Algae and Nutrients

• what is the main ecological role of algae?

  primary production
• what forms the base of aquatic food webs?

  photosynthesis by algae
• what % of global oxygen is produced by algae?

  70 %
• what do photosynthetic pigments absorb?

  specific bands of light
• what is the most common algal pigment?

  chlorophyll a
• what is the amount of chlorophyll a in a water sample proportional to?

  algal biomass
• how do we quantify (measure) chlorophyll a?

  measuring fluorescence = the absorbed light gets reemitted as longer less energetic wavelengths
• what are the three major nutrients in aquatic systems?

  carbon, nitrogen and phosphorous
• which concept describe the idea that organism growth is limited by one nutrient which is the least present in the enviornment?

  Liebig's law of the minimum
• what is the Redfield ratio?

  the average C:N:P ratio is 106:16:1
• what is stoichiometry?

  the determination of the proportions in which elements or compounds react with each other
• what is the ratio called which is the average C:N:P ratio?

  Redfield ratio
• what are the two nutrients algae can be either limited by?

  nitrogen or phosphorus
• aside from nitrogen and phosphorus, what else can algae be limited by?

  light
• what is algae never limited by?

  carbon
• in general, marine algae is limited by what?

  nitrogen
• in general, fresh water algae is limited by what?

  phosphorous
• what is it called when algae is limited by two factors?

  co-limitation
• where is the best place for algae to live?

  where there is the most light and nutrients
• where are the highest light levels found?

  surface
• where are the highest nutrient levels found?

  the bottom
• why are nutrient levels the highest at the bottom?

  nutrients can be stored in and leached out of the sediments
• what is it called when an increase in one thing results in a decrease in another?

  trade off
• what is the area called where there is a balance of light and nutrients?

  the deep chlorophyll maxima
• what is the deep chlorophyll maxima?

  where there is a balance of light and nutrients
• where is the deep chlorophyll maxima?

  at or near the thermocline = as shallow as can be while still having nutrients
• which tends to be more important, light or nutrients?

  light
• why must algae stay suspended?

  to stay in the epilimnion
• what can sinking velocity for small organisms be described by?

  stokes equation
• what are the three main selective pressures on algae?

  sinking, grazing and competition (growth)
• what are the four strategies for algae to overcome sinking?

  be small, be less dense, be flat, swim up
• how can some algae swim up?

  some algae have flagella and are motile
• why does being smaller help to overcome sinking?

  large spheres sink faster than small spheres
• why does being less dense help to overcome sinking?

  denser spheres sink faster
• how can algae become less dense?

  add air vacuoles or other lightweight structures such as oils
• how does being flatter help to overcome sinking?

  flatter objects with protuberances have more frictional drag and sink more slowly
• what are the three strategies to overcome grazing?

  avoid ingestion, avoid digestion, kill the grazer
• how do algae avoid ingestion?

  be big, hard or form a big colony
• how do algae avoid being digested?

  be covered in a gooey sheath to allow for viable gut passage
• how do algae kill grazers?

  being so toxic that the grazer dies