Light-Shade Adaptation : TWO STRATEGIES IN MARINE PHYTOPLANKTON

Using chlorophyll/P700 ratios, the size and number of photosynthetic units were estimated, as a function of light-shade adaptation in two species of marine phytoplankton: Skeletonema costatum, a diatom, and Dunaliella tertiolecta, a chlorophyte. In the diatom, light-shade adaptation is characterized primarily by changes in the size and not the number of P700 units, whereas in the chlorophyte, overall changes in chlorophyll content are related to changes in the number and not the size of P700 units. A correlation between the characteristics of P700 units and photosynthetic responses was not established. Both strategies of light-shade adaptation effectively harvest and transfer light energy to reaction centers, however, the Skeletonema strategy is more effective at subsaturating intensities. The two strategies may represent an evolutionary divergence in photosynthetic adaptation to variations in light intensity.     

Notes of food selection in the Antarctic krill, Euphausia superba

Analysis of the gut contents of Euphausia superba and of the phytoplankton composition in the area of the animals catchment served as a basis for answering the question whether or not E. superba is capable of food selection. It was found that the diatom Thalassiosira is preferred by E. superba as a food item and small pennate diatoms, Nitzschia, and Navicula are only tolerated as food. Other algae taxa, such as Tropidoneis, Dactyliosolen, Chaetoceros, and Gyrodinium, are clearly avoided. With respect to phytoplankton cell size, E. superba prefers cells with a length of 20–40 μm and cells larger than 70 μm are rejected. Trophic conditions only slightly affect the food selection of E. superba. Received: 4 September 1995/Accepted: 30 June 1996     

Coupling of nauplii release in barnacles with phytoplankton blooms: a parallel strategy to that of spawning in urchins and mussels

We examined the coupling between the release of nauplii in Semibalanusbalanoides and phytoplankton blooms, and compared it with themechanism synchronizing spawning with phytoplankton abundancein green sea urchins (Strongylocentrotus droebachiensis) andblue mussels (Mytilus edulis). Close contact with phytoplanktoncells is required to stimulate the release of nauplii in Semibalanus,whereas spawning in urchins and mussels is triggered by an extracellularmetabolite of phytoplankton. The response is concentration dependentand positively correlated with the frequency of moulting Themoulting rate in Semibalanus is reported to be directly correlatedwith food intake and thus larval release should be proportionalto feeding activity. The release of Semibalanus nauplii is morestrongly stimulated by the diatom Skeletonema costatum thanby Phaeodactylum tricornutum, whereas the highest response isobtained in treatments with nauplii of Artemia salina. We suggestthat these differences are related to size of the planktonicparticles (Artemia nauplii < Skeletonema < Phaeodactylum)Exposure to air, as occurs in the intertidal zone, does notinfluence significantly larval release Larval release in otherCrustacea may similarly be coupled to phytoplankton abundance.     

Seasonal variation in light- and temperature-dependent growth of marine planktonic diatoms in in situ dialysis cultures in the Trondheimsfjord,norway (63°N)

Three species of diatoms, Skeletonema costatum (Grev.) Cleve, Thalassiosira gravida Cleve, and T. pseudonana (Hustedt) Hasle et Heimdal, were grown in in situ dialysis culture in the Trondheimsfjord at depths of 0.5 and 4 m. The rates of growth and the chemical composition of exponentially growing cells were monitored and related to seasonal changes in illumination and temperature. Functions correlating growth rate with temperature were deduced. Growth took place from February to November. During this period temperature ranged from ?1 to 16°C, the average photon flux density (ifI) (per 24 h) from 9 to 570 μE · m^?2 · s^?1 (0.5 m depth), and the length of the days (I > 1 μE · m^?2 · s^?1) from 6 to 24 h. Light-limited growth was evident when the product of the average daily light and the chlorophyll/N ratio was < 10; this occurred mostly in early spring and late autumn. Peak densities (> 800 for the Thalassiosira spp. and > 1300–1400 μE · m^?2 · s^?1 for Skeletonema) seem to inhibit growth. The highest rates recorded were ≈1.6 doubl. · day^?1 (July, 15–16°C).The three species exhibit different ecological behaviour. Skeletonema is eurythermal (Q₁₀ = 1.8), whereas Thalassiosira pseudonana favours high temperatures, and T. gravida temperatures < 10°C. Moreover, Skeletonema has generally less chlorophyll and more phosphorus and ATP (≈ 1.4 ×) than the other two species. In Skeletonema, the ATP level seems related to the light-governed growth rate, and independent of temperature. In Thalassiosira no such correlation was found.     

Evaluation of halophilic microalgae isolated from Rabigh Red Sea coastal area for biodiesel production: Screening and biochemical studies

In the present study, different water samples from Red Sea coastal area at Rabigh city, Saudi Arabia were studied for their dominant algal species. Microalgal isolation was carried out based on dilution method and morphologically examined using F/2 as a growth medium. Dry weight and main biochemical composition (protein, carbohydrates, lipids) of all species were performed at the end of the growth, and biodiesel characteristics were estimated. Nannochloropsis sp., Dunaliella sp., Tetraselmis sp., Prorocentrum sp., Chlorella sp., Nitzschia sp., Coscinodiscus sp., and Navicula sp. were the most dominant species in the collected water samples and were used for further evaluation. Nannochloropsis sp. surpassed all other isolates in concern of biomass production with the maximum recorded dry weight of 0.89 g L^?1, followed by Dunaliella sp. (0.69 g L^?1). The highest crude protein content was observed in Nitzschia sp. (38.21%) and Dunaliella sp. (18.01%), while Nannochloropsis sp. showed 13.38%, with the lowest recorded lipid content in Coscinodiscus sp. (10.09%). Based on the growth, lipid content, and biodiesel characteristics, the present study suggested Dunaliella sp. and Nitzschia sp. as promising candidates for further large-scale biodiesel production.     

Growth and bioluminescence of Noctiluca scintillans on varying algal diets

The effects of food concentration and food quality on the growthrate and bioluminescence potential of the heterotrophic dinoflagellateNoctiluca scintillans were examined. The growth rate of N. scinullansvaried greatly with the phytoplankton food it was provided,and those foods yielding higher growth rates also produced cellsthat were smaller in diameter, but with a greater bioluminescencepotential per unit volume. Small phytoplankton species, includingIsochrysis galbana and an unidentified chrysophyte responsiblefor the Texas brown tide, supported the lowest growth rates.Other small flagellates (Dunaliella tertiolecta) and dinoflagellates(Gyrodinium dorsum, Prorocentrum minimum) supported moderategrowth rates. The highest growth rates were supported by diatomsand prasinophytes. Maximum growth rates (0.5 day^-1) were obtainedwith the diatom Thalassiosira sp. at concentrations     

Nutrient-induced competition between two species of marine diatoms

Competition experiments betweenPhaeodactylum tricornutum andSkeletonema costatum showed that even at temperatures higher than 10°C (i.c. 14°C), the development ofSkeletonema can be favoured by adjusting nutrient levels and nutrient ratios. Low NSi ratios were found to favourSkeletonema. Additionally, high NP ratios further enhanced the ability ofSkeletonema to dominate the cuftures. Contrary to some statements in literature, it seems that high concentrations of silicates are more important for the dominance ofSkeletonema costatum in large-scale cultures than just low temperatures. This finding is important with regard to stimulating the blooming ofSkeletonema costatum in natural phytoplankton populations as food for bivalve molluscs.     

Algae,bacteria and detritus as food for the harpacticoid copepod, Heteropsyllus pseudonunni Coull and Palmer

The harpacticoid copepod, Heteropsyllus pseudonunni Coull and Palmer, when fed Juncus roemerianus Scheele (needlerush) detritus produced significantly more eggs than when fed the alga Dunaliella sp. Five food rations and a starved control were used: A, algal concentration ≈ 10⁴ cells · ml^?1; LA, algal concentration 10³ cells · ml^?1; D, detritus concentration 0.25 g · ml^?1; LD, detritus concentration 0.025 g · ml^?1; LDLA, a mixture of the LD and LA rations. Geometric mean total egg production values were: LDLA 132.5; LD 132.6; D 120.5; A 65.8; LA 5.0. The LA results were significantly less (P = 0.05; Student-Newman-Keuls' test) than all others, while the A results were significantly less than the LDLA, LD and D results. The LDLA, LD and D results were not statistically different. Similar trends were obtained when mean brood sizes and mean number of broods were compared. In a second feeding experiment, using Juncus detritus, bacteria on sand grains, and algae (Nitzschia sp.) on sand grains, Heteropsyllus pseudonunni produced significantly more eggs (P = 0.05; SNK test) when fed detritus (166.0) or bacteria (132.2) than algae (58.9). The detritus and bacteria results were not significantly different.     

Feeding rates of planktonic copepods from a tropical sea

The feeding rates of the marine planktonic copepods, Eucalanus subcrassus Giesbrecht, Tortanus gracilis (Brady), Calanopia elliptica (Dana) (both male and female), Temora turbinata (Dana), and Paracalanus aculeatus Giesbrecht (only female) from tropical inshore waters have been studied. Newly hatched Artemia nauplii (for Eucalanus, Tortanus, and Calanopia), Dunaliella (for Temora), and Skeletonema (for Paracalanus) were used as food.Feeding rates were measured for a single individual through successive incubations once or twice a day until death to determine changes in feeding rate after collection. Copepods survived from a few days to three weeks. In general, feeding rates varied from day to day, but were less variable than the differences between day and night rates. In some cases, feeding rate consistently decreased up to the death of the copepod. Daily ration, estimated in terms of percentage body weight, was in the range of 28–329 ‰ Using the results together with the those of other workers, gives the relation between daily ration (Y, % body weight) and body weight of copepods (X; μg dry weight) at 20 °C as, logY = 2.531?0.377 logX.Copepods given Artemia nauplii as food killed more nauplii than were eaten. This phenomenon, tentatively called ‘over-hunting’, is possibly an important feeding behaviour for carnivorous copepods.     

Use of encapsulated live microalgae to investigate pre-ingestive selection in the oyster Crassostrea gigas

The involvement of algal chemical cues in the pre-ingestive selection of food particles in Crassostrea gigas was studied using a new approach. Live cells of two microalgal species, Nitzschia closterium and Tetraselmis suesica, were separately entrapped in small alginate microcapsules using an emulsification/internal gelation method. Microcapsule size was adjusted to be within the range of particles ingested by oysters. Using this technique, about 80% of microcapsules had a diameter ranging from 21 to 100 μm. The monitoring of entrapped algae showed that phytoplankton cells remained alive and maintained an active growth for at least 24 days. In particle selection bioassays, adult C. gigas were fed a mixture of microcapsules containing the above algae species as well as control empty alginate microcapsules. The comparison of the proportions of each microcapsule type in the diet and in pseudofeces revealed that those containing T. suesica were significantly ingested while those containing N. closterium were preferentially rejected. Since microcapsule material (alginate matrix) prevented physical contacts between algae cells and oyster feeding organs, this study clearly demonstrate that extracellular metabolites produced by microalgae play a crucial role in the pre-ingestive selection of particles in suspension-feeding bivalves.     

Attached and Free-Floating Bacterioplankton in Howe Sound, British Columbia, a Coastal Marine Fjord-Embayment

Factors which influence the attachment of bacterioplankton to particles (including phytoplankton) were investigated by using (i) water samples removed from a coastal temperate fjord over an annual cycle and (ii) unialgal cultures of Prorocentrum minimum, Dunaliella tertiolecta, and Skeletonema costatum. Silt and salinity levels in this fjord seawater did not appear to influence bacterial attachment, but the percent attached bacteria was inversely related to both chlorophyll a concentrations and primary productivities. During periods of high primary productivities the percent attached bacteria was low, whereas during periods of low, increasing, and declining primary productivities the percent attached bacteria was high. A similar pattern of bacterial attachment was observed when the three phytoplankton were grown as batch cultures. The percent attached bacterial numbers increased upon the initiation of algal growth and after these cells stopped growing, but not while the algae were growing. We suggest that a major factor influencing the attachment of bacterioplankton is the physiological condition of their major nutrient source, the phytoplankton; mainly free-living bacteria are associated with growing phytoplankton, whereas a much greater proportion of the bacteria are attached among senescent phytoplankton populations.     

The food chain dynamics of the oyster,clam, and mussel in an aquaculture food chain

The food chain dynamics of the edible mussel Mytilus edulis L., the American oyster Crassostrea virginica (Gmelin) and the hard clam Mercenaria mercenaria (L.) were investigated in large experimental tanks with flowing, filtered sea water and controlled addition of phytoplankton. The feeding rate of the mussel (5.36 μg carbon removed/l/g C animal was higher than that of the oyster (3.92) and clam (3.03) but the ecological efficiencies (net production/ingested food) × 100 of the clam (23.69 %) and the oyster (18.38 %) were higher than that of the mussel (10.01 %).The food chain efficiencies (net production/available food) were lower than the ecological efficiencies, suggesting under-exploitation of the available food. The clam, although having a lower feeding rate, was more efficient in utilizing the food it filtered and so showed the highest net production.The rates (μg-at/l/g C animal) of regeneration of nutrients, especially total inorganic nitrogen (mussel, 2.1723 × 10^?3; oyster, 7.4270 × 10^?3; and clam, 8.1750 × 10^?3) along with reported high biodeposition rates of bivalves suggest that multi-species aquaculture systems would be more efficient and productive than one-species systems.     

The impact of food type, temperature and starvation on larval development of Balanus amphitrite Darwin (Cirripedia: Thoracica)

The impact of diatom food species (Chaetoceros calcitrans and Skeletonema costatum), temperature and starvation on the larval development of Balanus amphitrite was evaluated. Starvation threshold levels for different ages of larvae (0- to 5-day-old) fed with C. calcitrans and S. costatum and then starved at 5, 15 and 25 °C temperature were estimated as ultimate recovery hour (URH; denoting the starvation point in hours at the end of which larvae can recover and continue development). Effect of temperature on starvation threshold varied significantly with larval age and food species. The URH declined with larval age at 5 °C, but not at 15 and 25 °C. The URH and grazing rates were high for early instars fed on C. calcitrans, and for advanced instars fed on S. costatum. Carbon gain through feeding was maximum for 2-day-old larvae when fed with C. calcitrans and decreased with larval age. However, when fed with S. costatum carbon gain increased with larval age. This confirms that with development the utility of food types changes. The differences in the carbon gain can be attributed to differences in grazing rate due to variations in the size of the diatom cells, larval intersetular distance, diatom sinking rate and the photo-taxic behavior of larvae. Molting was observed at times when larvae were undergoing starvation and this could be viewed as stress-induced molting, and it differed with the larval age and food organisms.     

Analysis of diversity of chromophytic phytoplankton in a mangrove ecosystem using rbcL gene sequencing

Phytoplankton forms the basis of primary production in mangrove environments. The phylogeny and diversity based on the amplification and sequencing of rbcL, the large subunit encoding the key enzyme ribulose‐1, 5‐bisphosphate carboxylase/oxygenase was investigated for improved understanding of the community structure and temporal trends of chromophytic eukaryotic phytoplankton assemblages in Sundarbans, the world's largest continuous mangrove. Diatoms (Bacillariophyceae) were by far the most frequently detected group in clone libraries (485 out of 525 clones), consistent with their importance as a major bloom‐forming group. Other major chromophytic algal groups including Cryptophyceae, Haptophyceae, Pelagophyceae, Eustigmatophyceae, and Raphidophyceae which are important component of the assemblages were detected for the first time from Sundarbans based on rbcL approach. Many of the sequences from Sundarbans rbcL clone libraries showed identity with key bloom forming diatom genera namely Thalassiosira, Skeletonema and Nitzschia. Similarly, several rbcL sequences which were diatom‐like were also detected highlighting the need to explore diatom communities from the study area. Some of the rbcL sequences detected from Sundarbans were ubiquitous in distribution showing 100% identities with uncultured rbcL sequences targeted previously from the Gulf of Mexico and California upwelling system that are geographically separated from study area. Novel rbcL lineages were also detected highlighting the need to culture and sequence phytoplankton from the ecoregion. Principal component analysis revealed that nitrate is an important variable that is associated with observed variation in phytoplankton assemblages (operational taxonomic units). This study applied molecular tools to highlight the ecological significance of diatoms, in addition to other chromophytic algal groups in Sundarbans.     

In situ microcosm experiments on the influence of nitrate and light on phytoplankton community composition

Phytoplankton blooms are fundamental features of coastal ecosystems, but the processes that select for blooms of certain species are not well understood. The aim of this work was to investigate experimentally the interaction of light and nutrients (nitrate) in structuring phytoplankton community composition in Pelorus Sound, New Zealand. Microcosm experiments were conducted in situ nine times throughout the year, providing controls and treatments for increased nutrients and decreased light. Nitrate availability was found to be limiting to phytoplankton growth during spring and summer. Small- to medium-sized, chain-forming diatom taxa such as Chaetoceros sp., Skeletonema sp., Pseudonitzschia sp. and Thalassiosira sp. responded most rapidly to nitrate enrichment, increasing their biovolume up to 32-fold during the 5-day experiments. A long-term phytoplankton monitoring database showed that these taxa have historically dominated the phytoplankton assemblage, suggesting that intense competition for nitrate is a key component in structuring the phytoplankton community. Many of the taxa that were able to withstand light reduction in the shaded treatments were rare historically in Pelorus Sound, suggesting that light is secondary to nitrate availability in structuring the phytoplankton community composition in this coastal embayment.     

LABORATORY STUDIES OF A GREEN NOCTILUCA FROM NEW GUINEA1,2

A strain of Noctiluca miliaris Suriray, containing in the vacuole a motile green flagellate, was collected off the north shore of New Guinea and maintained in culture in autoclaved seawater or an enriched seawater medium. In light, this green Noctiluca survived for at least a month and divided, without added food; while in darkness the symbiotic flagellate disappeared and the Noctiluca died within a few days, unless the food organism Dunaliella tertiolecta was present. Long-continued growth in light required the presence of Dunaliella, since the symbiotic flagellate was gradually lost under all the culture conditions assayed. All green Noctiluca assayed were luminescent. The light emitted per cell varied with the nutritional state of the host, and was as bright as a Japanese strain without symbionts when the Noctiluca was feeding on Dunaliella. In the absence of Dunaliella, the light emitted per Noctiluca depended on the light intensity in which cultures were maintained. The luminescent flash followed the same time course as that of other strains of Noctiluca without symbionts. No circadian rhythm of luminescence was present. Observations on both the growth and luminescence show that the flagellate symbiont contributes to the nutrition of the green Noctiluca. The symbiosis, however, is unstable in culture.     

DISSOLVED ORGANIC PHOSPHORUS EXCRETION BY MARINE PHYTOPLANKTON1,2

The amounts of extracellular dissolved organic phosphorus (DOP) produced by 8 species of marine planktonic algae under various conditions of light, salinity, and nutrition were compared. Large amounts, more than 20% of the total P in the system, were excreted by Cyclotella cryptica, Thalassiosira fluviatilis, Dunaliella tertiolecta, and Synechococcus under 1 or more of the experimental conditions. Excretion of DOP was proportional to light intensity in Dunaliella, Rhodomonas, Chlorella sp., and Coccolithus huxleyi. Phosphorus limitation reduced DOP production by Cyclotella and Thalassiosira, nitrogen limitation reduced DOP production by Phaeodactylum, Dunaliella, and Rhodomonas, and lack of iron reduced DOP levels in Cyclotella cultures. Salinity affected growth, but no clear relationship to DOP excretion was evident. The DOP eliminated during growth was reassimilated by the species that produced it and by other species, but lack of alkaline phosphatase reduced the amount of DOP that was available to certain algae.     

A 91-year record of seasonal and interannual variability of diatoms from laminated sediments in Saanich Inlet, British Columbia

Diatom seasonal succession and interannual variability werestudied using laminated sediments from Saanich Inlet, BritishColumbia, for the years 1900–1991. Frozen sediment coresallowed fine-scale sampling of laminae for each year. Thus,three ‘seasons’ for each year were identified basedon species composition. Thalassiosira species were indicatorsof spring deposition. Skeletonema costatum was abundant in samplesfollowing Thalassiosira, probably deposited in late spring andsummer. Rhizosolenia sp. was most abundant in fall/winter samples.Diatom stratigraphies were related to sea surface temperature,salinity, sea level and the Pacific North American Index (PNA)using canonical correspondence analysis (CCA). CCA showed thatspecies of a particular season generally had optima for temperatureand salinity characteristic of that time. Interannual changesin diatom species composition and abundance were most prevalentin the decades 1920–1940, with the exception of S.costatumwhich showed cyclic changes in abundance. Skeletonema was moreabundant during periods of cool temperatures, while littoraldiatoms were more abundant during times of heavy winter rains.Sea level was an important variable in CCA and while its relationshipto diatoms is not clear, it may be related to variations innutrient supply to diatoms in surface waters.     

Effects of food availability on the valve movements and feeding behavior of juvenile Crassostrea Virginica (Gmelin). I. Valve movements and periodic activity

The effects of changes in the availability of algal food on the valve movements of juvenile Crassostrea virginica (Gmelin) were investigated. Individual oysters were subjected to different conditions: (1) unfed in filtered sea water; (2) continuously fed, in which oysters were given an algal suspension maintained at a constant level (50 000 cells/ml) by an automatic turbidostat; (3) discontinuously fed, where oysters were alternately fed with the turbidostat for 12 h and unfed for 12 h; and (4) batch fed, in which oysters were given specific daily rations at two ration levels (maximum and 40%). Valve movements were concurrently recorded and periods of activity (valves open) and quiescence (valves closed) measured.Oysters fed continuously remained open an average of 94.3% of the time, whereas unfed oysters were open 35.1% of the time. Discontinuously fed animals were open 95.7% of the time during the times of feeding, but 60.6% of the time during the unfed periods. Activity in the batch-fed oysters was related to the ambient algal concentration in that both the percentage time open/hour and the duration of valve openness decreased with decreasing concentration. Time series analysis of valve movements showed that oysters exhibited a 24-h periodicity of activity when subjected to a 24-h feeding schedule (discontinuous and batch groups) but exhibited no consistent periodicity under the continuous feeding or unfed conditions.     

Summer phytoplankton distributions in the Weddell Sea

Summary The quantitative composition of phytoplankton was studied along a transect of 14 hydrographic stations, between the southern coast of the Weddell Sea and the Antarctic Peninsula, during the austral summer of 1984–1985. The most apparent feature of the phytoplankton distribution was the presence of a bloom of Phaeocystis at a frontal zone over the shelf break, and the marked contrast between a southern region, with high phytoplankton biomass, and a poorer region north of the shelf break. The most widely distributed diatom genus was Nitzschia (Fragilariopsis section). The phytoplankton assemblage of the southern region included the silicoflagellate Distephanus speculum, the diatom Rhizosolenia alata and several heterotrophic dinoflagellates such as Protoperidinium antarcticum and P. applanatum. The northern assemblage could be characterized by the abundance of flagellates and small dinoflagellates, and by diatoms such as Chaetoceros criophilum, Corethron criophilum Nitzschia kerguelensis and other Nitzschia species of the Fragilariopsis section.