CYCLE OF A STEPHANODISCUS SP. (BACILLARIOPHYTA)1

Studies of the life cycle of a centric diatom, tentatively identified as Stephanodiscus neoastraea Håkansson & Hickel, showed that sexual reproduction occurred every year in a freshwater lake (Lough Neagh, Northern Ireland). Male and female gametes were produced in cells below 55% of the maximum diameter during a 3–4-week period in late summer, following the return of nitrate concentrations above 10 μM NO_3-N. The frequency of sexual reproduction was linked to the cycle of diameter size reduction and regeneration. The times of largest decreases in cell diameter were during nutrient stress in summer and low light conditions in late autumn, rather than during the main spring growth period. So, environmental conditions (combined with the limited life-spans of individual cells) affected the rate of diameter reduction and, therefore, the length of the life cycle (3–4 years).     

Chronic infections of Haplosporidium nelsoni (MSX) in the oyster Crassostrea virginica

Oysters inhabiting areas enzootic for the parasite Haplosporidium nelsoni (MSX) are exposed to infective particles each summer, and it is often difficult to distinguish newly acquired lesions from older infections. To study long-term parasitism without the complication of new infections, MSX-infected oysters were moved from Delaware Bay to a disease-free area on the New Jersey coast. Because infections seen after the transfer were acquired in Delaware Bay during a known infective period, it was possible to determine how long oysters remained infected and how they were affected by chronic parasitism. Chronic infections displayed the same seasonal cycle (high levels in winter and late spring, low levels in summer and early spring) that occurs in enzootic areas with annual reinfection. Within individual oysters, chronic MSX became localized, relapsed into general infections, and then became localized again in a sequence that was probably controlled by temperature. Some experimental oysters survived with MSX for at least 4 years. Hemocytosis persisted in these oysters, and their poor condition suggested that chronically infected individuals would have lowered resistance to additional stress.     

Zooplankton densities in a Hydrilla infested lake

The number of individuals and species of zooplankton were sampled concurrently with Hydrilla biomass and water quality for one year in a small, eutrophic central Florida lake. Throughout the study, rotifer species and individuals dominated the zooplankton. The abundance of the zooplankton tended to remain high when Hydrilla biomass was at its seasonal low during late winter and early spring. When hydrilla growth increased in the late spring and summer months causing a decrease in total alkalinity, specific conductivity, water color, turbidity, orthophosphate and chlorophyll a concentrations; the abundance of the zooplankton declined. During this time, there was a shift from limnetic to littoral species, principally rotifers. Hydrilla growth did not affect the mean number of cladoceran or copepod species, but may have led to an increase in rotifer species.     

ALEXANDRIUM SATOANUM SP. NOV. (DINOPHYCEAE) FROM MATOYA BAY,CENTRAL JAPAN1

The gonyaulacoid dinofiagellate Alexandrium satoanum Yuki et Fukuyo sp. nov. is described from Matoya Bay, Pacific coast of central Japan. The species is distinctive in its conical epitheca with almost straight sides and dorsal concavity of the hypotheca. The plate formula is Po, pc, 4′, 6″, 6c, 10s, 5″″, and 2″″, including two accessory plates inside the sulcus. The apical pore plate is triangular and possesses an anterior attachment pore at the right margin. The first apical plate does not make contact with the apical pore plate and lacks a ventral pore. A posterior attachment pore lies at the center of the posterior sulcal plate. In Matoya Bay, vegetative cells occur as solitary cells or sometimes in pairs during late spring and early summer in low concentrations. In connection with this study, the following new combination is proposed: Alexandrium pseudogonyaulax (Biecheler) Horiguchi ex Yuki et Fukuyo comb. nov.     

Biological control of the black vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae) with entomopathogenic nematodes (Nematoda: Rhabditida)

Trials conducted under glasshouse conditions showed that control of Otiorhynchus sulcatus larvae in strawberry plants can be effective using Steinernema carpocapsae and Heterorhabditis megidis, given that temperature and moisture extremes are avoided. In field experiments, the double line T-Tape® drip irrigation system performed better than the single line T-Tape® system, effectively distributing the nematodes along and across strawberry raised beds, and placing them close to the root zone where O. sulcatus larvae feed. As soil temperatures are satisfactory for nematode infectivity from late spring to early autumn, nematode applications were aimed at late instar larvae during spring, and early instar larvae during summer. Late summer field treatment with S. carpocapsae induced 49.5% reduction of the early instar larvae, and field application of the same nematode species in late spring resulted in 65% control of late instar larvae. In the same trial, spring application of H. megidis caused 26% mortality of late instar larvae of O. sulcatus.     

Reproduction and growth of the Arctic hyperiid amphipod Themisto libellula Mandt

Summary The hyperiid amphipod, Themisto libellula, is abundant in Arctic seas and is an important prey for fish, birds and mammals. Characterization of its life cycle has been hampered by the lack of winter collections. In this study, that portion of the hyperiid population inhabiting the upper 30 m of the water column in Frobisher Bay was sampled periodically in winter, spring and summer during five consecutive years. In one year the winter and spring collections included large numbers of ovigerous females. These samples provide new information about timing of reproduction, size at maturity, fecundity, embryonic development, hatching, release and rate of growth of T. libellula in the Arctic. The average length of the ovigerous females was 23.3 mm. This and the summer growth rate of about 6 mm/month indicates that they can reproduce when one year old. Eggs are laid prior to early February, and although some young may be released from the marsupium as early as mid-March, most are liberated during April and May. The fecundity is significantly correlated with female length and an average 23 mm long individual had 275 embryos. The size-specific fecundity is similar to that of hyperiids from temperate and subtropical waters.     

Role of temperature in the germination ecology of three summer annual weeds

Summary Ambrosia artemisiifolia L., Chenopodium album L., and Amaranthus retroflexus L. are three summer annual weeds that occur in disturbed habitats. In nature, the peak germination season for A. artemisiifolia and C. album is in early to mid-spring, while in A. retroflexus the peak germination season is late spring to early summer. Furthermore, seeds of A. artemisiifolia germinate only in spring, while seeds of C. album and A. retroflexus germinate throughout the summer. In an attempt to explain the differential germination behavior of these three species in nature, changes in their germination responses to temperature during burial in a non-heated greenhouse from October 1974 to October 1975 were monitored. A high percentage of the seeds of all three species after-ripened during winter. Seeds of A. artemisiifolia and C. album germinated at temperatures characteristic of those in the field in early and mid-spring, but seeds of A. retroflexus required the higher temperatures of late spring and early summer for germination. Seeds of all three species germinated to higher percentages in light than in darkness. Non-dormant seeds of A. artemisiifolia that did not germinate in spring entered secondary dormancy. On the other hand, seeds of C. album and A. retroflexus that did not germinate when temperatures first became favorable for germination, did not enter secondary dormancy and, thus, retained the ability to germinate at summer field temperatures during summer. Thus, temporal differences in the germination behavior of these three species are caused by the differential reaction of the seeds to temperature during the annual temperature cycle.     

OCCURRENCE OF A EUROPEAN RED ALGA (SCHOTTERA NICAEENSIS) IN SOUTHERN AUSTRALIAN WATERS1

Schottera nicaeensis (Phyllophoraceae, Gigartinales), presently known only from the western Mediterranean Sea and the northeastern Atlantic coasts of Europe, is reported for the first time from the Melbourne region of Port Phillip Bay in southeastern Australia. The species is perennial in the Bay, although tetrasporophytes and cystocarpic plants are commonest in late spring and early summer. This seasonal pattern, and the vegetative habits of plants during the whole of the year, show similarities to populations described by other workers for Northern Hemisphere localities where comparable water temperature and daylength regimes obtain. The small Australian S. nicaeensis community is found at 5–9 m depths and is concentrated on lighthouse foundations adjacent to the main Port of Melbourne shipping channel. It is hypothesized that the species has recently been introduced into Port Phillip Bay, and a scenario for its possible means of import on ships is suggested.     

Year-class strength regulation in plaice (Pleuronectes platessa L.) on the Swedish west coast

Year-class strength of plaice (Pleuronectes platessa) has been studied over periods of 10 and 35 years, respectively, in two shallow sandy areas on the Swedish west coast. In one area, Gullmar Bay (N 58 ° 19 – W 11 ° 33), 0-group plaice were sampled quantitatively with a drop trap at 0–0.7 m depth and densities between 0.2 and 3.8 ind./m² were recorded in early summer. In the other area, Laholm Bay (N 56 ° 30 – W 12 ° 55), 0-group plaice were sampled semi-quantitatively in August with young-fish trawl at 1.5 m depths. Densities between 0.001 and 0.28 ind./m² were assessed.The effects of temperature and wind (in the winter and early spring) and predation (in early summer), on the recruitment of 0-group plaice were investigated. In Gullmar Bay high recruitment occurred after severe winters and in years when on-shore winds dominated during spring. No such correlations were found in Laholm Bay. In Gullmar Bay a significant inverse relationship was found between the density of O-group plaice in early summer and the biomass of brown shrimp (Crangon crangon) and the shore crab (Carcinus maenas), the main predators in the nursery area.The importance of physical and biological factors regulating recruitment in plaice are discussed.     

THE NATURAL LIFE CYCLE IN WILD POPULATIONS OF DIATOMA MONILIFORMIS (BACILLARIOPHYCEAE) AND ITS DISRUPTION IN AN ABERRANT ENVIRONMENT1

We studied how size variation in populations of Diatoma moniliformis Kütz. was influenced by environmental effects on the diatom life cycle. One of the two populations sampled monthly in the northern Baltic Sea grew under natural conditions; the other population was in a cooling water discharge channel of a nuclear power plant, where the temperature and flow rate of the water were artificially higher. The life cycle was synchronous at the natural site, with sexual reproduction occurring in the winter; most of the initial cells were found in March-April. After this, a reduction in cell size occurred, and the vegetative life cycle consisted of two parts. During the first part, cell volume decreased, whereas the surface area to volume ratio increased, and during the second part of the cycle, both of these parameters decreased. No direct evidence was found for the existence of a supra-annual life cycle in D. moniliformis, as convincing modes fm large cells were lacking in the size-frequency distributions. It was concluded from extrapolations of the data that the natural life cycle of D. moniliformis probably lasts 2 or 3 years. The changes in cell proportions during the life cycle fit well with annual growth cycles of D. moniliformis at the natural site (i.e. the cells had high surface area to volume ratios during the period of optimal growth in late spring [May-June]). At the site affected by cooling water discharge, the synchronization of the natural life cycle was disrupted, but some seasonal size variation did occur. Under natural conditions, auxosporulation is probably triggered by a combination of small cell size, low water temperature (0–3° C), and rapidly increasing light intensity or daylength in late winter to early spring. When these conditions were not met (e.g. at the heated site, the required low temperature was absent), auxosporulation did not occur simultaneously. This paper also presents scanning electron photomicrographs showing the typical shape and fine structure of the initial cell of D. moniliformis. These cells are semispherical in cross section, possess a pronounced curvature along the longitudinal axis, and are bent in the perualvar plane.     

Photosynthesis inCeratophyllum demersum. Carbon fixation rates in relation to the plants' physiological stage,and the contents of chlorophylland non-structural carbohydrates

Summary Since the role of the submerged aquatic macrophytes in the carbon cycle of lake Vechten (the Netherlands) is in study, attention is paid to several aspects of their productivity.Ceratophyllum demersum is a predominant macrophytic species in the littoral zone of this lake, occurring mainly from three to five metres depth. In situ measurements of its photosynthetic rate demonstrated a maximum in spring (May), followed by a distinct decrease early in summer and a second maximum in late summer. The spring maximum of the photosynthetic rate coincided with the maximum increase of plant biomass. Maximum biomass occurred in early autumn (August–September).Althoughinsitu measurements pointed to the upper plant portions (70 cm) as the most important with respect to photosynthetic activity, it was demonstrated under standard experimental conditions that lower portions might be equally active depending on the age of the plant. In the lake, light reduction with depth is one of the major causes in the commonly observed decrease in photosynthetic activity in lower plant parts.Comparison of the photosynthetic rates in plant tipsin situ and under standard experimental conditions indicated that in spring, both water temperature and the chlorophyll content of the plant limit photosynthesis. This was concluded since under experimental conditions (a) photosynthetic rate and chlorophyll content were strongly correlated during the first half of the growing season and (b) higher rates were measured thanin situ. In the subsequent stage, however, light and the distribution of non-structural carbohydrates (TNC) in the plant also play an important role.At the second half the growing season, the lower parts of plants growing in the lake lose gradually their buoyancy, caused by a deteriorating light climate resulting in a decreasing photosynthetic activity.     

Microclimate and production of peat moss Sphagnum palustre L. in the warm‐temperate zone

Sphagnum palustre L. is one of the few Sphagnum species distributed in the warm‐temperate zone. To elucidate the mechanisms that enable S. palustre to maintain its productivity under warm climatic conditions, we examined the temperature conditions and photosynthetic characteristics of this species in a lowland wetland in western Japan. Moss temperatures during the daytime were much lower than the air temperature, particularly during summer. The optimum temperature for the net photosynthetic rate was approximately 20°C, irrespective of the season, but summer and autumn samples maintained high rates at higher temperatures as well. The net photosynthetic rate at near light saturation was much higher during summer–autumn than during spring–winter. A model estimation in which net production was calculated from the photosynthetic characteristics and microclimatic data showed that both the low temperature of the moss colony and the seasonal shift in photosynthetic characteristics are among the mechanisms that enable this species to maintain its productivity under warm climatic conditions.     

Influence of spring and summer water temperature on brook charr, Salvelinus fontinalis, growth and age structure in the Ford River, Michigan

Synopsis The influence of late spring and summer water temperatures on brook charr, Salvelinus fontinalis, growth and age structure was evaluated from 1984 to 1991 in the Ford River, Michigan. Temperature was monitored and brook charr sampled for vital statistics from late May through September using fyke nets and weirs at four locations within a 25.8 km section of stream. Scale analysis was used to determine captured brook charr age, past length at age and relative annual growth rates. Late spring and summer water temperature patterns varied between years with the greatest variability occurring in May and June. Age and size structure also varied between years and was significantly related to temperature. Years with cooler late spring and summer temperature patterns were dominated by older (age 2 and 3), larger brook charr, while years with warmer spring and summer temperature patterns were dominated by younger (age 1), smaller brook charr. Spring and summer temperature did not appear to have a significant effect on the growth of age 0 or age 1 brook charr. However, temperature was negatively related to brook charr growth from age 2 on. As spring and summer water temperatures are critical to brook charr growth and survival, it is important that a streams thermal regime be considered when establishing management goals for this species.     

Population dynamics of the cattle tick Rhipicephalus (Boophilus) microplus in a subtropical subhumid region of Argentina for use in the design of control strategies

The population dynamics of Rhipicephalus microplus (Ixodida: Ixodidae) in northwest Argentina was analysed to support the design of strategic methods for its control. Both parasitic and non‐parasitic phases were studied. The seasonal activity of R. microplus in its parasitic phase was characterized by three peaks in abundance: the first in mid–late spring; the second in summer, and the third in autumn. The non‐parasitic phase of R. microplus was characterized by a long total non‐parasitic period observed after exposures of females from mid‐summer to early autumn, a short total non‐parasitic period observed after exposures of females from late winter to late spring, a short period of larval longevity in early and mid‐summer, and no hatch of the eggs produced by females exposed in mid‐ and late autumn and winter. Treatments of cattle administered during the period from late winter to late spring will act on small cohorts of R. microplus, preventing the emergence of larger generations in summer and autumn. A 17‐week spelling period starting in late spring and early summer will be necessary to achieve optimal control of R. microplus free‐living larvae. If spelling begins in mid‐ or late summer or in autumn, the required period will be 26–27 weeks.     

Experimental evaluation of planktonic respiration response to warming in the European Arctic Sector

The Arctic Ocean is the region on Earth supporting the steepest warming rate and is also particularly vulnerable due to the vanishing ice cover. Intense warming in the Arctic has strong implications for biological activity and the functioning of an Arctic Ocean deprived of ice cover in summer. We evaluated the impact of increasing temperature on respiration rates of surface marine planktonic communities in the European Arctic sector, a property constraining the future role of the Arctic Ocean in the CO₂ balance of the atmosphere. We performed experiments under four different temperature elevation regimes (in situ, +2, +4 and +6°C above the temperature of the sampled water) during cruises conducted in the Fram Strait region and off Svalbard during late fall–early winter, spring and summer. During late fall–early winter, where only three different temperatures were used, no response to warming was observed, whereas respiration rates increased in response to warming in spring and summer, although with variable strength.