Water Column-Fate of Organic Matter Lecture VI PDF

Water Column-Fate of organic Matter LECTURE VI 1  Water Column-Fate of organic Matter Synthesized organic matter=> transformations 1. Herbivores eating live algae and plant biomass 2. Detritivores & microbes consume dead organ...

Water Column-Fate of organic Matter LECTURE VI 1  Water Column-Fate of organic Matter Synthesized organic matter=> transformations 1. Herbivores eating live algae and plant biomass 2. Detritivores & microbes consume dead organic matter 3. Transport of matter from euphotic zone by water flow and gravity Look at – Principal organisms that consume organic matter – Major properties of these organisms 2  Water Column-Fate of organic Matter Consumption and transformations- aquatic food web – Classical view of water column communities Primary producers: – diatoms, dinoflagellates- in the sea – Diatoms, chlorophytes, desmids-freshwater Primary Consumers: – Copepods, cladocerans=> fish & insects –freshwater – Copepods, cladocerans=> fish=> whales, seals –marine Secondary => tertiary consumers Energy transfer efficiency=>10% Maximum 5 trophic levels can be sustained Energy is lost through respiration at each level Microbes are ignored 3 4  Water Column-Fate of organic Matter Organisms in classical food webs – 1° -Phytoplankton: diatoms, dinoflagellates,coccolithophores, cyanobacteria Freshwater diatoms, desmids, chlorophytes – 1° consumers -Zooplankton Protozoans, coelentrates, ctenophores, annelids, molluscs, arthropods (crustaceans)-marine Copepods, cladocerans,rotifers, insects –freshwater – 2° consumers- Nektons (large, swimming) Marine: Krills, Pelagic crabs, molluscs, squids, fish, sea turtles, snakes, seals, whales, penguins Freshwater: Crustaceans, insects, fish, amphibians, reptiles, mammals, birds 5  Organisms in classical food web category Freshwater Marine 1 Phytoplankton Diatoms, dinoflagellates, Diatoms, dinoflagellates, chlorophytes, desmids coccolithophores 2 zooplankton Crustaceans, rotifers, insects Coelentrates, ctenophores, chaetognaths, crustaceans 3 Nekton Crustaceans, insects, Crabs, krills, molluscs, squids, amphibians, reptiles, fish, turtles, mammals, birds mammals, birds 6 Water Column-Fate of organic Matter 3º consumer 2º consumer 1º consumer 1º producers 7  Water Column-Fate of organic Matter – New views of aquatic communities – Necessitated by new discoveries and developments Development of new methods of measurement of production New methods of counting using stains & fluorescence microscope Observations about activity & abundance of microbes Discovery of new kinds of producers Discovery of nearly ubiguitous photosynthetic picoplankton Discovery of nanoplankton- photosynthetic/ grazers & carnivorous – Categories of aquatic organisms based on size – Picoplankton < 1 µm (prochlorophytes related to chloroplasts) – Nannoplankton 2-20 µm (photosynthetic, grazers, carnivores) – Microplankton 20-200 µm (diatoms, flagellates, ciliates, radiolarians & acantharians) – Mesoplankton >200 (copepods, shrimps, crabs, gelatinous organisms) – Nektons 8 Water Column-Fate of organic Matter 9  Water Column-Fate of organic Matter – Importance of size in aquatic food webs 1. Studied in size range categories –sampling & handling methods are different 2. Size –principle criteria determining the structure of aquatic food webs 3. Smaller organisms carry out life activities faster than larger organisms –Surface area/volume ratio is larger in smaller organisms –Material transport across surfaces is faster in smaller organisms 4. Growth and generation time is faster in smaller organisms 5. Nutrient uptake by producers is more efficient (picoplankton -50- 80% nitrogen uptake in aquatic ecosystems) 10  Water Column-Fate of organic Matter Respiration rate wt-sp rates higher in smaller organisms  Water Column-Fate of organic Matter Release of nutrients by consumers 12  Water Column-Fate of organic Matter Chlorophyll concentration is higher in smaller organisms: wt- sp 1° production is higher in smaller organisms Primary production Biomass % total Rate (mg primary Chlo conc % total C/m/h) production mg/m chlo Marine water 1-31 1-90 0,5-1 1-90 Freshwater 1-8 16-70 0.3-1 0.2-43 13  Water Column-Fate of organic Matter Organisms abundance tends to be inversely proportional to size 14  Water Column-Fate of organic Matter Decrease in total biomass per ml of water as individual weight (micro- & macro-plankton) increases 15  Water Column-Fate of organic Matter Size is an important criteria in food selection – Predator-optimum foraging theory (selection of prey whose yield as food is higher than energy and time spent in chasing, subduing and eating the prey) Other criteria for food selection – Nutritive quality of food: herbivores/detritivores – Palatability (defensive cpds): herbivores/detritivores – Abundance of prey 16  Water Column-Fate of organic Matter Release, use & aggregation of dissolved organic matter (DOM) – Release: OM can be released in the form of DOM (dissolved ….) 10-50% of net primary production is released as exudates 15% DOM released during messy feeding by grazers More DOM released from dead matter during decay – Use: Use of DOM DOM released is used by micro-heterotrophs eg bacteria, fungi The higher the 1º production the higher the bacterial growth Hence a clear relationship between primary production and bacterial growth (Figure) 17 18  Water Column-Fate of organic Matter – Aggregation and recycling of DOM DOM aggregated into amorphous particles- ‘marine snow’ Marine snow is consumed by fish and invertebrates Microbial loop Better food that has higher quality than morphous detritus or particulate organic matter 19  Water Column-Fate of organic Matter Microbial loop- – Part of food web consisting of micro-organisms – 40% net primary production flux (pass) thru bacteria – Microbial loop is more important in deeper water layers than surface layers – DOM is absorbed by bacteria and the bacteria are fed on by very small secondary producers (primary consumers) – Bacteria => small ciliates=>large ciliates/ small microzooplankton – Food web can contain upto 3-5 trophic levels – Is microbial loop a link to the classical food web or a sink of energy? 20 Water Column-Fate of organic Matter 21  Water Column-Fate of organic Matter Transport of matter from euphotic zone 1. Sedimentation of Organic matter 2. Horizontal transport 3. Large particle sinking 4. Vertical ladders of migration 22  Water Column-Fate of organic Matter 1. Sedimentation Organic Matter (OM) – Stratification reduces rates of deposition and sinking of organic matter – Amounts of OM sinking depends on: production rate, depth, stratification +vely correlated with production -vely correlated with water depth – Break down of stratification leads to: Release of OM into bottom waters Transfer of nutrients to surface waters Oxygen supply to bottom water 23  Water Column-Fate of organic Matter 2. Horizontal transport: – Locally moving water layers: supply and remove particulate matter on sediment/ water interface – Long standing waves and seiches lead to resuspension of organic matter – Down slope transport into steep bottom gradients in the water body – Benthic storms lead to resuspension and horizontal transport of OM 24  Water Column-Fate of organic Matter 3. Large particle sinking – Include plant remains, leaves, seaweed fragments, animal carcases – Due to large size om easily passes the thermocline (stratified water) 25  Water Column-Fate of organic Matter 4. Vertical ladders of migration – Plankton & nekton migration to the surface waters to feed at night – Predators feeding at great depths then swim up – Re-suspension of material at mid-depth and re-ingestion and release of feacal pellets at lower depths – Also being viewed as a way of carbon sequestration from surface to the bottom 26  Water Column-Fate of organic Matter 1:sedimentation 3: Large particle sinking Food supplies to populations 4: vertical ladder 2: horizontal movt 27  River Transportation Rivers transport material in four ways: Solution - minerals are dissolved in the water and carried along in solution. This typically occurs in areas where the underlying bedrock is limestone. Suspension - fine light material is carried along in the water. Saltation - small pebbles and stones are bounced along the river bed and taken downstream. Traction - large boulders and rocks are rolled along the river bed.  Water Column: Top-Down Controls of water column communities Top-down control refers to when a community is structured or influenced by species in higher trophic levels in the food chain These can be species that may cause removal of original species in an ecosystem through competition Or predation where a top predator controls the structure or population dynamics of the ecosystem. Predation is easier to demonstrate than competition Predation-competition interaction is also easier to demonstrate in a closed system like lakes than oceans 29 Water Column: Top-Down Controls of water column communities Freshwater – Top predators can alter food webs in freshwater ecosystems (Nile perch in L. Victoria and Cichla in L.Gatun-Panama) Direct effects as a result of grazing Indirect effects as a result of predation 30 Water Column: Top-Down Controls of water column communities Example of introduction of Cichla into L. Gatun - Panama Before After introduction 31  Water Column: Top-Down Controls of water column communities Introduction of Cichla into L. Gatun - Panama – Complex food web are reduced to a simple web – High number of species reduced to few species – Loss of some functional groups leading to loss of trophic levels – Abundances of some species (group) changed – Structural morphology of some species could change – Water quality could also change Conclusion: Top-down controls in freshwater is well established and can be easily studied Example: Effect of introduction of Nile perch to L. Victoria 32  Water Column: Top-Down Controls of water column communities Marine – Not possible to do whole ecosystem manipulative experiments in order to establish the ‘Top-down control’ – No evidence that commercial over fishing activities do affect food webs (top-down control) – Marine fish have alternate high recruitment / low recruitment yet no effects been seen on food web during high recruitment – Low survival rate of juvenile fish means that food supply for adult stage is not affected – Some evidence suggest some top-down control by top marine predators such as mammals and birds. Increase and expansion of predators that share the same food as whales and birds (seals and penguins) Abundance of some marine mammals and birds 33