Developed by: Merrick, Richards Updated: August 2003 U1-m4-s1 Trophic Relationships

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s2 Microbial Food Webs

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s3 Microbial Food Webs  Bacteria and Fungi  Carbon flux evidence shows importance  Makes resources available  DOM  Detritus

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s4 How might energy be transferred to fish?

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s5 Energy Transfer  Microbes consumed by protozoans & micro- metazoans  Food particles are small (~5.0 µM bacterial cell)  Several trophic transfers within microbial web  Energy lost with each transfer:  typical models transfer 10% between levels  90% lost as entropy to system  More steps = more loss

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s6 Is this the only way to eat microbes?

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s7 Energy Transfer  Direct ingestion of biofilms!  Scraping  Ingestion with CPOM  Conversion to plankton  Scouring

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s8 Organic microlayer-microbial community on submerged objects in streams

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s9 Where is the production?  Bacterial production in the water column is modest  Benthic bacteria dominate community respiration  We don’t know enough...  Looking for a good research topic:  The importance of bacterial and fungal metabolism to Carbon cycling in lotic ecosystems?

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s10 Who eats the bacteria?  Water column  Bacterial size: average = 0.5 µm  Few suspension feeders able to capture that size prey:  Black fly larvae  Asiatic clam Corbicula  Protozoans most likely grazers  Flagellates µm in diameter  Ciliates - 25 µm in diameter on average

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s11 Who eats the bacteria?  Benthic  Associated with microlayers & periphyton  Benthic grazers of attached material  Deposit feeders that pass organic matter & associated microbes through their gut.

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s12 Microbial Web

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s13 Looking and the slide why are bacteria important?

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s14 Microbial Web

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s15 Microbial Food Webs: H 2 O column vs. benthos

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s16 Categorization of Trophic Relationships in Streams  How do we normally assign trophic relationships?

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s17 Trophic Relationships  Difficult to assign typical categories  Producer, grazer, carnivore, top predator  Trophic level  Assignment to guilds is easier  Guild = species that consume a common resource and acquire it in a similar fashion  Provides subdivision in feeding roles for both inverts and vertebrates  Same as functional groups (FFG, Inverts)

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s18  Shredders  Dominant food  Vascular macrophyte tissue  Coarse particulate organic material (CPOM)  Wood  Feeding mechanisms  Herbivores - Chew and mine live macrophytes  Detritivores - Chew on CPOM  Representatives  Scathophagidae (dung flies)  Tipulidae (crane flies) Macroinvertebrate functional roles in organic matter processing A caddisfly of the family Limnephilidae

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s19  Collectors  Dominant food  Decompose fine particulate organic matter (FPOM)  Feeding mechanisms  Filterers - Detritivores  Gatherers - Detritivores  Representatives  Filterers Hydropsychidae Simulidae (black flies)  Gatherers Elmidae (riffle beetles) Chironomini Baetis Ephemerella Hexagenia Macroinvertebrate functional roles A blackfly of the family Simulidae A caddisfly of the family Hydroptilidae

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s20  Scrapers  Dominant food  Periphyton (attached algae)  Material associated with periphyton  Feeding mechanisms  Graze and scrape mineral and organic surfaces  Representatives  Helicopsychidae  Psephenidae (water pennies)  Thaumaleidae (solitary midges)  Glossosoma  Heptagenia Macroinvertebrate functional roles A dipteran of the family Thaumaleidae

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s21  Predators  Dominant food  Living animal tissue  Feeding mechanisms  Engulfers - Attack prey and ingest whole animals  Piercers - Pierce tissues, suck fluids  Representatives  Engulfers Anisoptera (dragonflies) Acroneuria Corydalus (hellgrammites)  Piercers Veliidae (water striders) Corixidae (water boatmen) Tabanidae (deerflies & horseflies) Macroinvertebrate functional roles A stonefly of the family Perlidae A “true bug” of the family Notonectidae

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s22 Ecological roles  Macroinvertebrates play a variety of roles in food webs. Fig. 4.9, p.53 in Allan and Cushing, 2001

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s23 Feeding roles of invertebrate consumers in running waters Feeding RoleFood ResourceFeeding MechanismExamples ShredderNon-woody CPOM: leaves & associated microbiota Chewing and miningSeveral families of Trichoptera, Plecoptera, Crustacea: some Diptera, snails Shredder/gougerWoody CPOM and microbiota, especially fungi As aboveOccasional taxa among Dipter, Coleoptera, Tricoptera Suspension feeder/filterer- collector FPOM and microbiota, bacteria & sloughed periphyton Collect particles using setae, specialized filtering apparatus or nets and secretions Net-spinning Trichoptera, Simuliidae and some Diptera; some Ephemeroptera

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s24 Feeding roles of invertebrate consumers in lotic systems Deposit feeder/ collector-gatherer FPOM and microbiota, especially bacteria and organic microlayer Collect surface deposits, browse on amorphous material, burrow in soft sediments Many Ephemeroptera, Chironomidae and Ceratopogonidae GrazerPeriphyton, especially diatoms; and organic microlayer Scraping, rasping and browsing adaptations Several families of Ephemeroptera and Trichoptera; some Diptera, Lepidoptera, and Coleoptera PredatorMacrophytesPiercingHydroptilid caddis larvae Animal preyBiting and piercingOdonata, Megaloptera, some Plecoptera, Tricoptera, Diptera and Coleoptera

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s25 Which FFG/Guild?  Can be hard to determine  Food resources don’t separate cleanly  Leaf enriched w/ fungi supports algae & biofilm  However, classifications can be helpful  Changes based upon river characteristics

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s26 How would you identify food sources for invertebrate consumers?

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s27 Identifying food sources for invertebrate consumers?  Gut analysis  Diatom frustules easy to ID  Food of “soft” tissues turns to mush  Stable Carbon & Nitrogen Isotopic Analysis  Isotopic ratios reflect the food source   13 C/ 12 C ratio  In an animal’s tissue = record of recent feeding history  Reflects assimilation, not just ingestion.  Link or sink?  Zebra mussels

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s28 CPOM Consumers  Shredder-CPOM Linkage  Why are invertebrates important to CPOM breakdown?

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s29 Small Stream Model: Links between CPOM, fungi & bacteria  Model for a small stream within a temperate deciduous forest  CPOM -> FPOM  Physical abrasion  Microbial activity  Invertebrate shredders  DOM release  Chemical leaching  Microbial excretion & respiration  Much C enters detrital pools as feces and fragments

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s30 Who feeds?  Crustaceans  Snails  Insect Larvae

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s31 “Microorganisms on a leaf are like peanut butter on a cracker, with most of the nourishment provided by the peanut butter.” Cummins, 1974

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s32 Feeding preference of amphipods Microbe growth permitted Antibiotics Autoclaved  Amphipod - Gammarus sp.  Elm leaves consumed  Exp. Design  Control (with microbes)  + antibiotics  + steam sterilization

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s33 Invertebrate Consumers  Prefer ‘conditioned’ leaves  Conditioning by microbial colonization  Preference is for leaves at some peak stage of microbial growth.

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s34 How to measure microbial biomass?  ATP  Relative N content  Softening of leaf discs

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s35 Influence of conditioning time of discs of hickory leaves on utilization by Tipula abdominalis.

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s36 How do microbes help?  Microbial Production  Conversion to microbe biomass  Microbial Catalysis  Changes that render leaves more digestible  Partial digestion of substrate by microbes  Exoenzymes  The bulk of the energy comes from the leaf  So Cummins was not quite on target

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s37 Leaf digestion by inverts?  Where is the cellulase?  Found in some mollusks, crustaceans and annelids  Aquatic insects generally lack  Some have endosymbionts  Tipula (Crane Fly)  Primary source is microbial: bacteria & fungi  Exoenzymes

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s38 Contrasting feeding strategies of 2 CPOM detritivores Gammarus fossarumTipula abdominalis Feeding mechanismScrapes at leaf surfacesChews entire leaf Gut pH & digestive biochemistry Anterior gut slightly acidFore & midgut highly alkaline (up to 11.6) Its own enzymes and fungal exoenzymes attack leaf carbohydrates Result is high proteolytic activity but inactivation of fungal exoenzymes thus little activity toward leaf carbohydrates Posterior gut is alkaline, would digest microbial proteins and some leaf proteins EfficiencyHighly efficient at processing conditioned leaves at low metabolic cost Less dependent upon stage of conditioning, probably good at extracting protein, but at high metabolic cost. Other attributes of feeding ecology Highly mobile Polyphagous Low mobility Obligate detritivore

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s39 Consumers of FPOM

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s40 Consumers of FPOM  Collector-FPOM linkage  Poorly Understood  Where captured?  suspension or substrate  Rich sources  Sloughed periphyton  Organic microlayers  Particles from breakdown of CPOM

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s41 Suspension Feeding Ecology  Many suspension feeders at lake outlets  Densities decrease downstream  Blackflies 15X more abundant at outflow vs. 2 km downstream  Tricopteran net size dependent upon flow  Fine mesh more efficient but creates more drag  High flow => larger mesh size  Feeding on CPOM by one invertebrate makes more food available to FPOM consumers  32 P labeled alder leaves: more label transferred to suspension feeders (of FPOM) in the presence of a shredder

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s42 Collector-FPOM-bacterial linkage modeled for a small stream with a temperate deciduous forest

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s43 Black-fly Ecology  Extensively studied: pests, carriers of disease  Food size range: µm  May be reared on a bacterial suspension  May manipulate flow vortices to enhance feeding  Not limited to suspension feeding  Scraping substrate using mandibles and labrum  May deposit feed on FPOM  May ingest animal prey

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s44 Filtering stance of a black fly larva Filter apparatus: fringe of microtrichia Boundary layer typically at roughly the height of the upper fan

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s45 Deposit feeders  Least well understood guild  Some taxa shift opportunistically between this and shredding or collecting of FPOM  Common in early instars - switch to more specialized guilds later  Many “bulk-feed” from 1 - many X body weight to get enough nutrition from sediments  Seem to have fewer morphological modifications

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s46 Who are they?  Swift Streams  Mayflies, Caddisflies, Midges, Crustaceans, Gastropod Molluscs  Slow Currents (fine sediments)  Add oligochaetes and nemotodes

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s47 Vertebrates in Lotic Systems

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s48 Feeding Ecology of Riverine Fishes  Fish are the principle vertebrates in streams. Others?  Most stream fishes invertivores > piscivores > herbivores  North America: 55 / 700 species are herbivores

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s49 Are there morphological features that would tell us what a fish eats?

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s50 Feeding Ecology of Riverine Fishes  You are what you eat?  Form follows function  You can tell what a fish (mostly) eats by  Specialization of dentition  Jaw shape  Body form  Alimentary tract  Many fish are flexible in feeding habits  Some change feeding habits during life cycle

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s51 Trophic guilds of stream fishes for temperate N. America GuildDescriptionOccurrence by species (%) Comments for tropical streams PiscivorePrimarily fish, some Large inverts 16May consume part or specialize on whole Benthic invertebrate feeder Primarily immature insects 33Most common in small to mid-order streams Surface & H 2 O column feeder Consumes surface prey (terrestrial) & drift (zoops & inverts of benthic origin) 11Diverse surface foods in forested headwaters and during seasonal flood Generalized invertebrate feeder Feeds at all depths11Similar category PlanktivoreMidwater specialist on phyto-and zooplankton 3Seasonally important in large rivers

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s52 Trophic guilds of stream fishes for temperate N. America GuildDescriptionOccurrence by species (%) Comments for tropical streams Herbivore - detritivor Bottom feeder ingesting periphyton and detritus: includes mud feeders with long intestinal tracts 7Herbivory may be subdivided into micro- and macrophytes, and detritus feeders separated from mud feeders OmnivoreIngests a wide range of foods: plant, animal, detritus 6Similar category ParasiteEctoparasite (e.g. lampreys) 3Ectoparasite (e.g. candirú catfishes)

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s53 Multiple Jobs  Many fish are “flexible” feeders  Must use the same care here as FFGs But, morphology does follow function  Incredible specialization  Nut eaters  Fin/Eye/Scale eaters

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s54 Guilds change as environment changes

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s55 Profile of an Amazonian floodplain river, showing main channel, side arms, and extent of flooded forest.

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s56 Abundance of 3 fish feeding guilds in small forested streams in Panama (a) Cichlasoma & Pimelodus: generalized invertivores (b) Brycon: detritivore when small, omnivore when larger (c) catfish feeding on periphyton

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s57 Lotic food webs

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s58 Water on the Web  This presentation includes material from Water on the Web (WoW) WOW Water on the Web - Monitoring Minnesota Lakes on the Internet and Training Water Science Technicians for the Future - A National On-line Curriculum using Advanced Technologies and Real-Time Data. University of Minnesota-Duluth, Duluth, MN Authors: Munson, BH, Axler, R, Hagley C, Host G, Merrick G, Richards C.  I would also like to thank Dr. Jewett-Smith for her contributions to this presentation