The two species of sprat in New Zealand waters (Sprattus antipodum and S. muelleri)

Two broadly sympatric species of sprat are shown to inhabit New Zealand waters, the more slender Sprattus antipodum (Hector, 1872) and the more common and deeper‐bodied S. muelleri (Klunzinger, 1872). Overlap in most morphometric and meristic characters had earlier led to their synonymy, but recent protein analysis suggested otherwise. This is now confirmed by distinct differences in shape and dentition of the basihyal plate, vertebral numbers, scale sculpture, and fresh colour. The five known species of Sprattus are keyed and the genus diagnosed and discussed.     

The German Bight (North Sea) is a nursery area for both locally and externally produced sprat juveniles

To better understand the role of the German Bight (GB) as a nursery area for juvenile North Sea sprat Sprattus sprattus we sought to determine whether the area may receive only locally or also externally produced offspring. We sampled juveniles during 3 trawl surveys in the GB in August, September, and October 2004 and applied otolith microstructure analysis in order to reconstruct their distributions of the day-of-first-increment-formation (dif). These were contrasted with spatial and seasonal patterns of sprat egg abundance in the GB and its adjacent areas, observed during 6 monthly plankton surveys. It was found that the majority of juveniles originated mainly from April/May 2004, coinciding with high spawning activity west of the GB, whereas spawning and larval production inside the GB peaked notably later, in May/June. This indicated that a large proportion of juveniles was produced outside the GB and transported subsequently into it through passive and/or active migration. Shifts to later mean difs from one survey to the next and length distributions indicative of the simultaneous presence of multiple cohorts, supported the notion that the GB is a complex retention and nursery area for sprat offspring from different North Sea spawning grounds and times. Later born juveniles had significantly faster initial growth rates than earlier born conspecifics, which was likely temperature-mediated, given the strong correlation between back-calculated growth histories and sea surface temperature as a proxy for thermal histories of juveniles (r² = 0.52).     

Spatio-temporal distribution of floating objects in the German Bight (North Sea)

Floating objects facilitate the dispersal of marine and terrestrial species but also represent a major environmental hazard in the case of anthropogenic plastic litter. They can be found throughout the world's oceans but information on their abundance and the spatio-temporal dynamics is scarce for many regions of the world. This information, however, is essential to evaluate the ecological role of floating objects. Herein, we report the results from a ship-based visual survey on the abundance and composition of flotsam in the German Bight (North Sea) during the years 2006 to 2008. The aim of this study was to identify potential sources of floating objects and to relate spatio-temporal density variations to environmental conditions. Three major flotsam categories were identified: buoyant seaweed (mainly fucoid brown algae), natural wood and anthropogenic debris. Densities of these floating objects in the German Bight were similar to those reported from other coastal regions of the world. Temporal variations in flotsam densities are probably the result of seasonal growth cycles of seaweeds and fluctuating river runoff (wood). Higher abundances were often found in areas where coastal fronts and eddies develop during calm weather conditions. Accordingly, flotsam densities were often higher in the inner German Bight than in areas farther offshore. Import of floating objects and retention times in the German Bight are influenced by wind force and direction. Our results indicate that a substantial amount of floating objects is of coastal origin or introduced into the German Bight from western source areas such as the British Channel. Rapid transport of floating objects through the German Bight is driven by strong westerly winds and likely facilitates dispersal of associated organisms and gene flow among distant populations.     

Dynamics of Phaeocystis pouchetii blooms in the Wadden Sea of Sylt (German Bight,North Sea)

The colony-forming alga Phaeocystis pouchetii (Haptophyceae) forms regular blooms in spring and early summer in the German Wadden Sea. This paper gives a summary of observations of Phaeocystis blooms in 1975, 1976, and 1981 in the Wadden Sea of Sylt (German Bight, North Sea).The onset of Phaeocystis pouchetii blooms started after the decline of diatoms at low inorganic nutrient concentrations, when particularly inorganic phosphate had dropped to minimal concentrations. Phaeocystis blooms did not start unless water temperatures were above 7°C in the investigation area, and the admixture of organic substances seemed to be an important factor in controlling the onset and the size of Phaeocystis blooms.As diatom populations increased again at the end of the Phaeocystis blooms, a causal relationship between the successive development of both algal groups, possibly in combination with other abiotic factors, cannot be excluded.     

Mobile sand deposits and shoreface sediment dynamics in the inner German Bight (North Sea)

This paper presents a conceptual model for the net bedload transport regime on the shoreface of the German Bight. The model is based on the spatial distribution of the surficial sediment cover (North Sea sands) which is identical to the uppermost layer in the seismic recordings. Sediment thickness was measured using very high resolution seismic profiling (chirp sonar) and vibrocoring. The three-dimensional sediment distribution was estimated using geostatistical methods (cokriging). The results demonstrate a longshore sand distribution with three distinct zones. In Zone 1 (0–10 m water depth) the sediments attain their maximum thickness of 10±2.5 m. Between 10 and 15 m water depth a relatively thin sand layer of 0.4–1.5 m is observed within Zone 2. The seaward adjacent Zone 3 (15–20 m water depth) is characterized by an averaged sand thickness of 2–3 m with local maxima of 5–6 m. Further offshore, the sand layer decreases to about 1–2 m thickness. The net bedload transport directions inferred from this sediment zonation comprise a longshore sediment bypassing in Zone 1 which results in a substantial sediment supply to the innermost part of the German Bight due to bedload convergence. Shore-normal bedload transport shifts sand to and fro across the coastal profile although the net directional transport is seawards. This results in sediment depletion between the 10 and 15 m-isobaths (Zone 2) and an adjacent sediment accumulation in deeper waters (Zone 3).     

Development of habitat models for Nephtys species (Polychaeta: Nephtyidae) in the German Bight (North Sea)

The aim of the study was the development of habitat models for Nephtys species (Polychaeta: Nephtyidae). The investigation area was the German Bight, the southeastern part of the North Sea. Models were developed based on field data collected between 2000 and 2006. In addition, data on environmental variables were retrieved from long-term monitoring data sets and from the sediment map by Figge [Figge, K., 1981. Nordsee. Sedimentverteilung in der Deutschen Bucht. Map No. 2900. Publisher: Deutsches Hydrographisches Institut, Hamburg]. The statistical modelling technique used was multivariate adaptive regression splines (MARS). Models were fitted individually for each species. Evaluation of predictive discrimination and predictive accuracy of the developed models was by calculation of the area under the receiver operating curve (AUC) or sensitivity and specificity, respectively. Habitat models with best predictive fit were selected for the presentation of habitat suitability maps.Six Nepthys species were found: Nephtys assimilis, N. caeca, N. cirrosa, N. hombergii, N. incisa and N. longosetosa. N. hombergii was most common whereas N. incisa and N. longosetosa were rare. Habitat preferences varied considerably among the species. For all investigated Nephtys species except N. longosetosa a habitat model could be developed based on four predictor variables. The habitat models with best predictive fit were those for N. cirrosa and N. hombergii. The N. caeca habitat model was of limited predictive accuracy and only accept predictive discrimination. The number of predictors as well as the relative importance of the respective predictors in the model varied among the different species. Direct comparison of most suitable habitats for the different species based on modelling revealed that in the mostly sandy regions parallel to the German coast in water depths up to 20 m an overlap between N. caeca, N. hombergii and N. cirrosa exists. In the deeper central German Bight with mostly fine sands with increased mud contents N. hombergii, N. assimilis and, at least partially and rare in numbers, N. incisa co-occur. It can be concluded that important sediment characteristics like grain size median and mud content as well as water depth and mean salinity are useful parameters to describe the habitat requirements of most Nepthys species in the German Bight. However, additional variables need to be incorporated into such analyses.     

Abundance and composition of decapod larvae at Saint Paul's Rocks (equatorial Atlantic)

We investigated the effect of interannual variation on the biodiversity and distribution of decapod larvae at Saint Paul's Rocks, an isolated small group of equatorial islands linked to the Atlantic Mid‐Ocean ridge. Zooplankton samples were collected between 2003 and 2005 from a range of different environments off the archipelago. Horizontal surface hauls were conducted in the inlet and at three increasing distances from the archipelago, both in the morning and at night, using a 200‐μm mesh net. Decapod larvae collected included 11 species and 37 individual taxa. Seven of them have not previously been recorded in the area. Samples taken at the shortest distance from the archipelago exhibited a significantly greater abundance than samples taken further away. No significant differences were detected between months in terms of decapod larvae abundance in the inlet. However, in the open ocean at night, the mean abundance was much higher in May and July. Decapod larvae abundance was much higher at night for both the open ocean and the inlet. Brachyuran and caridean larvae exhibited the greatest abundance and frequency in the inlet, mainly represented by the first‐stage larvae of: Grapsus grapsus, Plagusia depressa, Platypodiella spectabilis and Alpheidae. In contrast, Sergestidae holopelagic shrimps were the most abundant and the most frequent larvae in the surface waters of the open ocean. The composition, abundance and distribution of decapod larvae were very similar during the 2 years sampled. Species accumulation curves indicate that even greater diversity exists, demonstrating that long‐term research is important for acquiring accurate knowledge about the biodiversity of dynamic ecosystems such as those at Saint Paul's Rocks.     

Development of habitat models for Nephtys species (Polychaeta: Nephtyidae) in the German Bight (North Sea)

The aim of the study was the development of habitat models for Nephtys species (Polychaeta: Nephtyidae). The investigation area was the German Bight, the southeastern part of the North Sea. Models were developed based on field data collected between 2000 and 2006. In addition, data on environmental variables were retrieved from long-term monitoring data sets and from the sediment map by Figge [Figge, K., 1981. Nordsee. Sedimentverteilung in der Deutschen Bucht. Map No. 2900. Publisher: Deutsches Hydrographisches Institut, Hamburg]. The statistical modelling technique used was multivariate adaptive regression splines (MARS). Models were fitted individually for each species. Evaluation of predictive discrimination and predictive accuracy of the developed models was by calculation of the area under the receiver operating curve (AUC) or sensitivity and specificity, respectively. Habitat models with best predictive fit were selected for the presentation of habitat suitability maps.Six Nepthys species were found: Nephtys assimilis, N. caeca, N. cirrosa, N. hombergii, N. incisa and N. longosetosa. N. hombergii was most common whereas N. incisa and N. longosetosa were rare. Habitat preferences varied considerably among the species. For all investigated Nephtys species except N. longosetosa a habitat model could be developed based on four predictor variables. The habitat models with best predictive fit were those for N. cirrosa and N. hombergii. The N. caeca habitat model was of limited predictive accuracy and only accept predictive discrimination. The number of predictors as well as the relative importance of the respective predictors in the model varied among the different species. Direct comparison of most suitable habitats for the different species based on modelling revealed that in the mostly sandy regions parallel to the German coast in water depths up to 20 m an overlap between N. caeca, N. hombergii and N. cirrosa exists. In the deeper central German Bight with mostly fine sands with increased mud contents N. hombergii, N. assimilis and, at least partially and rare in numbers, N. incisa co-occur. It can be concluded that important sediment characteristics like grain size median and mud content as well as water depth and mean salinity are useful parameters to describe the habitat requirements of most Nepthys species in the German Bight. However, additional variables need to be incorporated into such analyses.     

Interannual variability in the biochemical composition of newly hatched larvae of the spider crab Maja brachydactyla (Decapoda,Majidae)

The spider crab Maja brachydactyla is an important commercial species in Europe and supports intensive fisheries in the NE Atlantic. A field survey was performed to assess long‐term and consecutive interannual (2005–2010) variation of the biochemical composition of newly hatched larvae of M. brachydactyla. Larval biochemical profiles differed significantly among years, with pronounced differences being recorded in 2010. Differences among batches of newly hatched larvae were mainly explained by the contribution of triacylglycerols and, to a lesser degree, by protein and lipid content. The use of different nutrition indices is discussed. The biochemical composition of newly hatched larvae from M. brachydactyla was highly variable, even though surveyed broodstock was obtained from the same local population and was always sampled during the same season. The unpredictable biochemical profiles of newly hatched larvae may condition their survival and recruitment. This largely overlooked aspect of larval variability should be considered in future fisheries management strategies and captive production of marine organisms that still rely on wild seeds.     

Geographical distribution and age composition of Euphausia superba larvae (Crustacea：Euphausiacea) in the South Shetland Islands region and southern Scotia Sea in relation to environmental conditions

Spatial distribution patterns of the different life stages of Euphausia superba in the region of the South Shet- land Islands and southern Scotia Sea （Antarctica） were assessed based on scientific survey data collected in lanuary and February of 2010. Adults, eggs, nauplii, metanauplii, calyptopis I-Ill, and furcilia I-II were found in the investigation. The abundance of larvae averaged 1 172.8 ind./mz, with calyptopis I and II as the dominant stages. Habitat occupancy patterns varied among Euphausia superba at different stages, and three sub-regions were identified by cluster analysis. The degree of larval development increased from west to east. Larvae were not observed north of the South Shetland Islands. Calyptopis I was predominant in the water between Elephant Island and the South Orkney Islands, which featured no thermocline. Older stages, including calyptopis II and III and furcilia I and II, were common in north and northeast of the South Orkney Islands, which were characterized by high temperature and high chlorophyll concentration. Distri- bution and abundance of the early life stages of E. superba were associated with specific environmental con- ditions. According to Biota-Environment matching （BIOENV）, the distributions of E. superba larvae were correlated with a combination of temperature at the surface and 200 m, and 0-100 m integrated chlorophyll a concentration.