Aquatic Ecology Course

Zoo 374

البيئى Aquaticالنظامecosystem

An aquatic ecosystem is an ecosystem located in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems

and freshwater ecosystems.

Marine ecosystem

Marine ecosystems cover approximately 71% of the Earth's surface and contain approximately 97% of the planet's water.

They generate 32% of the world's net primary production األولية األنتاجية. They are

distinguished from freshwater ecosystems by the presence of dissolved compounds, especially salts, in the water. Approximately 85% of the dissolved materials in seawater are sodium and chlorine. Seawater has an average salinity of 35 (ppt).

Marine ecosystem (cont.)

Fish caught in marine ecosystems are the biggest source of commercial foods obtained

from wild populations . Environmental problems concerning marine ecosystems include unsustainable exploitation of marine resources (for example overfishing of certain species), marine pollution, climate change, and building on coastal areas.

Freshwater ecosystemFreshwater ecosystems cover 0.8% of the earth's surface. They generate nearly 3% of its net primary production. Freshwater ecosystems contain 41% of the world's known

fish sp .There are 3 types of freshwater ecosystems:

Lentic :slow-moving water, including pools, ponds and lakes .

Lotic :rapidly-moving water: streams & rivers .Wetlands :areas where the soil is saturated or

inundated for at least part of the time .

Biological aspects of sea

The resources of the sea are:

Living Non-Living

(Biological) (Physical)

( البيولوجية ( الحية حية الغير( الفيزيائية(

Biological (Living) resources

• Are living animals and plants collected for human use

• It is the main reserve of protein

food either from fisheries

or aquaculture.

Non-living resources

Physical resourcesResult from the deposition, precipitation, or accumulation of useful substances in the ocean or seabed.

1) Oil and gases

About 1/3 rd of the world oil and gas is pumped out of the ocean floor.

2) Minerals: salts.

3) Desalination as source of freshwater

Only 0.017% of Earth’s water is fresh and about 0.6% is available as ground water.

4) Marine Energy

Result from the extraction of energy directly from the heat or motion of ocean floor.

Marine Biology and Marine Ecology

Marine biology differs from marine ecology as: Marine Ecology is focused on how organisms interact with each other and environment.Marine Biology is the study of the animal itself.

The marine environment for all organisms consists of non-living, abiotic factors and living, biotic factors.

Biotic Factors الحيوية العواملThe biotic factors are the interactions among living organisms.

حيوية الغير Abiotic Factors العواملLight, temperature, pH, salinity, substratum, nutrients, pressure, dissolved gases, tides, currents.

Marine Biological EcosystemsBiological Definitions

Plankton :- organisms that float suspended in the water column and have insufficient swimming ability and its transport is done by ocean currents (no directive means for locomotion).phyto-or zoo- or bacteria.

• Nekton :- strongly swimming organisms such as fish, mammals, and squid (active swimmers).

• * Benthos :- organisms that live in intimate contact with the ocean floor.

Marine Bacteria

Phytoplankton

Phyto-Benthos &Macro-algae

Zooplankton

ZoobenthosInvertebrate

animals

Nekton

0.2-2 µm

20-200 µm

0.2-2 mm

• Phytoplankton (Primary Producers األولي المنتج )

• Phytoplankton are the autotrophic component of the plankton.

• The name comes from the Greek words phyton, or “plant“.

• Most phytoplankton are too small to be individually seen with the naked eye.

• When those small cells present in high enough numbers, they may appear as a green or red discoloration of the water due to the presence of chlorophyll or carotein within their cells.

Dinoflagellates

Phytoplankton blooms

Diatoms

DinoflagellatesDinoflagellates

• Bacterioplankton (Recyclers)• Bacterioplankton refers to the bacterial component

of the plankton that drifts in the water column. • They are found in both sea and fresh water.• Many are saprophytic المترممات: They obtain

energy by consuming organic material produced by other organisms.

• Many other Bacterioplankton species are autotrophic التغذية and derive energy from , ذاتيةeither photosynthesis or chemosynthesis.

• Like other small plankton, the Bacterioplankton are preyed upon by zooplankton (usually protozoans).

Cyanobacteria

• Zooplankton (Consumersالمستهلكا

( ت• Zooplankton are heterotrophic

(sometimes detritivorous) type of plankton.

• The name of zooplankton is derived from the Greek zoon meaning “animal”.

• Many zooplankton are too small to be seen individually with the naked eye.

Northern krill

Jelly fish

Copepods

Zooplankton are initially the sole prey item for almost all fish larvae.Fish larvae use up their yolk sacs and switch to external feeding for nutrition. Zooplankton limitation can in turn strongly affect the larval survival, and consequently breeding success and stock strength, of fish species.

•Importance of zooplankton To Fish

• Holoplankton Vs Meroplankton

• Holoplankton are those organisms that spend their entire life cycle as part of the plankton (e.g. most algae, copepods, salps, and some jellyfish).

• Meroplankton are those organisms that are only planktonic for part of their lives (usually the larval stage), and then graduate to either the nekton or a benthic (sea floor) existence. Examples of meroplankton include the larvae of sea urchins, starfish, crustaceans, marine worms, and most fish.

A chain of salps near the surface.

Copepods

Pennate and centric diatoms

Again

• Biozone

Pelagic

Neritic Oceanic

benthic

littoral

supralittoralintertidal

subtidal

High medium low

Prof.Dr.Hanan M Mitwally, Marine Biology

plankton

Nekton

Benthos

pelagic

Ass. Prof.Dr. Hanan M. Mitwally

BiozonesBiozonesBiological HabitatsBiological Habitats

Benthic zone

Pelagic zone

Pelagic

NeriticProductive Coastal

Water

OceanicDeep waters of

open ocean

•The word pelagic comes from •the Greek pélagos, = open sea.

• Neritic zone:• It is extending from low tide mark to the edge of the

continental shelf.• Characters of Neritic zone:

• Shallow depth ≈ 200 meters.• well-oxygenated water • Low water pressure.• Stable temperature and salinity levels. • High photosynthetic activities from phytoplankton

and floating sargassum . • At the edge of the neritic zone, the continental shelves

end rapidly descending to the deeper oceanic crust and the pelagic zone.

• Oceanic zone• Any water in the sea that starts

beyond the continental shelves.• offshore, high light levels,

upper regions of water column

• Conditions change with depth: the pressure increases and there is

less light.

Again

Benthos & Nekton

• Benthos

Benthic Flora Benthic Fauna

SeagrassGreen Algae

Kelp Bed

Red Algae Brown Algae

Megafauna

Macrofauna Meiofauna

Microfauna

Prof.Dr.Hanan M Mitwally, Marine Biology

Kelp bed

Prof.Dr.Hanan M Mitwally, Marine Biology

Aquatic Vegetations

Kelp bed

Marsh grass

Seagrass BedMontaza Bay,Alexandria,

By Prof., Hesham Mostafa

Again

Nekton in Open Ocean Ecosystems

Nekton are pelagic animals that swim freely, independent of water motion or wind, (the active swimmers of the oceans) and are often the best-known

organisms of marine waters .

Nekton

Nekton (Cont.)- Plankton and herbiverous nekton live in photic zone, some graze on plant material throughout the water column.- Carnivorous nekton live mostly below the photic zone, move vertically in search of food.- Omnivorous nekton are most common at bathyl depths.- Detritus feeders tend to occur at depths greater than carnivores.

Nekton (Cont.)

Most nekton are chordates, animals with bones or cartilage. This category of nekton includes :

*Bony fish (most common)

*Cartilaginous fish (sharks and rays)

*Mammals (whales, seals, porpoises and dolphins)

*Reptiles (Turtles, snakes, iguana and saltwater crocodiles)

*Sea birds (Penguins)

Prof.Dr.Hanan M Mitwally, Marine Biology

B=Marine Mammals

Otters Polar bear

Dolphin

Prof.Dr.Hanan M Mitwally, Marine Biology

Sea lions walrus

Seals Manatees

Dugongs, or sea cows as they are sometimes called, are marine animals which can grow to about three metres in length and weigh as much as 400 kilograms. They are the only marine mammals in Australia that live mainly on plants. The name sea cow refers to the fact that they graze on the seagrasses, which form meadows in sheltered coastal waters. As dugongs feed, whole plants are uprooted and a telltale-feeding trail is left. Dugongs are more closely related to elephants than to marine mammals such as whales and dolphins, but manatees are their closest living aquatic relatives.

Oceanic birds spend most of their lives in or on the water and derive their sustenance 

The Albatross is almost as much a marine animal as a whale.

They spend months wandering great distances over the oceans.

They sleep while floating on the ocean surface, drink seawater, and feed on cuttlefish, other small marine animals. 

They return to land only to breed Well-known species include the wandering albatross, a

huge bird with a 3.4 m (11 ft) wingspread. Albatrosses nest on barren islands, close to shore; usually

the nest is a depression in the ground containing a single egg.

* Penguins are true marine animals* They only come on shore to breed, return to the same breeding grounds every year * The rest of the time they are in the water or on the ice

* The diet of the Penguins is unremarkable; it consists of small shoaling animals, small fish and various crustaceans

* These animals, in turn, feed on zooplankton, which feed on phytoplankton

As mentioned before, Most nekton are chordates, animals with bones or cartilage. This category of nekton includes: * Bony fish (most common)* Cartilaginous fish (sharks and rays)* Mammals (whales, seals, porpoises and dolphins)* Reptiles (Turtles, snakes, iguana and saltwater crocodiles)* Sea birds (Penguins)

Others are molluscan nekton like cephalopods, as squid, clams and octopus which are invertebrates, animals with no bones. However, molluscan nekton have no outer shells.

Nekton are the top predators in most marine food chains (Figure 1). The distinction between nekton and plankton is not always sharp. Many large marine animals, such as marlin and tuna, spend the larval stage of their lives as plankton.

Figure 1: Generalized aquatic food web.

Parasites, among the most diverse species in the food web, are not shown.

Key factors in nekton growth :-

* Swimming ability - need streamlined cross-section for minimal drag.

* Buoyancy - need specialized adaptations to help keep afloat (air sacs, liquid fats).

* Search for prey - most food searches occur at night or in aphotic zone; need sonar or keen eyesight to find prey.

Position of Nekton in the Animal Kingdom

Phylum: ChordateSubphylum (1): Vertebrata (animals have a dorsal cord, notochord, vertebrae)

Superclass 1: Gnathostomata (craniata = have cranium, jaws)Class (1): Osteichthyes (bony fish = teleosts)Class (2): Chondrichthyes (cartilaginous fish as sharks and rays)Class (3): ActinopterygiiClass (4): CrossopterygiiClass (5): AmphibiaClass (6): Reptilia

Class (7): AvesClass (8): Mammalia

Superclass 2: Agnatha (acraniata = no cranium, no jaws)Order: Cyclostomata (Lamprey, petromyzon, Hagfish)

Subphylum (2): HemichordataSubphylum (3): CephalochordataSubphylum (4): Eurochordata (tunicate)

Phylum Chordata found in the fresh and salt waters of the world. Living species range from the primitive, jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes.

FISHES

• Main Characters:-

• All fish live in water• Have gills• Have fins (rays-spines)• Scales (sometimes not exist)• Finfish can be further subdivided into demersal fish

(living on or near the sea bed and including round and flat white fish, less fat fish) and pelagic fish (living in mid-water or near the surface and including oil-rich fish).

Bony Fish (Class: Osteichthyes, Teleosts):

Members of this class characterized by:- 1) Bony skeleton 2) Fins, may be:- Paired fins (one fin on each side of the fish), as

pectoral fins and pelvic fins. Unpaired fins (one fin in all the body) as dorsal, caudal and anal fins.

3) Scales: are used to determine the fish age. May be cycloid or ctenoid.

4) Caudal peduncle: as it is thinner the fish becomes faster. 5) Presence of gas bladder

Class (1): Osteichthyes (bony fish = teleosts)

A diagram of general fish morphology

These are generalised diagrams on the shape of bony fish. There are great number of differences between species. These differences can relate to body shape, relative size of each fin, Number of rays, colour, shape and function, as well as internal structure and positioning of the organs. These diagrams are based on the typical shape of bony fishes.

one gill opening on either side, sometimestiny, or only single opening on throat

Cartilagenous Fish (Class: Chondrichthyes)

The Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage rather than bone.

This Class could be divided into 2 subclasses:

S. Class 1:- Elasmobranchii

)e.g: rays, skates and sharks(

S. Class 2:- Holocephali

)e.g: chimeras = ghost sharks = elephant fish(

General characteristics:* Animals from this group have a brain weight relative to

body size that comes close to that of mammals, and is about ten times that of bony fishes, One of the explanations for their relatively large brains is that the density of nerve cells is much lower than in the brains of bony fishes, making the brain less energy demanding and allowing it to be bigger.

* Their digestive systems have spiral valves, and with the exception of Holocephali, they also have a cloaca.

* In rays, the pectoral fins have connected to the head and are very flexible.

* As they do not have bone marrow, red blood cells are produced in the spleen and special tissue around the gonads. They are also produced in an organ called Leydig's Organ which is only found in cartilaginous fishes.

* A spiracle is found behind each eye on most species.

* Their tough skin is covered with dermal teeth (again with Holocephali as an exception as the teeth are lost in adults, only kept on the clasping organ seen on the front of the male's head), also called placoid scales or dermal denticles, making it feel like sandpaper. It is assumed that their oral teeth evolved from dermal denticles which migrated into the mouth.

S. Class 2:- Holocephali

e.g: chimeras

The chimaeras are characterized by having tooth plates in their mouths for crushing hard food and a dorsal spine with a venom sac at its base. They are found in deep subarctic and Antarctic waters and are an evolutionary backwater. Outside the breeding season they live on the continental shelf up to 200 metres deep.

S. Class 1:- Elasmobranchii (e.g: rays, skates and sharks)

Members of this subclass characterized by:-

1) Have no swim bladders. 2) Have five to seven pairs of gill clefts opening individually to the

exterior. 3) Have rigid dorsal fins, and small placoid scales. 4) The teeth are in several series; the upper jaw is not fused to the

cranium, and the lower jaw is articulated with the upper. 5) The inner margin of each pelvic fin in the male fish is grooved to

constitute a clasper for the transmission of sperm. 6) These fishes are widely distributed in tropical and temperate waters. 7) Have a flexible skeleton made of cartilage. For this reason, they are

known as cartilaginous fishes. 8) In Rays and skates are dorsally compressed. Pectoral fin is

modified for swimming.

Class (2): Chondrichthyes (cartilaginous fish)

A diagram of general Ray morphology

5 pairs of gill openingson underside of head

A diagram of general Shark morphology

5 gill openings laterally on either side of

head or body

Fins and their modifications

• Types:-Paired (pectoral, pelvic)Unpaired (dorsal, anal, caudal)

1) Dorsal fin: used to facilitate its advance in water.

* Anguilla sp., poisonous fish, spiny-rayed fish, soft-rayed fish, remora, rays, bottom fish.

2) Pelvic fin: making balance, generally behind the pectoral fin but there are some modifications (change position).

* Anguilla sp., gobia, rays.

3) Pectoral fin: making balance and sometimes for advancing. Rarely change the position.

* Trigla sp., Exocoetus sp.

4) Anal fin: present between anus and caudal fin. Used for up and down movement and defense. No change in position.

* Pipe fish, freshwater species, eel.

5) Caudal fin: consists of 2 lobes (epicaudal and hypocaudal), help in movement “peduncle”, no spines.

* eel, hippocampus.

How does the fish move?

1) Fins…..slow movement.

2) Muscles or myotomes……contraction and protraction

3) Expelling the water through respiration.

Variations in fish habitat:

- The pelagic fish are those that spend most of their life in the upper layers of the water and feed mainly on plankton or other pelagic fish.- Demersal fish are those that spend most of their adult life close to the bottom, or on the bottom substrata, and feed mainly on benthic organisms.- The anadromous fish spend part of their life in salt water and migrate periodically for spawning purposes into fresh water.- The anadromous salmon can be caught on the open seas in the same areas as pelagic species.

Demersal fish• They are slow moving, dorso-ventrally flattened and

bottom feeding fish. The mouth is fully or slightly vented towards ventral side. The dorsal side of body is relatively dark; they are either carnivores or detritus feeders. The young spends early life at the pelagic level.

• Marine fish production largely depends on presence of demersal fishes. However, though they are bottom dwelling fish, only a few species live at great depths of the sea floor, and these fishes have almost no commercial importance (Demersal fish of commercial interest are mainly confined to the upper 200 m, the rest are used as a fish meal).

• Those fish found living on or near the bottom of the sea. They contain little oil (1-4% fat) and called Non-oily fish

• e.g. cod, dogfish, haddock, halibut, plaice, saithe, skate, sole, Sea Catfish, Jewfish, Silvery Croaker, Seabream, Perch, Eel, Grouper, Silver Bream, Indian Barracuda, Black Bass, Rabbit Fish, Crab Eater, and whiting. Several species of sharks also live near the bottom and can be grouped as demersal fishes

• The deep-water demersal fishes are generally divided into two categories, benthic and benthopelagic. The benthic fishes are those that have a close association with the seabed and include species such as skates and flatfishes. Benthopelagic fishes are those that swim freely and habitually near the ocean floor and, in the areas where deep-water fisheries are commercially viable, they comprise most of the exploited biomass.

Milk fish

Cat fish

Solea sp.

Devil rays

Biodiversity

• Despite the importance of marine ecosystems, increased human activities have caused significant damage or are serious threats to the marine biodiversity. These activities can be overfishing, pollution, introduction of exotic species or coastal development. For this reason, conservation plans are necessary to save the marine ecosystems from being lost.

Categories• For the Coastal Zones the subcategories are:• Rocky shores

• Sandy shores

• Continental shelf

• Open oceans

• Deep Sea

• Sea ice ecosystems

• Coral reefs

• Seagrass meadows

• Mangroves

• Salt marshes

• Estuaries

I- Rocky Shores

I- Rocky Shores

• A rocky shore is an intertidal area that consists of solid rocks. It is often a biologically rich environment and can include many different habitat types like steep rocky cliffs, platforms, rock pools and boulder fields. Because of the continuously action of the tides, it is characterized by erosional features. Together with the wind, sunlight and other physical factors it creates a complex environment. Organisms that live in this area experience daily fluctuations in their environment. For this reason, they must be able to tolerate extreme changes in temperature, salinity, moisture and wave action to survive.

Zonation

• Each region on the coast has a specific group of organisms that form distinct horizontal bands or zones on the rocks. The appearance of dominant species in these zones is called vertical zonation. It is a nearly universal feature of the intertidal zone.

 

Supratidal zone

• When the tide retreats, the upper regions become exposed to air. The organisms that live in this region are facing problems like desiccation, temperature changes and feeding. This upper region is called the supratidal or splash zone. It is only covered during storms and extremely high tides and is moistened by the spray of the breaking waves. Organisms are exposed to the drying heat of the sun in the summer and to extreme low temperatures in the winter. Because of these severe conditions, only a few resistant organisms live here. As fungi and microscopic algae living together and sharing food and energy to grow. Also snails which are well adapted to life out of the water by trapping water in their mantle cavity or hiding in cracks of rocks. Other common animals are isopods, barnacles.

Intertidal zone (littoral zone)

• Because the intertidal zone is a transition zone between the land and the sea, it causes heat stress, desiccation, oxygen depletion and reduced opportunities for feeding. At low tide, marine organisms face both heat stress and desiccation stress. The degree of this water loss and heating is determined by the body size and body shape. When body size increases, the surface area decreases so the water loss is reduced.

Subtidal zone (sublittoral zone)

• is the region below the intertidal zone and is continuously covered by water. This zone is much more stable than the intertidal zone. Temperature, water pressure and sunlight radiation remain nearly constant. Organisms do not dry out as often as organisms higher on the beach. They grow much faster and are better in competition for the same niche. More essential nutrients are acquired from the water and they are buffered from extreme changes in temperature.

Problems and adaptations

• Air

• Light

• Temperature

• Salinity stress

• Desiccation stress

• Predation

• Wave action

Problems and adaptations• Air: Intertidal organisms are regularly exposed to air and

water. Air differs physically from seawater in important features. This influences the ability to exchange gas and their overall thermal balance with the surrounding environment.

• Attachment and body changes are also required. When exposed to the air, the organisms directly absorb solar radiation. The buffering capacity of water, because of the high rate of heat conductivity, disappears and the body temperature increases. In contrast to this, heat loss is much lower in air than in water. An adaptation to heating is the vaporization of internal water reserves.

Problems and adaptations• Light: Sunlight is another parameter that influences

the organisms. When there is too much sunlight, organisms dry out and the capacity to capture light energy can be weakened. The light that is not used or dissipated can cause damage to subcellular structures. Too little sunlight reduces the growth and reproduction of the organism, because photosynthesis is reduced. Algae can avoid absorbing too much light by changing the amount of pigments they produce. When free radicals are produced from an excess of light, they can be scavenged and deactivated.

Problems and adaptations• Temperature:. The organisms must be resistant to temp. changes to

survive. Most of the marine organisms are ectothermic (need the warmth from the environment to survive). When the air temperature is too low, the organisms must cope with physiological threats associated with cold stress. The body fluids can then reach their freezing point & ice crystals develop. This causes damage to cell membranes and increasing the osmotic concentration of the remaining fluids. To avoid this cold stress, organisms can migrate to habitats that are more suitable. For sessile organisms ,they can develop physiological and behavioral adaptations such as gaping shells (mussels). Some organisms have developed antifreeze proteins. When the temperature is too high, heat stress appears. Heat stress accelerates rates of metabolic processes. This can be avoided by evaporative cooling combined with circulation of body fluids.

Problems and adaptations

• Salinity stress: When the osmolality of the cell is lower than the surrounding medium, the cell loses water from the internal fluids to the environment (hyperosmotic stress). When the intracellular osmolality is higher than the environment, there is an influx of water into the cell from the environment (hypoosmotic stress).

Problems and adaptations• Desiccation stress: Organisms are threat by

desiccation during emersion at low tides. Dehydratation due to evaporative water loss is the most common mechanism. Highly mobile organisms can avoid the desiccation by migrating to a region that is more suitable. Less mobile organisms restrict various activities (reduced metabolism) and attach more firmly to the substrate. Physiological features by reduction in water permeability of membranes, reduction of metabolic and developmental rates.

Problems and adaptations• Predation: strategies to escape from predation 1)

calcification. It makes them tougher and less nutritious. 2) production of chemicals, These chemicals can be produced all the time such as toxins, but other chemicals are only produced in response to stimuli (inducible defense). 3) Bioluminescence, The light is used for warning, blinding, making scare, misleading or attracting the predator. 4) camouflage. This can be visually or chemically. Visual camouflage means that the prey becomes invisible to the predator by using the same colors as the environment. Chemical camouflage is the passive adsorption of chemicals. The predator does not smell the prey anymore, because the smell is masked.

Problems and adaptations• Wave action: permanent attachment (Bivalves).

But this strategy can not be used by organisms that have to move to feed themselves. These organisms have to make a compromise between mobility and attachment. Another way to be protected is to burrow themselves into the sediment. But an alternative is to seek protected habitats.

Why are rocky shores important?

• Providing a home for a lot of organisms • Nursery area for many fish and crustacean

species • Shelter in areas where seaweeds break the

waves power • Providing food for fishes • Algal beds important food source for rare and

threatened species like sea turtles • Feeding ground at low tide for wading birds • Stabilization inshore sediment

Chemical aspects of the sea

The chemical constituents of seawater

dissolved gases major elements minor elements organic matter

1 -Dissolved GasesThe gases dissolved in sea water are in constant equilibrium with the atmosphere but their relative concentrations depend on each gas' solubility, which depends also on salinity and temperature.

As salinity increases, the amount of gas dissolved decreases because more water molecules are

immobilised by the salt ion .

As water temperature increases, the increased mobility of gas molecules makes them escape from the water, thereby reducing the amount of gas dissolved.

1 -Dissolved Gases (cont.)

Nitrogen , oxygen and CO2 are the most aboundant & important gases dissolved in s.w

Nitrogen:Represents 64% of total dissolved gases in s.w.

Almost inert i.e. has very low solubility and chemical reactivity.

Nitrogen requirements of marine organisms must be met by nitrogenous compounds (dissolved – particulate – dissolved plant & animal tissue in the sea).

Oxygen:* Its deficiency is fatal to aquatic organisms, i.e. many fish died not from the direct toxicity of pollutants but due to O2 consumption in pollutants biodegradation.Presence of O2 is fatal to other organisms (anaerobic bacteria).Oxygen sources: 1- mainly from the atmosphere(The solubility of O2 is directly proportion with the atmospheric pressure & inversely proportion with water temperature and salinity) 2- secondly, the photosynthesis.

CO2:

Used by plants during photosynthesis.

Affects the acid-base balance in s.w by forming bicarbonate and carbonate ions under varying conditions [ Buffering action ].

These interactions can become quite complex, and have major impacts on the distribution of life in the ocean.

1 -Dissolved Gases (cont.)

All gases are less soluble as temperature increases, particularly nitrogen, oxygen and CO2 which become about 40-50% less soluble with an increase of 25ºC.

When water is warmed, it becomes more saturated, eventually resulting in bubbles leaving the liquid. Fish like sunbathing or resting near the warm surface or in warm water outfalls because oxygen levels there are higher. The elevated temperature also enhances their metabolism, resulting in faster growth, and perhaps a sense of wellbeing

Likewise if the whole ocean were to warm up, the equilibrium with the atmosphere would change towards more CO2 (and oxygen) being released to the atmosphere, thereby

exacerbating global warming .

Only six elements and compounds comprise about 99% of sea salt:

(1 Chlorine (2 Sodium(3 Sulfate(4 Magnesium (5 Calcium (6 Potassium

2 -Major constituents:( elements have concentration> 1 mg/l in s.w):

Salinity and the main salt ions

The salinity of sea water (usually 3.5%) is made up by all the dissolved salts.

N.B.The salinity of the oceans changes slightly from around 32ppt to 40ppt. Low salinity is found in cold seas, particularly during the summer season when ice melts. High salinity is found in the ocean 'deserts' in a band coinciding with the continental deserts. Due to cool dry air descending and warming up, these desert zones have very little rainfall, and high evaporation. The Red Sea located in the desert region but almost completely closed, shows the highest salinity of all (40ppt) but the Mediterranean Sea follows as a close second (38ppt). Lowest salinity is found in the upper reaches of the Baltic Sea (0.5%). The Dead Sea is 24% saline, containing mainly magnesium chloride MgCl2. Shallow coastal areas are 2.6-3.0% saline and estuaries 0-3%.

Salinity and the main salt ions

Marine plants (seaweeds) and many lower organisms have no mechanism to control osmosis, which makes them very sensitive to the salinity of the water in

which they live .

Salinity affects marine organisms because the process of osmosis transports water towards a higher concentration through cell walls.

A fish with a cellular salinity of 1.8% will swell in fresh water and dehydrate in salt water. So, saltwater fish drink water copiously while excreting excess salts through their gills. Freshwater fish do the opposite by not drinking but excreting copious amounts of urine

while losing little of their body salts .

Density

The density of fresh water is 1.00 (gram/ml or kg/litre) but added salts can increase this. The saltier the water, the higher its density. When water warms, it expands and becomes less dense. The colder the water, the denser it becomes. So it is possible that warm salty water remains on top of cold, less salty water. The density of 35ppt saline seawater at 15ºC is about 1.0255, or s (sigma)= 25.5. Another word for density is specific gravity.

3 -Minor elements:( elements and compounds have concentration <

1mg/l)

-Nutrient salts:Nitrogen compounds include:

1 -Dissolved inorganic nitrogen(DIN) represented by:

Nitrate(NO3), Nitrite(NO2), Ammonia(NH3).2- Dissolved organic nitrogen (DON).3- Particulate nitrogen (PN).

-Nutrient salts:Phosphorous compounds include:

1- Dissolved inorganic phosphorus (DIP)Mainly orthophosphates (H3 PO4 )

2- Dissolved organic phosphorus (DOP).3 -Particulate phosphorus ( PP ).

Importance of phosphorus as a nutrient element:1- It is the limiting element for the production of

aquatic environment.2- It is a part of DNA & RNA molecules

[ molecules that store energy (ATP & ADP)] 3-Ca phosphate is a building block for bones &

teeth.4- Phospholipids found in all biological molecules.

The main nutrients for plant growth are nitrogen (N as in nitrate NO3-, nitrite NO2-, ammonia NH4+), phosporus (P as phosphate PO43-) and potassium (K) followed by Sulfur (S), Magnesium (Mg) and Calcium (Ca). Iron (Fe) is an essential component of enzymes and is copiously available in soil, but not in sea water (0.0034ppm). This makes iron an essential nutrient for plankton growth. Plankton organisms (like diatoms) that make shells of silicon compounds furthermore need dissolved silicon salts (SiO2) which at 3ppm can be rather

limiting .

N.B.

Deep sea temperature, oxygen & nutrients

In this diagram one can see how light penetrates no deeper than 150m for photosynthesis. Indeed at 800m, the ocean is pitch dark. In the surface mixed layer above the thermocline, water mixes sufficiently to sustain life. Gas exchange with the atmosphere is near-perfect such that the oxygen concentration in the water is in equilibrium with the atmosphere. But it rapidly decreases below 50-75m as photosynthesis declines while animals use up most oxygen. At around 800m oxygen levels reach a minimum (as also carbondioxide levels reach a maximum, not shown). Towards the deep and bottom water, oxygen levels increase slightly due to an influx of cold bottom water from the poles. Due to lack of oxygen, deep sea fish cannot be very active.

 

Freshwater Ecosystems

Only 3% of the world's water is fresh. And 99% of this is either

frozen in glaciers and pack ice or is buried in aquifers. The remainder

is found in lakes, ponds, rivers, and streams.

Freshwater ecosystemFreshwater ecosystems cover 0.8% of the earth's surface. They generate nearly 3% of its net primary production. Freshwater ecosystems contain 41% of the world's known

fish sp .There are 3 types of freshwater ecosystems:

Lentic: slow-moving water, including pools, ponds and lakes .Lotic: rapidly-moving water: streams & rivers .

Wetlands: areas where the soil is saturated or inundated for at least part of the time .

Importance of fresh water ecosystems

Fisheries

Aquaculture

Sources

Lakes

Rivers

Some studies about distribution, origin and morphometry of the world’s large

lakes were done. Natural lakes, freshand salt with a surface area greater

than 500 sq km were included.

They are 253 known lakes.Large lakes occur on all continentsexcept Antarctica, but nearly half

of them are found in North AmericaThese data show that the large lakes

of the world occupy a surface area of 1,456,000 sq km and they have

an estimated volume of 202,000km3

Large lakes account for about 90%of the total surface area and

volume of water held in all lakes of the world. ,

Lakes

Fisheries management in Fresh water ecosystem

Firstly, we have to know the difference between :

Natural aquatic ecosystems

Modified aquatic ecosystems

Natural aquatic ecosystems

* Fishes and other aquatic resources are captured from a great variety of freshwater ecosystems, most of which are natural.

• Natural aquatic ecosystems include lakes, swamps and floodplains, collectively called standing waters, and rivers and streams, collectively called running waters.

*Distribution of natural waters- The distribution pattern of natural freshwaters among the

continents is uneven which has important implications for aquatic production, inland fisheries and aquaculture.

- For example, the greatest occurrence of standing waters is in the relatively unproductive northern areas of the Northern Hemisphere. In contrast, the distribution of running waters in the form of perennial rivers is more homogeneous, with the exceptions of the great deserts of North and Southwest Africa, the Arabian Peninsula and Australia.

- The status and trends of aquatic ecosystems, both natural and modified, are closely linked to the condition of adjacent terrestrial ecosystems.

Modified aquatic ecosystems

• Nearly all inland water bodies have been modified to some extent through human intervention. For instance, the enriching effects of excess fertilizers and livestock wastes in the runoff from farmland and lakes have caused biological environmental impacts on rivers and streams.

* New ecosystems have been created by the physical modification of natural aquatic ecosystems, such as rivers and streams that have been dammed to form reservoirs and irrigation systems for agriculture.

• Reservoirs themselves can be engineered in special ways to facilitate, for example, fish passage and fish capture or otherwise to stimulate increased production through habitat enhancement for a specific species.

* Natural and modified ecosystems are further transformed in their particular community structures through biodiversity - by the introduction of new species - and by periodic stocking.

SO,,,,,,,.* All modifications affect the fisheries potential of aquatic

ecosystems. Many are subtle, with long-term irreversible effects and may eventually prove negative.

* Large reservoirs are among the most conspicuous man-made aquatic ecosystems. Many small water bodies seem natural but, in fact, are reservoirs that have been created primarily as community water supplies, to water livestock or to irrigate crops……….. Such water bodies can have multiple uses, including fisheries and aquaculture but, to be successful, they require well-planned integrated watershed management. Rice paddies are a prime example of an agricultural crop system that produces a second crop - fish - which in turn enhances the rice production.

Fish resources in lakes

The degree of resource utilization differs greatly from lake to lake and according to two main types of fisheries: demersal/inshore and pelagic/offshore.

Currently, the demersal/inshore resources are heavily exploited or overexploited. In Asia, there is a relatively advanced national capacity for the development of enhanced fisheries but less experience in social and political issues. African large lakes are receiving adequate biological attention through a number of international activities, with research focusing particularly on lakes Victoria, Tanganyika and Malawi. However, governmental support in some African countries is still low, with little money allocated from national budgets for their development.

Fish resources in lakes (Cont.)

Africa, especially East Africa, is endowed with numerous lakes that support very important fisheries, in turn providing a livelihood to millions of people and contributing significantly to food supply. In many of these lakes fisheries are reaching a state of maturity and consequently management problems are rising. For 11 lakes, shared by 11 countries of eastern Africa, fisheries employs close to half a million people, with perhaps three times as many engaged in secondary activities and related services, thus supporting about 4 percent of the population of the region as a whole

The State of World Inland Fishery Resources

Fishes, lampreys, amphibians, crustaceans and molluscs constitute the broad groups of inland resources that directly or indirectly support fisheries (see FAO statistics). Some 11 500 fish species - 41 percent of all fishes - are exclusively freshwater and about 1 percent are diadromous.

Due to statistical problems, the state of inland water resources must be implied from other information. Trends in annual capture data provide one line of evidence. Globally, the trend for capture has been for modest annual increases of about 2 percent during the last two decades of the twentieth century. From a continental perspective, trends show increases in Asia, Africa and Latin America, decreases in the Commonwealth of Independent States and Baltic States (former USSR), North America and Europe, and stability in Oceania.

The State of World Inland Fishery Resources (Cont.)

Another line of evidence on the state of inland resources comes from the status and trends of ecosystems. Generally, it can be inferred that aquatic ecosystems are in a state of decline throughout most of the world. How can this be reconciled with an apparent trend for increases in capture output from inland resources?

One reason is a human-induced enriching of aquatic systems from agriculture and urban sources to produce more fish. Another is that the combined effects of fishing and physical and chemical changes in inland waters have caused a shift to species that are more productive per unit of area, weight-wise, but may be of lesser economic value.

Better governance -- with attention to aquatic ecosystem management such as habitat enhancement and stocking interventions -- along with broad approaches to management, such as integrated watershed management, also increase inland output.

Factors affecting the fisheries and fish production in lakes

Natural factors1 (Peripheries erosion

2) Lake area reduction3) Sea water level rise

4 (Lagoon saltation5 (Sea lagoon connection siltation

Human related factors1 (Agriculture

2 (Industrial sewage discharge3 (Land reclamation

4 (Coastal constructions5 (Illegal fishing

6 (Recreational activieties7 (Increasing population

8 (Number of boats and fishermen9 (Pollution

These factors, some of them or even one of them may cause drastic changes in the environmental conditions of lakes all over the world affecting the fisheries of the lakes as well as the fish communities inhabiting these lakes .

WHY….. not only lakes ????

Fresh-water habitats are extremely diverse, and include both still-water environments like lakes and ponds, and flowing-water environments like rivers and streams.

Still-Water HabitatsLakes and ponds

• Like oceans, lakes have pelagic and benthic zones. The temperature of lake water varies depending on depth, and can also change dramatically over seasons. The epilimnion is the topmost layer of lake water. It is significantly warmer than deeper areas due to heating by sunlight. The hypolimnion layer describes deeper, colder lake water. Many of the nutrients in lakes collect at lake bottoms.

• Turnover occurs when all the water in a lake is nearly thermally uniform and mixed, distributing nutrients throughout the water. Turnover occurs twice a year in many temperate lakes, but may occur only once in subtropical environments, or not at all in permanently stratified lakes.

Still-Water Habitats (Cont.)

• Lakes also can be described as either oligotrophic or eutrophic (or in between these two extremes).

• Oligotrophic lakes have low levels of nutrients and low productivity. They generally contain cold, highly oxygenated water and support species adapted to these conditions. Eutrophic lakes, on the other hand, have plentiful nutrients and are highly productive. Species that inhabit eutrophic lakes must be tolerant of low oxygen levels and warm temperatures. In general, oxygen levels in lakes depend on the amount of water circulation, the surface area that is exposed to air, and levels of oxygen consumption by living organisms.

Still-Water Habitats (Cont.)

Flowing-Water Habitats Rivers and StreamsThe habitats available in rivers and streams differ in several

ways from those in lakes and ponds. 1) Because of the current (flowing water), the water is usually

more oxygenated. • River species generally have special adaptations for living in water

currents. Some species are sessile and live anchored to the river bottom. Other species have evolved adaptations such as suckers or hooks to keep themselves from being washed away. Still other species are strong swimmers. Many of these have flattened bodies that help them resist the pressure of the current.

• Compared to lakes, rivers tend to be well-oxygenated because of the constant motion of the water. Temperatures can change quickly in rivers, but do not span as great a range as in lakes or other still water. Because there is less penetration of light in flowing water, plant diversity is generally lower in.

2) Photosynthesizers play a minor role in the food chains here; a large fraction of the energy available for consumers is brought from the land; e.g., in falling leaves.

Thank You for your attention