13.4 How are energy and nutrients passed along in marine ecosystems?

A biotic community = assemblage of organisms that live together within some definable area or habitat.

ecosystem = biotic community plus abiotic environment with which organisms exchange energy and chemical substances.

Ex. kelp forest biotic community includes all organisms living within or near the kelp and receiving some benefit from it

Ex. kelp forest ecosystem includes all those organisms plus the surrounding seawater, the hard substrate onto which the kelp is attached, and the atmosphere where gases are exchanged.

**two of the most important commodities passed along in marine ecosystems are energy and nutrients.

Flow of Energy in Marine Ecosystems

energy flow in photosynthetic marine ecosystems is not a cycle, but a unidirectional flow based on a continuous supply of solar energy.

Ex. algae-supported biotic community: energy enters system, algae abosbr solar radiation. photosynthesis converts this solar energy into chemical energy (carbs) which is used for algae’s respiration —> chemical energy passed onto animals that consume algae for growth —> animals expend mechanical and heat energy which are progressively less recoverable forms of energy until residual energy becomes dissipated w/in the ecosystem as heat, thereby increasing entropy.

• ecosystem relies on a constant input of energy in the form of sunlight

Producers, Consumers, and Decomposers

3 basic categories of organisms w/in an ecosystem:

• producers

• consumers

• decomposers

producers nourish themselves through photosynthesis or chemosynthesis

Ex. algae, plants, archaea, photosynthetic bacteria, ALL = autotrophic organisms

consumers and decomposers = heterotrophic bc they depend, either directly or indirectly on the organic compounds produced by autotrophs for their energy supply.

consumers eat other organisms and are categorized as:

• herbivores - feed directly on plants or algae

• carnivores - feed only on other animals

• omnivores - feed on both

• bacterivores - feed only on bacteria

decomposers i.e. bacteria break down organic compounds that comprise detritus (dead and decaying remains and waste products of organisms) for their own energy requirements. in decomp process, compounds are released and recycled as they become available again as nutrients for use by autotrophs.

Flow of Nutrients in Marine Ecosystems

flow of nutrients depends on biogeochemical cycles, so named bc they involve biological, geological, and chemical components.

• matter doesn’t dissipate and become lost as energy does, but it’s cycled from one chemical form to another by various members of biotic community

Biogeochemical cycling

(1) chemical components of organic matter enter biological system through photosynthesis

(2) chemical components passed from producer on to consumers through feeding

(3) when organisms die, some of the material is used and reused w/in euphotic zone, while some sinks as detritus

(4) some of the detritus feeds organisms living in deep water or on the sea floor, while some undergoes bacterial or other decomposition processes that convert organic remains into usable nutrients

(5) upwelling hoists these nutrients to the surface again —> used by algae and plants to begin the cycle again

Oceanic Feeding Relationships

as producers make food available to consumers, food passes from one feeding population to the next. only a small percentage of the energy (avg 10%) taken in at any level is passed on to the next bc energy is consumed and lost, mostly as heat at each level —> RESULT = producers’ biomass in ocean >>>> mass of top consumers i.e. sharks or whales

Feeding Strategies

for most marine animals, obtaining food occupies majority of their time. some animals are streamlined, fast, and agile, and are able to obtain food through active predation. other animals move move leisurely or not at all, and obtain food by filtering it from seawater or locating it as deposits on the sea floor

modes of feeding in animals that live along sediment-covered shores

• suspension feeding (filter feeding) = organisms use specially designed structures to filter plankton from seawater

  • Ex. barnacles attach to hard surfaces and use their legs to strain passing food particles from the water

  • Ex. clams bury themselves in sediment and extend siphons up to surface, pumping in overlying water and filtering from it suspended plankton and other organic matter

• deposit feeding = organisms feed on food items that occur as deposits i.e. detritus and sediment itself which is coated in organic matter

  • Ex. amphipod Orchestoidea feeds on more concentrated deposits of organic matter on sediment surface

  • Ex. segmented worm feeds by ingesting sediment and extracting organic matter from it

• carnivorous feeding = organisms directly capture and eat other animals, predation can be passive or active

  • passive = waiting for prey items and ensnaring them

  • active = seeking prey

Trophic Levels

most zooplankton are herbivores so they eat diatoms and other marine algae. larger herbivores feed on larger algae and marine plants that grow attached to ocean bottom near shore

herbivoers then eaten by larger animals (carnivores) that are eaten by other pops of carnivores - each feeding stage = trophic level

• generally, individual members of feeding population are larger but not a lot larger than the organisms they eat (some exceptions i.e. whale east krill)

• transfer of energy from one population to another is a continuous flow of energy. small-scale recylcing and storage interrupt flow, slowing the conversion of potential chemical energy to kinetic energy, then to heat energy, and finally the energy is so dissipated in the form of heat that it becomes useless

Transfer Efficiency

transfer of energy between trophic levels is very inefficient, especially at lowest level. efficiencies of diff algal species vary, but avg ~2%, meaning that only 2% of light energy available in sunlit surface waters is ultimately synthesized into food by algae and made available to herbivores

gross ecological efficiency at any trophic level = ratio of energy passed on to next higher trophic level divided by the energy received from the trophic level below.

Ex. ecological efficiency of herbivorous anchovies = energy consumed by carnivorous tuna that eat anchovies, divided by the energy contained in the phytoplankton the anchovies consumed

some chemical energy taken in as food by herbivores is excreted as feces, the rest assimilated. of the assimilated chemical energy, much is converted through respiration to kinetic energy for maintaining life, and what remains is available for growth and reproduction. Thus, only about 10% of the food mass consumed by herbivores is available to the next trophic level.

efficiency of energy transfer between trophic levels depends on many variables:

• young animals have higher growth efficiency than older animals

• when food is plentiful, animals expend more energy in digestion and assimilation than when food is scarce

most ecological efficiencies in natural ecosystems average about 10%, but range between 6% and 15%.

• there is some evidence that EEs in populations important to present fisheries may run as high as 20%

true value of this efficiency is important bc it determines the size of the fish harvest that can be taken safely from the oceans w/out damaging the ecosystem

Food Chains, Food Webs, and the Biomass Pyramid

loss of energy between each feeding population limits the # of fedding populations in an ecosystem. if there were too many levels, there wouldn’t be enough energy to support the organisms in higher and higher trophic levels. in addition, each feeding population must necessariy have less mass than the population it eats. RESULT = individual members of a feeding population are generally larger in size and less numerous than their prey.

Food Chains

food chain = sequence of organisms through which energy is transferred, starting w/ organism that is the primary producer, then herbivore, then 1+ carnivores, then culminating in “top carnivore” which usually not preyed upon by other organisms

bc energy transfer between trophic levels = inefficient, it’s better for fishers to target pops that feed as close to primary producers as possible i.e. primary consumer (herbivore) or secondary consumer (carnivore)

• this increases biomass available for food and # of individuals available to be taken by the fishery

Food Webs

feeding relationships are not normally simple - normally top carnivores in a food chain feed on a # of diff animals, each of which has its own simple or complex feeding relationships or food chains

animals that feed through food web rather than food chain more likely to survive bc they have alternative foods to eat should oe of their food sources diminish in quantity or even disappear

RECAP transfer or energy between various trophic levels operates at low efficiencies, averaging only 2% for marine algae and 10% for most consumer levels

Biomass Pyramid

ultimate effect of energy transfer between trophic levels can be seen in oceanic biomass pyramid —> shows survival of each large organisms, many levels of progressively larger populations of smaller-size organisms must exist to support those higher on the pyramid

ESSENTIALLY: # of individuals and total biomass decrease at successive trophic levels bc amount of available energy decreases. organisms increase in size at successive trophic levels up the pyramid

RECAP

food chain = linear feeding relationship among producers and one or more consumers

CONCEPT CHECK 13.4

(1) Describe the flow of energy through the biotic community and include the forms into which solar radiation is converted. How does this flow differ from the manner in which matter is moved through the ecosystem?

energy flow = linear, solar radiation converted into chemical energy through photosynthesis in plants, relies on a continuous supply of solar energy, unlike flow of nutrients/matter which is cyclic and nondirectional

(2) Describe the three types of feeding strategies utilized by marine organisms.

• filter/suspension feeding = organisms have specially designed structures to filter plankton from seawater

• deposit feeding = feed on food items occurring as deposits, either eat detritus or consume sediment and then extract organic matter from it

• carnivorous feeding = eat other animals

(3) Describe the advantage a top carnivore gains by eating from a food web, as compared to a single food chain.

if one of their prey dies out or population declines, they have a larger food web to rely on and won’t be screwed in terms of finding food

(4) Describe trends that occur in number of individuals, total biomass, and organism size at successive trophic levels going up a biomass pyramid. What conditions produce an inverted biomass pyramid?

• as you go up biomass pyramid, lower # of individuals, lower total biomass, and larger organism size

• conditions = very low energy transfer between trophic levels bc energy efficiency is bad

• inverted pyramid cauused by : smaller population of phytoplankton w/ very high turnover rate supportoing large population of zooplankton

**depends on turnover rates of different trophic levels