Estuaries fresh & salt meet

1. Estuariesfresh & salt meet Tremendously Productive DETRITUS

2. Origin and Types • Drowned river valleys or coastal plain estuaries • Bar-built estuary • Tectonic estuary • Fjords

3. Drowned or Coastal Plain • 18K yr last ice age • Chesapeake Bay, Delware and St Lawrence, Thames

4. Bar-built Estuary • Sand bars and barrier islands • Barrier between ocean and river’s freshwater • Texas coast, N. Carolina coast, N. Sea coast

5. Tetonic Estuaries • Land subsided from crust’s movements • San Francisco Bay

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

7. 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

8. Types of Communities • Open water: anadromous and catadromous • Mud flats: infauna, meiofauna • Salt marshes: cord grass • Oyster reefs • Sea grass beds • Mangrove forest

9. The body Diversity Adaptations

11. 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

12. 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 Energy Budgets IF I = E Growth = 0 I < E Growth = I > E Growth = +

13. Keystone System Circulatory system

14. 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

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

16. 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

17. 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

19. Osmoregulation: ability to hold constant total electrolyte and water content of the cells. Critical for survival and success

20. 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)

21. 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)

22. Osmotic concentration determined by • measuring freezing point depression • vapor pressure of the solution • Seawater osmotic concentration: 1000 mOsm • 470 mmol Na & 550 mmol Cl

23. Two categories of osmotic exchange Obligatory has little control such as trans-epithelial diffusion, ingestion, defecation, metabolic water production Regulated physiologically controlled and help maintain homeostasis (active transport)

24. 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)

25. 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

26. Euryhaline: • Stenohaline: • isomotic: • osmoconformer: • osmoregulator:

29. Four groups of regulation dealing with water in fishes • Hagfish • Marine elasmobranchs • Marine teleosts • Freshwater teleosts and elasmobranchs

30. Five groups of regulation dealing with ions in fishes • Hagfish • Marine elasmobranchs • Marine teleosts and lampreys • Freshwater teleosts • Euryhaline and diadromous teleosts

32. Aganthans • Lampreys live in sea and freshwater but hagfish are strictly marine • Both employ different solution to life in the sea

33. Hagfish • Are the only true vertebrates whose body fluids have salt concentration similar to seawater • Have pronounced ionic regulation

34. 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

35. 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.

36. 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

37. 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)

38. 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

39. 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

40. 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

41. 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????

42. 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)

43. 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

44. 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