Estuariesfresh & salt meet

Tremendously Productive

DETRITUS

Origin and Types

• Drowned river valleys or coastal plain estuaries

• Bar-built estuary

• Tectonic estuary

• Fjords

Drowned or Coastal Plain

• 18K yr last ice age

• Chesapeake Bay, Delware and St Lawrence, Thames

Bar-built Estuary

• Sand bars and barrier islands

• Barrier between ocean and river’s freshwater

• Texas coast, N. Carolina coast, N. Sea coast

Tetonic Estuaries

• Land subsided from crust’s movements

• San Francisco Bay

Fjords

• Cut by retreating glaciers• Steep wall• Alaska• Norway• Chile• New Zealand

Physical Characteristics• Salinity: 35 ppt vs ~0 ppt

– Salt Wedge: bull sharks– Tides offer wide fluctuations

• Substrate– Sand to mud– Mud rich in organic matter, anoxia

• Temperature– Daily and seasonal

• Suspended sediments– Feeding apparatus

Types of Communities

• Open water: anadromous and catadromous

• Mud flats: infauna, meiofauna

• Salt marshes: cord grass

• Oyster reefs

• Sea grass beds

• Mangrove forest

The bodyDiversity

Adaptations

Body Plans Provide Diversity

• A Question of Adaptation• Often – Consumer and Consumed Co-Evolve• Driver of Speciation – Exploitation of New Energy

Resources• Topics on the diversity of fishes

– Anatomy• Skin – keeps the body intact, etc.• Jaws –respiration and feeding• Appendages – locomotion and buoyancy

– Cardiovascular system– Respiratory system

Energy Budgets

Intake ( I = Income)• Macronutrients

– Carbohydrates– Fats/Oils– Proteins

• Micronutrients– Vitamins– Essential

• Fatty Acids• Amino Acids• Sugars

Energy Use (E = Expenditure)• Respiration• Osmoregulation• Movement• Feeding• Digestion

• Reproduction

IFI = E Growth = 0I < E Growth = I > E Growth = +

Keystone System Circulatory system

Plausible Scenarios• Ancestor chordates evolved in an isotonic setting

– All were marine since the start

• No osmotic gradients• No energy required for osmoregulation• Body surface was highly permeable• Some ion regulation• Kidneys were exclusively for excretion• When early vertebrates invaded freshwater

– Osmotic disruption resulting in excess water• Absorption through thin epithelium• Water intake from feeding

• Need to solve this problem along with ion balance

Osmosis is the tendency of water to move between two solutions of different osmolarity separated by a barrier permeable for water (e.g. membrane).

Living organisms

• an aqueous solution with solutes contained within a series of membrane system

• volume [solutes] maintained within a narrow limits for the optimal function

• deviations from physiological composition: incompatible with life

• maintain the proper concentrations of body fluid which invariably differ from the environment

• unlike cell walls of plants, the animal cellular plasma membrane is not equipped to deal with high pressure differences or large volume changes

Where are the regulated areas?

• Intracellular osmoregulation is the active regulation that guarantees the absence of pressure gradients across plasma membranes, aka cell volume regulation

• Extracellular osmoregulation is the active, homeostatic regulation that maintains the osmotic concentrations in the body fluids, even if the environmental osmotic concentration changed.

• Mainly water and NaCl are maintained

Osmoregulation: ability to hold constant total electrolyte and water content of the cells.

Critical for survival and success

Concepts of osmorality

• Osmotic concentration of a solution can be expressed as osmorality (osmoles per liter)

• Concentration of a dissolved substance is expressed in units of molarity (number of moles per liter solution)

• Osmorality of a nonelectrolyte (sucrose) equals the molar concentration: 1M = 1 Osm per liter

• Osmorality of an electrolyte (NaCl) has a “higher” osmorality because of ionic dissociation and hence exerts a “higher” osmotic force– Not exactly because concentration and the interactions

between ionic charges with water can influence the system

– Along with the low osmotic coefficient of NaCl (Φ = 0.91)

• Osmotic concentration determined by – measuring freezing point depression– vapor pressure of the solution– Seawater osmotic concentration: 1000 mOsm

• 470 mmol Na & 550 mmol Cl

Two categories of osmotic exchange

Obligatory

has little control such as trans-epithelial diffusion, ingestion, defecation, metabolic water production

Regulatedphysiologically controlled and help maintain

homeostasis (active transport)

Two Strategies to minimize this problem

• Decrease the concentration gradient between animal to environment

• Lower the permeability to the outside in areas that are compromised (gills, gut)

Even so

• Always some diffusive leaks• For a counter-flow system to equal this leak

– needs energy– Osmoregulators spend 5% to 30% of their metabolism in

maintaining osmotic balance

• Highly variable aquatic environment – Freshwater– Brackish water– Seawater– Hypersaline water (Med )– Soft water runoffs

• Euryhaline:

• Stenohaline:

• isomotic:

• osmoconformer:

• osmoregulator:

Four groups of regulation dealing with water in fishes

• Hagfish

• Marine elasmobranchs

• Marine teleosts

• Freshwater teleosts and elasmobranchs

Five groups of regulation dealing with ions in fishes

• Hagfish

• Marine elasmobranchs

• Marine teleosts and lampreys

• Freshwater teleosts

• Euryhaline and diadromous teleosts

Aganthans

• Lampreys live in sea and freshwater but hagfish are strictly marine

• Both employ different solution to life in the sea

Hagfish

• Are the only true vertebrates whose body fluids have salt concentration similar to seawater

• Have pronounced ionic regulation

Lamprey

• Egg & larvae develop in fresh water

• Some species stay, some migrate to sea

• Adults return to breed (anadromous fish)

• Osmotic concentration about 1/4 to 1/3 of the seawater

• Face similar problems to that of the teleosts

Marine Elasmobranchs & Holocephalans

• [Salt] at about 1/3 of seawater

• Osmotic equilibrium achieved by the addition of large amount of organic compounds– primarily urea (0.4M)– various methylamine substances

• 2 urea :1 TMAO

• trimethylamine (TMAO), sarcosine, betaine, etc.

• Blood osmotic concentration slightly greater than seawater

• Water is taken up across the gills, which is used to remove excess urea via urine formation

• Small osmotic load for the gills• Urea and TMAO are efficiently reabsorbed

by the kidneys

But

• Urea disrupts, denatured, cause conformational changes in proteins, collagen, hemoglobin, and many enzymes

• Some elasmobranch proteins are resistance to urea• Yancey & Somero (1979):

– Proteins are actually protected by the presence of TMAO

– found to have a consistent ratio of 2 urea to 1 TMAO (also in Holocephalan and Latimeria)

Neat invention

• Strategy of using waste products as an economical way for osmoregulation; unlike the invertebrates which invest on free amino acids to increase serum osmorality

• ionic composition is different from seawater, hence still need to spend energy for ionic regulation

• Need to have the ornithine-urea cycle

Freshwater elasmobranchs

• sawfish, bull shark (C. leucas), stingrays are euryhaline– live in brackish and even freshwater for long

time (Bull in Lake Nicaragua, Mississippi rivers)

• Urea (25-35%), sodium, and chloride are reduced as compared to sw counterparts

• produce copious flow of dilute urine to deal with the water influx

• In freshwater rays, they abandoned urea retention, and reduced ionic content to cope with this problem

• These freshwater rays are not able to make urea when presented in seawater

Coelacanth

• Blood composition is similar to the marine elasmobranchs

• Total osmorality is less than seawater• This maybe due to the habitats they live in:

aquifers feeding into the caves and fissures that could presumably lower salinity: hence a localized hyperosmotic to the surrounding????

Teleost Fish

• Maintain osmotic concentration at about 1/4 to 1/3 of seawater

• Marine teleosts have a somewhat higher blood osmotic concentration

• Some teleosts can tolerate wide range of salinities• Some move between fresh and salt water and are

associated with life cycle (salmon, eel, lamprey, etc)

Marine teleosts

• Hyposmotic, constant danger of losing water to surrounding via the gill surfaces

• Compensate for water loss by drinking• Salts are ingested in the process of drinking• Gain water by excreting salt in higher

concentration along the length of its convoluted tubules

• Produce small amount but very concentrated urine– 2.5 ml/kg body mass/day

• Kidney cannot produce urine that is more concentrated than the blood

• Need special organ, the gills

• Active transport requires energy

• Water loss from gill membrane and urine

• Fish drink to balance the water deficits

• Na and Cl secreted via the gill’s chloride cells

• Gut: for elimination of divalent salts