ngular: alga) are photosynthetic protists, usually aq a phylogenetically meaningful term, but widely used ite their complexity, algae are NOT PLANTS responsible for most photosynthesis in the ocean covers 70% of the planet’s surface) ater dominated by macroalgae with large, multicellula critical as food for near-shore animals t kelp Macrocystis pyrifera, sea lettuce Ulva lactuca n dominated by phytoplankton: single-celled nthesizers that fix CO 2 the basis of the food web; they are eaten by little ch are eaten by fish, which are eaten by bigger fish. Algae
Transcript
Algae (singular: alga) are photosynthetic protists, usually aquatic - not a phylogenetically meaningful term, but widely used - despite their complexity, algae are NOT PLANTS
Algae are responsible for most photosynthesis in the ocean (which covers 70% of the planet’s surface)
Shallow water dominated by macroalgae with large, multicellular bodies; critical as food for near-shore animals - giant kelp Macrocystis pyrifera, sea lettuce Ulva lactuca
Open ocean dominated by phytoplankton: single-celled photosynthesizers that fix CO2
- form the basis of the food web; they are eaten by little critters, which are eaten by fish, which are eaten by bigger fish...
Algae
No gametophyte (haploid body) -- Gametes are only haploid cells
Gametic life cycle
sperm + eggs
Sporic life cycle
common among multicellular protists like algae; one stage built out of haploid cells, another made of diploid cells
Alternation of Generations:haploid & diploid stages may look different
meiosis only occurs in the sporophyte stage
Alternation of GenerationsMany protists exhibit alternation of generations, in which a multicellular haploid stage alternates w/ multicellular diploid stage
1) Meiosis produces spores (N, haploid), which grow into a whole haploid body called the gametophyte
2) The gametophyte produces gametes (sperm + eggs) by mitosis
3) Syngamy produces the zygote, “the baby” (2N, diploid)
4) The zygote grows into the sporophyte stage (2N, diploid), which undergoes meiosis...
Macroalgae: 3 lineages
Phylum Chlorophyta: Green Algae
Chloroplasts very similar to those in true plants
- chlorophyll a and b
Green algae share a common ancestor with land plants, and are
included in the “Kingdom Plantae” by some
Some Chlorophytes live symbiotically with fungi as lichens,
super-organisms that grow on rocks in moist terrestrial
environments
Phylum Rhodophyta: Red Algae
Red from an accessory pigment, phycoerythrin
- allows absorption of blue + green light, the wavelengths that
penetrate the deepest in ocean water (red is reflected)
Some have lost their plastids,
become parasites on other algae
- may explain why endosymbiosis
occurred repeatedly in this group
Nori, used in sushi rolls,
is the red alga Porphyra
Phylum Stramenopiles - Brown algae
Largest, most complex multicellular colonies of any protist
- convergent evolution has resulted in many plant-like features
- blades look like leaves; stipes look like stems;
holdfasts look like roots
However, brown algae lack true tissues which exist in land plants
Blade
StipeHold-fast
Phylum Stramenopiles - Brown algae
Giant kelp Macrocystis can grow 1 meter per day, 60 m in a year!
- fastest growth rate of any organism on the planet
Grows here in CA because coastal upwelling brings nutrient- rich bottom water to the surface
- supports a diverse community of fish + other animals that depend on the kelp to support the food web
Phylum Stramenopiles - Brown algae
Diploid (2N)
Haploid (1N)
spores
sporophyte
gametophytes(male + female)
Microscopic photosynthesizers: 3 lineages
Diatoms (Phylum Stramenopiles)Diatoms contribute half of the primary production in marine ecosystems
- secrete 2-valve shell of silicate (glass) over plasma membrane
Phylum DinoflagellataPossess 2 flagella that twirl as they swim (Greek dinos, whirling)
Can be autotrophic (photosynthetic), heterotrophic, or some can even switch back and forth (mixotrophic)
Include the photosynthetic endosymbionts of hard corals
Phylum Dinoflagellata
Can cause red tides, up to 100 million cells per liter
- use up all O2, leading to mass kills of sea life
- locally, create intensebioluminescence inbreaking waves at night
Phylum DinoflagellataInclude photosynthetic endosymbionts of hard corals
Can cause red tides, up to 100 million cells per liter
- increasing in frequency, due to run-off from agriculture
- produce potent toxins, which concentrate in filter feeders (clams, mussels) and are very dangerous to humans:
- saxitoxins: Paralytic Shellfish Poisoning
- other toxins: Diarrhetic or Amnesiac poisoning
Liu & Diamond (2005)Nature 435:1179-1186
Increasing incidenceof red tides in Chineseseas …
…coincident with increased economic Development (GDP)
Economic development can occur at the expense of environmental quality
