Estuariesfresh & salt meet

Tremendously ProductiveDETRITUS

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 BudgetsIntake ( 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

Obligatoryhas 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