Seasonal occurrence and abundance of caridean shrimp larvae at Helgoland,German Bight

Plankton samples were collected from January 1985 to January 1986 three times per week at Helgoland to study seasonal occurrence and abundance of caridean shrimp larvae. A total of eleven species were obtained. Ninety-one % of all larvae collected during the sample period belonged toCrangon crangon L. andCrangon allmanni Kinahan, 6% toPhilocheras trispinosus Hailstone and 3% to the remaining eight species. Collections were generally dominated byC. crangon larvae. However,C. allmanni larvae were most abundant in June coinciding with hatching activities of the population near Helgoland.C. allmanni was observed to have the highest density of all species with approximately 8 larvae per m³. Larvae ofEualus occultus (Lebour),Eualus pusiolus (Kroyer),Hippolyte varians Leach andAthanas nitescens Leach were most likely released by populations inhabiting the rocky intertidal zone around Helgoland. The presence ofProcessa modica Williamson & Rochanaburanon andProcessa nouveli holthuisi Al-Adhub & Williamson in the German Bight was verified by observations of a series of different developmental stages. Larvae of the rare speciesCaridion steveni Lebour were also recorded. The observed shrimp species were placed into three different groups with respect to their seasonal occurrence. Possible advantages of the timing of larval dispersal relative to predation and food availability are given. The results on seasonal occurrence and relative abundance are discussed in relation to environmental factors (temperature, salinity) as well as to the geographical distribution of the species.     

Die Biomasse mariner Makrobenthos-Gesellschaften im Einflußbereich der Klärschlammverklappung vor der Elbemündung

The macrofauna of a dumping area in the eastern part of the German Bight (North Sea) was investigated in July, August and November, 1978 at five stations situated on a transect including central and peripheral areas of the dumping region. Abundance and biomass (ash free dry weight) of the macrofauna and its variation from July to November were analysed as well as the biomass of different taxa. Molluscs dominated over polychaetes, crustaceans and echinoderms. A positive correlation seemed to exist between mud content and biomass at the peripherally situated stations. In the central sewage sludge area, however, the biomass values were reduced. In late autumn the biomass decreased in the entire area due to the death ofDiastylis rathkei, Abra alba andPectinaria koreni. These species were replaced by the molluscNucula turgida and polychaeteNephtys hombergii. In autumn the biomass values also showed a distinct minimum at the central stations.     

Different zooplankton structures in the German Bight

In August 1982, a net of 48 stations with altogether 208 samples was investigated in the eastern German Bight with respect to temperature, salinity, as well as the amount and species composition of the mesozooplankton (>80 μm). The data were arranged into different structures by means of a cluster analysis. Four different clusters were found: (a) a “Wadden sea water” with few holoplankton organisms but a higher amount of spionid larvae; (b) a “German Bight water” with a maximum occurrence of turbellaria (Alaurina composita) and medium concentrations of copepods; (c) a mixing area between these two water masses with highest amounts ofOikopleura dioica, Temora longicornis, Acartia sp., mussel larvae and larvae of the spionid worms; (d) a “North Sea water” mass with highest concentrations ofPseudocalanus elongatus, Paracalanus parvus undOithona similis. The differences in the concentrations of the species mentioned between the four clusters were significant on the 0.1%-level.     

An alternative mode of larval development inScoloplos armiger (O. F. Müller, 1776) (Polychaeta,Orbiniidae)

During a three-year plankton monitoring at the island of Helgoland (German Bight, North Sea), pelagic larvae ofScoloplos armiger (O. F. Müller, 1776) were observed to occur regularly from February to April. Up to the present day, only benthic development within egg cocoons has been described (Anderson, 1959). Planktonic larvae comprise early, ovoid trochophores up to advanced stages with 11 setigers. The main morphological difference between the two larval types is the more numerous differentiation of lateral cilia by the pelagic larvae. Annual alterations in appearance and abundance suggest that reproduction is correlated with water temperature.     

Zur Ökologie der Polychaeten des Helgoländer Felslitorals

The ecology and distribution of the polychaetes inhabiting the rocky interidal zone of the island of Helgoland (German Bight, North Sea) were studied at five ecologically different stations.Scolelepis squamata, Microphthalmus sczelkowii andOphryotrocha gracilis were the only typical intertidal polychaetes observed. Of the 53 polychaete species documented, eight were recorded for the first time in the German Bight. Two species and one subspecies had not been described previously. The following invironmental variables were measured and, where possible, related to the occurrence of the polychaetes: pH, redox potential, O₂ diffusion rate, temperature, salinity, particle-size distribution, and amount of organic particles. In the investigation area the number of species and their frequency maxima increase horizontally from east to west. This appears to be due to the increasing diversity of microhabitats in the substratum, as well as to conditions of O₂ supply or H₂S presence. Vertically, the number of species increases with water depth. The potential effects of temperature and salinity on the distribution patterns are discussed.     

Dinoflagellate resting cysts as factors in phytoplankton ecology of the North Sea

The occurrence and distribution of dinoflagellate resting cysts were investigated at 11 locations in the south-eastern part of the North Sea. Twenty-six known cyst species and 7 unknown cyst types, which may act as seed population for planktonic dinoflagellate blooms, have been recorded for the first time in the area. The most common cysts in recent sediments were those ofScrippsiella trochoidea, Zygabikodinium lenticulatum, Peridinium dalei, Scrippsiella lachrymosa, Protoceratium reticulatum, Protoperidinium denticulatum, andP. conicum. At all stations,S. trochoidea dominated the cyst assemblages with a maximal abundance of 1303 living cysts/cm³ in the uppermost half centimetre. Cysts of the potentially toxic dinoflagellatesAlexandrium cf.excavatum andA. cf.tamarense were scarce. In the upper 2-cm layer of sediment, dinoflagellate cysts were found in concentrations of 1.8 up to 682 living cysts/cm³. Empty cysts constituted 22–56% of total cyst abundance. The comparative distribution of the cysts showed a general increase in abundance from inshore sites to the offshore area, whereby sandy stations exhibited the lowest cyst abundance and diversity. The wide distribution of living and empty cysts ofScrippsiella lachrymosa suggests that its motile form, which has not been officially recorded in the area until now, is a common plankton organism in German coastal waters. The relatively high abundance of cysts in recent sediments demonstrates the potential importance of benthic resting stages for the initiation of dinoflagellate blooms in the study area.     

Beiträge zum Mesozooplankton des Nordsylter Wattenmeers

Contributions to the mesozooplankton of the northern Wadden Sea of Sylt. From June 1975 to June 1976 temperature, salinity, mesozooplankton (>76 µm), phytoplankton and seston (dry weight, particulate organic carbon and nitrogen) were measured at different stations in the northern Wadden Sea of Sylt (German Bight, North Sea). Maxima of the planktonic copepods, which form the biggest part of the zooplankton, occurred in the summer months from June to September. Larval development from nauplii to adults was observed inAcartia clausi, Acartia discaudata, Centropages hamatus andTemora longicornis; generation times ranged from 3 (Temora longicornis) to 7 1/2 weeks (Centropages hamatus) at ca. 20 °C. Organic carbon produced by zooplankton was about 0.4 g C m^–3 year^–1 and zooplanktonic carbon decomposed in the area studied amounted to about 1.4 g C m^–3 year^–1. Meroplanktonic larvae made up ca. 60 % of the organic carbon produced by zooplankton, indicating great influence of the benthos on the water column in this very shallow part of the German Bight.     

Biotoxic activity in the Mucorales

The toxigenicity of representatives of 15 species of Mucorales (Absidia glauca, Actinomucor elegans, Cunninghamella elegans, Helicostylum piriforme, Mortierella isabellina, Mortierella (Mucor) rammaniana, Mucor hiemalis, Mucor mucedo, Mucor spinosus, Phycomyces blakesleeanus, Rhizopus oligosporus, Rhizopus stolonifer, Syncephalastrum racemosum, Thamnidium elegans, Zygorhynchus moelleri) towards the larvae of brine shrimp (Artemia salina) and the growth of pea seedlings (Pisum sativum) and tobacco plants (Nicotiana tabacum) was evaluated. The fungi were cultivated on malt extract agar and aqueous solutions of the cultures were tested.Thamnidium elegans showed a marked toxic action towards brine shrimp (mortality: 74.1%) andPhycomyces, Actinomucor andSyncephalastrum were only weakly toxic. Length and weight of stems of pea seedlings were moderately reduced by extracts ofAbsidia, Cunninghamella, Zygorhynchus andThamnidium and to a lesser degree byMucor spinosus. Cunninghamella andMucor spinosus also inhibited the development of pea hypocotyls. The length of tobacco stems was reduced byMortierella ramanniana, Rhizopus stolonifer andCunninghamella elegans. Wilting or other toxic phenomena were never observed with both test plants. Considering the present results and data from literature it is suggested that species of Mucorales have only a weak toxigenicity.     

Studies on the life cycle and reproduction of the parasitic amphipodHyperia galba in the North Sea

The structure of aHyperia galba population, and its seasonal fluctuations were studied in the waters of the German Bight around the island of Helgoland over a period of two years (1984 and 1985). A distinct seasonal periodicity in the distribution pattern of this amphipod was recorded. During summer, when its hosts—the scyphomedusaeAurelia aurita, Chrysaora hysoscella, Rhizostoma pulmo, Cyanea capillata andCyanea lamarckii—occur in large numbers, supplying shelter and food, a population explosion ofH. galba can be observed. It is caused primarily by the relatively high fecundity ofH. galba which greatly exceeds that of other amphipods: a maximum of 456 eggs was observed. The postembryonic development is completed in the medusae infested; only then are the young able to swim and search for a new host. The smallest fréely-swimming hyperians obtained from plankton samples were 2.6 mm in body size. The size classes observed as well as moult increment and moulting frequencies in relation to different temperatures suggest that two generations are developed per year: a rapidly growing generation in summer and a slower growing generation in winter that shifts to a benthic mode of life and hibernation. For short periods, adult hyperians may become attached to zooplankters other than scyphomedusae. However, when releasing the progeny, they are dependent on the presence of these coelenterates. Apparently, a host specificity does not exist. During daytime, the hyperians seem to avoid a host change; only 0.2% of all the individuals sampled in the plankton during the day were not associated with medusae. The heavy infestation of medusae by this crustacean leads to a weakening and a progressive breakdown of these important predators on fish larvae.H. galba occupies a specific position in the marine food web which is discussed in detail.     

Trace Metals in Mesozooplankton of the North Sea: Concentrations in Different Taxa and Preliminary Results on Bioaccumulation in Copepod Collectives (Calanus finmarchicus/C. helgolandicus)

Trace metals (Cd, Cu, Zp, Pb, Ni) were determined in different zooplankton taxa to assess their role in the biogeochemical cycle in the North Sea. Results of semi-static bioaccumulation experiments on board ship using collectives of Calanus finmarchicus/C. helgolandicus were in agreement with a net accumulation strategy, thus meeting an inevitable precondition for their utilization as biomonitors. Cd, Cu and Zn concentrations in field samples of zooplankton displayed a pronounced variability between taxa, with Cd ranging from 0.13 mg kg-1 (d.w.) in fish larvae to 5I mg kg-1 in hyperiid amphipods. Almost no information is available about metal requirements of copepods. However, most of our and worldwide reported Cu concentrations in calanoid copepods (6-22 mg kg⁻¹) coincided with estimates of enzymatic requirements of decapod crustaceans. Cd levels in Calanus collectives increased significantly from 0.68 mg kg-1 in the German Bight to 11 mg kg⁻¹ at some stations around Scotland above 59° N, in line with literature data reported for benthic decapod crustaceans.     

Larval development of two species of barracuda,Sphyraena guachancho andS. tome (Teleostei: Sphyraenidae), from southeastern Brazil

Morphological development of barracudas (Sphyraena guachancho andS. tome) is described, based on larval and juvenile specimens collected in the southeast Brazilian Bight. Preflexion larvae of the two species are similar, butS. tome larvae can be distinguished from those ofS. guachancho by having small melanophores on the midbrain and a row of melanophores along the ventral midline of the lower jaw and isthmus. Flexion and postflexion larvae ofS. tome are more slender than those ofS. guachancho. Morphology and pigment patterns ofS. tome are similar to those ofS. borealis from the north Atlantic. whereasS. guachancho larvae are similar toS. barracuda in having a fusiform body, advanced position of the pelvic fins and a heavily pigmented tail region, but differ in having a fleshy tip on the lower jaw in postflexion and juvenile stages.     

The taxonomy ofVaccinium sectionHemimyrtillus

In view of their awnless stamens and pseudo-10-loculed berries borne on short racemes several NE Asian species ofVaccinium (includingV. hirtum, V. smallii, V. versicolor, andV. yakushimense) were transferred toVaccinium sectionCyanococcus by Sleumer (1941). Subsequently, however, Stevens (1969) and Vander Kloet (1972, 1981) argued on the basis of further study that these taxa should be transferred instead to sectionHemimyrtillus. Phenetic analyses of data from representatives of sectionsCyanococcus andHemimyrtillus, including NE Asian taxa transferred by Sleumer, demonstrate the distinctness of the two sections and support the assignment of the NE Asian taxa to sectionHemimyrtillus. A revised taxonomic treatment and key to the species ofVaccinium sectionHemimyrtillus is provided.     

Hybridisation,genomic constitution and generic delimitation inElymus s. l. (Poaceae: Triticeae)

Intergeneric crosses were made between representatives of the genomically-defined generaElymus, Agropyron, Elytrigia, Pseudoroegneria, andThinopyrum. The genomic constitution ofElytrigia repens, the type species ofElytrigia, is shown to be SSH, a genomic combination otherwise found only inElymus. The S genome ofPseudoroegneria has almost always a dominant influence on the morphology of the taxa of which it is a component.Wang (1989) showed that the J genome inThinopyrum and the S genome have considerable homoeology, with a mean c-value of 0.35 in diploid SJ hybrids. A genetic coherence from S to SJ^e, J^e, J^eJ^b, and J^b can be expected, agreeing with the continuous morphologic variation pattern observed. Because of the absence of morphological discontinuities between the taxa,Pseudoroegneria (S),Elymus (SH, SY, sometimes with additional genomes),Elytrigia (SSH, SSHX), andThinopyrum (SJ, SJJ, J) are best treated as a single genus,Elymus, following the generic concept ofMelderis in Flora Europaea and Flora of Turkey. The basic genomic constituents ofElymus will then be the S and/or J genomes.Agropyron, with diploids, tetraploids, and hexaploids based on the P genome is morphologically distinct from other genera inTriticeae. In a few species ofElymus andPseudoroegneria, a P genome is an additional constituent. In these cases the P genome has a negligible morphological influence. Therefore, it seems reasonable to maintainAgropyron as a separate genus.     

Parasite transfer from crustacean to fish hosts in the Lübeck Bight,SW Baltic Sea

Four helminth parasites out of 19 species found in the Lübeck Bight, Baltic Sea, were chosen for investigations on the transfer from invertebrate to small-sized fish hosts: larvae of the tapewormsSchistocephalus sp. andBothriocephalus sp. (Cestoda) living in planktonic copepods as primary hosts;Podocotyle atomon (Digenea) andHysterothylacium sp. (Nematoda) were found in benthic crustaceans, especiallyGammarus spp. These hosts were the prey of 3 gobiid fishes,Gobiusculus flavescens (feeding mainly on plankton),Pomatoschistus minutus (preferring benthos), andP. pictus (feeding more on plankton than benthos). Because the fishes selected smaller sizes of crustaceans, they ingested all stages of the copepods but only the smaller-sized groups of gammarids which were often less infested by parasites. In order to evaluate the probability for a fish to be parasitized by a helminth, an infestation potential index (IP) was calculated.Podocotyle atomon andHysterothylacium sp. revealed an IP which was far lower in gobies than expected when the prevalences of the previous hosts were taken into consideration. The IP of tapeworm larvae was mainly influenced by the feeding pressure of the gobiid predators, which might change with developmental stage and season. It is concluded that parasite transfer to the next host decreases when sizes of prey and predator differ only moderately. This mechanism can reduce the numbers of parasites transferred to less suitable or wrong hosts.     

Differential recruitment of bivalve species in the northern Wadden Sea after the severe winter of 1995/96 and of subsequent milder winters

High recruitment of the bivalves Cerastoderma edule, Mytilus edulis, Macoma balthica and Mya arenaria in summer after severe winters is an often reported phenomenon in the Wadden Sea. After the severe winter of 1995/96 however, only Cerastoderma and Mytilus followed this pattern in the Sylt-R?m? Bight. Repeated sampling of Cerastoderma, Macoma and Mya following a severe (1995/96), a moderate (1996/97), and a mild winter (1997/98) revealed that early recruitment was highest after the mild winter. In Cerastoderma the eventual high recruitment at the end of summer 1996 was caused by reduced benthic mortality. Low recruitment of Macoma and Mya after the severe winter may have been caused by a higher susceptibility to epibenthic predation and/or a higher susceptibility to passive re-suspension than in Cerastoderma and Mytilus. In all cases, post-settlement processes were decisive for reproductive success. Received in revised form: 7 May 2001 Electronic Publication     

Lead and cadmium contents in selected macrofauna species from the Dogger Bank and the eastern north Sea

Lead and cadmium concentrations were measured in the polychaetesNephtys hombergi andN. caeca, in the sea-urchinEchinocardium cordatum, and in the bivalveVenus striatula obtained from the Dogger Bank and the eastern North Sea. The cadmium concentrations determined in all four species from these areas were relatively equal, except for an increase in concentration found in those species from the northeastern part of the Dogger Bank. A lower lead content was generally observed in the individuals taken from the German Bight than in those from the Dogger Bank, especially from its northeastern part. In the case of lead, it is possible to divide the southern North Sea into three regions according to the different concentration levels by statistical treatment: the less contaminated German Bight, the more contaminated central Dogger Bank and the highly affected northeastern Dogger Bank. The results obtained contradict the prevailing opinion that offshore invertebrate populations are, in comparison to individuals from coastal regions, less affected by contaminants such as heavy metals.     

Ovule and seed anatomy ofCistaceae and relatedMalvanae

Ovule and especially seed anatomy of eight species ofCochlospermaceae, Bixaceae, Cistaceae, Monotoideae, Pakaraimaeoideae (two subfamilies ofDipterocarpaceae), andSarcolaenaceae were investigated. All representatives show a bixoid chalazal region in the seed as probable exclusive synapomorphy among angiosperms. The palisade layer of the exotegmen is curved inwards at its proximal end and forms a dome-shaped structure. A plug of hypostase tissue with an annulus/core structure fits into this dome. Moreover, two additional tissue types in the hypostase can be found in some representatives of the group. These and other micromorphological, wood anatomical, and floral morphological characters, indicate that the taxa form a monophyletic group close toMalvales s. str. The form of the starch grains in the endosperm is compared and is described for the first time forPakaraimaea (Dipterocarpaceae) andLeptolaena (Sarcolaenaceae). The position ofDiegodendron close toBixa and the presumably more distant positions ofMuntingia andNeuradaceae are discussed.     

Anatomical changes and evolutionary trends in the foliar epidermis of extant and fossil Euro-Mediterranean oaks (Fagaceae)

The differentiation of foliar epidermis structures, cuticles, stomata, and indumentum of most of the extant Euro-Mediterranean taxa ofQuercus have been studied by light and scanning electron microscopy, and compared with other genera and fossil material. Results allow the recognition of the subgg.Sclerophyllodrys, Cerris andQuercus, and of various sections and even individual species. The cyclocytic stomata type, regarded as plesiomorphic, is found in the geologically oldest representatives of the familiy (Dryophyllum, resp.Eotrigonobalanus) and in the relatively old, evergreen to semi-evergreen species ofQuercus subgg.Sclerophyllodrys andCerris. These taxa also have relatively thick and smooth cuticles. Anomocytic stomata, thinner cuticles and the presence of crystalline wax flakes are regarded as apomorphic features and characterize the deciduous taxa of subg.Quercus. These changes are interpreted as ecological adaptations to the changing climates from the Tertiary to the present. An analysis of the various character combinations found in macrofossils and the often poor species separation inQuercus suggest that hybridization has played a major role in the evolution of the Euro-Mediterranean oaks.     

Macrobenthos ofPotamogeton andMyriophyllum beds in the upper reaches of Canal de Mira (Ria de Aveiro,NW Portugal): Community structure and environmental factors

The community structure of the macrobenthic fauna (>0.5 mm) ofPotamogeton andMyriophyllum beds of the upper reaches of Canal de Mira (0.5–2) and of macrofauna density (369, 240 ind m^–2).Potamopyrgus jenkinsi, Corophium multisetosum andLimnodrilus hoffmeisteri are dominant species in the study area. The community of station 1 includes an important set of taxa usually associated to freshwater habitats (oligochaetes, leeches and insect larvae) whilst in station 3 typically estuarine species (Cyathura carinata, Leptocheirus pilosus, Nereis diversicolor, Streblospio shrubsolii) occur. A succession of peak densities of different taxonomic groups during the year indicates seasonal variation in the community structure. The faunal assemblage of the study area is compared with similar ones in NE Atlantic and Mediterranean coastal systems.