Dolioletta Gegenbauri Research Articles

Research on the seasonal variation of zooplankton community in Daya Bay, South China Sea

Changes in zooplankton composition, abundance, and some species in response to environmental variation were investigated over four seasons (2020) in Daya Bay. In total, 129 taxa of zooplankton (16 groups of planktonic larvae and 20 indeterminate species) were identified. Zooplankton communities exhibited a significant seasonal shift in abundance and taxonomic composition. The maximum number of zooplankton species was recorded in winter (72 species) and the lowest in spring (42 species). However, the abundance was highest in spring (1,372.01 ± 1,071.14 individuals/m³) and lowest in autumn (50.93 ± 34.05 individuals/m³). Pearson correlation analyses demonstrated that the zooplankton abundance and the variations of indicator species were obviously correlated with environmental parameters (e.g., salinity, temperature, pH, and chlorophyll-a). Based on specificity and occupancy analysis, a total of eight species were selected as indicator species. It is noteworthy that some kollaplankton (such as Dolioletta gegenbauri and Doliolum denticulatum) could potentially cause disaster to the nuclear power plant cooling system because of their relatively large body size and huge blooms in spring. In addition, Centropages tenuiremis blooms in spring and Penilia avirostris blooms in summer could attract assemblages of larval or adult pelagic fish, which would also threaten the cooling system security in Daya Bay. In conclusion, our results suggest that zooplankton communities and some species may be considered as favorable indicators of the marine environment.

Zooplankton community variability in the South Atlantic Bight (2015–2017)

Abstract In the South Atlantic Bight (SAB), responses of zooplankton communities to physical dynamics were evaluated monthly at two sites on the continental shelf offshore from Savannah, GA, USA, between December 2015 and December 2017. Zooplankton were collected in oblique net tows (202-μm). Samples were collected in two regions of the middle shelf: inner edge (Site 1: 25 m isobath, n = 22) and outer edge (Site 2: 40 m isobath, n = 21). Samples were also collected at a third site on the 40 m isobath, ~20 nm south of Site 2 in July and August 2016. Temperature, salinity and fluorescence data were recorded at each site. Overall, 57 taxa were identified with total abundances varying from 1 × 103 to 81 × 103 ind.m−3. Small copepods predominated; notably Paracalanus spp. The highest abundance was recorded in October 2016 at Site 1, following deep mixing induced by Hurricane Matthew. Interannual variability of zooplankton abundance was significant, with higher abundances in 2016 compared with 2017, reflecting higher river runoff in 2016. Samples from Site 3 yielded the largest Dolioletta gegenbauri bloom documented in the SAB. This 2-year time-series, for the first time, suggests that zooplankton communities on the SAB middle shelf region are significantly influenced by continental precipitation patterns.

Dolioletta advena sp. nov., a New Species of Doliolid (Tunicata, Thaliacea) from the Adriatic Sea

The Adriatic Sea, as a part of Mediterranean, is one of the best investigated areas in the world regarding zooplankton. Nevertheless, in the last decade four new species of gelatinous zooplankton were described from the Adriatic Sea. Whether these species are newcomers or they were simply overlooked is still under investigations. Here we provide a description of a new species of Doliolida from the genus Dolioletta, Dolioletta advena sp. nov., found in the Adriatic Sea in August 2021, in a period of high sea temperatures and salinities, suggesting its thermal predilection. Its blastozooids dominated the studied doliolid blastozooid communities in the South Adriatic, except in the 50–100 m depth layer at a coastal Lokrum station. Blastozooids of D. advena sp. nov. possess unique morphological features which easily distinguish it from other doliolid species: the most prominent feature being the curved digestive tract where the intestine does not form a tight coil as in other Dolioletta species. The placement of this species in the genus Dolioletta is corroborated by COI phylogenetic analysis which showed that D. advena sp. nov. forms a well-supported monophyletic clade with Dolioletta gegenbauri (81% bootstrap support). In addition to D. advena sp. nov. COI sequence, we provide COI sequences of five doliolid and one pyrosomatid species, which will greatly improve the availability of thaliacean sequences for metabarcoding studies. The origin of D. advena sp. nov. is unknown, but given the fact that doliolids are well investigated in the Mediterranean Sea, it is likely that it arrived with sea currents either through the Suez Canal or the Strait of Gibraltar. Future investigations will confirm or reject this hypothesis.

On the Predation of Doliolids (Tunicata, Thaliacea) on calanoid Copepods

The main goal of this contribution was to determine the effect of predation of the often abundant to dominant doliolid Dolioletta gegenbauri (Tunicata, Thaliacea) on the abundance of co-occurring planktonic copepods by feeding on their eggs. Previous oceanographic investigations revealed that doliolids had ingested eggs of small calanoid copepods. The ecological significance of such feeding could not be quantified completely because the environmental abundance of such eggs was not known. In this study, the eggs and nauplii of the neritic calanoid Paracalanus quasimodo (Crustacea, Copepoda) were offered to gonozooids and phorozooids of D. gegenbauri with a 6–6.5 mm length together with three species of phytoplankton; i.e., simulating diet conditions on the shelf. We hypothesized that copepod eggs of a similar size as food particles would be readily ingested whereas small nauplii, which could escape, would hardly be eaten by the doliolids. Our results revealed that doliolids have the potential to control small calanoids by ingesting their eggs at high rates but not their nauplii or later stages. Late copepodid stages and adults of co-occurring calanoid species could cause less mortality because they prey less on such eggs than doliolids of a similar weight. However, certain abundant omnivorous calanoid species with pronounced perception and/or capture abilities can prey successfully on the nauplii of small calanoids.

The microbiome of the pelagic tunicate Dolioletta gegenbauri: Apotential link between the grazing and microbial food web.

Bloom-forming gelatinous zooplankton occur circumglobally and significantly influence the structure of pelagic marine food webs and biogeochemical cycling through interactions with microbial communities. During bloom conditions especially, gelatinous zooplankton are keystone taxa that help determine the fate of primary production, nutrient remineralization, and carbon export. Using the pelagic tunicate Dolioletta gegenbauri as a model system for gelatinous zooplankton, we carried out a laboratory-based feeding experiment to investigate the potential ecosystem impacts of doliolid gut microbiomes and microbial communities associated with doliolid faecal pellets and the surrounding seawater. Metabarcoding targeting Bacteria and Archaea 16S rRNA genes/Archaea) and qPCR approaches were used to characterize microbiome assemblages. Comparison between sample types revealed distinct patterns in microbial diversity and biomass that were replicable across experiments. These observations support the hypothesis that through their presence and trophic activity, doliolids influence the structure of pelagic food webs and biogeochemical cycling in subtropical continental shelf systems where tunicate blooms are common. Bacteria associated with starved doliolids (representative of the resident gut microbiome) possessed distinct low-biomass and low-diversity microbial assemblages, suggesting that the doliolid microbiome is optimized to support a detrital trophic mode. Bacterial genera Pseudoalteromomas and Shimia were the most abundant potential core microbiome taxa, similar to patterns observed in other marine invertebrates. Exploratory bioinformatic analyses of predicted functional genes suggest that doliolids, via their interactions with bacterial communities, may affect important biogeochemical processes including nitrogen, sulphur, and organic matter cycling.

Feeding of Marine Zooplankton on Microplastic Fibers

The goal of our study was to examine the effects of low abundances of nylon fibers on feeding rates of calanoid copepods (Crustacea, Copepoda) and doliolids (Tunicata, Thaliacea) in the presence of diatoms at near environmental concentration levels. In addition, we examined microscopically the fecal pellets produced by copepods and doliolids in the presence of fibers. Adult females of the calanoid Eucalanus pileatus and early gonozooids of Dolioletta gegenbauri (both of similar dry weight) cleared the diatom Rhizosolenia alata at similar rates. Nylon fibers were cleared at higher rates by Dolioletta gegenbauri compared to Eucalanus pileatus. Examination of fecal pellets revealed that copepods and doliolids could ingest the about 300 µm long fibers. The latter also ingested the occasionally occurring fibers of > 1 mm length. It appears that in seawater fiber abundances of about seven fibers ml−1 did not have a negative effect on feeding of either E. pileatus or D. gegenbauri. As doliolids and copepods remove plastic fibers from seawater by packing them into their pellets, they might play a role in the reduction of microplastic pollution and the microplastic transfer from the water column to the seafloor. Calanoid copepods may limit ingesting fibers by not perceiving them, as compared to doliolids which do not seem to be able to avoid ingesting them.

Basin-scale distribution of salps and doliolids in the transition region of the North Pacific Ocean in summer: Drivers of bloom occurrence and effect on the pelagic ecosystem

The large-scale distribution of thaliaceans in relation to environmental variables was investigated over 4500 km in the transition region of the North Pacific (36°N–43.6° N, 141.5° E–164.5° W) in the summer of 2016–2019. Three main patterns occurred in the thaliacean bloom formations with specific and annual variabilities. Thalia democratica, the most dominant thaliacean species in this region, formed an intensive bloom (>100 ind m−3) of up to 300 km, mainly south of the subarctic boundary between 160° E and 180°. The bloom was accompanied by a dense water mass which was associated with high nutrient concentration and N/P ratio, indicating that this species thrived under the influence of the HNLC water mass from the subarctic region. A Dolioletta gegenbauri bloom was observed east of 180° and the north of the subarctic boundary in association with higher chlorophyll a levels. Doliolum denticulatum and Doliolum nationalis increased with sea surface temperature and pico-sized chlorophyll a, suggesting adaptation to oligotrophic subtropical waters. Estimated grazing and downward flux by Thalia democratica bloom corresponded to 63–80% and 20–26% of daily primary production, respectively, indicating that the bloom enhanced the biological pump in the HNLC-like environment dominated by small phytoplankton. Doliolids function as important components of the microbial food web through the consumption of varied organic matter. Thaliaceans utilise the specific niche which suspension-feeding copepods find difficult to colonise, indicating that bottom-up control of oceanographic conditions determines the mesozooplankton community and food-web structure in the transition region.

Selective feeding and linkages to the microbial food web by the doliolid Dolioletta gegenbauri

AbstractGelatinous zooplankton play a crucial role in pelagic marine food webs, however, due to methodological challenges and persistent misconceptions of their importance, the trophic role of gelatinous zooplankton remains poorly investigated. This is particularly true for small gelatinous zooplankton including the marine pelagic tunicate, Dolioletta gegenbauri. D. gegenbauri and other doliolid species occur persistently on wide subtropical shelves where they often produce massive blooms in association with shelf upwelling conditions. As efficient filter feeders and prodigious producers of relatively low‐density organic‐rich aggregates, doliolids are understood to contribute significantly to shelf production, pelagic ecology, and pelagic–benthic coupling. Utilizing molecular gut content analysis and stable isotope analysis approaches, the trophic interactions of doliolids were explored during bloom and non‐bloom conditions on the South Atlantic Bight continental shelf in the Western North Atlantic. Based on molecular gut content analysis, relative ingestion selectivity varied with D. gegenbauri life stage. At all life stages, doliolids ingested a wide range of prey types and sizes, but exhibited selectivity for larger prey types including diatoms, ciliates, and metazoans. Experimental growth studies confirmed that metazoan prey were ingested, but indicated that they were not digested and assimilated. Stable isotopic composition (δ13C and δ15N) of wild‐caught doliolids, during bloom and non‐bloom conditions, were most consistent with a detrital‐supplemented diet. These observations suggest that the feeding ecology of D. gegenbauri is more complex than previously reported, and have strong and unusual linkages to the microbial food web.

Distribution, biomass, and species composition of salps and doliolids in the Oyashio–Kuroshio transitional region: potential impact of massive bloom on the pelagic food web

The Oyashio–Kuroshio Transitional Region (OKTR) is a nursery ground for pelagic fishes; thus, community succession of mesozooplankton is pivotal to understand prey availability, and it subsequently affects recruitment success. We investigated the surface distribution, biomass, and species composition of thaliaceans (salps and doliolids) that potentially have a significant impact on the food web and biogeochemical cycle by forming intensive blooms. A total of 11 thaliacean species were recorded from 62 locations along two transects at 36° N and 38.5° N extending from 142° E to 180° in May to June 1993. Salps and doliolids were found at 93% and 84% of the stations, respectively, and their biomass values varied widely in space (0.00011–79.56 and 0.00001–5.11 mg C m−3 for salps and doliolids, respectively). Thalia democratica was the most dominant salp and particularly abundant at stations east of 165°E on the 36°N-line; the abundance varied from 103 to 1379 ind m−3. Dolioletta gegenbauri and Doliolum denticulatum were dominant doliolids, although their biomass values were far lower than that of salps. Multivariate statistical analysis with PRIMER revealed that the distribution of thaliaceans in the OKTR was not uniform in space and was affected by oceanographic conditions; doliolids tended to occur in much warmer (14.10–15.63 °C) and saline water mass (34.54–34.72) than salps (13.16–14.95 °C and 34.40–34.53). In terms of population clearance rates, the most dense salp blooms have the potential to sweep > 200% of their resident water per day, indicating that salp blooms cause deleterious feeding conditions for pelagic fishes through non-selective filter feeding.

The Effects of Microplastics on Dolioletta gegenbauri (Tunicata, Thaliacea).

Oceanographic studies revealed the abundance of minute plastic particles in coastal regions. Such particles, called microplastics, are abundant in sizes smaller than 100µm ESD (Equivalent Spherical Diameter) and can be collected and ingested by planktonic copepods. Those animals are the most abundant metazoans on our planet. Abundantly co-occurring with planktonic copepods in subtropical and temperate neritic waters are doliolids (Tunicata, Thaliacea), which can dominate subtropical shelves because of their high asexual reproductive performance. Our studies were designed to examine the effects of polystyrene beads at low abundance, compared with phytoplankton, on abundantly occurring gonozooids of Dolioletta gegenbauri. Our findings reveal that such abundance of microplastic particles, in the presence of environmental concentrations of phytoplankton, reduces rates of feeding, growth, and oxygen consumption of this tunicate. Feeding rates on phytoplankton in the presence of beads were reduced by up to 58%, growth rates by up to 85%, and oxygen consumption rates by up to 33%. We conclude that such microplastic particles could limit the often in situ encountered pronounced proliferation of this tunicate species (Deibel in: Bone (ed) The biology of pelagic tunicates, Oxford University Press, Oxford, 1998).

Cultivation of the Marine Pelagic Tunicate <em>Dolioletta gegenbauri</em> (Uljanin 1884) for Experimental Studies

Gelatinous zooplanktons play a crucial role in ocean ecosystems. However, it is generally difficult to investigate their physiology, growth, fecundity, and trophic interactions primarily due to methodological challenges, including the ability to culture them. This is particularly true for the doliolid, Dolioletta gegenbauri. D. gegenbauri commonly occurs in productive subtropical continental shelf systems worldwide, often at bloom concentrations capable of consuming a large fraction of daily primary production. In this study, we describe cultivation approaches for collecting, rearing, and maintaining D. gegenbauri for the purpose of conducting laboratory-based studies. D. gegenbauri and other doliolid species can be captured live using obliquely towed conical 202 µm mesh plankton nets from a drifting ship. Cultures are most reliably established when water temperatures are below 21 °C and are started from immature gonozooids, maturing phorozooids, and large nurses. Cultures can be maintained in rounded culture vessels on a slowly rotating plankton wheel and sustained on a diet of cultured algae in natural seawater for many generations. In addition to the ability to establish laboratory cultures of D. gegenbauri, we demonstrate that the collection condition, algae concentration, temperature, and exposure to naturally conditioned seawater are all critical to the culture establishment, growth, survival, and reproduction of D. gegenbauri.

Diet and trophic interactions of a circumglobally significant gelatinous marine zooplankter, Dolioletta gegenbauri (Uljanin, 1884).

Gelatinous zooplankton play a crucial role in marine planktonic food webs. However, primarily due to methodological challenges, the in situ diet of zooplankton remains poorly investigated and little is known about their trophic interactions including feeding behaviour, prey selection and in situ feeding rates. This is particularly true for gelatinous zooplankton including the marine pelagic tunicate, Dolioletta gegenbauri. In this study, we applied an 18S rRNA amplicon metabarcoding approach to identify the diet of captive-fed and wild-caught D.gegenbauri on the midcontinental shelf of the South Atlantic Bight, USA. Sequencing-based approaches were complimented with targeted quantitative real-time polymerase chain reaction (PCR) analyses. Captive-fed D.gegenbauri gut content was dominated by pico-, nano- and micro-plankton including pico-dinoflagellates (picozoa) and diatoms. These results suggested that diatoms were concentrated by D.gegenbauri relative to their concentration in the water column. Analysis of wild-caught doliolids by quantitative real-time PCR utilizing a group-specific diatom primer set confirmed that diatoms were concentrated by D.gegenbauri, particularly by the gonozooid life stage associated with actively developing blooms. Sequences derived from larger metazoans were frequently observed in wild-caught animals but not in captive-fed animals suggesting experimental bias associated with captive feeding. These studies revealed that the diet of D.gegenbauri is considerably more diverse than previously described, that parasites are common in wild populations, and that prey quality, quantity and parasites are likely all important factors in regulating doliolid population dynamics in continental shelf environments.

Striking taxonomic differences in summer zooplankton in the northern South China Sea: implication of an extreme cold anomaly

An extreme persistent cold anomaly was prevailing in the South China Sea in February 2008. In order to understand the effect of the cold anomaly on zooplankton community, the zooplankton composition, abundance and biomass were analyzed in the northern South China Sea in August 2007 and August 2008. A total of 467 zooplankton species representing 16 groups were identified, with 275 species in August 2007 and 351 in August 2008. Copepods were the most dominant zooplankton group in the study area. Compared with 2007, a dramatic decline was observed in the abundance of four dominant copepod species: Subeucalanus subcrassus, Temora discaudata, Nannocalanus minor and Temora turbinata in 2008. Moreover, zooplankton abundance declined from 133.37 ind./m3 in August 2007 to 75.49 ind./m3 in August 2008. In contrast, the abundance of medusa, such as Diphyes chamissonis, and tunicate, such as Doliolum denticulatum and Dolioletta gegenbauri, increased during the same season. Cluster analysis showed that there was a difference in zooplankton community structure between the two years. These variations in zooplankton communities were indicative of an anomalous oceanographic condition along with the extreme cold event in 2008.

In situ observations of a doliolid bloom in a warm water filament using a video plankton recorder: Bloom development, fate, and effect on biogeochemical cycles and planktonic food webs

AbstractWe investigated distribution patterns of a doliolid (Dolioletta gegenbauri) bloom in relation to the physical environment using a video plankton recorder in the Oyashio–Kuroshio mixed water region. Using 12 km transects, doliolid blooms were encountered at a horizontal scale of about 2–3 km, which corresponds to submesoscale physical events. Doliolids were also consistently encountered in the subsurface layer above the pycnocline in warmer (> 14ºC) and higher‐salinity (> 34) water masses, and seawater density was the most critical factor affecting distribution depth. Compared to previous studies, the density and biomass of the blooms observed in this study (77 mgC m−3and 4600 inds m−3) were highest in the open ocean. Bloom formation consisted of two phases; first, the seeding population of a nurse stage increased rapidly to 2000 inds m−3by asexual reproduction, followed by asexual production of phorozooids. Estimated population clearance rates revealed that these dense patches could potentially sweep the surrounding water within 2–3 d. The incidence of exhausted and shrunken zooids was significantly correlated with patch density, suggesting that mortality was due to overgrazing. Shrunken doliolids appeared to sink below the pycnocline, corresponding to 8–17% of the particulate organic carbon flux at 150 m. Hydromedusae, pelagic polycheates, and sapphirinid copepods preyed on the doliolids. These results indicate that doliolids, which were seeded by populations originating from the Kuroshio, formed dense blooms in response to submesoscale physical events and would alter the sinking particle properties (i.e., biological pump) and the epipelagic food web structure through their grazing and mortality.

Reliability of qPCR for quantitative gut content estimation in the circumglobally abundant pelagic tunicate Dolioletta gegenbauri (Tunicata, Thaliacea)

Gelatinous metazooplankton play a crucial role in marine planktonic food webs. Because of methodological difficulties encountered while studying them in situ relatively little is known about their ecology, including their diet or in situ rates of feeding. In this study we report the development of a differential length amplification quantitative PCR (dla-qPCR) assay targeting the 18S rRNA gene to validate the use of qPCR-based approach to quantify consumption of specific plankton prey by the doliolid Dolioletta gegenbauri. We also present an initial application of a qPCR-assay to estimate consumption of the centric diatom Thalassiosira spp. on the southeastern continental shelf of the United States where doliolids stochastically bloom in response to upwelling events. Results indicate that prey DNA was not significantly digested during passage through the gut of D. gegenbauri. Molecularly estimated feeding rates were in the same range as those estimated from clearance rates in laboratory feeding studies. In the field, the centric diatom Thalassiosira spp. was detected in the gut of wild caught D. gegenbauri at very low abundance that was consistent with its relative rarity in the water column at the time of collection. Thus, both experimental and field investigations support the hypothesis that a qPCR approach will be useful for the quantitative investigation of the in situ diet of D. gegenbauri without introduced biases associated with cultivation.

北部湾北部生态系统结构与功能研究VI：浮游动物空间生态位及其分化

根据2006-2007年北部湾北部海域4个航次调查资料，采用<em>K</em>-优势度曲线法对浮游动物种（类）群进行排序分析，运用Levins公式和Pianka指数分析了主要优势种（类）群的生态位宽度值和生态位重叠程度，并通过除趋势典范对应分析（DCCA）研究生态位分化状况。结果表明，该海区浮游动物优势种（类）群按生态位宽度值可划分为广生态位、中生态位和窄生态位三大类型。其中，广生态位的种（类）群如肥胖软箭虫、亚强次真哲水蚤、长尾类幼体等具有较强的生态适应性，生活范围较广；窄生态位的种（类）群，对环境的适应性较差，对海流和水团等环境因素的变化具有指示意义。生态位宽度能够反映种（类）群丰度季节变化，但不能反映具体丰度大小。北部湾北部全年主要优势种（类）群的生态位宽度值介于0.08-0.77之间，并且各优势种（类）群的生态位宽度差异较大，种对间生态位重叠值介于0.02-0.89之间，平均生态位重叠指数为0.45，种（类）群之间利用资源环境的互补性较强，这与海域内生境多样化并且各优势种对环境适应能力的差异存在一定联系。DCCA分析表明，影响浮游动物分布的主要因子是水深、温度和盐度，其次是叶绿素a和溶解氧。;The concept of ecological niche had remained as one of the core ideas in ecological research for almost a century, which was closely linked with interspecific competition, resource utilization had played an important role in the study of community composition and function,of the relationships among species,biodiversity,community succession and population evolution. Based on four seasonal investigations (Spring 2007, Summer 2006, Autumn 2007 and Winter 2006) in northern Beibu Gulf from 2006 to 2007, the niche breadth, niche overlap, spatial differentiation and environment effects on the abundance and spatial distribution of zooplankton were studied with qualitative and quantitative methods. The cumulative top 80% of zooplankton dominant populations were selected by the K-dominant curve method, then the niche breadths and their overlaps of zooplankton were measured using the formulas proposed by Levins Niche Breadth index and the Pianka Niche Overlap index, and the spatial niche differentiation was studied by using Detrended Canonical Correspondence Analysis (DCCA) method. The results showed that the zooplankton dominant species in northern Beibu Gulf were classified in to three groups, <em>i e.,</em> wide niche breadth groups (<em>B</em>_i=0.60-0.77), middle niche breadth groups (<em>B</em>_i=0.30-0.60), narrow niche breadth groups (<em>B</em>_i=0.08-0.30) based on the niche breadth value. The niche breadths of zooplankton such as <em>Sagitta enflata</em>, <em>Subeucalanus subcrassus</em> and Macrura larvae were wider, which was related with their own characteristics and the capability of adapting environment, while the species whose niche breadths were narrower such as <em>Doliolum denticulatum</em> and <em>Dolioletta gegenbauri</em> will be considered as an indicative significance for ocean currents and water masses. Niche breadth could reflect the zooplankton abundance with the seasonal dynamic changes,and also could objectively reflect the species in the habitat in which the distributions of degree but it could not reflect the Accurate zooplankton abundance. The niche breadth values of dominance zooplankton species ranged between 0.08 and 0.77 in the whole year and The niche breadth difference among the dominant populations was great; The niche overlap values of dominance zooplankton species ranged between 0.02 and 0.89 in the whole year and the average niche overlap index was 0.45, there was strong complementarity in terms of the utility of resource among zooplankton populations, which had certain relationship with northern Beibu Gulf habitat diversification and the strong complementarity in terms of the utility of resource among zooplankton populations. The Detrended Canonical Correspondence Analysis result showed that depth, temperature and salinity had more important influence on the species spatial distribution than Chlorophyll a and dissolved oxygen.

Sapphirinid copepods as predators of doliolids: Their role in doliolid mortality and sinking flux

We investigated predatory behavior of sapphirinid copepods on doliolids around the Kuroshio Extension at stations experiencing blooms of Dolioletta gegenbauri. Onboard observations showed that adult Sapphirina nigromaculata was an active predator of doliolids, with a preference for internal tissues. When entering a doliolid body cavity, sapphirinids left a characteristic bite mark around the fringe of oral and atrial aperture or hole on the tunic of the doliolid. In situ observations with a video plankton recorder (VPR) revealed that association between sapphirinids and doliolids was common in the field. Adult sapphirinids and doliolids exhibiting the characteristic evidence of an attack (bite mark or hole) were found in sediment traps at a depth of 50 m, indicating that the association between these taxa was due to predation. Early copepodites, which were not observed in sediment‐trap samples, appeared in the VPR observations to have a semi‐parasitic phase when they attached themselves to nurse chains. The maximal daily ration of sapphirinids estimated by onboard experiments ranged between 29% and 37% of their body carbon weight. Although the mean predation effect by sapphirinids on the doliolid population biomass was only 0.7% d−1, sapphirinids potentially had a greater effect on doliolid abundance at the termination of doliolid blooms. Some of the attacked doliolids were discarded by the sapphirinids and contributed to the sinking flux below 150 m, the importance of which as a source of detritus likely increased with depth. Sapphirinids, despite their relatively low abundance in the water column, play a specific role in driving community succession and biogeochemical cycling.

Seasonal and spatial patterns of Penilia avirostris and three tunicate species in the southern Mid-Atlantic Bight

The cladoceran Penilia avirostris and three tunicate species, Oikopleura dioica, Dolioletta gegenbauri and Thalia democratica, form a mesozooplankton group which ingests a wide range of particles from pico- to micro- plankton, grows rapidly due to asexual reproduction, and thus can have major impacts on phytoplankton populations. These four zooplankton species were the most abundant tunicate and cladoceran species in a study where zooplankton were sampled biweekly at five stations across the inner continental shelf in the Mid-Atlantic Bight in 2005, 2006 and 2007. Vertical tows were taken at shallow stations and depth stratified vertical tows at stations >10m. P. avirostris and O. dioica had highly predictable seasonal cycles with peak abundances in July and August. D. gegenbauri also was present during this time period if upwelling favorable winds were present, which implies cross shelf transport from source populations in slope waters and the Gulf Stream. T. democratica only appeared in pulses when southerly winds were increasing in strength. The co-occurrence P. avirostris and the tunicate species with abundant Synechococcus and heterotrophic nanoflagellates during highly stratified summer conditions provide potential connections to microbial food webs as well as grazing opportunities on event scale blooms of dinoflagellate and diatoms species present in the area.

A contribution to the knowledge of the thaliacean faunas of the eastern mediterranean and the red sea

ABSTRACT In the sector of the Mediterranean east of the 22nd meridian, five species of Salpidae (Thalia democratica, Salpa fusiformis, Ihlea punctata, Pegea confoederata and Cyclosalpa pinnata polae) and five species of Doliolidae (Doliolum denticulatum, Doliolum nationalis, Doliolina sp., Doliolina intermedium (?)' and Dolioletta sp.) were caught during a series of cruises. At the same time, four species of Salpidae (Thalia democratica, Salpa cylindrica, Brooksia rostrata and Ritteriella amboinensis) and two species of Doliolidae (Doliolina mulleri krohni and Doliolum denticulatum) were recorded in the Gulf of Elat (Gulf of 'Aqaba), Two further species, Salpa maxima and Dolioletta gegenbauri tritonis, previously recorded from this area, were not found again in these last catches. Pyrosomidae are missing in both areas. The two faunas are very different, having in common only a few widely distributed species.

Oxygen consumption of fecal pellets of doliolids (Tunicata, Thaliacea) and planktonic copepods (Crustacea, Copepoda)

Zooplankton fecal pellets are a major component of the carbon cycle in the ocean. The goal of our study was to quantify oxygen consumption rates of fecal pellets of doliolids and copepods during initial degradation of fecal pellets in the water column. Fecal pellets were collected from gonozooids of the doliolid Dolioletta gegenbauri and adult females of the calanoid copepod Eucalanus pileatus feeding on the diatom Thalassiosira weissflogii, and the phytoflagellate Isochrysis galbana, and the latter on T. weissflogii only. Oxygen consumption of fecal pellets was quantified by applying non-invasive optical sensors, keeping the pellets continuously suspended in their experimental vessels. Oxygen consumption rates of pellets of doliolids and copepods ranged between 4 and 16 and 1 and 5 nmol O2 mL 21 h, respectively. Average oxygen consumption rates were 212 pmol O2 h 21 for a doliolid pellet (range of 80–329 pmol O2 h ), and 101 pmol O2 h 21 for a copepod pellet (range of 50–211 pmol O2 pellet 21 h). Variations in oxygen consumption were closely related to the type of pellets, and the abundance of pellet-associated heterotrophic prokaryotes. Average numbers of heterotrophic prokaryotes per doliolid pellet reached values of up to 3 10, whereas prokaryotic numbers per copepod pellet approached 8 10. Average cell volumes of pellet-associated heterotrophic prokaryotes were enhanced by a