lecture 9 (diatoms) Flashcards
what are stramenopiles, what is a unifying characteristic
brown algae, golden brown diatoms etc. also known as heterokonts.
unifying feature = two flagella that are different in length and ornamentation in vegetative or reproductive cells
describe stramenopile flagella and their function in terms of movement
heterokont flagella
one long, forwards directed flagellum with hairs (pulls forwards)
one shorter, smooth flagellum (“rudder”)
why are diatoms so important in the ecology of the ocean?
hugely abundant, drive the biological carbon pump (responsible for over 20% of C fixation), responsible for ~40% of the oceans PP. huge part of sediment accumulation (diatomaceous earth)
in which environments do planktonic diatoms flourish?
cold, nutrient rich waters (marine upwelling), and recently circulated lake waters (but can also be found under/in polar ice)
what are the two main diatom forms?
pennate (oval shape, bilateral symmetry) and centric (like a Petrie dish, radially symmetrical)
what are the advantages of a cell wall to diatoms?
herbivore defense (sometimes spikey), protection, inert to enzymatic attack
what is the frustule made of?
2 valves of silica (SiO2) which can be highly ornamented
what dinoflagellate causes damage to fish gills
Chaetoceras
araphid vs raphid diatoms
pennate diatoms without (araphid) or with (raphid) a raphe
raphid have a raphe system (longitudinal slits) for gliding motility
epitheca
the top valve of a diatom with the epivalve and epicingulum
hypotheca
the bottom half of a diatom with the hypovalve and hypocingulum
diatom cingulum
the girdle (with girdle bands)
aerolae definition and function
pores that penetrate the diatom frustrule
function: movement of gases, nutrients etc.
rimoportulae or labiate processes definition and function
tubular, passes through the valve of diatoms and the inside end is lipped
function: polysaccharide excretion (attachment/movement)
fultoportulae definition and function
central strutted processes without an external extension
function = secretion of chitin fibrils for flotation
where are girdle bands?
they run around the diatom frustule, visible from the girdle view (side)
can diatoms produce toxic blooms?
yes
describe asexual reproduction in diatoms
the parent cells and girdle bands lie outside the newly forming daughter valves, with each of the daughter valves enclosed in silicalemma.
new valve is always the hypotheca (smaller valve)
this decreases the size over several generations
when is sexual reproduction of diatoms triggered?
when the diatoms reach about 1/3 the size of the maximal size
describe sexual reproduction of diatoms, and its role in size regeneration
dependent on many environmental cues, when diatom is too small, then produces an auxospore which restores the typical cell with maximum size
describe the life cycle of centric diatoms
gametic life cycle, oogamous (1-2 eggs per parental cell, 4-128 flagellated sperm per parental cell).
gametes fuse, creating a zygote which becomes a large auxospore
describe the life cycle of a pennate diatom
gametic life cycle isogamous (2 ameboid gametes, similar in size, no flagella)
begins with pairing of parental cells in a common mucilage (4 parental halves in a group).
frustules open, protoplasts and nuclei fuse to create an auxospore
ways that diatoms can slow sinking
small size and appendages, formation of chains, oil droplets, ionic regulation
diatom pigments
chl a, chl c, b-carotene, xanthophylls (especially fucoxanthin)
storage products of diatoms
chysolaminaran, lipids
can diatom spores develop under low Si availability?
spores cannot, but resting cells can
describe the differences between diatom resting cells and spores
resting cells: dormant state of vegetative cells, can develop under low Si, occurs in freshwater diatoms
spores: have thick frustule with less ornamentation, cannot develop under low Si, coastal marine centric diatoms
describe the silica deposition vesicles
secretes the new valves which become hypothecas
describe motility of diatoms
flagellar apparatus is highly reduced (present in some gametes)
benthic raphid pennates move using the raphe which extrudes strands of mucilage
what is the distinctive accessory pigment in diatoms?
fucoxanthin
what environmental conditions will cause diatoms to switch to heterotrophy?
low irradiance and high dissolved organics (eg. in the dark)
why are diatoms so successful in early spring in temperate zones, and upwelling zones in oceans?
they need lots of nutrients, and upwelling brings silica that they need to grow up to the surface
why are biogenic siliceous sediments most common in the oceans?
because freshwater diatoms don’t use as much silica
what does the term “silicate ocean” refer to?
subarctic pacific, southern ocean, and upwelling areas where there is more sedimentation of SiO2 than CO3Ca
what “kind” of ocean (silicate or carbonate) typically has greater carbon export to deep waters and why?
Silicate oceans have greater drawdown of carbon
this is because of the balance between photosynthesis and calcification (coccolithophores make CO2 in calfication process)
what “kind” of ocean (silicate or carbonate) typically has greater carbon export to deep waters and why?
Silicate oceans have greater drawdown of carbon
this is because of the balance between photosynthesis and calcification (coccolithophores make CO2 in calfication process)
