Regulation of microbial production in intertidal mudflats : the role of Amphibola crenata, a deposit feeding gastropod

Interactions between the deposit feeding gastropod Amphibola crenata and the microbial community in intertidal mudflats were studied in laboratory and field experiments in two New Zealand estuaries. The study was mainly designed to reveal the effect of deposit feeding on bacterial and microalgal production and assess the importance of these microorganisms to the nutrition of the snail. The secondary aim was to compare the influence of Amphibola to external factors which regulate microbial production on the mudflat. Short-term effects of deposit feeding on bacterial production were examined by monitoring the recolonisation of Amphibola faeces by bacteria. Long-term effects on bacterial production were studied in artificial enclosures in the field where the effect of snail density on bacterial numbers and activity was monitored. These same enclosures were also used to study the effect of grazing by the snail on standing crop and productivity of the epibenthic algae. Assimilation of bacterial carborn by Amphibola was experimentally measured, and the contribution of bacterial and microalgal carbon to the snail’s carbon budget was estimated. The effect of microbial biomass on the feeding behaviour of Amphibola was also examined. It was found that a pulse in bacterial production occured during the recolonisation of Amphibola faeces by bacteria. This appeared to be similar in magnitude to the amount of bacterial biomass consumed by the snail - approximately 4. 5 mg C/m²/day. Amphibola also had a minor long-term influence on bacterial numbers and activity, but no clear effect on productivity was apparent. Grazing by Amphibola caused a substantial reduction in microalgal standing crop and productivity and affected the species composition of the microalgal community. Both the bacteria and microalgae serve as significant sources of carbon for the snail, but a large additional input of carbon is required to meet its nutritional needs. Other possible sources of carbon for the snail include meiofauna and non-living organic material. Amphibola was also found to alter its feeding rate in response to changes in microbial biomass, in a manner which may improve the return for feeding effort. In overview, it appears that Amphibola and the sediment bacteria similarly influence the other 's productivity while Amphibola has a greater effect on the microalgae than the microalgae have on Amphibola. Ultimate control of microbial productivity was concluded to be external to these relationships, with the snail acting only to modify seasonally determined levels of productivity

Ice-brine and planktonic microheterotrophs from Saroma-ko Lagoon, Hokkaido (Japan): quantitative importance and trophodynamics

International audienceCopyright (c) 1996 Elsevier Science B.V. All rights reserved. Biologists have rarely had the opportunity to investigate the community characteristics and dynamics of heterotrophic microorganisms in highly productive first-year sea ice. In this study, sterile seawater was used as a salinity buffer to extract the ice-brine microheterotroph communities (bacteria, flagellates and ciliates&rpar; from a coastal lagoon in Japan (Saroma-ko, Hokkaido; 44°N, 144°E&rpar; during the late winter (February−March&rpar; of 1992. This procedure reduced osmotic shock during the melting of ice cores and allowed the recovery of up to 323% more cells than the traditional melting method. Most of the organisms were concentrated in the bottom 3−4 cm of the ice, where abundances were up to 33 times higher than in the plankton. In ice and plankton samples, heterotrophic flagellates were dominated by small species (<8 μm, mainly choanoflagellates&rpar; and cryothecomonad-type cells while ciliates were dominated by a photosynthetic species, Mesodinium rubrum. In contrast to higher latitudes, increased snow cover appeared to favor the development of protozoa beneath the relatively thin 30−40 cm ice cover of Saroma-ko Lagoon. Temporally, a successional sequence was observed between protozoa and the bacterial compartment. Bacteria decreased in abundance throughout the sampling period while protozoa increased or attained their maximum number in late winter, toward the end of the sampling period. These observations support previous suggestions of the existence of a functional microbial food web within the sea-ice community. Heterotrophic flagellate biomass greatly exceeded bacterial biomass in the sea ice (30−60×&rpar;. Coupled with similar potential growth rates, this suggests the utilization of additional (non-bacterial&rpar; food items by ice-brine flagellates. Finally, the effects of salinity variations (ranging between 15 and 120 psu&rpar; on potential microheterotroph growth rates are discussed

Protozoan Bacterivory in the Ice and the Water Column of a Cold Temperate Lagoon.

International audience> Abstract Bacterial abundance and bacterivorous protist abundance and activity were examined in ice-brine and water column communities of a cold temperate Japanese lagoon (Saroma-Ko Lagoon, Hokkaido, 44 degreesN, 144 degreesE), during the late winter phase of ice community development (February-March 1992). Bacterial abundance averaged 6 and 1 x 10(5) cells ml-1 in the ice-brine and plankton samples, respectively, and generally decreased during the sampling period. Bacterivorous protists, identified based on direct observation of short-term (<1 h) ingested fluorescently labeled bacteria (FLB) in their food vacuoles, were largely dominated by flagellates, mainly cryothecomonad-type and chrysomonad-like cells and small dinoflagellates of the genus Gymnodinium. Bacterivorous ciliates included mainly the prostomatid Urotricha sp., the scuticociliates Uronema and Cyclidium, the choreotrichs Lohmaniella oviformis and Strobilidium, and the hypotrich Euplotes sp. Protist abundance averaged 4 x 10(3) and 8.1 cells ml-1 in the ice-brine and 0.3 x 10(3) and 1.2 cells ml-1 in the plankton, for flagellates and ciliates, respectively. In contrast to bacteria, the abundance of protists generally increased throughout the sampling period, indicating predator-prey interactions. Protistan bacterivory, measured from the rate of FLB disappearance over 24 h, averaged 36% (ice) and 24% (plankton) of bacterial standing stock and exhibited the same seasonal pattern as for protist abundance. The calculated specific clearance (range, 2-67 nl protozoa-1 h-1) and ingestion (<1-26 particles protozoa-1 h-1) rates were likely to be minimal estimates and grazing impact may have been higher on occasion. Indications for the dependence of "bacterivorous protists" on nonbacterial food items were also provided. Although alternative sources of bacterial loss are likely to be of importance, this study provides evidence for the potential of protozoan assemblages as bacterial grazers in both sea ice-brine biota and water column at the southern limit of sea ice in the northern hemisphere

Influence of surface texture and microhabitat heterogeneity in structuring nodule faunal communities

Manganese nodules provide an important habitat for sessile benthic organisms, many of them novel foraminifera, in the abyssal Pacific. The surface texture and microhabitat heterogeneity of nodules may play a significant role in structuring these communities. We analyzed the distribution of foraminiferal species on 20 nodules collected using either a USNEL box corer or the Nautile submersible sampling tool at a 5000-m-deep site in the Tropical North Pacific. The nodules had an upper region characterized by two microhabitats, namely raised surfaces and intervening depressed surfaces. The more or less vertical sides of the nodules were regarded as a third microhabitat. The upper region had a predominantly smooth texture while the sides had a rough texture. We tested whether the percent cover of each of the 34 species examined was distributed evenly over the three microhabitats and the two surface textures (smooth vs rough). More than half (20 out of 34) of species covered a greater area on smooth surfaces than on rough surfaces, while one-third of the species (12 out of 34) occurred more on raised microhabitats than on depressed surfaces and nodule sides. These two results are closely interrelated, since 78% of the raised surfaces were characterized by a smooth texture. The nodule-encrusting species were feeding either on suspended particles or on particles deposited on the nodule surfaces. Because most species had a mat-like or domed morphology, we suspect that nodule surface feeding was more prevalent. Current flow, which transports propagules and particulate food, may be the main environmental factor explaining the observed faunal distributions, as it is in the case of other hard-substrate assemblages

Changes in sea-ice phagotrophic microprotists (20-200 µm) during the spring algal bloom, Canadian Arctic Archipelago

International audienceHeterotrophic microflagellates and ciliates (i.e., 20–200 μm size fraction) were examined for evidence of their response to the spring accumulation of algal biomass in the bottom of the annual sea ice in Resolute Passage (Canadian High Arctic, 74°N, 95°W). The most abundant heterotrophic microflagellates were dinoflagellates in the water column and cryothe-comonad-type cells in the ice. Ciliates were exclusively represented by typical planktonic species in the water column while the ice community was characterized by the occurrence of benthic-type species. This contrasts with observations in the Antarctic and at the southern limit of sea ice in the northern hemisphere, where annual sea ice seems to serve as a temporary habitat for planktonic communities. Protist biomasses in Resolute Passage were one to two orders of magnitude higher in the ice than in the plankton. In the ice, a seasonal increase in the biomass of phagotrophic microprotists as well as in the number of micrometazoa (from our microprotist samples) followed the spring algal bloom. These observations (1) support previous suggestions of the existence of a functional microbial food web within sea-ice communities and (2) indicate that micrograzers may represent one of the basic levels of the ice food web that responds to the seasonal accumulation of algal biomass. Heterotrophic microprotists growing in the ice accumulated about 4 mg C m−2 d−1, a net production rate that is two to four times higher than those reported for sea-ice bacteria (both Arctic and Antarctic), and represented 1–9% of the net production of ice algea in the early season at resolute. A carbon budget exercise indicated that the required energy for microprotozoan growth in the later season, when algal biomass was declining, corresponded to 1–8% of the net biomass loss from the ice algal populations. The specific growth rates of microprotozoan populations within the ice (0.04–0.18 d−1) appeared to increase significantly with decreasing algal productivity. This may be critical for the protracted heterotrophic food web in multi-year ice and to many consumers during the long polar winter

Data from: Multi-parametric study of behavioural modulation in demersal decapods at the VENUS cabled observatory in Saanich Inlet, British Columbia, Canada

Understanding biological rhythms in benthic ecosystems and their modulation by habitat cycles has important implications for resource and ecosystem management. The recent development of permanent, multi-sensor seafloor observatories in deep-water environments provides opportunities for the in situ investigation of the behaviour of benthic organisms in relation to habitat variability. This paper describes a multi-disciplinary investigation at the VENUS observatory platform in Saanich Inlet, an intermittently anoxic fjord (Vancouver Island, Canada). A remotely operated digital camera (103 m depth) was used to document changes in the abundance of shrimp (Spirontocaris spp.) and the squat lobster (Munida quadrispina), as well as bacterial mat coverage (Beggiatoa spp.). These data were used as proxies of diel rhythms related to day–night and internal tidal cycles. Seafloor photos were acquired hourly during consecutive days, before, during and after oxygen intrusion events in the fall of 2009. In order to relate biological fluctuations to habitat cycles, bottom water pressure, temperature, dissolved oxygen, and nitrate data were also acquired from the observatory database. Periodogram analysis showed a weak internal-tide-associated rhythmicity for Spirontocaris spp. that was absent in M. quadrispina and in bacterial mat coverage. Waveform analysis confirmed the absence of any day–night fluctuation in all tested species. However, a rapid intrusion of oxygenated water at the study site influenced visual counts of species, possibly blurring detectable activity rhythms. Temperature and nitrate fluctuations were more accentuated during spring tides but cross-correlation analysis indicated an absence of species responses to these habitat variables. Results are discussed within the context of the complex oceanographic dynamics of Saanich Inlet and with respect to understanding the ecological consequences of expanding hypoxia in the global ocean

Carbon flows through the microbial food web of first-year ice in Resolute Passage (Canadian High Arctic)

International audienceCopyright (c) 1996 Elsevier Science B.V. All rights reserved. Ice algal communities are host to thriving populations of microheterotrophs whose trophic role remains poorly understood. We report here an inverse modelling analysis of the microbial food web associated with the spring bloom of ice algae at Resolute Passage in the High Arctic. Carbon flows among microbial components (ice algae, autotrophic and heterotrophic nanoflagellates, microflagellates and ciliates&rpar; and their exchanges with particulate and dissolved organic carbon (POC and DOC&rpar; were inferred from the observed changes in standing stocks of these compartments between 13 April and 22 May 1992. Calculations were made for three phases of the blooms development and for two sites under thin and thick snow cover. Observed DOC accumulations within the bottom ice originated largely from the ice algae. However, calculated production rates were too high to result strictly from normal physiological exudation. Mechanical or physiological stresses that disrupt the integrity of the cells and grazing by zooplankton at the ice−water interface may well be involved in this process. Inverse modelling confirmed field and experimental evidence that nanoflagellates may directly assimilate DOC to support their growth. Patterns in trophic flows between sites with thin and thick snow cover were similar. In contrast, trophic interactions changed as the bloom progressed: production of DOC and detritus from the ice algae were the only significant carbon flows during the early phase; bacterivory developed and peaked during the middle phase and was superseded by DOC utilization and herbivory by flagellates and ciliates during the late phase. Only ca. 20% of the DOC produced was utilized by the microheterotrophs. Direct links from DOC and ice algae to protists potentially increase the efficiency of C transfers within the ice-associated microbial food web; on the other hand, low recovery efficiency limits the role of the microbial loop in recycling DOC