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

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Presentation on theme: "Intensive aquaculture can produce yields that are orders of magnitude beyond natural ecosystems How to maximize energy flow to fish Increased nutrient."— Presentation transcript:

1 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

2 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 Lepeophtheirus salmonis

3 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.

4 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

5 The River Continuum Concept Zones in a river system are less distinct But they are functionally very important Physical forces change gradually along a river Elevation ↓ Slope ↓ Temperature and nutrients ↑ Drainage area 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

6 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.

7 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

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

9 Shredders enhance microbial action (bacteria & fungi) convert CPOM to FPOM Food for microdetritivores Detritus processing in a stream

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

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

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

13 Stream Fragmentation, A wier blocking fish movement a hanging culvert can block fish movement The River Discontinuum: Dams and wiers

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


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