Standing on the Shoulders of Giants: Plankton at the Base of the Pyramid

This is done by autotrophs (life that makes its own food) (almost) All life depends on transfer of solar energy This is done by autotrophs (life that makes its own food) Autotroph = plant!! All animals are heterotrophs (life depends on other life for its food) Heterotroph = YOU!

Today’s focus = plankton (‘ wanderers’) These are the BASE of the ocean’s food pyramid Plankton are floating, drifting organisms

‘Plankton’ refers to lifestyle, not a life form. Phytoplankton= group of planktonic organisms that are AUTOTROPHS Function like plants - photosynthesize (or in a few cases, chemosynthesize) What do plants need for photosynthesis?

+ Remember, chemical equation for photosynthesis: 6 H20 + 6 CO2 +solar energy--> C6H12O6 + 6 O2 Water Carbon dioxide Light + Inorganic nutrients (P,Fe,S…) - these are needed for the protein molecules that facilitate photosynthesis in the cells.

Water: lots of it in ocean! Carbon dioxide: lots of it because highly soluble in water Light: this is tricky because it requires certain wavelengths for photosynthesis AND minimum intensities …look further at light….

Phytoplankton are found in the photic zone: … in the upper part of the ocean.

Different wavelengths penetrate to different depths: what we mean is that all wavelengths other than blue get absorbed in the water above 100 m

Why is this important? Consider what it means to see a color: When you see blue, it means that all other colors absorbed.

Chlorophyll is the most common chemical for photosynthesis and it appears green: That means that the chloroplasts are absorbing red and violet wavelengths for the solar energy

The red and violet wavelengths do not penetrate very deep into the ocean:

This means that most photosynthesis takes place within the upper 100 m. Some plants adapt by using xanthophyll, a photosynthetic pigment that is brown or yellow. These pigments absorb light in the blue-green range and extend the depth range a bit for autotrophs.

An additional complication: phytoplankton are ALIVE! This means that they also USE energy. Some of the sugar they make with photosynthesis has to be used by them to live.

Below ~60 m, phytoplankton consume more than they make! Thus, light is only sufficient in upper 60 m of ocean!

Put in notes: Only blue light penetrates into the water more than ~100 m, so most photosynthesis takes place in the shallowest part of the ocean where there is sufficient red and violet light for chlorophyll to work. Other photosynthetic pigments will allow photosynthesis to work up to 60-90 m (200-300 ft) depth, but the light is so weak that phytoplankton use more sugar than they make below depths of ~60 m (200 ft).

Primary productivity in the ocean is a surface feature. This accounts for 40% of the carbohydrates made by all primary producers (=autotrophs) each year. Land = 60% Ocean = 40% Also, phytoplankton make ~40% of oxygen each year!

Summary: phytoplankton limited to shallow waters of ocean. If in shallow water, then enough water, carbon dioxide, light. WHAT’S LEFT? Inorganic nutrients! Inorganic nutrients are the limiting factor in the growth and distribution of phytoplankton

Inorganic nutrients are depleted rapidly by phytoplankton unless they are replenished. WHERE DO THEY GET REPLENISHED? Regions of upwelling Near continents

Regions of upwelling occur where the thermocline is weak or nonexistent: Polar regions, esp. Antarctica!

Near continents because of greater light in spring and runoff: Nutrient mixing due to storms in fall Increasing light

Chlorophyll concentration in late spring:

So, what exactly do phytoplankton look like? Tiny!! Diatoms=most common type smaller than a period (0.1 mm) shells made of SiO2 (same composition as glass) silica is source of deep ocean sediment

There you go again with gravity! Diatoms have to float in the upper 3 m of water (because they use lots of red light), but they are making a silica shell that is heavy. How do they float? Instead of saving the photosynthesis products as sugar, they convert them to fatty acids and oils. Oil floats on water! (so the diatoms are buoyant). There you go again with gravity!

Dinoflagellates -- another major type of phytoplankton they have little whips called flagella to move and orient themselves to maximize light

 Dinoflagellates are bioluminescent: This is cool! Video courtesy of MAR-ECO

Dinoflagellates are also responsible for red tides, a type of harmful algal bloom. These can produce a strong neurotoxin that kills fish and shellfish (AND the people who eat them!)

Some plankton are primary consumers (heterotrophs that eat primary producers) These are called zooplankton (animal plankton)

The most important zooplankton is krill=small, thumb-sized arthropod Primary food source in Antarctic oceans for birds, fish, squids, whales -- LARGEST BIOMASS OF ANY ORGANISM!!

Baleen whales use filters to strain water and mud for krill: One of the largest animals lives off one of the smallest…

However, YOU do not see much evidence of the base of the food pyramid! The more obvious evidence of primary producers in the ocean (but only contributes 2-5%): Seaweed (and algae)!

Seaweed are algae! Algae are mostly unicellular but seaweed is multicellular. Seaweed are: green (=chlorophytes) brown (=phaeophytes) red (=rhodophytes) Kelp! Most common Remember: light penetration and pigments!

Mangrove trees can live in SALT water:

Mangroves are very important because they bind soil and provide habitat for many other organisms: (Florida mangrove swamps)

Next time… The Animals!