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This 6 page Class Notes was uploaded by Sidnee Notetaker on Monday October 19, 2015. The Class Notes belongs to BIOEE 1540 at Cornell University taught by Bruce C. Monger in Fall 2015. Since its upload, it has received 14 views.
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Date Created: 10/19/15
Pelagic Food Webs Thursday ctober 15 2 15 9 PM I Definitions A Pelagic the water column environment B Benthic the seafloor environment includes coral reefs and rocky intertidal C Plankton unable to swim horizontally against ocean currents but may move vertically in the water column phytoplankton zooplankton D Nekton able to swim against ocean currents eg fish squid sea turtles E Major Zooplankton Groups in Marine Food Webs 1 Holoplankton Planktonic organisms that live their entire life in fluid suspension a Examples i Copepods ii Shrimp iii Arrow Worms iv Some Jelly Fish 2 MeroplanktonPlanktonic organisms that spend only part of their life in fluid suspension a Examples i Crabs ii Barnacles iii Oysters iv Fish Larvae I ZooplanktonHoloplankton A F W 35 hgl Omar 39 i nus 39 L Food web Page 1 l I fix Barnacle I Snail Worm Pelagic Food Chains A Simplified View of Pelagic Food Webs A Classifying Organisms into Broad Categories Based on Feeding Mode 1 Broadest Possible Grouping a Autotrophs Group of organisms whose carbon for growth comes from non organic sources For example phytoplankton are autotrophs because they use C02 for their carbon needs b Heterotrophs Group of organisms whose carbon for growth comes from previously formed organic carbon material For example herbivorous zooplankton are heterotrophs because they consume phytoplankton for their carbon needs Carnivores would also be heterotrophs 2 A More Refined Grouping a Trophic Level Nutritional feeding level within a food chain or food web eg primary producer ie autotroph primary consumer herbivore secondary consumer first carnivore tertiary consumer second carnivore etc Simplified Pelagic Food Chain Conceptualization Top Tropic Level Second Tropic Level First Tropic Level B The First Question to Ask 1 Is the Organism Autotrophic or Heterotrophic a Does the organism contain chlorophyll i yes then it is an autotroph ii no then it is a heterotroph 2 Is the heterotrophic organism a primary consumer or a secondary consumer or a tertiary consumer etc a This question has the potential of being difficult to answer because all Food web Page 2 heterotrophic organisms share the same trait of not having chlorophyll To get to the answer the following logic is used i Life in fluid suspension does not allow animals the opportunity to sit around and nibble on their prey over an extended period of time ii Animals in general must consume their prey whole iii The need to consume whole prey puts strong constraints on the size of prey that can be consumed by an organism iv Optimal prey size is often set by the size of the consumer s mouth size and as a ruleofthumb prey size is often about 110 the consumer s size 3 As a general rule the preferred prey size is approximately 110 of consumer size a Size determines almost everything about an organism s positionrole in the community of pelagic organisms except for the possibility of containing or not containing chlorophyll i It determines who will eat it all organisms 10 times bigger than it ii t determines who it will eat all organisms 110 its own size r Marine Food Webs are Said to be Strongly SizeStructured C Trophic Transfer Efficiency 1 A central question to address is what determines the efficiency of carbon or energy transfer from one trophic level to another ie the trophic transfer efficiency 2 The overall Trophic Transfer Efficiency depends on two factors a Exploitation Efficiency i The efficiency with which a consumer population is able to find capture and ingest all of the potential prey present in the environment b Gross Production Efficiency i The physiologicalbiochemical efficiency of converting ingested prey into consumer biomass c Trophic Transfer Efficiency Exploitation Efficiency x Gross Production Efficiency Exploitation Efficiency Find Capture and Ingest Prey A Exploitation Efficiency a game of hind and see 1 Evolution has worked long and hard to create some pretty elaborate strategies for this game of hide and seek in ocean a strategies for detecting prey b strategies for capturing prey once detected c counter strategies to avoid detection in the first place d counter strategies to frustrate capture if detected B Strategies for Finding Prey 1 Locomotion a Cruising rely on your own locomotion to encounter prey b Ambush rely on the locomotion of your prey to come to you 2 Perception a Visual perception b Mechanosensory c Chemosensory 3 Raptorial a grasp prey with appendages 4 Direct interception a bump into prey and engulf 5 Filtering a sieve large volumes of water 6 Entanglement a set net or trap Food web Page 3 C Strategies to Escape PredationConsumption 1 Avoid Encounters or Detection a remain motionless b be transparent c separate by time andor space 2 Frustrate the Capture Process a very small or large size refuge from predation b spines mechanical defense c escape response d SchooHng I Many zooplankton species exhibit bioluminescence shortterm bursts of light One theory for its existence is predator avoidance Creating a large flash of light as a predator approaches momentarily stuns and confuses the predator long enough for the prey species to make its escape D Diel Vertical Migration Avoid Detection Depth 1 Much of the zooplankton community migrates up to the surface layer of the ocean at night to feed in the dark while also avoiding visual predators like small fish During the day they migrate down to the safety of the darkness found at depth Examples of Two Very Different Grazer Exploitation Ef ciencies in Two Very Different Ocean Environments A Spring Blooms In the Temperate North Atlantic 0 Region During long winter periods grazers copepods mainly smk into the deep ocean and enter a diapause i el hibernation stage and thereby become decoupled from any variations in primary production above In spring phytoplankton standing stock can Initially grow to very high density because it is not held in check by strong grazrng pressure phytoplankton growth is decoupled from grazing until the large grazers have a chance to come out of diapause grow and reproduce to the high numbers needed to control increases in phytoplankton abundance This allows for exceptional phytoplankton blooms during the decoupled period o 390quot K39Jf39hi txplortation efficrency is very low in this case much of phytoplankton is not found by grazers and instead sinks into the deep ocean as dead phytoplankton cells rt tmh rrstm Viv39eJiidbhv F Exploitation Efficiency Main Points Exploitation Efficiency expresses the efficiency with which members of a given trophic level are able to find capture and ingest members of the next lower trophic level 1 Strategies used to escape predation can be described by three basic strategies avoid encounters eg vertically migrate or avoid detection eg be transparent and frustrate capture have spines or be very large or very small trophic interaction in question For example 8 Tropical Environments 1 Grazers remain active throughout the year and consume phytoplankton as fast as it is made 2 Any increase in production is qumkly met by an increase in consumption 3 This leaves standing stock of phytoplankton nearly constant throughout the year F39iyl CI JIJ 39 if r n Exploitation efficiency is very high in this case almost all phytoplankton IS found and consumed by grazers Exploitation Efficiency can range greatly 10 and 90 depending on the particular a In the case of tropical oceans where grazing is tightly coupled to primary production the grazers find and ingest almost all of the phytoplankton cells Food web Page 4 Consequently exploitation efficiency of grazers is high b In the case of the early part of the spring bloom in the North Atlantic much of the phytoplankton does not get ingested and instead sinks to the bottom of the ocean Consequently exploitation efficiency of grazers is low during this period G Gross Production Efficiency Diagram of a Material Budget for a Primary Consumer Trophx Level 2 Trophic Level 1 movcnurn l Gross Growth Production Efficiency Amount of CONSUMER BIOMASS produced divided by amount of PREY INGESTED This efficiency ranges between 20 and 60 H Trophic Transfer Efficiency Summary 1 Trophic Transfer Efficiency is a Function of A Exploitation Efficiency 10 to 90 B Gross Production Efficiency 20 to 60 2 The combined effect of both exploitation and gross production efficiencies yields an overall trophic transfer efficiency of about 10 to 20 III And for the remainder of the lecture we will make things simple and only use a flat 10 trophic transfer efficiency Question Suppose you had phytoplankton productions of 1000 biomass units per year and you had a food chain with 3 trophic steps between phytoplankton and fish that you wanted to catch each year phytoplankton gt zooplankton gt small sh gt your sh 1000 100 10 1 How much sh production would you expect each year if tropic transfer ef ciency is 10 for each trophic step a 1000 biomass units of sh per year b 100 biomass units of sh per year c 10 39 39 39 r ear d 1 biomass units of sh per year IV The Consequences of a Food Chain Length on Fisheries Production A Trophic Transfer Efficiency and Harvestable Yield 1 This example assumes 10 trophic transfer efficiency B Recall from the primary production lectures that small cells have the growth advantage at low nutrient conditions This fact is vitally important Food web Page 5 Dominant Cell Diameters of Phytoplankton Assemblage 0 1000 M m LOW HIGH Nutrient Concentration C The number of trophic levels between phytoplankton and harvestable fish is smaller in high nutrient regions such as coastal upwelling regions 091 Ouch 7 quotwk huh 0 o 39 r quot m 394 b a 0 gt39 A WMMI 9wquot l trunk kw quot 39 A a quot 21 g t quotA quot 5 d l Wm Q 1 Livding legion I Wk link 7 I 5 14 A Q 5quot Wx q 1 phytoplankton are larger in more nutrient rich regions so commercialharvestable fish can feed directly on phytoplankton and thereby skip several trophic levels and bypass associated ecological efficiency losses of additional trophic steps Highest production of hawestahle fsh is n the coastal eceah reion l imam Estimated Fish Deeanie Previrlee Pnnrg g Pm gt n Transfer ng gn i EggESE 3 Predattieri l I I I I II Been Errteam V 399 K 10939 101 V E 5 3 40 it 103 D Lipwelllirig Areas 023 x 10939 139 20 f C 43 l X 105 The specific numbers above are net se important What is impertarit is this i The sperm esteem regierl eerrlprises meat of the glehall seari primary predectien but phyteplahkten in this regien are small and so there are a let ef tre hie steps If stepsi tie net tie harvestable sh and each trophic step reduces carbon biomass predestien by 1 i st fer T steps there is a 1M U relciustieh aiteglether 2 The teastall regieh has iess essralll prirrlar gir production hut it bene ts Hreatl 0 by having iiust 2 trophic stes tie harveststile sh which makes for were ef cient tanstar sf Earhart tram l irirna reducer tel harvestable sh in this regime and se it is this reglien that is the mast predtretirre fer sh Food web Page 6