Biol. 317 Lecture: Living in Seawater - (Ch. 3)

Brief overview: Organisms respond to
* aquatic medium
* salinity
* water temperature
* dissolved gases
* hydrogen sulfide
* underwater sunlight
* moonlight
* bioluminescence
* underwater sound
* gravity (sinking/floating)
* drag
* pressure
* loss of body heat

Emphasis will be on common responses (adaptations) to the challenge of life in the sea

Seawater:
* more or less fast-moving water molecules (faster means warmer)
* temperature and polarity affect density
* dissolved gases (oxygen, carbon dioxide, etc.)
* dissolved sea salts (electrically charged ions)
* surface tension, viscosity

Salinity:
* g inorganic salts/kg water
* g/kg = pp thousand = 0/00
* average about 34.7 0/00
* major constituents (99.9%) are invariant as salinities change
* 55 % chloride; 30 % sodium
* Red Sea twice as salty as Baltic Sea, but % the same
* Dead Sea is about 315 0/00
* measure one - predict others
* minor constituents
* parts per million (ppm)

Organism responses to salinity:
* osmosis is regulation of salt levels in cells
* most marine organisms are osmoconformers
* many marine vertebrates - get rid of salts
* in freshwater habitats -organisms take up salts
* marine fish - chloride cells
* marine mammals, birds - salty urine/salt glands (gulls)
* estuarine animals can survive changing salinity (euryhaline)
* salts can be used to absorb organic molecules for food

Temperature
* water has high heat capacity - how much energy does it take to raise temp. by 1° C?
* aquatic organisms are buffered against rapid change
* deepwater is especially stable
* how would life differ if ice was more dense than water?
* thermocline - tropics and summer in temperate oceans
* thermocline is barrier to vertical exchange

Responses to temperature
* warmer means faster
* tunas are endothermous
* temperature limits range
* temperature a reproduction cue? (many use photoperiod)
* cold-water animals might breed only every two years
* animals adjust spawn time - promote offspring survival
* temperature limits on development important
* animals found deeper towards equator (submergence)
* Chthamalus - Balanus (compare p. 68 with 317-318)

Dissolved Gases
* organisms respire: O2
* plants photosynthesize: CO2
* most animals avoid: H2S

* O2 is scarce in ocean
* max. is 12 ppm (saturation level in cold surface water)
* organisms control subsurface O2 levels
* cold water holds more O2
* bacteria quickly deplete O2

* CO2 is abundant in ocean
* uptake of CO enhanced by: CO2 -> carbonic acid (Fig. 3.9)
* plants have renewable CO2
* ocean is a CO2 sink
* CaCO3 a common skeleton
* greenhouse gases could affect oceanic carbonate buffering

Reading:
* How do plants and animals take up gases?
* Why do diving animals need more O2?
* How do they get it?
* What are pluses/minuses of gills in animals?
* Where is H2S found?
* Why is it toxic to animals?
* How do animals cope?