•

Intensive aquaculture can produce yields that are orders of magnitude beyond natural ecosystems How to maximize energy flow to fish

Increased nutrient loading —

fertilization

+ ammonia and anoxia tolerant species Shortening the food chain —

primary consumers

(eg carps, tilapia or mullets) Don’t rely on natural recruitment and managing the life cycle—

stocking/hatcheries

Increasing consumption efficiency —small pens

intensive feeding

Increased assimilation efficiency —feeding with easy to digest food

pellets

Increased production efficiency —low

activity species that don’t mind crowding, , highly turbid

water

Lepeophtheirus salmonis

Many aquaculture proponents argue that aquaculture reduces harvesting pressure on wild fisheries.

Salmonid aquaculture not very trophically efficient, food pellets made from by-catch of wild species Major water quality issues —nutrient pollution from cages, anti-fouling paint, antibiotics, habitat destruction Transmit diseases to wild salmonids —bacteria, viruses, protozoans, fungi, “fish lice” –parasitic copepods and other Crustacea Genetic problems when domestic escapees compete with or interbreed with wild fish

Argulus

Summarizing concepts on Secondary production •The organic matter produced by primary producers (NPP) is used by a web of consumers •NPP is used directly by primary consumers (herbivores and detritivores), which are in turn consumed by carnivores.

•Measurement of 2 o Production is done by estimating the rate of growth of individuals and multiplying by the number of individuals per unit area in the cohort (age or size group).

•The efficiency of secondary production ranges from 5-20% (Avg 10%) at each trophic level.

•Efficiency depends on several factors--palatability, digestibility, energy requirements for feeding (activity costs)(eg homeotherms vs poikilotherms , other limiting factors eg water, and nutrient quality of food.

•Trophic efficiency can be represented as the product of CE*AE*PE, each of which is dependent on one or more of the above factors.

•The yields of many important fisheries depends on a combination of NPP, the length ofthe food chain leading to the fish being harvested, and the efficiency of each step.

•Many of the species that we harvest or very high in the food chain, so a great deal of NPP is required to support them.

•Lakes have

zonation

structured by physical forces such as light, wind and waves.

•different zones in the lake had different types of plants and animals

•Zones in a river system are less distinct •But they are functionally very important

The River Continuum Concept

Physical forces change gradually along a river •

Elevation

↓ • •

Slope

↓

Temperature

•

Drainage area

and

nutrients

↑ and discharge ↑ •

Width

of channel and floodplain ↑ •Mean

velocity

↑ •Mean

depth

•

Turbidity

↑ ↑ •

Sediments

, erosional, alluvial, to depositional • •

Shading

↓

Periphyton

,

macrophytes

↑, then ↓ •

Phytoplankton and zooplankton

↑ •

Coarse detritus

input highest upstream •

Fine detritus

accumulates downstream •

Benthic invertebrate community

changes

shredders, grazers, collectors

•

Fish

community changes •

Cold

water to

warm

water species http://www.d.umn.edu/~seawww/depth/rivers/art/figure1_4.jpg

Allochthonous input —Detritus processing •Dead plant biomass breaks down slowly and their nutrients can remain tied up in as organic detritus for long periods of time •Primary production in many ecosystems depends more on its recycling rate ie mainly decomposition of plant detritus, than on loading rates •Aquatic plants break down more rapidly than terrestrial plants, and woody plants are very slow to decompose because they contain lignin, which most bacteria and fungi can’t digest.

Leaf processing

•Wetting and breadown of cuticle •Leaching of soluble components (DOM) •Colonization by bacteria and fungi •Increase in protein content •Colonization by invertebrates •Enhances microbial action •Breakdown into small fragments

Invertebrate detritiivores find leaves much more to their liking after they have been colonized by bacteria and fungi

Detritus processing in a stream

Shredders

enhance microbial action (bacteria & fungi) •convert CPOM to FPOM •Food for microdetritivores

Processing of FPOM by microdetritivores Shredders-macrodetritivores collectors-microdetritivores Filter-feeders, deposit-feeders

Litter bag experiments have been used to study decomposition of detritus •Nutrient content of the detritus, especially N greatly increases decomposition rate, •as does increased temperature •and mesh size 100 % Weight remaining % Larger invertebrates get into the litter bags if the mesh is coarse 0.5 mm mesh 2 mm mesh 10 20 days 30

The interplay between the autochothonous and the allochtonous food chain Allochthonous input Autochthonous input

The River Discontinuum: Dams and wiers Stream Fragmentation, A wier blocking fish movement a hanging culvert can block fish movement http://www.cee.mtu.edu/~dwatkins/images/aqua3pics/hatchery-weir.jpg

http://www.nzfreshwater.org/thumbnails/culvert.jpg

Dams/Reservoirs interrupt the river continuum •create entirely new habitats