Natural ingestion rates and grazing impact of the marine cladoceran Penilia avirostris Dana in Tolo Harbour, Hong Kong

The gut fluorescence method was used to study algal grazingby Penilia avirostris in a semiestuarine embayment. Grazingimpact estimated from ingestion rate and animal abundance revealedthat only {small tilde}1% of the algal biomass was grazed perday by the cladocerans.     

Embryonic development time of Penilia avirostris Dana, 1852 in a tropical bay in Brazil.

Development time of embryos in the brood pouch of the cladoceran Penilia avirostris Dana, 1852, was estimated by collecting zooplankton daily for 15 days in surface water of Guanabara Bay, Brazil. Each day the maturity stage of embryos of 90 parthenogenic females was noted. Total development time (egg to birth) varied from 2 to 3 days, the immature phase (stages I to IV) being generally longer (2 days) than intermediate and mature phases (1 day, stages V to XII). Similar results were obtained from Bottrell's equation, which takes water temperature into account.     

Feeding, growth and food conversion of the marine cladoceran Penilia avirostris

Ingestion and clearance rates, feeding behaviors and life historyvariables of the marine cladoceran Penilia avirostris were evaluatedover a range of food concentrations encountered in nature (0.01–3.0mm³ 1^–1 of Isochrysis galbana). Ingestion rates increasedand clearance rates decreased with increasing food concentration.No maximum feeding thresholds were observed over the range ofalgal concentrations offered. Weight-specific ingestion ratesdecreased with increasing body weight. Feeding behaviors suchas mandibular activity, abdominal claw rejections of cloggedfeeding structures and feeding appendage activity decreasedat a food level of 0.3 mm³ l^–1 of l. galbana. Peniliaavirostris had very poor survivorship at extremely low (0.01mm³ l^–1 and high (3.00 mm³ l^–1) food levels. Mortalitywas hardly affected at food levels of 0.03–1.0 mm³ l^–1Reproduction did not occur at food levels of     

The trophic role of the marine cladoceran Penilia avirostris in the Gulf of Trieste

The herbivory of the marine cladoceran Peniliaavirostris was studied in the Gulf of Trieste(Northern Adriatic) from June 1993 to December1994 using the gut fluorescence method. P. avirostrisoccurred from June to December, butreached its greatest abundance in the summer months.A significant correlation between the gut pigmentcontent and chlorophyll a concentration in thesurface layer was established. Observations with anepifluorescence microscope revealed that the guts werefilled with fluorescing nanoplankton and picoplankton(cyanobacteria). Quantitative estimates indicated thatP. avirostris grazed less than 5% of theavailable chlorophyll a in more than half of allmeasurements, but removed most of the availablechlorophyll a in the surface layer during someperiods in September. It can therefore be concludedthat P. avirostris, together with planktonicprotists, plays an important role within the microbialloop.     

Patterns of jellyfish abundance in the North Atlantic

A number of explanations have been advanced to account for the increased frequency and intensity at which jellyfish (pelagic cnidarians and ctenophores) blooms are being observed, most of which have been locally directed. Here, we investigate seasonal and inter-annual patterns in abundance and distribution of jellyfish in the North Atlantic Ocean to determine if there have been any system-wide changes over the period 1946–2005, by analysing records of the presence of coelenterates from the Continuous Plankton Recorder (CPR) survey. Peaks in jellyfish abundance are strongly seasonal in both oceanic and shelf areas: oceanic populations have a mid-year peak that is more closely related to peaks in phyto- and zooplankton, whilst the later peak of shelf populations mirrors changes in SST and reflects processes of advection and aggregation. There have been large amplitude cycles in the abundance of oceanic and shelf jellyfish (although not synchronous) over the last 60 years, with a pronounced synchronous increase in abundance in both areas over the last 10 years. Inter-annual variations in jellyfish abundance in oceanic areas are related to zooplankton abundance and temperature changes, but not to the North Atlantic Oscillation or to a chlorophyll index. The long-term inter-annual abundance of jellyfish on the shelf could not be explained by any environmental variables investigated. As multi-decadal cycles and more recent increase in jellyfish were obvious in both oceanic and shelf areas, we conclude that these are likely to reflect an underlying climatic signal (and bottom-up control) rather than any change in fishing pressure (top-down control). Our results also highlight the role of the CPR data in investigating long-term changes in jellyfish, and suggest that the cnidarians sampled by the CPR are more likely to be holoplanktic hydrozoans and not the much larger meroplanktic scyphozoans as has been suggested previously. Guest editors: K. A. Pitt & J. E. Purcell Jellyfish Blooms: Causes, Consequences, and Recent Advances     

Diel reproduction and vertical distributions of the marine cladocerans, Evadne tergestina and Penilia avirostris, in contrasting coastal environments

Evadne tergestina and Penilia avirostris were sampled duringseveral diel cycles in the well-mixed, turbid Inland Sea ofJapan and the more stratified, less turbid Gulf of Mexico shelf.Parthenogenetic female Evadne contained embryos with pigmentedeyes only at night, and apparently released neonates near dawnor in the morning. There was no significant diel vertical migrationin the Gulf of Mexico, and a ‘reverse’ migrationin the Inland Sea. Female Penilia could contain mature embryosat any time, but were most likely to do so at night. Peniliadid not migrate dielly, and in the Gulf of Mexico was concentratedin a nepheloid layer near the bottom.     

An indoor mesocosm system to study the effect of climate change on the late winter and spring succession of Baltic Sea phyto- and zooplankton

An indoor mesocosm system was set up to study the response of phytoplankton and zooplankton spring succession to winter and spring warming of sea surface temperatures. The experimental temperature regimes consisted of the decadal average of the Kiel Bight, Baltic Sea, and three elevated regimes with 2°C, 4°C, and 6°C temperature difference from that at baseline. While the peak of the phytoplankton spring bloom was accelerated only weakly by increasing temperatures (1.4 days per degree Celsius), the subsequent biomass minimum of phytoplankton was accelerated more strongly (4.25 days per degree Celsius). Phytoplankton size structure showed a pronounced response to warming, with large phytoplankton being more dominant in the cooler mesocosms. The first seasonal ciliate peak was accelerated by 2.1 days per degree Celsius and the second one by 2.0 days per degree Celsius. The over-wintering copepod populations declined faster in the warmer mesocosm, and the appearance of nauplii was strongly accelerated by temperature (9.2 days per degree Celsius). The strong difference between the acceleration of the phytoplankton peak and the acceleration of the nauplii could be one of the “Achilles heels” of pelagic systems subject to climate change, because nauplii are the most starvation-sensitive life cycle stage of copepods and the most important food item of first-feeding fish larvae. Priority programme of the German Research Foundation—contribution 3.     

Feeding selectivities and food niche separation of Acartia clausi, Penilia avirostris (Crustacea) and Doliolum denticulatum (Thaliacea) in Blanes Bay (Catalan Sea, NW Mediterranean)

Selectivity-size spectra, clearance and ingestion rates andassimilation efficiencies of Acartia clausi (Copepoda), Peniliaavirostris (Cladocera) and Doliolum denticulatum (Doliolida)from Blanes Bay (Catalan Sea, NW Mediterranean) were evaluatedin grazing experiments over a wide range of food concentrations(0.02–8.8 mm³ L^–1 plankton assemblages from BlanesBay, grown in mesocosms at different nutrient levels). Acartiaclausi reached the highest grazing coefficients for large algae>70 µm (longest linear extension), P. avirostris forintermediate food sizes between 15 and 70 µm, and D. denticulatumfor small sizes from 2.5 to 15 µm. Penilia avirostrisand D. denticulatum acted as passive filter-feeders. Acartiaclausi gave some evidence for a supplementary raptorial feedingmode. Effective food concentration (EFC) decreased linearlywith increasing nutrient enrichment for D. denticulatum andfollowed domed curves for A. clausi and for P. avirostris withmaximum values at intermediate and high enrichment levels, respectively.Clearance rates of crustacean species showed curvilinear responseswith narrow modal ranges to increasing food concentration. Clearancerates of D. denticulatum increased abruptly and levelled intoa plateau at low food concentrations. Mean clearance rates were13.9, 25.5 and 64.1 mL ind.^–1 day^–1, respectively.No clearance could be detected for A. clausi at food concentrations<0.1 mm³ L^–1 and for P. avirostris at food concentrations     

Spatial and temporal variations of Penilia avirostris and Evadne tergestina (Crustacea,Branchiopoda) in a Tropical Bay,Brazil

We analysed monthly samples collected in Guanabara Bay, with a conical net of 200 m mesh during 1985. The bay was divided into three areas: an outer region (area A), influenced by oceanic waters; an inner region (area C), influenced by fluvial inflow; and a transition region (area B) with intermediate features. Penilia avirostris and Evadne tergestina were observed in the three areas, with greatest densities, however, in the outermost region, which had the highest salinities and lowest temperatures. Penilia avirostris was more abundant in summer (March), a period with the greatest relative densities of nanoplankton. Evadne tergestina was also abundant in summer, but its peak fell in November, a period with a relative increase in microphytoplankton density in the bay. The two species disappeared in winter: Penilia avirostris was absent from May to August, whereas Evadne tergestina disappeared in August and September.     

Alien vascular plants in Iceland: Diversity,spatial patterns,temporal trends,and the impact of climate change

The present study provides first comprehensive and up-to-date results on alien plant taxa in Iceland since 1967. We evidenced the presence of 336 alien vascular plant taxa, including 277 casuals and 59 naturalised taxa, two being invasive. The distribution of the alien flora exhibits a clear spatial pattern showing hotspots of occurrence and diversity within areas of major settlement centres. Altitude above sea level and temperature-related variables proved to be the most important factors shaping alien plant distribution in Iceland. Predictive modelling evidenced that arctic areas of Iceland and the Central Highlands are under serious risk of alien plant invasion due to climate change. The results provide crucial information for alien and invasive plant management and contribute data for meta-analyses of invasion processes worldwide.     

Phytoplankton and chemico-physical parameters of the Scardovari Lagoon (Po Delta,North Adriatic Sea) during 1991 and 1992

Abstract

During research directed towards the employment of the biological resources of the North Adriatic lagoons, from January 1991 to December 1992, in both tidal phases, a survey was carried out on the phytoplankton and the chemico-physical parameters of the Scardovari lagoon. Data analyses allowed two different areas to be distinguished: one inner, which was generally characterized by high phytoplanktonic densities (St. 3–4), the other outer, which was more influced by marine load (St. 1–2). Photosynthetic picoplankton was dominant in terms of cell number in most samples. Phytoplanktonic fraction >2 μm was represented mainly by diatoms, which showed the higher species number. During the sample observation, some dinoflagellates, considered toxic or potentially toxic, were found. Their presence was important because of their effect on the bivalve mollusc cultures.     

Mass occurrence of an introduced crustacean (Caprella cf. mutica) in the south-eastern North Sea

The caprellid amphipod Caprella mutica is indigenous to coastal waters of north-east Asia and was first recorded in European waters in 1995. We now detected mass occurrences of > 3000 individuals per m² in harbours of the two islands of Sylt and Helgoland in the German Bight, North Sea. Currently, Caprella mutica seems to be restricted to artificial hard substrata but we expect it to become a new species in natural hard bottom assemblages of that region as well.     

A foe in woe: American mink (Neovison vison) diet changes during a population decrease

The invasive American mink has been a component of Iceland's fauna since the 1930s. Hunting statistics indicate that until 2003 the population size was increasing, but thereafter decreased rapidly. The Icelandic marine environment has experienced various changes in recent years, including rising sea temperature and sand-eel collapse followed by seabird recruitment failure and population declines. Furthermore the arctic fox population has increased at least six-fold in the last three decades. Mink stomach content analysis in the period 2001–2009 revealed diet changes, and signs of reduced prey availability for this generalist predator, that were most significant in males. The most marked shift in composition was a decrease in consumption of birds. Our findings suggest that climate events, together with competition with increasing numbers of arctic foxes over terrestrial food, contributed to the sharp reduction in the mink population from 2004 and onwards. Despite their generalist behaviour, mink have apparently failed to respond fully to these environmental changes, and this susceptibility may benefit attempts to control their numbers. The results are relevant to the ability of top predators in general to cope with diverse ecosystem alterations triggered by climate change.     

Changes in the macrozoobenthos of the intertidal zone at Helgoland (German Bight, North Sea): a survey of 1984 repeated in 2002

Changes in the presence and absence of invertebrates as well as in species conspicuousness were documented in a rocky intertidal community based on surveys in 1984 and 2002. In 2002 six vertically and/or morphologically different stations of an intertidal platform were sampled. Five of these six habitats had already been surveyed in 1984. Replicating precisely the method of the first assessment, presence/absence changes as well as changes in species conspicuousness of 83 invertebrate species were documented, indicating that this intertidal community changed considerably during the 18-year interval. Compared with the study in 1984, 27 species newly appeared, whereas 32 species disappeared. Furthermore, 16 species increased in conspicuousness, whereas eight invertebrates decreased. The total number of species in 2002 was 154 versus 158 in 1984. Although algal species were not recorded as thoroughly as invertebrates, a massive decline in cover of Halidrys siliquosa was noted. Conversely, two invasive algal species became established after 1984, Sargassum muticum (since 1988), a cosmopolitan fucoid alga that prefers shallow subtidal areas for colonization, and Mastocarpus stellatus (introduction in the 1980s) that particularly colonized areas in the mid intertidal. In 1984 the mid intertidal zone was dominated by the brown alga Fucus serratus, whereas in 2002 the blue mussel Mytilus edulis and the periwinkle Littorina littorea were the most conspicuous organisms. Annual mean sea surface temperature (BAH measurements) warmed by 1.1°C over the past four decades. Range-related community shifts, introductions of non-indigenous species and the input of pollutants, are considered to explain long-term ecological changes in the invertebrate community at Helgoland.     

Spread of Microcosmus squamiger (Ascidiacea: Pyuridae) in the Mediterranean Sea and adjacent waters

The Mediterranean Sea is subject to an ever-increasing arrival of non-indigenous marine organisms. Microcosmus squamiger is a solitary ascidian that inhabits shallow rocky littoral habitats. It probably originated in Australia and it has shown great invasive potential in other parts of the world. In the Mediterranean, M. squamiger has only been reported at a few sites in Spain and Italy. However, the closely related species Microcosmus exasperatus has been reported in several areas of the western Mediterranean. As these species can be easily confused, we re-examined most of the material from previous studies and our personal collections. In addition, sampling was done at several sites along the western Mediterranean and Atlantic coasts. The results showed that the majority of the M. exasperatus reports correspond to M. squamiger, and that M. squamiger is common on the Atlantic shores. This suggests that M. squamiger has entered the Mediterranean through the Gibraltar Strait, while the restricted distribution in the eastern Mediterranean of M. exasperatus suggests that this species is probably a Lessepsian migrant. In the Mediterranean Sea, M. squamiger has the ability to occupy extensive areas of hard substrata and to outcompete native species. Further studies are necessary to assess what impacts this invasive species have on native communities.     

Frequency of Buddleja davidii Franch. (Buddlejaceae) in Germany along ecological gradients

In Central Europe as in most other temperate regions of the world, Buddleja davidii has become a very successful invader. A thorough observation, documentation and analysis of the spread of invasive species is the precondition for the understanding of invasion processes. Therefore, I documented the occurrence of the species along a west–east transect as well as an altitudinal transect, and I tried to reconstruct the spread of the species in the course of the last decades along railroad areas, which have proved to be the most favorized habitats for colonization of Buddleja. Additionally, a literature review is given on its general spread and distribution in Germany. Based on the investigation of 52 stations, the results show that the species, in Germany, has its optimum in the Rhein-Ruhr- and the Rhein-Main-area, that its abundance significantly decreases from west to east and with increasing altitude. A literature review combined with own investigations shows, that it was very successful in Germany on ruins of World War II but decreased and sometimes totally disappeared in cities of East Germany and of the altitudinal higher regions of Germany, i.e. also in many towns of South Germany. In West Germany, the recent spread started about three decades ago and is still in process. As cold winters seem to be the limiting factor for the spread of Buddleja, even an accelerated spread of this species and perhaps a loss of its ruderal character can be expected, considering the progress of climate change.     

Long-term changes in the macrozoobenthos around the rocky island of Helgoland (German Bight,North Sea)

The paper briefly summarizes what is known about long-term changes (facts, causes, consequences) in the macrozoobenthos of intertidal and subtidal hard-bottom communities around the island of Helgoland (German Bight, North Sea). There is increasing observational evidence that these communities (spectrum and abundances of species) are changing on a long-term temporal scale. The reasons are diverse and mainly anthropogenic. A shift in North Sea climate towards more oceanic conditions may be among the most important factors driving the recent changes in species spectrum. Many of the species which have been recorded as new to the Helgoland area during the past decade are southern (oceanic) species which may be considered as indicators of a warming trend.Communicated by K. Wiltshire     

A novel spermatozoan ultrastructure in the shrimp Hippolyte obliquimanus Dana, 1852 (Decapoda: Caridea: Hippolytidae)

The aim of this study was to describe and illustrate the morphology of the spermatozoon of the Western Atlantic shrimp, Hippolyte obliquimanus. Individuals were sampled from Itaguá Beach (Ubatuba, southern Brazil). The male reproductive system was dissected and morphological analysis was undertaken using a stereomicroscope, a light microscope, and transmission electron and scanning electron microscopes. When viewed from the nuclear or acrosomal poles, each spermatozoon has many translucent radiating arms (about 20) from a denser cell body, while laterally the cell body and arms resemble a “cnidarian medusa”, with all the arms projecting away from the bell-like cell body. This sperm morphology is distinct from the “thumbtack”-shaped spermatozoa observed in the majority of carideans but has similarities to the spermatozoa of Rhynchocinetes spp. The morphology of sperm of several species of the genus Hippolyte resembles the spermatozoon of H. obliquimanus with the presence of posterior nuclear arms, but it is necessary to study other Hippolyte species to place these arms in the context of the genus.     

Latitudinal variation of life-history traits of an exotic and a native impatiens species in Europe

Understanding the responses of invasive and native populations to environmental change is crucial for reliable predictions of invasions in the face of global change. While comparisons of responses across invasive species with different life histories have been performed before, comparing functional traits of congeneric native and invasive species may help to reveal driving factors associated with invasion. Here we compared morphological functional trait patterns of an invasive species (Impatiens parviflora) with its congeneric native species (I. noli-tangere) along an approximately 1600 km European latitudinal gradient from France (49°34′N) to Norway (63°40′N). Soil nitrogen was recorded during six weeks of the growing season, and light, soil moisture, and nutrient availability were estimated for each sampled population using community weighted means of indicator values for co-occurring species. Temperature data were gathered from nearby weather stations.Both the native and invasive species are taller at higher latitudes and this response is strongest in the invasive species. Seed mass and number of seeds per capsule increase in I. noli-tangere but decrease in I. parviflora towards higher latitudes. Surprisingly, plant height in the invasive I. parviflora decreases with increasing soil nitrogen availability. The latitudinal pattern in seed mass is positively related to temperature in I. noli-tangere and negatively in I. parviflora. Leaf area of both species decreases with increasing Ellenberg indicator values for nitrogen and light but increases with increasing soil moisture. Soil nitrogen concentrations and Ellenberg indicator values for nitrogen have significant positive (I. noli-tangere) and negative (I. parviflora) effects on the number of seeds per capsule. Our results show that the native I. noli-tangere has efficient reproduction at its range edge while the invasive I. parviflora shows a marked decrease in seed size and seed number per capsule. These patterns are unrelated to the growth and obtained size of the plants: even low soil nitrogen availability in the north seemed not to limit plant growth and size. Our results suggest that the invasive I. parviflora tends to become more invasive at lower latitudes by producing heavier seeds and more seeds per capsule.     

Reappearance of Eumarcia fumigata (G.B. Sowerby II, 1853) (Bivalvia: Veneridae) into the Swan River,Western Australia

ABSTRACT

The venerid bivalve Eumarcia fumigata was a common species in Western Australia (WA) during the Pleistocene, where it was distributed as far north as Shark Bay. It became extinct in WA as the climate changed several thousand years ago but remains common in eastern Australia from southern Queensland to South Australia and Tasmania. The species has recently reappeared in the Swan River, probably due to shipping movements. Of the > 60 marine and estuarine species introduced into WA it is only the third confirmed introduction from eastern Australia, and the first that is a reappearance in the Swan River of a species present in the geological past. The present reappearance of E. fumigata, and the introduction of other species, has been made possible by the removal of a rocky bar at the mouth of the estuary and the creation of more marine conditions in the lower Swan estuary.