Aspects of Marine Animal Physiology Respiration Gaseous Exchange Osmoregulation

Basics Aerobic respiration: process by which almost all living organisms obtain the energy they need Oxidation of organic molecules (glucose) glucose + oxygen  carbon dioxide + water This is a simplified version and does not show all the intermediate rxns involved Key: respiration converts chemical energy of glucose into a form which can be used by organisms (for muscle contraction, growth, etc) All heterotrophic organisms obtain the organic molecules either directly or indirectly from autotrophic organisms (food chains/webs)

Limits to Diffusion Organisms need to exchange materials with their environment Include respiratory gases (O2 and CO2), nutrients, and excretory products (waste substances produced as result of metabolism)

In relatively small and simple organisms (protozoa), exchange takes place across entire body surface As organisms increase in size and complexity, there are specialized exchange surfaces such as lungs or gills (adapted for the exchange of materials)

Surface Area to Volume Ratio As the size of an organism increases, it’s surface area decreases in relation to its volume Very small organisms have a relatively large surface area in relation to their volume

Why Cells Aren’t Big All organisms need to exchange substances such as food, waste, gases and heat with their surroundings. These substances must diffuse between the organism and the surroundings. The rate at which a substance can diffuse is given by Fick's law: Rate of Diffusion  = surface area x concentration difference distance

Why Cell’s Aren’t Big Investigation The rate of exchange of substances therefore depends on the organism's surface area that is in contact with the surroundings. The requirements for materials depends on the volume of the organism, so the ability to meet the requirements depends on the surface area : volume ratio. As organisms get bigger their volume and surface area both get bigger, but volume increases much more than surface area.

Growing cells 1µm 2µm 3µm 4µm 5µm 6µm SA/V Ratio Demonstration Why it's REALLY Important

How are surface area and volume affected by growth? SA/V Volume /µm3 Surface area /µm2 Size /µm 1 2 3 4 5 6 6 24 54 96 150 216 1 8 27 64 125 216 6 3 2 1.5 1.2 1

Results This means that diffusion over the surface of a large organism may be insufficient to meet it’s needs Diffusion of respiratory gases into and out of cells would be too slow Some larger organisms are flattened (which is an adaptation to increase their surface area) Most complex organisms have specialized exchange surfaces (lungs and gills)

Transport Systems in Large Mammals There is an exchange of materials between organisms and their environment; there is also a need for transport of materials within Oxygen and nutrients transported to respiring tissues, CO2 and wastes are removed In many small organisms, transport occurs by diffusion or active transport In larger organisms – the distances are too great and diffusion alone is too slow

Large animals have internal transport systems to ensure that substances are delivered efficiently to cells and tissues and wastes are transported away Usually consists of blood, pumped around the body by one or more muscular hearts Fish have a single circulatory system Blood pumped from heart to gills; blood then flows around the rest of the body before it is returned to the heart

Life in Water Atmospheric air = 21% oxygen Concentration of DO much lower in water Solubility of oxygen in sea water is rather lower than fresh water (due to presence of dissolved salts in sea water) Solubility of oxygen also decreases as the temperature increases

[DO] in sea water at equilibrium with atm/cm3 oxygen per dm3 Temperature /°C [DO] in sea water at equilibrium with atm/cm3 oxygen per dm3 7.97 10 6.35 15 5.79 20 5.31 30 4.46

Larger, more complex animals have a specialized gas exchange surface Many small marine animals (cnidarians) obtain oxygen they require by diffusion across their body surface Larger, more complex animals have a specialized gas exchange surface Often associated with a transport system for respiratory gases etc.

Majority of aquatic animals have gills Large SA for diffusion of respiratory gases Highly active fish have relatively large SA compared to slower fish Also have respiratory pigments (hemoglobin and hemocyanin) High affinity for oxygen Assist in the uptake of oxygen from environment

Coral polyps (Cnidaria) have no specialized gas exchange organs Do have a large surface area Diffusion across body wall obtains enough O2 Gas exchange also occurs across the surface of their gastrovascular cavity

Pumped Ventilation Many bony fish maintain almost constant flow of water through gills (ie: grouper) Achieved by pumping action of the mouth and operculum Water is drawn into mouth as the volume of the oral cavity increases (think of using a straw) Water is then drawn through the gills by the action of the opercular covers they increase the volume of the opercular cavity Results in a lower pressure than in the oral cavity

Ram Ventilation Tuna swim continuously with mouth open to maintain a constant flow of water over gills Fish alter the degree of mouth opening during ram ventilation to keep drag to the minimum Some species (mackerel) change from pumped to ram ventilation as their swimming speed increases to between 0.5 – 0.8 m/sec Reduces energy cost of maintaining opercular pumping at higher swimming speed

Ram Ventilation Pumped Ventilation

Many marine animals maintain a different concentration of ions in their body fluids from the surrounding sea water As seen in the table, concentrations of ions of the two inverts are similar to those of water [ions] in blood plasma of toadfish, eel, and salmon are much less than seawater Useful site

Concentration of Ions in Seawater Compared to the Fluids of Animals Sample [Solute]/millimoles per dm3 Na+ K+ Sea water Approx 450 10 Mussel (body fluid) 474 12 Jellyfish (body fluid) 10.7 Toadfish (plasma) 160 5 Eel (plasma) 177 3 Salmon (plasma) 212

Vertebrates vs Invertebrates Most marine inverts are osmoconformers: the concentration of solutes in their body fluid is the same as the surrounding sea water This means water enters and leaves equally, no overall change in water content of organisms Marine verts with osmotic concentrations of solutes lower than that of seawater lose water by osmosis Require mechanisms to maintain their body solute and water content

Osmoregulation Osmoregulation: process by which living organisms maintain the solute and water content in their blood and body fluids Marine bony fish (teleosts) have an internal solute concentration approx 1/3 of sea water

Osmoregulation in a Marine Bony Fish Drinking sea water Water and some ions lost in urine Na+ and Cl- ions secreted by gills Water lost from gills by osmosis

Osmoregulation Marine bony fish drink sea water Excess salts in water are absorbed in intestine Sodium and chlorine ions are actively secreted by chlorine secretory cells (present in gills) Process requires energy (provided by respiration)

Osmoconformers Most marine inverts (including mussels) are osmoconformers Internal osmotic concentration is the same as their surroundings Their internal concentrations of individual solutes are not necessarily the same as in sea water Indicates they have the mechanisms to regular their internal solute concentrations

Concentrations of ions in the body fluid of a mussel and sea water Sample Concentration of ions/millimoles / kg of water Na+ Mg2+ Ca2+ K+ Cl- Mussel 474 52.6 11.9 12.0 553 Sea water 478.3 54.5 10.5 10.1 558.4

Eurohaline Organisms able to tolerate a range of salinities (such as estuarine conditions) Shore crab Carcinus maenas is common in much of world can tolerate salinities down to 6 ppt Species of fish which migrate from sea into fresh water (including salmon, eels) Use different mechanisms to control [ions] in their cells in their different environments When a salmon migrates into freshwater, the active ion transport in the gills changes direction Stenohaline: everybody else (limited tolerance)