free-living phagotrophic protistsflagellates ciliates crustacea fish radiolarians salps baleen...

Karen Selph, OCN 626, Fall 2009

Free-living Phagotrophic Protists

Introducing the role of remineralization and placingprotists in a food web context


Tuesday:Feeding selectivelyModel Protist: Ingestion (methods) and Metabolism

Today:Last few slides: Metabolism -- growth efficiency and temperature effects

Continue with:1) Excretion, Remineralization in the Model Grazer2) How do protists link to higher trophic levels?

Size considerations...3) Metazoans that directly impact the microbial food web


Metabolism: Excretion/Remineralization

New Handout...


ProtistExcretion

Grazing of flagellate on diatomNo bacteria With bacteria

flagellate abundance

diatom abundance

particulate nitrogen

NH4 & urea

Goldman & Caron 1985


Factors affecting Excretion RatesCiliate feeding on bacteria Flagellate feeding on bacteria

Ferrier-Pages & Rassoulzadegan 1994


Why “waste” that food?Concept: Organisms tend to retain the nutrientsthat are limiting to growth and excrete the nutrientsthat are available in excess.

Underlying assumption: Organisms try tomaintain a constant stoichiometry of elements,such as C, N, P, in their own cells throughconserving or excreting/egesting food.


Prey (food) Quality Matters

Caron et al. 1990

GGE (G/I)Paraphysomonas (flagellate) fed phytoplanktongrown in chemostats

n.b., GGE’s probably 10-15% high,because of re-ingestion


Elemental RatiosOrganism C:N N:CBacteria 5.0 0.20Phagotrophic Protist 5.5 0.18Algae (healthy)* 6.6 0.15Algae (N-limited) 10.0 0.10

*healthy ratio from Redfield ratio

N:C (predator) < N:C (prey), then excess N excretede.g., protozoa feeding on bacteria excrete excess N, butif feeding on algal cell would conserve N.


Relative Importance of Microbial LoopOrganisms with regard to Remineralization

Who are the important nutrient cyclers?An example:

DOM BACT ALGAE Parameter BACT ZOOFL CILIATE Ingestion(C) 100 100 100Respiration (C) 40 40 40 AE 1.0 0.8 0.8 GGE 0.6 0.4 0.4 C:N(prey) 6.6 5 6.6 C:N(pred) 5 5.5 5.5


DOM Uptake by Bacteria

Bacteria are generally not efficient recyclers ofnutrients (Nitrogen).

High GGE, C:N(bact) << C:N(DOM)

Bacteria C:N = 5, DOM C:N = 6.6 (from algae)


Impact of Bacterial GGE?

Kirchman et al. 1991

Amon & Benner 1994

Cycling of DOC during diatom blooms: two examples

Bacterial GGE

HMW: mainly polysacharides (high C:N)LMW: mainly amino acids (low C:N)


Food (DOM) qualitymatters

Bacteria grown on substrates,ranging in C:N from 1.5 - 10

At C:N > 6 (~algal C:N),GGE = 40-50%, Nitrogen regeneration: 0-20%

Bacteria are significant respirersof C, but if DOM poor in N, they have little role in N remineralization


Protists feeding on bacteria

Protist C:N = 5.6, Bacteria C:N = 5

Bacterivores expected to excrete and egesta significant portion of consumed food.

Protist C:N > Bacteria C:N


Protist feeding on Algae

Protist C:N = 5.6, Algae C:N = 6.6

Protist herbivores would be expected to excreteand egest less, because their elemental ratio iscloser to that of their prey.


Protist Egestion: Contribution to DOM poolStrom et al. 1997

Protist Grazer: in allexperiments, more DOCproduced in presence ofgrazing.16-37% of algal carbonreleased as DOC (30%carbohydrates)

Copepod Grazer: in 2/4experiments, more DOCproduced in presence ofgrazing


SummaryRole of organisms as nutrient remineralizers

increases with1) low GGE2) low C:N(prey) relative to C:N(pred)3) small size = high specific rates

- because larger organisms (metazoans) also have to fuel metabolic products into reproduction

- also, sinking velocity of fecal material decreases with small size


Phagotrophic Protists as Links to Higher TrophicLevels

• Bigger organisms tend to feed on smaller ones...10:1 predator:prey size ratiosFilter feeders vs. Direct Interception feeders

• Metazoan predators that are important microbial loop consumers vs. those that aren’t• Implications for food web efficiency• “Classic” vs. Microbial Food Web• High vs. Low Energy Ecosystems


Prey:Predator Size Ratios

All organisms feed selectively, theoptimal range of prey beingdetermined by:• Sensory mechanisms & thresholds for detecting prey• Physical constraints on contact (encounter) frequency• Minimum size that can be effectively captured/handled• Maximum size that can be effectively captured/handled


Feeding Mechanisms: Searching for Food

Body Size (length)0.001 mm 0.01 0.1 1 10 100 1000 very large

DirectContact

Filter feedingStructures

Chemo &MechanicalReceptors

Visual

Flagellates Ciliates Crustacea Fish

Radiolarians SalpsBaleen whales

behavior: exploit patchesStrategy: increase surface are atexpense of mass & organizationalcomplexity

Increasingly complex sensory & capture mechanisms are required to offset the factthat organism mass increases at a faster rate than surface area

figure after a drawing by M. Landry,pictures from J. Drazen (fish), D. Keith (salp),K. Sime (whale), www.mbayaq.org (copepod), R. Patterson (flagellates)


Food particle size as a function of predatorsize

Fenchel 1986

filled circles: filter feedersopen circles: direct interception

feeders

line = 1:10 food:predator size


Protist optimum Prey Selection: Is it 10:1?

Hansen et al. 1994


1) predators of autotrophs2) prey of

mesozooplankton3) predators of

juvenile/naupliarmesozooplankton

4) predators and prey ofother HTD

Dinoflagellate’splace in food webs


Metazoans:Raptors above/on the 1:10 line

raptorial feedersambush predators/raptors


Metazoan predators: Crustaceans -- hard-bodied (chitin exoskeleton) withspecialized, segmented feeding, swimming, and sensory appendages. Responsive to

mechanical, chemical and light cues. Daily vertical migration in many forms.

Photo credits:copepod: www.jaffeweb.ucsd.edueuphausiid: Uwe Kils, http://krill.rutgers.eduamphipod: www.yale.edu/inverts/caribs/podpages/batea.htmlshrimp larvae: geochange.er.usgs.gov/sw/impacts/biologycrab larvae: ibss.iuf.net/people/skryabin/merop.htmllobster larvae: Russell Bradford, CSIRO

Copepods:Copepods: most numerous multicellular animals. Many species benthic or parasitic.Most are <3 mm, the largest free-living form ~16 mm. Suspension feeding via watercurrents generated by mouth parts, particles strained by appendages with fine setae.Raptorial feeding by forms with larger, less setose maxillae and maxillipeds forgrasping and manipulating prey. Most pelagic forms omnivorous.

EuphausiidsEuphausiids:: stalked compound eyes, shrimp-likebody. Omnivorous, some suspension feed on largerphytoplankton, highly motile, some exhibit schooling(e.g., krill in Antarctic waters).

AmphipodsAmphipods: sessile compound eyes, legs usually modified for grasping. Most benthic,most open ocean forms live on, or in association with, gelatinous zooplankton. Most arepredators.

The crustaceans also include shrimp, crabs, lobster and many other forms that are planktonic only aslarvae (meroplanktonmeroplankton, as opposed to holoplankton - plankton for entire life).


Crustaceanfeeding

appendages

Filter feeder PredatorCutting edgeof mandible

filter feeder:crushing mandible,fine hairs on appendagese.g., Calanus sp.

predator:slicing mandible,no hairs on appendagese.g., Euchaeta sp.


Why they don’t feed on small organisms

Nival & Nival 1976

Herbivorous copepod, Acartia clausi~15 µm

~7 µm

~5 µm Florian Hantzshewww.der-nordfahrer.de


chaetognath: R. Hopcroft, Univ. Alaska - Fairbankschaetognath head: http://lifesci/ucsb.edu/~haddock/planktonchaetognath with copepod: Jean-Marie Cavanihac,www.microscopy -uk.org

Metazoan Predators: Chaetognaths -- “arrow worms” with elongated bodyseparated into head, trunk, and tail. Exclusively marine. Head with paired eyesand prehensile, chitinous jaws with hooks. Ambush predator, responds tomechanical cues, swallows prey (copepods, fish larvae, other chaetognaths) whole.Hermaphroditic, testes in tail, ovaries in trunk.


Metazoans:Filter feeders below 1:10 line

filter feeders

microbial looporganisms


Gelatinous Zooplankton: grouped by morphological traits, not geneticrelatedness, bodies with high water contents, secrete mucus nets so that animal iseffectively bigger and can capture more food

Photo credits:ctenophores: www.divediscover.whoi.edu & Marsh Youngbluth, life.bio.sunysb.edu/marinebio/planktonmedusae: www.ucmp.berkeley.edu/cnidaria & www.oceanexplorer.noaa,gov/explorationssalps: www.divediscover.whoi.edu & www.biology.duke.edu/johnsenlab/research/ultratrans.html

Ctenophores:Ctenophores: “comb jellies”, characterized bybands of joined cilia around body surface.Tentaculate forms have 2 tentacles with specialsticky cells to entangle prey; Lobate types captureprey contacting their large lobed feeding surfaces.

MedusaeMedusae:: carnivores, food captured withtentacles armed with paralyzingnematocysts. Siphonophores, includingthe Portugese Man-of-War, are particularlysignificant in oceanic waters.

SalpsSalps:: Barrel-shaped animal with muscle bands thatcontract to force water into a buccal opening and outof an atrial opening. Ciliary-mucus filter feeders -particles in the water current entering the buccalopening are captured on a net of mucus strands.Chiefly oceanic -- sometimes occur in dense swarms.


Appendicularians(Hemichordata)

Because of house mesh size, potentially important asgrazers of picoplankton

a.k.a. larvaceans -- mature forms retainappearance of tadpole chordate larvae,head with tail. Body enclosed in a feeding“house”. Undulations of tail cause water toenter house through coarse filter where fineparticles are concentrated. The house isabandoned periodically and a new house isbuilt. Old houses are important componentof marine snow.

jellyzone.com


Short-circuits vs. Baby-steps effect on food webFilter feeders that “Short-circuit” the food chain:Appendicularians (1 - 10 mm) Bacteria & Sm. flagellatesSalps (~10 cm) Sm. flagellatesNeocalanus spp., SubArctic Pacific (5 - 10 mm) 2 µm+Anchovetta (10+ mm) DiatomsBaleen Whales (10s of meters) Krill

Raptorial feeders that reduce food web efficiency:Paraphysomonas (flagellate) Diatoms (1/2 size)Didinium (ciliate) Paramecium (ciliate) (equal size)Oblea (dinoflagellate) Lg. Diatoms (e.g., Ditylum)Pelagic Foraminifera CopepodsLg. Predatory Copepods CopepodsSharks Other large prey


Classic View of simple, linear food chain:diatoms copepods fish


Trophic Trophic Cascades:Cascades: this model of ecosystems hypothesizes that, bytheir presence or absence, higher trophic levels will determinewhether or not blooms will occur at the base of the system (asopposed to just resource limitation/sufficiency)

Reckermann & Veldhuis 1997

Western Arabian Sea plankton:Calbet & Landry 1999

Location: Station ALOHAManipulation:Bacterial net growth in asize-truncated food web

Bacteria

2 - 5 µm HF

5 - 20 µm HF

Implied Grazer Chain:


Fish (GGE = 0.2)

MacroZP (GGE = 0.2)

MesoZP (GGE = 0.2)

Ciliate (GGE = 0.3)

Flagellate (GGE = 0.3)

Phyto = 100

Ocean Ecosystems DividedOLIGOTROPHIC

(Low Latitude)

Bacteria (GGE = 0.4)

0.06

0.3

1.3

6.3

21

2050 50

EUTROPHIC(High Latitude)

FISH

COPEPODS

PHYTO=100

100

30

6

PHYTO=100(UPWELLING)

FISH

100

20


Low Energy Stable Systems

Low nutrients(oligotrophic)

Small Phytoplankton(high surface:volume ratio)

Long food chains(small consumers at base)

Low energy Lack of nutrient re-supply

Relatively stablesystem


High Energy Unstable Systems

High nutrients(eutrophic)

Large Phytoplankton(small, too!)

High energy(storm activity, eddy

action, upwelling, etc.)

Unstable (dynamic) system

Short food chain (dynamic)(superimposed on stable long food chain)

Composite Spring PictureMean Chlorophyll (µg/l) at the surface


Food Web Structure

Fish

Copepods

zooflagellates

H-Bacteria

HeterotrophicAutotrophic

diatoms &dinoflagellates

a-flagellates

cyanobacteria

Macro+

Meso

Micro

Nano

Pico

Ciliates

DOM Nutrients

flag level 1flag level 2flag level 3

viruses

oligotrophic

eutrophic

Mixotrophs

free-living phagotrophic protistsflagellates ciliates crustacea fish radiolarians salps baleen...

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