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Home , Microbial loop, Oligotroph

TheThe AquaticAquatic FoodFood WebWeb andand thethe MicrobialMicrobial LoopLoop Intensive System

Compound feed

Removal of waste products Extensive System

Compound feed

Removal of waste products Aquatic

Food Chain - of formed by trophic levels - stepwise system of trophic levels

I. First - Primary Producers II. Second Trophic Level - Primary Consumers () III. Third Trophic Level - Secondary Consumers () IV. Fourth Trophic Level - Tertiary Consumers V. …. VI. Highest trophic level - “Top”predator Biocoenoses - Compartements

Littoral Pelagial euphotic

Benthal Compensation depth*

Profundal aphotic Sediment

* Between cm and > 30 meters, dependent on season, weather, species, amount of , suspended particles

hv 6 CO2 + 6 H2O → C6H12O6 + 6 O2

CD*

Macronutrients: N, P, S, K, Mg, Ca, Na, Cl, (Si) Trace elements: Fe, Mn, Cu, Zn, B, Si, Mo, V, Co

* Between cm and > 30 m, depending on season, weather, species, turbidity (amount of phytoplankton)

• Conversion of CO2 to depending on the availability of light • Excluding feeding, photosynthesis is the main input of C- source and natural food for aquatic in aquaculture • Primary producers: Macrophytes, algae, , („purple “, green bacteria) light O H2O 2 Chloroplast CO2 (CH2O)

n CO2 + 2n H2A → (CH2O)n + n H2O+ 2n A

n CO2 + 2n H2O → (CH2O)n + n H2O+ n O2 light heat

Light reaction (PSI and PSII) H O 2 O2

2 NADP+ 2 NADPH/H+ 3 ADP 3 ATP heat

Dark reaction () carbohydrates CO2 (CH2O)

„Dark“ respiration in mitochondria Trophic status

= Intensity of organic photoautotrophic production

Dependent on: 1. climate (light and temperature) → annual PP in decreases from tropics to poles 2. cultural (enrichment from catchment and man‘s activities) 3. morphometric (size and shape)

temperate ultra-oligotrophic Ptot < 5 µg/L oligotrophic Ptot 5-10 µg/L mesotrophic Ptot 10-30 µg/L eutrophic Ptot 30-100 µg/L hypereutrophic Ptot > 100 µg/L

Phytoplankton () C:N:P = 106:16:1 Peripyhton (Hillebrand & Sommer 1999) C:N:P = 119:17:1 Trophic status

= Intensity of organic photoautotrophic production

Dependent on: 1. climate (light and temperature) 2. cultural (enrichment from catchment and man‘s activities) 3. morphometric (size and shape)

temperate low → PRODUCTION → high shallow morphometric eutrophic eutrophic DEPTH deep oligotrophic morphometric oligo-mesotrophic Trophic status

temperate tropical

in tropical lakes with temperatures in hypolimnion > 20°C oxygen is always depleted

• Dimitic: circulation 2 times in spring and autum

• Warm monomictic: subtropical, 1 mixis in winter

• Oligomictic: sporadic mixis • Warm polymictic: frequent mixis due to nocturnal cooling Photosynthesis

I0 radiance ‘ I0

Izeu depth

PAR (photosynthetic active radiation) 380-740 nm (bacteria > 800 nm) ‘ Zeu :Izeu = 0.01 I0 Photosynthesis

P rate/ volume [mg C m-3 h-1] depth

mesotroph eutroph hypertroph gross rate P radiance [µE m-2 s-1] Photosynthesis

P rate/ volume [mg C m-3 h-1]

zeu

depth zeu

zeu zeu oligotroph mesotroph eutroph hypertroph

Pmax

-2 -1 Ik =20-300 µE m s

I gross rate P k radiance [µE m-2 s-1] limitation saturation inhibition Universal Phylogenetic Tree Macrophyta

• Contribution of macrophytes to total primary prodcution depends on ratio of littoral : pelagial → high in swallow tropical lakes

• Utilization of littoral production by benthic consumers mainly by DOM release and microbial decay, taken up as with bacterial and fungal cells • Direct usage only by few groups (snails, insect larvae, beetles) Phytoplankton / Algae

• unicellular or filamentous eukaryotic organisms • green, blue-green, yellow-brown due to photosynthetic pigments

Micrasterias sp. Euglena sp. Pediastrum sp. Nietzschia sp.

Scenedesmus sp. Thalassiosira sp. Volvox sp. Asteriolampra sp. Cyanobacteria

• Prokaryotes, APP • Bluish pigment phycocyanin,also Chl a, red or pink forms phycoerythrin (e.g. Red Sea: blooms of a reddish species of Oscillatoria, pink color of African flamingos from Spirulina) • Chloroplast in plants: from symbiotic cyanobacterium, taken up by green algal ancestor of the plants in the Precambrian

• N fixation - convert N2 into organic nitrogen (cultivation of rice: floating fern Azolla distributed among rice

paddies, cyanobacterium Anabaena in its leaves fixes N2 → inexpensive natural for the rice plants) Cyanobacteria

Oscillatoria sp. Anabaena sp.

• Blooms undesirable → many species produce populations toxic to humans and animals (microcystin, anatoxin) • Species of Anabaena and Oscillatoria responsible for off- flavor of Chemotrophy

Pelagic Food Chain

PP planktivorous piscivorous

Primary consumers Secondary consumers herbivorous carnivorous

(CH2O) + O2 → CO2+ H2O + energy

Plankton: (small) organisms that float or drift in water body, i.e. viruses, bacteria, fungi, algae, , metazoa

Size Organisms ~ N / ml

Femtoplankton > 0.2 µm Viruses 0.1-40 * 107

Picoplankton 0.2-2 µm Bacteria 0.5-10 * 106 Nanoplankton 2-20 µm Fungi, algae, protozoa (HNF)

Microplankton 20-200 µm Algae, protozoa (Rotatoria)

Mesoplankton 0.2-2 mm Algae, protozoa, metazoa

Makroplankton 0.2-2 cm Metazoa (e.g. Euphausia)

Megaplankton > 2 cm Metazoa (e.g. jelly fish)

Nekton: own movement > current

• plankton rotifers • motile, movement is overpowered by currents • herbivor, carnivor or (phyto- and zooplankton) • Freshwater: protozoa, rotifers, cladocerans, • Marine: jellyfish, salps, krill copepods cladocerans Protozoa

• Unicellular • Predators algae, bacteria, and microfungi • important food source for microinvertebrates • important ecological role in the transfer of bacterial and algal production to successive trophic levels

Stalked

Free swimmers Chemotrophy

Benthic Food Chain

Primary consumers Secondary consumers

Herbivorous Carnivorous animals animals (larvae of (insects, insects, turbellaria, Benthic fish snails, grass crustacea, etc. carp)

→ Interactions with pelagic food chain

• organisms living in association with bottom sediments • filter feeders (molluscs), consumers of detritus (shredder, tubifex), grazer • includes oysters, clams, crabs, oligochaete worms (Tubificids), polychaete worms, small , anemones, insect larvae (Diptera), Gastropods (snails) The Aquatic Food Chain

• The amount of total energy passed from one level to the next is decreased (heat loss, inefficiencies)

• The number of organisms at each successive level is reduced

• The total biomass decreases at each successive trophic level ihrtohclvl < trophic levels Higher Zooplankton ~ > (multiple times) Phytoplankton Turnover Total Biomass (g) 10 000 1 000 ↔ 100 10 Standing crop Food ChainandEnergyFlow 1 3 4 5 1 2 Phytoplankton

Zooplankton Trophic Level

Fish

Fish

Fish „Feeding Fish to Fish“

Naylor et al. 2001 Aquaculture Production

Ecological pyramid of global aquaculture production in 1999 according to taxonomic group and trophic level (FAO 2001) Control Mechanisms

Fish

Zooplankton Top down Bottom up

Algae, bacteria

Nutrients

Syntheses: McQueen et al (1989): low levels by bottom up, high levels by top down Persson et al. (1988): alternated, number of levels & top level by bottom up Interactions

1 2 1. Daphnia suppresses protozoans, bacteria prevail as small freely dispersed rods and cocci 2. When copepods dominate, ciliates are preferentially consumed, HNF exert strong grazing pressure on planktonic bacteria, results in altered morphological and taxonomical bacterial composition with a high degree of grazing-resistance (e.g. filamentous forms and bacterial aggregates) Interactions

Influence of

Fish (0.2E) Fish (0.1E)

Daphnia (2E) Daphnia (1E) Copepods (1E)

herbivorous Zooplankton herbivorous Zooplankton (20E) (20E)

Primary Producers Primary Producers (100E) (100E) The Aquatic Food Chain

„Food chains do not exist in real “

• Interactions between pelagic and benthic food chain • Almost all organisms are eaten by more than one predator • One animal - more than one level? → size selecting filter feeders (Daphnia), diet overlap (omnivors) • Trophic level changes during ontogenesis, e.g. planktivorous juveniles of piscivorous fish (pike, perch) • Detritivors act on each level The Aquatic

Food Web • Interacting food chains • Defines feeding relationships among organisms • Traces the flow of energy and the cycling of materials (e.g. carbon)

• More “realistic” than simple food chains • More complicated Remineralisation

O2 CO2 O CO O CO CO2 2 2 O2 CO2 2 2

anorganic

PER, feces, sloppy feeding, lysis and autolysis, dead organisms

• PER (phytoplankton extracellular release) up to ~15% of fixed C • Zooplankton/Daphnia: 18-100% of algal-C, ¼ as DOC, rest particulate feces The Role of Detritus

Detritus = non-living organic matter, particulate (POM) and dissolved (DOM) • important source for some organisms • in bottom sludge, anaerobic bacteria release low molecular weight compounds, which bind to detritus • anaerobic is probably more desirable in because it does not consume O2 and its byproduct is not CO2 • unfortunately anaerobic decomposition is not that efficient Degradation of Organic Matter

leaching DOM

POM Attachment / ectoenzymes colonization of DOM ()

Fragmentation by mechanical shredders (gammarus, DOM larvae of diptera, enhancement of POM trichoptera) surface DOM : POM 10:1 ImportantPolysaccharides Polymers

Cellulose - ß-1,4-linked glucose - up to 15 000 monomers - cell walls of plants, fungi

Xylan - polymers of various sugars, (ß 1-4)-linked /Hemicellulose - various branches (glucans, mannans, xylans...) - 30 –100 monomers

Chitin - ß-1,4-linked N-Acetylglucosamine - parallel / antiparallel, linked to proteins and glucans - arthropoda, fungi,

Starch -up to 106 monomers glucose - amylose linear (α1-4), amylopectin branched (α1-4) (α1-6) - storage polymer of plants

Lignin - 18-30 % of wood - complex structure of phenylpropan derivates (C-O, C-C)

- slow degradation, radicals (O2) DegradationCellulases of Polymers

Example: Cellulose („Cellulosome“)

• Endo-(ß-1,4)-Glucosidases internal cleavage of (cellulose) molecules → increase amount of free ends

• Exo-(ß-1,4)-Glucosidases sequential cleavage of oligomers from the ends of the chains → release of cellotriose, cellobiose

• Dextrinases (ß-Glucosidases, Cellobiase) cleavage of oligomers → release of dimers and monomers (glucose) Model for Detritus Processing

Autochthonous Polymers Allochthonous DOM/POM Polynucleotides (DNA, RNA), DOM/POM polysaccharides, proteins, lipids, waxes, lignins, polyphenols, humic matter endoactivity ezymatic extracellular Microbial eoyeiainprocesses depolymerization

Oligomers Microbial Nucleotides, sugars (DCCHO), peptides enzyme (DCAA), lipids, polyphenols systems Nucleotidases, Dimers Phosphatases, Nucleotides, sugars, peptides, lipids Glucosidases, Proteases, Lipases, Ligninases, Monomers (UDOM) Sulfatases, ...

by aquatic organisms Amino acids (DFAA), sugars (DFCHO), fatty acids Extracellular release of DOM exoactivity rapid uptake Microbial Microbial biomass community Algae, bacteria, fungi, viruses, control processes protozoa growth

Higher food web processes After Münster 1991 Michaelis-Menten-Model

• 80-90% of DOM is polymeric • Depolymerization is rate-limiting step in nutrition of microheterotrophs

v

vmax

k1 k E + S ES 3 E + P Vmax/2 k2

[S]

Km Bacteria

• Numbers in different : Eutrophic freshwater systems 1- 40 x 106 Coastal waters < 0.5 -10 x 106 Open ocean 0.01-2.5 x 106 Aquatic sediments 1-20 x 109

• In the , bacteria are quite small, in sediments adsorbed onto sediment particles →difficult to quantify • Most effective group producing extracellular enzymes • Metabolically most diverse group: chemo-organo- chemo-litho- photo-litho-autotroph photo-organo-heterotroph Fungi spores

• Dominate breakdown of leaves and allochthonous detritus (ligninases, polyphenoloxidases) • Their activity increases palatability of the substrate to detritus feeders • Estimation: production of fungi is similar to that of bacteria, but so far only little is known about their taxonomy, biology and (Bärlocher) • Vegetative hyphae, spores

leaf and fungi grazed by snails

aquatic fungi on a dead leaf Secondary Production by Microbes

Secondary production (DOM to POM) by heterotrophic microorganisms is of great quantitative importance in most aquaculture situations • microbes can attack organic substrates that can’t be utilized by animals • microbes produce particulate food materials from dissolved organic material • link between DOM and classical food chain, lead to fast turnover • also competitors to primary producers for nutrients (esp. when limiting) Protozoa: HNF

Heterotrophic nanoflagellates (HNF) 2-20µm • most important predators of bacteria • grazed by large flagellates and ciliates

Bodo saliens Plagioselmis prolonga Microbial Loop

hebivorous Algae carnivorous Zooplankton Zooplankton Fish

Anorg. Phototrophic nutrients

DOM POM

Heterotrophic picoplankton Ciliates HNF regeneration grazing origin and microbial processes Aerobic Microbial Processes

• Oxidation of OM (OC) to CO2 (main consuming process of O2 in aquaculture ponds)

• Oxidation of NH4 to NO3 via NO2 (also consumes large quantity of O2)

• Oxidation of reduced S-compounds (H2S, elemental S) to SO4 (low O2 demand in aquaculture)

• Conversion of CO2 to biomass by autotrophic bacteria (small amount of biomass produced in aquaculture facilities, compared to biomass by algae) Anaerobic Microbial Processes

•O2 depletion may lead to complete deoxygenation or anoxia in deeper layers of lakes or , esp. in shallow lakes with high plant production, deoxygenation of sediment and water occurs frequently • Can produce compounds that are toxic to cultured animals

• Reduction of NO3 and NO2 yields N2 gas or NH4,in aquaculture not welcomed due to the toxicity of NH4 and NO2, while N2 production is beneficial

• Reduction of oxidized S-compounds to H2S, toxic to most animals at even very low concentrations

• Consumption of OM without the reduction of O2, results in products which are not fully oxidized (alcohols, organic acids) Bacterial Respiration Processes

E0‘ organotrophy CO -0.4 2 n 2 -0.3 reduced respiratory chains ⇒ less energy yield -0.2 + NH4 ⇒ slow growth rates -0.1 lithotrophy - NO2 0.0 chemoorganoheterotrophy, NO - +0.1 3 anaerobic denitrifying bacteria +0.2 Chemolithoautotrophy, - aerobic NO3 +0.3 nitrifying bacteria anaerobic respiration N +0.4 2 +0.5 +0.6 +0.7 +0.8 O2 H2O aerobic respiration Nitrogen Cycle

Nitrification - NO2

N2 organic ass imi N-Fixation lation NH2- - am NO3 assimilatory groups mon ifica oxic nitrate reduction tion + NH4 NH3 anoxic assimilation

- NH2- NO2 ion icat groups onif amm

dis sim ila tor N y n 2 itr ate re NO du Denitrification cti on N2O Alternative Electron Acceptors

Sequence of electron acceptors in the sediment

E0‘[mV] range E [V]

O2/H2O +820 Aerobic respiration 0.6-0.4

- NO3 /N2 +751 Denitrification 0.5-0.2

- NO3 /NH4 +363 Nitrate ammonification 2+ MnO2/Mn +390 Mangan reduction 0.4-0.2

Fe3+/Fe2+ +150 Iron reduction 0.3-0.1

2- - SO4 /HS -218 Sulfate reduction 0.0-(-0.15)

S0/HS- -240 Sulfur reduction

CO2/CH4 -244 (-0.15)- (-0.22) Fermentation

• Chemo-organo-heterotroph metabolism • Organic compounds serve as primary electron donors and ultimate electron acceptor (disproportionation) • ATP is produced via substrate level phosphorylation not via membran potential and proton motive force • Little energy yield: C only partially oxidized, ΔEh between substrate and product is small → Glucose respirated: 36 - 38 ATP → Glucose fermented: 2 - 4 ATP, 2 - 4 NADH

• Products: CO2, H2, ethanol, butanol, formiat, acetate, propionate, lactate, ... Sediment

• „Solid material that settled down from a state of suspension“ • 3 major sources: detrital (erosion, catchment), biogenic, authigenic • Complex environment (interstitial), strong gradients in chemical (Eh, pH) and microbial parameters • Number of microorganims 3-4 magnitudes higher than in pelagial • Sediment respiration as a measure of decomposition (BOD), related to trophic status, quantity and quality of available organic carbon and concentration of electron acceptors • Absorption/desorption processes, crucial redox conditions at sediment- water-interface → influence overlying water

• P and NH3 may be released from sediments into the water (internal loading) → nutrient enrichment • Bioturbation → heterogenity, deeper Eh gradient, less steep Manipulation

Aqua“culture“ = manipulation of environment

Problem: direct use of that itself is vulnerable to water pollution () Polyculture

• Culturing more than one species of organism in the same pond • Maximizing fish production by raising a combination of species with different food habits, better utilization of available natural food Plankton feeders silver carp (1), bighead carp (2), Nile tilapia, blue 3 tilapia 1 2 Herbivores grass carp (3), rohu, guorami, Tilapia zillii 4

Piscivorous fish Bottom feeders (OM, clams, (control unwanted insects, worms, snails, bacteria): reproduction) catfish, common carp (4), milkfish, snakeheads, cichlids, Tilapia sp. largemouth bass Enhancement of

Input of organic material • Manuilowa,1951: fish ponds of 28 ha, 6 t organic fertilizer → numbers of zooplankton increased from 200 - 300 to 14 000 – 25 000/l • Kusnezov,1955: Wolga-delta, bights for raising of carp and bream, by cutting reed → after 5-6 days fish dead → wind distributed reed on water surface → shading, decomposition let to oxygen depletion and fish mortality

→Take into account amount of O2 needed for decay of OM CO2 Balance

+ - + 2- CO2 + H2O ↔ H2CO3 ↔ H + HCO3 ↔ 2H + CO3

pH < 6 CO2 - pH 7-10 HCO3 2- pH >10 CO3

CO2 + H2O + CaCO3 ↔ Ca(HCO3)2 Study: Bangladesh

Experimental design • 12 ponds (mean depth 1.2 m) drained, aquatic vegetation in embankment removed, limed, fertilized with cow dung • different amounts of bamboo poles • 10 days before stocking with fish

Catla Rohu Kalbaush /orange-fin labeo planktonic feeder periphytic feeder opportunistic, bottom feeder

Azim et al. 2004. Aquaculture 232:441-453 Bangladesh, Azim et al. 2004

Relationship between combined net fish yield and substrate density

Mean values of water quality parameters in control, 50% substrate (S-50), 75% substrate (S-75) and 100% substrate (S-100) ponds Bangladesh, Azim et al. 2004

Comparison of yield parameters of 3 species in control, 50% substrate (S-50), 75% substrate (S-75), 100% substrate (S-100) treatments Study: Shading

Shading of pond led to higher numbers of zooplankton

• Phytoplankton C:N:P 106:16:1 → C:N 6.625 • Acartia sp. 48.3 ± 0.8% C, 12.4 ± 0.2% N → C:N ratio 4.5 ± 0.1 • cladocerans Bosmina longispina maritima and Evadne nordmanni lower N content (9.3–10.8%) and higher C:N ratio of 5.1–5.7 (Walve and Larsson, 1999)

• N-limitation in phytoplankton → increase C:N ratio of their grazers → negative effect on copepod growth and reproduction (Van Nieuwerburgh et al. 2004) • P-limitation (Elser et al. 1998) Environmental Problems

Water Waste and nutrient loadings (solids, N, P, chemicals, antibiotics, salinisation) Impacts on benthos and , on species composition/diversity (tolerant species dominate), quality indices, stimulation of blooms, , oxygen depletion

Biodiversity Escaped stocks → competition with/genetic contamination of local stocks, competition for feed and space, predators pressure on prey species, disease transmission → directly or indirectly reduced

Terrestrial environment (coastal areas) Salinisation of soils, excessive clearance of and protective cover → degradation Environmental Problems

Integrated -aquaculture systems use low levels of inputs → less reliance on heavy feed and , lower densities of farmed organisms → less chances of causing serious pollution and disease risks than intensive, feedlot-type systems

BUT: development of better domesticated breeds increases international demand → increased transfers of exotic breeds