Bacterivory of a mudflat nematode community under different environmental conditions

The fate of the benthic bacterial biomass is a topic of major importance in understanding how soft-bottom environments function. Because of their high abundance, production and nutritional value, benthic bacteria may constitute an important food resource for benthic fauna. The trophic role of bacteria for a nematode community on the Brouage mudflat (Marennes-Oléron-France), dominated by three species: Chromadora macrolaima (64% of the abundance), Daptonema oxycerca (15%) and Ptycholaimellus jacobi (8%), was determined in grazing experiments using ¹⁵N pre-enriched bacteria. On intertidal flats, seasonal, tidal and circadian cycles induce strong variations in environmental conditions. Grazing experiments were performed in order to measure the effects of abiotic (temperature, salinity and luminosity) and biotic (bacterial and algal abundances) factors on assimilation rates of bacteria by nematodes. In order to assess simultaneously bacteria and algal assimilation rates, algal abundances were modified adding ¹³C pre-enriched Navicula phyllepta. Assimilation rate was significantly lower at 5°C; moreover, general trend shows a prominent temperature effect with an optimum around 30°C. Assimilation at salinity 18 was not significantly different from the assimilation at salinity 31. Assimilation was higher under light conditions than in the dark. Above 10⁹ bacteria ml⁻¹, assimilation of bacteria remained unaffected by bacterial abundance. However, assimilation of algae increased with the algal concentration. Nematode kept feeding under conditions of stress, which are typical of the surficial sediment habitat and they appeared to be principally dependent on the algal resource.     

Beat frequency of cilia in the branchial basket of the ascidian Ciona intestinalis in relation to temperature and algal cell concentration

To elucidate the effects of temperature and algal cell concentration on pumping of water in the ascidian Ciona intestinalis a number of different experiments were performed. Beat frequency of the lateral cilia in the openings of the branchial sac was measured in intact specimens using a microprojection objective and a monochrome CCD video camera. At constant low algal cell concentration, beat frequencies increased linearly with temperature from 4.0 Hz (±0.5) at 7.4 °C to 13.6 Hz (±1.6) at 20.1 °C. At a constant temperature of 15 °C, beat frequency decreased with increasing algal cell concentration from approximately 3000 to >10 000 Rhodomonas sp. cells ml⁻¹. The decrease was observed both in experiments where the ascidians had been acclimated to a fixed algal cell concentration and in experiments with changing concentrations. Effect of algal cell concentration on squirting/siphon closure and flow velocity in the exhalent siphon was measured using a thermistor. At low algal cell concentrations, flow velocity in the exhalent siphon was stable, apart from a few short squirts. At very high algal cell concentrations, the flow velocity was reduced and much less stable, with prolonged squirting. The effect of gut content on filtration was studied in experiments with specimens acclimated to high algal cell concentrations. Results showed a close relation between gut clearance and filtration rate. From the experimental results and a qualitative analysis of the Ciona-pump it was concluded that the ciliary beat frequency is proportional to the water flow through the sea squirt and that changes in pumping caused by temperature or algal cell concentration are under nervous control or governed by enzyme kinetics, rather than being a result of physico-mechanical properties, i.e. pump efficiency versus flow resistance, of the ascidian pump. Received: 6 October 1997 / Accepted: 8 October 1998     

Recruitment and juvenile survival in the sea hare Aplysia juliana (Gastropoda: Opisthobranchia)

The specificity in settling response of larval Aplysia juliana (Quoy and Gaimard, 1832) on species of its food algae, Ulva spp., provided a rare opportunity for the quantitative study of recruitment and early survival rates in a non-sessile marine invertebrate. Post-metamorphic juveniles spend about 3 weeks feeding and growing on the algae before moving to the rocky habitat of the adults. Recruitment and survival were studied by collecting weekly samples of algae and holding them in the laboratory until the recruits were large enough to be seen and reliably counted. Recruitment occurred throughout the year, although the rates were relatively low in late winter and spring. Recruitment was monitored relative to algal weight and bottom area. Variation in larval abundance and algal standing crop influenced recruitment to the study area. Mortality during the juvenile stage was very high in all cases, although the rates and shapes of the survivorship curves varied between algal species and location.     

The effects of light and thallus scour from<Emphasis Type="Italic"> Ecklonia radiata</Emphasis> canopy on an associated foliose algal assemblage: the importance of photoacclimation

Kelp canopies have long been recognised for their influence on the structure of algal assemblages on sublittoral reefs. In Marmion Lagoon, Western Australia, we investigated how a canopy of the small kelp Ecklonia radiata affected the associated foliose algal assemblage and what potential mechanisms were responsible for the effects we observed. Light levels and physical abrasion (thallus scour) by an E. radiata canopy were manipulated in an orthogonal fixed-factor experiment that revealed that changes in light, but not thallus scour, had a significant effect on the composition of the algal assemblage. Reduced light levels were associated with a decrease in the Shannon-Wiener diversity index and an increased dominance of the foliose algae Pterocladia lucida and Rhodymenia sonderi. Photobiological investigations of three foliose species, P. lucida, R. sonderi and Chauviniella coriifolia indicated that they were able to photoacclimate to low light levels by increasing thallus absorption by up to 11%. Photoacclimation was also evident by an increase in the maximum rate of electron transport under low-light conditions. We conclude that the E. radiata canopy in Marmion Lagoon structures the foliose algal assemblage through the modification of the light environment and that this effect may be mediated by differences in the ability of different species of foliose algae to photoacclimate.Communicated by M.S. Johnson, Crawley     

Food availability and diet composition of three coexisting Mediterranean limpets (Patella spp.)

The gut contents of three intertidal patellid limpets were analysed by collecting foraging specimens on a breakwater on the Tyrrhenian coast (central Italy) between May 1988 and October 1989. The three species coexist there showing a different, but partially overlapping zonation: Patella aspera dominates the infralittoral fringe; the majority of P. caerulea inhabits the lower midlittoral, while P. rustica is most abundant in the upper midlittoral. The algae present on slivers of substratum over which each limpet collected was moving were identified. Moreover, floristic surveys were made along the shore in order to characterize the algal cover of the different zonal belts. The floristic study revealed that the basic elements of algal communities typical of western Mediterranean rocky shores are present in the study area. The algae found on the slivers under the foraging limpets were generally representative of the algal community typical of the same zone. There was a marked difference between the diets of P. rustica and P. aspera due to the fact that the first species forages on a few low lying epilithic and endolithic Cyanophyceae, while P. aspera feeds on a large number of species belonging to all the main algal classes and life forms considered, including frondose epilithics and epiphytics. The diet of P. caerulea resembles that of P. aspera in algal heterogeneity, but is dominated by Cyanophyceae as in P. rustica. A detailed analysis of the differences between gut contents of each limpet species and the relative slivers showed an obvious general correspondence, but revealed also that the diets of the three species do not completely reflect the availability of algae. These findings suggest that the basic diet segregation mechanism between the three populations is their zonal separation. However, the difference in gut contents of heterospecific limpets foraging in the same zone suggests the existence of supplementary morphy-functional or behavioural mechanisms for diet segregation between the three species.     

Alteration of photosystem II activity by atrazine on Chlamydomonas reinhardtii synchronized and asynchronized cell cycle cultures

Inhibition of photosystem II (PSII) activity by atrazine was investigated in the green alga Chlamydomonas reinhardtii during different states of the cell cycle. The algal cultures were maintained under continuous light or under light/dark cycle (16/8?h) to obtain homogenized cell cycle distribution. The cycle state of algal population was determined by the DNA content using flow cytometry and defined as newly divided cells before the initiation of DNA replication (G₀/G₁) and cells at the end of the replication cycle with fully duplicated DNA content (G₂/M). Under different synchronized states of the cell population, the photosynthetic activity was investigated after treatment at 10, 100, and 1000?µmol?L^?1 atrazine exposed for 24?h by using fluorescence parameters related to PSII activity measured with a plant efficiency analyzer and pulse-amplitude modulated methods. In this study, we found that the atrazine effect was different depending on cell cycle phases and the period of illumination. Algal cells under light–dark cycle showed inhibition of the PSII electron transport leading to an increase of heat energy dissipation by the PSII reaction center. Algal cells grown under continuous light was shown to be more resistant to atrazine than the cells grown under light–dark cycle.     

Sequestration of dietary secondary metabolites by three species of sea hares: location,specificity and dynamics

We examined the location of squuestered secondary metabolites in three species of sea hares, Stylocheilus longicauda, Dolabella auricularia, and Aplysia californica (Opisthobranchia: Anaspidea). The sea hares ate a natural diet or were fed an artificial diet containing secondary metabolites in the laboratory. In all three species, sequestered secondary metabolites were located almost exclusively in the digestive gland, an internal organ, rather than in the exterior parts of the body, in eggs, or in ink (released when sea hares are disturbed). S. longicauda, a specialist sea hare, was able to sequester measur-able amounts of all six algal metabolites offered (caulerpenyne, halimedatetraacetate, pachydictyol A, malyingamides A and B, and ochtodene) and two (luffariellolide and Dysidea spp. brominated diphenyl ether) of three sponge metabolites offered (chondrillin was not sequestered). Malyngamides A and B, found in the host plant of S. longicauda, were sequestered at high, but not unique concentrations. D. auricularia, a generalist sea hare, was fed caulerpenyne, pachydictyol A and malyngamide B; patterns of sequestration of these three compounds did not differ markedly between S. longicauda and D. auricularia. S. longicauda did not lose measurable amounts of malyngamides after 18 d on a malyngamide-free diet. These results suggest that sea hares have generic mechanisms for sequestering algal metabolites rather than mechanisms that are tightly linked to particular compounds, that these mechanisms do not differ dramatically between species, and that sequestered secondary metabolites are not located optimally for defense.     

Carbohydrate metabolism in the marine diatom Skeletonema costatum

This is a study on the metabolism of the algal biochemical constituents of a marine diatom, Skeletonema costatum. The carbohydrates, protein, and lipid, of the diatom grown under light and dark conditions were analyzed. The composition of the organic compounds did not vary in the alga grown under continuous light conditions throughout the experiment, although a little accumulation of carbohydrate and lipid was observed in the stationary phase of the algal growth. When the diatom, at maximum growth stage, was transferred to darkness, 44.4% of the carbohydrate, 57.8% of the protein, and 27.0% of the lipid were used by respiration within a few days. Detailed analysis of the algal carbohydrate demonstrated that low molecular weight carbohydrates, consisting of glucose, and -1,3-glucan, were readily metabolized by algal respiration, leaving cell-wall carbohydrates consisting of mannan and pentosan which are immune to algal respiration. The respiratory utilization of carbohydrates is discussed in relation to the rapid decay of glucan from marine particulate matter during the course of its sinking to further depths in the ocean, as observed previously by the present author.     

锌在不同磷源条件下对铜绿微囊藻生长与产毒的影响

针对磷和微量元素对藻类生长的共同作用,研究不同磷源条件下锌对藻细胞生长与产毒的影响。实验选用铜绿微囊藻为藻种,分别以无机磷磷酸氢二钾(K_2HPO_4)、小分子有机磷甘油磷酸钠(NaGly)和大分子有机磷卵磷脂(LEC)为磷源,研究不同锌(Zn~(2+))含量对藻细胞的藻密度、碱性磷酸酶活性(alkaline phosphatase activity,APA)以及胞内藻毒素(MC-LR)的影响。研究发现:以NaGly为磷源时微量元素锌对藻细胞生长的促进效果显著,而以K_2HPO_4或LEC为磷源时,锌含量的变化对藻细胞生长无显著影响。APA不仅与磷源有关而且与锌含量相关,以LEC为磷源时的APA显著高于以K_2HPO_4或NaGly为磷源时的APA,且锌含量越低APA越低,以K_2HPO_4为磷源时锌含量越低APA越高,而锌对以NaGly为磷源时的APA几乎没有影响。磷源与微量元素锌对藻细胞的产毒均产生影响,NaGly有利于藻毒素的产生; LEC不利于藻细胞的产毒,但锌含量越低藻细胞的产毒量越多。综上所述,磷源与微量元素锌共同作用对藻细胞的生长与产毒产生影响,小分子有机磷NaGly与锌的效果显著。     

Nutritional effect of five species of marine algae on the growth,development, and survival of the brine shrimp Artemia salina

Five species of unicellular algae of the same age, cultured bacteria-free under standard growth conditions, were analyzed for chemical composition and fed to different size classes of Artemia salina. The green algae Chlamydomonas sphagnicolo, Dunaliella viridis, Platymonas elliptica and Chlorella conductrix had significantly higher percentages of protein and lipid than did the diatom Nitzschia closterium. Total ash value was highest in populations of N. closterium. Shrimp fed Chlamydomonas sphagnicolo cells assimilated highest percentages of organic matter, while those fed Chlorella conductrix had lowest assimilation rate. Respiration rates were inversely proportional to animal size (weight) and algal cell volume. Growth, survival, rate of sexual maturtion, and sex ratio were dependent on the growth and assimilation efficiencies obtained from each respective algal food. Shrimp fed Chlamydomonas sphagnicolo, D. viridis, or P. elliptica cells displayed highest growth and assimilation efficiencies.     

Annual cycles of phytoplankton community-structure and bloom dynamics in the Neuse River Estuary, North Carolina

The spatiotemporal distributions of major phytoplankton taxa were quantified to estimate the relative contribution of different microalgal groups to biomass and bloom dynamics in the eutrophic Neuse River Estuary, North Carolina, USA. Biweekly water samples and ambient physical and chemical data were examined at sites along a salinity gradient from January 1994 through December 1996. Chemosystematic photopigments (chlorophylls and carotenoids) were identified and quantified using high-performance liquid chromatography (HPLC). A recently-developed factor-analysis procedure (CHEMTAX) was used to partition the algal group-specific chlorophyll a (chl a) concentrations based on photopigment concentrations. Results were spatially and temporally integrated to determine the ecosystem-level dynamics of phytoplankton community-constituents. Seasonal patterns of phytoplankton community-composition changes were observed over the 3 yr. Dinoflagellates reached maximum abundance in the late winter to early spring (January to March), followed by a spring diatom bloom (May to July). Cyanobacteria were more prevalent during summer months and made a large contribution to phytoplankton biomass, possibly in response to nutrient-enriched freshwater discharge. Cryptomonad blooms were not associated with a particular season, and varied from year to year. Chlorophyte abundance was low, but occasional blooms occurred during spring and summer. Over the 3 yr period, the total contribution of each algal group, in terms of chl a, was evenly balanced, with each contributing nearly 20% of the total chl a. Cryptomonad, chlorophyte, and cyanobacterial dynamics did not exhibit regular seasonal bloom patterns. High dissolved inorganic-nitrogen loading during the summer months promoted major blooms of cryptomonads, chlorophytes, and cyanobacteria. Received: 12 September 1997 / Accepted: 12 December 1997     

Growth and reproduction of the generalist opisthobranch Haloa japonica: effect of algal seasonality on growth rate

The life history of Haloa japonica (Pilsbry), especially the seasonality of growth and reproduction, was investigated from 1992 to 1995 on a flat rocky shore exposed at low tide at Kattoshi, Hakodate Bay, Japan. To estimate the effect of environmental seasonality on growth rate, we conducted two sets of field cage experiments in which algal food was controlled. H. japonica was shown to have an annual life cycle. Spawning occurred from late April to mid-July. Recruitment occurred in June. Simultaneously, large adults disappeared from the habitat. A rapid increase in wet weight of H. japonica was observed in early spring, and coincided with the bloom of the membranous green alga, Monostroma angicava. Under field cage experiments, individuals feeding on both M. angicava and Polysiphonia japonica grew faster than those feeding on only P. japonica. Growth rates of H. japonica feeding on only P. japonica, however, did not vary from February to April. These results suggest that seasonal variation in the algal community limits the growth of H. japonica in early spring at Kattoshi. This factor is relatively more important as a limiting factor on the growth of H. japonica than the physical environment in this season.     

Feeding four species of pelagic copepods under experimental conditions

Different qualitative and quantitative aspects of feeding with varied compositions of diets have been studied in 4 species of pelagic copepods: Calanus helgolandicus, Centropages typicus, Temora stylifera and Acartia clausi. By feeding copepods different algal concentrations, it was shown that when food concentration increases grazing rate decreases; the ingestion rate remains fairly constant in the lower range of concentrations, but then increases, reaching a plateau at higher algal concentrations. There is a significant correlation between daily food intake and fecal pellet production. On a pluri-algal diet, selective grazing is observed: larger phytoplankton cells are more efficiently removed than smaller ones. Using Artemia nauplii, it is shown that the copepods studied are also able to eatch and ingest animal prey. Increased daily food intake affects respiration and oviposition. Metabolic requirements, gross growth-efficiency, and food assimilation have been ealculated in Calanus helgolandicus, Centropages typicus and T. stylifera for a large range of algal concentrations.     

Functional identity and functional structure change through succession in a rocky intertidal marine herbivore assemblage

Despite the great interest in characterizing the functional structure and resilience of functional groups in natural communities, few studies have examined in which way the roles and relationships of coexisting species change during community succession, a fundamental and natural process that follows the release of new resources in terrestrial and aquatic ecosystems. Variation in algal traits that characterize different phases and stages of community succession on rocky shores are likely to influence the magnitude, direction of effects, and the level of redundancy and complementarity in the diverse assemblage of herbivores. Two separate field experiments were conducted to quantify per capita and population effects and the functional relationship (i.e., redundancy or complementarity) of four herbivore species found in central Chile during early and late algal succession. The first experiment examined grazer effects on the colonization and establishment of early-succession algal species. The second experiment examined effects on the late-successional, dominant corticated alga Mazzaella laminarioides. Complementary laboratory experiments with all species and under natural environmental conditions allowed us to further characterize the collective effects of these species. We found that, during early community succession, all herbivore species had similar effects on the ephemeral algae, ulvoids, but only during the phase of colonization. Once these algae were established, only a subset of the species was able to control their abundance. During late succession, only the keyhole limpet Fissurella crassa could control corticated Mazzaella. The functional relationships among these species changed dramatically from redundant effects on ephemeral algae during early colonization, to a more complementary role on established early-successional algae, to a dominant (i.e., keystone) effect on late succession. This study highlights that functional relationship within consumer assemblages can vary at different phases and times of community succession. Differentiation in herbivore roles emphasizes the need to evaluate consumer's impacts through different times of community succession, and through experimental manipulations to make even broad predictions about the resilience or vulnerability of diverse intertidal assemblages to human disturbances.     

Reproduction ofCalanus glacialis under ice in spring in southeastern Hudson Bay,Canada

In situ egg production rates ofCalanus glacialis Jaschnov females caught under the ice cover of southeastern Hudson Bay, Canada, between early April and mid-June 1986 were measured by direct observations and by an egg-ratio method in order to investigate the role of ice microalgae and under-ice phytoplankton production in copepod reproduction. Egg production commenced, although at low rates, in early May, about 3 wk after the onset of measurable concentrations of ice microalgae at the ice-water interface. Egg production increased to about 12 eggs female^–1 d^–1 in early June, after the ice cover began to melt. The time taken by immature adult females to reach maturity in the field was estimated to be ca. 3 wk (between late April and mid-May) by visual evaluation of gonad maturity in preserved females. In the laboratory, females caught on 10 April and maintained in saturating concentrations of the diatomThalassiosira weissflogii took only a few days to produce eggs at high rates, indicatingC. glacialis was food-limited during the ice algal bloom at the interface. We suggest that ice algal grazing changes the timing, relative to high food concentrations in the water column, of reproduction inC. glacialis by promoting oogenesis and oocyte maturation.Contribution to the programme of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec)Please send all reprint requests to Dr. Runge at his current address: Institut Maurice-Lamontagne, Ministère des Pêches et Océans, C. P. 1000, Mont-Joli, Québec G5H 3Z4, Canada     

Resource utilization for decorating in three intertidal majid crabs (Brachyura: Majidae)

 For three spider crabs (Tiarinia cornigera, Micippaplatipes and Pugettia quadridens quadridens), patterns of algal utilization for decorating were compared with the dynamics of algae on an intertidal rocky shore reef where the crabs co-occurred. T. cornigera and P. quadridens quadridens were most abundant from autumn to spring when the dominant algae (Boodleacoacta, Sargassum hemiphyllum, S. thunbergii and Corallina pilulifera) occurred in high coverage, while M. platipes was most abundant from spring to autumn. Monthly change of algae used for decorating was not correlated with algae growing in the crab habitat for T. cornigera, but for M. platipes, it was positively correlated for two algal species, and for P. quadridens quadridens, negatively correlated for one algal species. Each species of the spider crabs used some algal species preferentially for decoration. Decorating preference experiments conducted in the laboratory showed that M. platipes and P. quadridens quadridens exhibited similar preference to their algal utilization in the field, whereas for T. cornigera, algal preference in the experiment differed from utilization in the field. Comparisons between materials used for decoration and gut contents revealed that T. cornigera and M. platipes used algal species differently for decorating and feeding, while P. quadridens quadridens used the same algal species for both decorating and feeding. Different tactics for camouflage are discussed in terms of algal utilizations by the three majid species. Received: 25 September 1999 / Accepted: 22 June 2000     

Energy budgest,growth and filtration rates in Mytilus edulis at different algal concentrations

Growth of Mytilus edulis L. was measured in aquaria with through-flowing sea water at different levels of constant algal concentrations. The amount of food and oxygen consumed by the mussels were measured over given periods as well as the changes in dry organic weight during the same periods. From these parameters it was possible to make simple energy budgets and to compare the estimated growth with actual growth, and, further, to determine growth efficiences at different food levels. Energy budgets were made for mussels grown at algal concentrations of 0, 1.6×10³, 3.0×10³ and 26.0×10³ Phaeodactylum tricornutum cells x ml^-1. The estimated growth was found to be close to actual growth at algal concentrations above maintenance level and the net growth efficiency was found to be between 18% (3.0×10³ cells x ml^-1) and 61% (26×10³ cells x ml^-1). It has been shown that the filtration rate is independent of algal concentrations between about 1.5×10³ to 30×10³ P. tricornutum cells x ml^-1. Outside this range a decrease in filtration rate was noticed.     

The effect of limiting nutrient on metal toxicity to selenastrum capricornutum

Metal toxicity on selenastrum capricornutum were examined by batch culture and chemostat culture system. EC₅₀ values under nutrient‐limited condition and saturated condition were compared. The two EC_5Os differed by a factor of 10.6 for Cd in batch test, and differed by a factor of 6.5 in continuous test. Both batch and continuous test results indicate that inhibition on algal growth is more severe under nutrient‐limited conditions compared to that under near saturation conditions.

Strong correlation, as characterized by the correlation coefficient ρ, were found between the activation level (nutrient requirement) and the tolerance of microorganisms to the toxicant. ρ is equal to 0.9 for the case of Cd in batch test and 0.6 in continuous test. The theory in this study provides generally good estimations to the dose‐response relationship at limiting nutrient conditions. The study indicate that nutrient conditions constitute an important factor in algal toxicity tests.     

Growth pattern andβ-dimethylsulphoniopropionate (DMSP) content of green macroalgae at different irradiances

Growth rates and intracellular-dimethylsulphoniopropionate (DMSP) concentrations of five green algal species collected from different geographic regions in 1986 and 1989 were determined under four photon flux rates. InUlothrix implexa, U. subflaccida andAcrosiphonia arcta from Antarctica, growth was light-saturated at lower irradiances than in temperateUlva rigida from Southern Chile andBlidingia minima from Germany. The DMSP content ofUlothrix implexa, A. arcta andUlva rigida was directly correlated with the light factor: with increasing irradiance, algal DMSP level increased. In contrast, inUlothrix subflaccida andB. minima DMSP concentrations gradually decreased up to a photon flux rate of 30µmol m^–2 s^–1, then increased markedly under the highest photon flux rate tested. In non-growing, dark-incubatedA. arcta DMSP content was reduced by 35%, while the DMSP pool of all other species remained unchanged, at the level of pre-culture conditions. Under full darkness all plants exhibited a significantly higher DMSP concentration compared with algae grown at low photon flux rates of 2 to 30µmol m^–2 s^–1. These data show a correlation between growth pattern and DMSP biosynthesis, and may point to a species-specific minimum amount of light energy necessary for DMSP accumulation.Contribution no. 302 of the Alfred Wegener Institute of Polar and Marine Research     

Preliminary study on the consumption of dissolved organic matter (exudates) of bacteria and phytoplankton by the marine bivalve Venus verrucosa

The utilisation of the exudates of bacteria (Lactobacillus sp.) and phytoplankton (Pavlova lutheri) by the clam Venus verrucosa Linné under identical experimental conditions was studied. 61.7% of the bacterial exudates were consumed but only 19.9% of the algal exudates. V. verrucosa would seem to assimilate bacterial products more easily than phytoplankton exudates. The study was performed in 1980.