Hans J. Hartmann

Contribution of Ciliated Microprotozoans and Dinoflagellates to the diet of three Copepod species in the Bay of Biscay

Predation of three calanoid copepods (Calanus helgolandicus, Temora longicornis and Centropages chierchiae) on phytoplankton, dinoflagellates and ciliates was estimated in the Gironde estuarine plume (Bay of Biscay) during winter by means of in situ incubations. Both phytoplankton and ciliates were part of the diet of those three species, while only Centropages chierchiae also included a significant portion of dinoflagellates in its diet. The clearance rates of Calanus helgolandicus for ciliates and phytoplankton reached 2.8 and 4.0 ml copepod−1 h−1, respectively, those of Temora longicornis were 3.2 and 1.8 ml copepod−1 h−1, and those of Centropages chierchiae were 4.3 and 0.8 ml copepod−1 h−1.Neither Calanus helgolandicus nor Temora longicornis selected dinoflagellates, given the low clearance rates measured for this prey category (0.05 and 0.03 ml copepod−1 h−1, respectively). By contrast, Centropages chierchiae included dinoflagellates in its diet, with a clearance rate of 4.9 ml copepod−1 h−1. Within a given prey category (ciliates or dinoflagellates), all three copepods selected larger prey types (>40 μm) over smaller ones (≤40 μm). This implies a better detection and capture of larger motile prey compared to small ones. The results are discussed with regard to the omnivorous feeding behavior of these copepods observed here, during a late winter phytoplankton bloom.

Mechanisms of food selection in Daphnia

A conceptual behavioural and mechanistic Holling-type model of food selection in Daphnia pulicaria is derived from SEM observations with animals feeding on mixtures of spherical-cylindrical diatoms, oblongate green algae, and filamentous cyanobacteria, as well as ultrafine particles. The algae used were Stephanodiscus hantzschii (≤6 µm length), Monoraphidium setiforme (≥20 µm), and Oscillatoria aghardii (strands, ≥80 µm). Cell (strand) selection can occur at any or all of three stages: (i) interception from the feeding currents, (ii) collection and channeling to the food groove, and (iii) compaction and transport to the mouth. During each stage, given equal initial cell densities, elongate cells are more likely to escape collection than spherical cells and are more likely to be rejected. In addition, filaments require increased handling time at stages (ii) and (iii) and promote entanglement with limb 5 and the postabdominal claw. Food is collected primarily with the aid of limbs 3 (and 4), but limbs 1 and 2 also intervene. Neither the leaky sieve hypothesis alone nor any other single-process hypothesis explains the observations on examined in corpore positions, morphology, and derived movements of the feeding limbs. Attachment and mucus appear to be important for the ingestion of bacteria and ultrafine particles.

Pelagic food web patterns: do they modulate virus and nanoflagellate effects on picoplankton during the phytoplankton spring bloom?

As agents of mortality, viruses and nanoflagellates impact on picoplankton populations. We examined the differences in interactions between these compartments in two French Atlantic bays. Microbes, considered here as central actors of the planktonic food web, were first monitored seasonally in Arcachon (2005) and Marennes-Oléron (2006) bays. Their dynamics were evaluated to categorize trophic periods using the models of Legendre and Rassoulzadegan as a reference framework. Microbial interactions were then compared through 48 h batch culture experiments performed during the phytoplankton spring bloom, identified as herbivorous in Marennes and multivorous in Arcachon. Marennes was spatially homogeneous compared with Arcachon. The former was potentially more productive, featuring a large number of heterotrophic pathways, while autotrophic mechanisms dominated in Arcachon. A link was found between viruses and phytoplankton in Marennes, suggesting a role of virus in the regulation of autotroph biomass. Moreover, the virus-bacteria relation was weaker in Marennes, with a bacterial lysis potential of 2.6% compared with 39% in Arcachon. The batch experiments (based on size-fractionation and viral enrichment) revealed different microbial interactions that corresponded to the spring-bloom trophic interactions in each bay. In Arcachon, where there is a multivorous web, flagellate predation and viral lysis acted in an opposite way on picophytoplankton. When together they both reduced viral production. Conversely, in Marennes (herbivorous web), flagellates and viruses together increased viral production. Differences in the composition of the bacterial community composition explained the combined flagellate-virus effects on viral production in the two bays.

Short-term variations of the abundance and biomass of planktonic ciliates in a eutrophic lake

Short-time spatio-temporal variations of planktonic ciliates in a eutrophic lake were examined for evidence of diel vertical migration in relation to food supply (bacteria, nanoplankton, and detritus) and physico-chemical parameters. Two campaigns were conducted during successive summers in Lake Aydat, France. Ciliates were less abundant during the first campaign (July 1988; global means 1500 cells/1 and 61.0 μgC/l) than during the second (July 1989; 5000 cells/l; 110.8 μgC/l). On both dates, ciliate abundance decreased from surface to depth, while biomass increased. Each layer (epilimnion, metalimnion, hypolimnion) was inhabited by a separate ciliate community, generally dominated by bacterivores/detritivores. There was no clear evidence of vertical migrations across major physical-chemical boundaries. Circadian variations in each layer occurred independently of light-dark rhythms, partly due to micropatchiness. Temporal variability increased from the vertically mixed epilimnion (C.V. = 32%-41%) to the well stratified deeper zones (C.V. = 41%-100%). Ciliate biomass was negatively and significantly correlated to temperature and dissolved oxygen, and to most principal food parameters. The vertical differences in ciliate biomass were linked to the long-term (seasonal) evolution of the lake system (correlations with temperature, oxygen) and its larger-sized food resources (correlations with chlorophyll, nanoplankton, detritus). By contrast, circadian variations of ciliates were linked to availability of bacteria, an important food resource for many ciliate species of this study.

Potential Effect of Freshwater Virus on the Structure and Activity of Bacterial Communities in the Marennes-Oléron Bay (France)

Batch culture experiments using viral enrichment were conducted to test the response of a coastal bacterial community to autochthonous (i.e., co-existing) or allochthonous riverine viruses. The effects of viral infections on bacterial dynamics and activity were assessed by epifluorescence microscopy and thymidine incorporation, respectively, whereas the effect of viral infection on bacterial community composition was examined by polymerase chain reaction-single strand conformation polymorphism 16S ribosomal RNA fingerprinting. The percentages of high nucleic acid-containing cells, evaluated by flow cytometry, were significantly correlated (r2 = 0.91, n = 12, p < 0.0001) to bacterial production, making this value a good predictor of active cell dynamics along the study. While confinement and temperature were the two principal experimental factors affecting bacterial community composition and dynamics, respectively, additions of freshwater viruses had significant effects on coastal bacterial communities. Thus, foreign viruses significantly reduced net bacterial population increase as compared to the enrichment treated with inactivated virus. Moreover, freshwater viruses recurrently and specifically affected bacterial community composition, as compared to addition of autochthonous viruses. In most cases, the combined treatment viruses and freshwater dissolved organic matter helped to maintain or even enhance species richness in coastal bacterial communities in agreement to the ‘killing the winner’ hypothesis. Thus, riverine virus input could potentially influence bacterial community composition of the coastal bay albeit with modest modification of bulk bacterial growth.

Evidence for the contribution of ciliates to denitrification in a eutrophic lake.

High levels of nitrate reductase (NR) activity were found during a field survey in the epilimnion and metalimnion of a temperate lake (Lake Aydat, France) during summer stratification, when nitrates were analytically undetectable (< 0.5 mg L(-1)). We hypothesized that the NR activities were due to phytoplankton in the epilimnion, due to the ciliate Loxodes at the mid-depth oxic/anoxic interface and preferentially due to bacteria in the anoxic hypolimnion of the lake. In support of the hypothesis, a significant negative correlation was detected in the metalimnion between the abundance of Loxodes and nitrate concentrations, indicating nitrate use by the ciliate, and significant positive correlations were found between bacteria and nitrite concentrations at depth. The correlations are corroborated by additional evidence from chlorophyll a/NRA ratios, nitrite dynamics, and lake circulation patterns. Other ciliates besides Loxodes did not appear to significantly contribute to NRA potential. The data suggest that facultatively anaerobic ciliates such as Loxodes may be significant contributors to denitrification in eutrophic planktonic ecosystems.

Microbial interactions in marine water amended by eroded benthic biofilm: A case study from an intertidal mudflat

Abstract In shallow macrotidal ecosystems with large intertidal mudflats, the sediment–water coupling plays a crucial role in structuring the pelagic microbial food web functioning, since inorganic and organic matter and microbial components (viruses and microbes) of the microphytobenthic biofilm can be suspended toward the water column. Two experimental bioassays were conducted in March and July 2008 to investigate the importance of biofilm input for the pelagic microbial and viral loops. Pelagic inocula (

“Marine Areas of Responsible Fishing”: A Path Toward Small-Scale Fisheries Co-Management in Costa Rica? Perspectives from Golfo Dulce

This chapter analyzes participatory management processes of small-scale fisheries in two Pacific embayments of Costa Rica, a centralized state of Central America where fisheries management is traditionally “top-down”, data deficient, and poorly adapted to local biological and socio-economic conditions. We provide an historical overview of coastal activities governance and fisheries national context, and describe different participative approaches to small-scale fishery management. The Marine Area of Responsible Fishing (Area Marina de Pesca Responsable, or AMPR), created in 2008, is a management tool developed by the Costa Rican government to effectively involve fishers organizations in small-scale fisheries management. In this paper, we compare participative management initiatives associated with AMPRs in the Golfo Dulce and Golfo de Nicoya (Palito and Tarcoles), and Marine Protected Areas (MPAs) in Cahuita and Marino Ballena National Parks. Based on our analysis, we recommend ten measures to improve the small-scale fisheries co-management process. Among these, five recommendations stand out: (1) increase the participation of artisanal fishers in the development of collective choice rules; (2) allocate costs and benefits of management measures among artisanal fishers; (3) improve local leadership; (4) improve understanding and transparency of the management process; and (5) formalize and implement strategic fisheries management plans.

Preliminary analysis of the fish species of the Pacific Central American Mangrove of Zancudo, Golfo Dulce, Costa Rica.

The aim of the present paper is to provide first information on the mangrove fish community of the tropical fjord-like Golfo Dulce (GD), to study its importance for fish diversity and fisheries in the area and to give preliminary results on its spatial–temporal variation. Eighty-two species belonging to 30 families were identified. More than half of them belonged to the estuarine transient fish group and only 14 species were estuarine resident, highlighting the importance of the Zancudo mangrove as a transition area. The most diverse families were Sciaenidae, Carangidae and Haemulidae for both rainy and dry seasons. As much as 71% of the species captured were of first or second grade economic value and only 11% had no commercial value. Comparing our data with fisheries and scientific surveys inside and outside the gulf suggests the importance of the Zancudo mangrove for regional fisheries and fish diversity. Multidimensional scaling (MDS) indicated gradual changes in the fish community composition from the river mouth to the more internal sampling sites for rainy and dry seasons. Moreover, shifts in abundance and species composition between seasons were observed, mainly an increase in the differences between the boundaries and the central zones of the mangrove. These changes were attributed to the higher salinity differences between sites during the dry season forcing the occasional visitor fish downstream and freshwater fish taxa upstream. While the results contribute to initiatives for participative fisheries management in the region, further studies are needed to analyse the variations in detail.

Impact of biofilm resuspension on mesozooplankton in a shallow coastal ecosystem characterized by a bare intertidal mudflat

A prey–predator experimental setup was conducted in a shallow coastal ecosystem characterized by a bare intertidal mudflat to test if benthic biofilm resuspension causing microalgae inputs and carbon export toward nanoflagellates would favour the highest planktonic trophic level (i.e. mesozooplankton) when nutrient concentrations are high in the water column. Mesozooplankton predation and somatic production were studied by comparing the evolution of the prey assemblage (diversity and abundances) in the presence and absence of these predators during 24 h experiments. The results were then statistically analysed according to the cross-calculation method. Biofilm resuspension caused (i) a direct input of benthic microorganisms that had changed prey structure in term of diversity and/or size and (ii) a differential growth ability between prey taxa. Both reasons implied a bottom-up control on both micro- and mesozooplankton. The carbon export toward heterotrophic nanoflagellates favoured pelagic ciliate growth while mesozooplankton benefited from largest diatoms with high growth rates, both benthic and R-strategist pelagic species. Even if these microbial and herbivorous pathways are controlled by benthic inputs, they seemed to be totally disconnected since ciliates represented only a small part of mesozooplankton diet. The sensitivity of mesozooplankton production appeared species-dependent with the most tolerant taxa dominating the zooplankton assemblages. This suggests a role of the intensities and the frequencies of biofilm resuspension on the spatio-temporal structuring of mesozooplankton in macrotidal coastal ecosystems.