A physical context for gelatinous zooplankton aggregations: a review

The magnitude and extent of jellyfish blooms are influenced not only by the biology and behavior of the animal, but also by the geographic setting and physical environment. Hydrography alone is often thought to cause or favor gelatinous zooplankton aggregations, however, it is clear that interactions between biology of the animal and physics of the water are very important sources of population variations, especially at local scales. We summarize the role of physical processes and phenomena that promote aggregations of gelatinous zooplankton. We have identified and discussed a suite of physical gradients that can be perceived by gelatinous zooplankton. These include light, gravity, temperature, salinity, pressure and turbulence. A recurring theme is accumulation of jellyfish around physical discontinuities such as fronts (shelf-break, upwelling, tidal and estuarine) and pycnoclines (thermoclines and haloclines). Interestingly, there are few data to suggest that large-scale, quasi-stationary features, such as the largest oceanic fronts, serve to physically aggregate gelatinous animals at a similar scale. Rather, examples of local aggregations appear to dominate the literature. We also discuss various jellyfish behaviors that are theorized to promote aggregation, feeding and reproduction in relation to physical discontinuities.     

Collection and culture techniques for gelatinous zooplankton

Gelatinous zooplankton are the least understood of all planktonic animal groups. This is partly due to their fragility, which typically precludes the capture of intact specimens with nets or trawls. Specialized tools and techniques have been developed that allow researchers and aquarists to collect intact gelatinous animals at sea and to maintain many of these alive in the laboratory. This paper summarizes the scientific literature on the capture, collection, and culture of gelatinous zooplankton and incorporates many unpublished methods developed at the Monterey Bay Aquarium in the past 15 years.     

A universal BMV-based RNA recombination system--how to search for general rules in RNA recombination

At present, there is no doubt that RNA recombination is one of the major factors responsible for the generation of new RNA viruses and retroviruses. Numerous experimental systems have been created to investigate this complex phenomenon. Consequently, specific RNA structural motifs mediating recombination have been identified in several viruses. Unfortunately, up till now a unified model of genetic RNA recombination has not been formulated, mainly due to difficulties with the direct comparison of data obtained for different RNA-based viruses. To solve this problem, we have attempted to construct a universal system in which the recombination activity of various RNA sequences could be tested. To this end, we have used brome mosaic virus, a model (+)RNA virus of plants, for which the structural requirements of RNA recombination are well defined. The effectiveness of the new homomolecular system has been proven in an experiment involving two RNA sequences derived from the hepatitis C virus genome. In addition, comparison of the data obtained with the homomolecular system with those generated earlier using the heteromolecular one has provided new evidence that the mechanisms of homologous and non-homologous recombination are different and depend on the virus' mode of replication.     

Diurnal changes in zooplankton respiration rates and the phytoplankton activity in two Chilean lakes

Phytoplankton spatial distribution patterns in the Abra of Bilbao (a semienclosed coastal body of water) and adjacent shelf waters have been studied during June–July 1983 and May–June 1984. Small naked dinoflagellates, cryptophyceans and an unidentified nanoplankton component, were a common feature in all surveys. In July 1983 a dense bloom of nanoplankton developed inside the Abra which, in contrast to the community in the adhacent waters, contained high densities of small diatoms, naked dinoflagellates, cryptophyceans and the Haptophyta Phaeocystis pouchetii. Microplankton was mainly composed of dinoflagellates in July 1983, and of diatoms in June 1983 and May–June 1984. Microplankton abundance was highest in May–June 1984 and decreased from the shelf to the Abra. A principal component analysis performed separately on each cruise revealed the differences in the structure of the phytoplankton community between the Abra of Bilbao and the adjacent shelf waters.     

New records of Amphipoda Hyperiidea in associations with gelatinous zooplankton

Associations between Amphipoda Hyperiidea specimens and gelatinous zooplankton such as cnidarians, ctenophores or salps are known in the literature. It is well established that many hyperiids are intimately associated with gelatinous zooplankton during part or all of their life-cycles, and that the associations could be of commensal or of parasitic nature, sometimes very highly species-specific. Although conventional net sampling usually does not preserve evidence of these associations, 12 instances of association (I.A.) were found in nine of the 49 samples collected during the 'FINEP XI Cruise', carried out on the Southeast coast of Brazil (23–28 °S), in January 1980. Lestrigonus bengalensisGiles, 1887 (11 specimens) and Simorhynchotus antennarius(Claus, 1871) (one specimen) were found inside salps and siphonophores. The study of the nature of these associations is essential to the understanding of the evolution of the group.     

Comparison of carbon-specific growth rates and rates of cellular increase of phytoplankton in large limnetic enclosures

Potential carbon-specific growth rates of phytoplankton wereestimated from a series of measurements of photosynthetic radio-carbonuptake over 4- and 24-h exposure periods in the light fieldsof three large limnetic enclosures (‘Lund Tubes’),each providing different limnological and trophic conditions.Photosynthetic behaviour and short-term, chlorophyll-specificcarbon-fixation rates conformed to well-established criteriabut, over 24 h, the net retention represented 23–82% ofthe carbon fixed during the daylight hours. Potential mean growthrates (k'_p, of the photo-autotrophic community were calculatedas the net exponential rates of daily carbon-accumulation relativeto derived, instantaneous estimates of the cell carbon-content.Apparent actual community growth rates (k'_D were calculatedas the sum of the exponential rates of change of each of themajor species present, corrected for probable rates of in situgrazing and sinking, and expressed relative to the fractionof total biomass for which they accounted. The correspondingvalues were only occasionally similar, k'_p generally exceedingK'_D by a factor of between 1 and 30 or 1 and 14, depending uponthe carbon:chlorophyll ratio used. The ratio, K'_p/K'_D was foundto vary inversely both to k'_D and to k_n, the net rate of changein phytoplankton biomass, suggesting that measured carbon fixationrates merely represent a capacity for cellular increase which,owing to other likely limitations upon growth, is seldom realized.Apparent rates of loss of whole cells do not account for theloss of carbon; that the ‘unaccounted’ loss rates(K'_p–K'_D varied in direct proportion to K'_p (i.e., losseswere least when chlorophyll-specific photosynthetic productivitywas itself limited) is best explained by physiological voidingof excess carbon (for instance, by respiration, photorespiration,excretion) prior to the formation of new cells.     

Associations between gelatinous zooplankton and hyperiid amphipods (Crustacea: Peracarida) in the Gulf of California

Hydrobiologia - Hyperiid amphipods are pelagic crustaceans that live associated with gelatinous zooplankton including medusae, ctenophores, siphonophores, and salps. Standard plankton sampling...     

Associations between gelatinous zooplankton and hyperiid amphipods (Crustacea: Peracarida) in the Gulf of California

Hyperiid amphipods are pelagic crustaceans that live associated with gelatinous zooplankton including medusae, ctenophores, siphonophores, and salps. Standard plankton sampling disrupts natural associations, so the most reliable way to determine an association is through direct observation of the organisms in their environment. The planktonic fauna of the Gulf of California dwelling between 10 and 3000 m was surveyed using SCUBA diving and a remotely operated submersible (ROV) during March 2003. Here we report our observations on a total of 14 symbiotic associations found between the hyperiid amphipods and various taxa of gelatinous zooplankton. We found parental care behavior in a group of amphipods (Oxycephalidae) in which this phenomenon has not been previously reported. For two hyperiid species, Euthamneus rostratus and Vibilia australis, we present the first information on their symbiotic relations. Additional hosts were discovered for other well-known and widely distributed hyperiid species (i.e. Brachyscelus crusculum, Hyperoche medusarum). Photographic evidence of some of these interactions is included in this contribution. This is the first survey of these relationships in the Gulf of California, and many aspects of the ecology and biology of these symbioses remain to be studied.     

Evidence for tidally-induced vertical migration of some gelatinous zooplankton in the Wadden Sea area near Sylt

Gelatinous zooplankton is more abundant in the Wadden Sea area of North Sylt than in the adjacent North Sea. The hypothesis is tested that medusae maintain their position in the North Sylt Wadden Sea by ascending to the surface at flood tides and descending to the bottom during ebb tides, thus avoiding the strong ebb currents which could carry them out of this food-rich area. Surface sampling at a main tidal channel revealed great differences between high tide and low tide abundances of five species of medusae in the surface layer.Rathkea octopunctata, Sarsia tubulosa, Eucheilota macultata andPleurobrachia pileus were all more abundant around high tide than during low tide. Bongo net sampling in different depth layers revealed thatPleurobrachia pileus, Bougainvillia ramosa andEucheilota maculata showed a preference for the surface layers around high tide, whereas most of the individuals were found in the deepest layer around low tide. The results suggest tidally-induced vertical migration of medusae in tidal channels. This may assist maintenance of the populations in the Wadden Sea area near Sylt.     

A comparison of pump sampling systems for live zooplankton collection

Simultaneous and sequential tests of pump sampling equipment showed that sampling mortality of Lake Michigan zooplankton collected from the cooling water intake of a nuclear power plant was dependent on the sampling method used. Two sampling devices and two pump types were tested to determine which combination resulted in the lowest sampling mortality. An in-line filter trap located on the suction side of the pump provided the lowest sampling mortality. Higher sampling rates were achieved with a centrifugal pump without increasing sampling mortality.     

Diel variations in respiration, excretion rates, and nutritional status of zooplankton from the Pampulha Reservoir, Belo Horizonte, MG

This investigation is focused on the experimental determination of diel cycles of metabolic activity of zooplankton in a tropical reservoir. Water and zooplankton used in laboratory experiments were collected from the Pampulha reservoir. The experimental units were incubated in the light (1500 Lux) and in the dark at 25.0 +/- 1.0 degrees C during different periods of the diel cycle. At the end of each experiment, the following variables were measured: temperature, dissolved oxygen, ammonia, and orthophosphate as well as the composition, abundance and dry weight of the zooplankton. The specific respiration and excretion rates were determined considering the differences in concentration between experimental and control units. The effect of diurnal cycle on respiration rates was clearly more intense than the effect of light. The average values of respiration rates obtained in the morning hours oscillated between 0. 015 and 0.016 mgO(2)mgDW. hr(-1) (light and dark incubations). At night, these rates were higher and ranged from 0.020 to 0.035 mgO(2)mgDW. hr(-1). Increased biomass of zooplankton and longer incubation times produced lower respiration rates. The excretion rates of ammonia were higher at night, reaching a mean value of 4.2 microgN-NH(4)/mg DW. hr(-1) in illuminated units. The phosphate excretion rates were more elevated in the morning, reaching 0.58 microgP-PO(4)/mg/DW. hr(-1) illuminated vessels. The nanoplankton was able to actively absorb ammonia as well as phosphate. The highest ammonia absorption rates were measured at night, whereas the nanoplankton absorbed phosphorus only in the morning hours. The nutritional status of zooplankton also showed short-term variations. The mean phosphorus content of zooplankton biomass also varied between day and night as well as with incubation time. It ranged from 0.58-2.17%, whereas organic matter variation was more conservative, oscillating around 70-92% in all occasions.     

A comparison of methods for measuring primary productivity and community respiration in streams

Carbon dioxide and oxygen exchange procedures for measuring community metabolism (two open stream methods and three chamber methods) were compared on the same reach of a third-order stream. Open stream methods were complicated by high diffusion rates and yielded net community primary productivity estimates lower than those obtained with chamber methods. Chamber methods yielded variable productivity and respiration data. However, when normalized for chlorophyll a, productivity estimates from the chamber methods were within an expected range for the system. Balances of photosynthesis and respiration from the chamber methods were similar between methods and indicated that autotrophic or heterotrophic processes could dominate the system. Considerations in applying the various procedures are discussed.     

The SOS screen in Arabidopsis: A search for functions involved in DNA metabolism

The SOS screen, as originally described by Perkins et al. (1999) [7], was setup with the aim of identifying Arabidopsis functions that might potentially be involved in the DNA metabolism. Such functions, when expressed in bacteria, are prone to disturb replication and thus trigger the SOS response. Consistently, expression of AtRAD51 and AtDMC1 induced the SOS response in bacteria, even affecting E. coli viability. 100 SOS-inducing cDNAs were isolated from a cDNA library constructed from an Arabidopsis cell suspension that was found to highly express meiotic genes. A large proportion of these SOS⁺ candidates are clearly related to the DNA metabolism, others could be involved in the RNA metabolism, while the remaining cDNAs encode either totally unknown proteins or proteins that were considered as irrelevant. Seven SOS⁺ candidate genes are induced following gamma irradiation. The in planta function of several of the SOS-inducing clones was investigated using T-DNA insertional mutants or RNA interference. Only one SOS⁺ candidate, among those examined, exhibited a defined phenotype: silenced plants for DUT1 were sensitive to 5-fluoro-uracil (5FU), as is the case of the leaky dut-1 mutant in E. coli that are affected in dUTPase activity. dUTPase is essential to prevent uracil incorporation in the course of DNA replication.     

Time-series measurement of grazing rates of zooplankton and bivalves

The current state of the art in automated measurement of grazingrates of zooplankton and bivalves is evaluated. Limitationsto the development of automated methods are discussed with referenceto theoretical considerations. Different approaches to time-seriesmeasurements are examined, and some inadequately investigatedtime scales for measurement of grazing rates are outlined. Levelsof automation of existing experimental systems are described,and a recently developed grazing system based on in vivo fluorescenceadvanced. The new system is suited to use with zooplankton orbivalves, but depends on precise calibration of in vivo fluorescence.It facilitates rapid measurement of functional response to foodconcentration, estimation of time-series rates at constant foodconcentrations, and measurement of rates while simulating patchyfood distribution. Results derived from experiments with krill(Nyctiphanes australis) and cockles (Chione stutchburyi) usingthis grazing system are presented, and some future directionsfor instrument development suggested.     

A comparison of estimates of productivity and consumption by zooplankton for planktonic ciliates in Lake Ontario

A multiple regression equation predicting growth rate for ciliatesfrom cell size and temperature was combined with measurementsof biomass to estimate the productivity of ciliates in the epilimnionof Lake Ontario. This method predicts daily production to biomassvalues for ciliates of up to 5 day^–1 and leads to theconclusion that ciliate production could equal half of the carbonfixation by phototrophs. Consumption of ciliates by metazoanzooplankton was estimated by incubating samples passed through44 µm screens, and determining the increase in abundanceof ciliates over 24 h. These rates are much lower, >1 day^–1and often near zero. Production estimates based on these latterrates would be 3–4% of primary production Possible explanationsfor this discrepancy include both predation within the microzooplanktoncommunity and food limitation, as well as bottle effects However,the lower production estimates are still compatible with ciliatesplaying a major role as grazers in this ecosystem