microalgae & ecology

Question 1

what is microalgae?

Answer 1

phytoplankton & microphytobenthos
major primary producers

Question 2

why are oceans important?

Answer 2

from biomass viewpoint - tropical forests as sites of photosynthetic carbon fixation

Question 3

what waters are most productive?

Answer 3

coastal waters
regions of upwelling / ocean current convergence
- vital for fisheries production

Question 4

what scientific evidence is contradictory?

Answer 4

phytoplankton cells also accumulate volatile metabolites
diffuse into atmosphere and increase green house gas

Question 5

what is microphytobenthos?

Answer 5

marine microalgae also important components of muddy & sandy sediments
- provide food for marine invertebrates

Question 6

what is biofouling?

Answer 6

large number of diatoms live on surface of both inorganic & living substrates

Question 7

what are ‘nuisance’ blooms?

Answer 7

phytoplankton may be locally abundant
red tide phenomena

Question 8

how can a nuisance bloom be a problem?

Answer 8

produce toxic metabolites
utilise all available nutrients / O2
toxins accumulate in filter feeders eg. shellfish
issue in marine & freshwater
major environmental & public health hazard

Question 9

what are microalgal symbionts?

Answer 9

Endosymbiotic dinoflagellates live in anemones, coral polyps, tridacnid clams etc.
Believed to play significant role in carbon economy of coral reefs

Question 10

what is the classification of microplankton?

Answer 10

(60μm upwards) – mainly diatoms and dinoflagellates. Extensively studied from net samples

Question 11

what is the classification of nanoplankton?

Answer 11

(5-20 μm). Small unicellular (often motile) species. Include coccolithophorids, green algae, chrysophytes, cryptomonads. From sedimented or centrifuged samples.

Question 12

what is the classification of picoplankton?

Answer 12

< 5 μm). Unicellular marine prokaryotes. Eukaryote flagellates, cyanobacteria, bacteria, archaea. Poorly studied, identified using molecular probes. Many undiscovered spp. – fastest moving field of research.

Question 13

what is the main storage product of fucoxanthin?

Answer 13

Main storage product: chrysolaminarin (β1-3 glucan) droplets
Oil globules
Unique cell coat Petri dish-like Quartzite frustule.
Rigid cell walls can pass through zooplankton gut without digestion

Question 14

what are Centrales (Biddulphiales)

Answer 14

radially symetric
non motile
single celled - filaments
motile sperm & eggs

Question 15

what are Pennales (Bacillariales)

Answer 15

bilaterally symetric
motile (w/ raphe)
single cell / colonial rafts
protoplast exchange

Question 16

what are pyrrophyta?

Answer 16

dinoflagellates
Chlorophyll a + c, peridinin, dinoxanthin
Unique nucleus w/ condensed chromatin
Starch between outer plastid membrane & inner envelope.
Food vacuole (accumulation body)
Can use a pallium (temporary pseudopodial extension) or a peduncle (tube-like feeding appendage) for predation

Question 17

what are nanoplankton?

Answer 17

5-20upm
Coccolithophorids (coccoliths) produce calcium carbonate scales impregnated by calcite. Historically abundant in warm oceans (c.f. chalk) - major C sink.

Question 18

what is picoplankton?

Answer 18

<5upm
Merismopedia and other cyanobacteria

Question 19

what is the classification of microalgae based on?

Answer 19

Photosynthetic and accessory pigments
Plastid fine-structure
Storage reserves
Cell (coat) wall composition and morphology
Flagellum morphology and fine-structure
Use of molecular markers (small and large ribosomal subunit DNA, proteins such as actin, elongation factor alpha, plastid and mitochondrial genes.

Question 20

how do microalgae reproduce asexually?

Answer 20

involves mitosis followed by cell separation. Leads to rapid increase in populations. Some planktonic algae have a doubling time of < 10 hrs, around 24 hrs (mitosis synchronised with circadian clock – often occurs during night

Question 21

what is binary fission like in microalgae reproduction?

Answer 21

cell nucleus divides
followed by cell division
sometimes remain for some time as siamese twins - some Dinophysis spp

Question 22

what is cell division like in diatoms?

Answer 22

problem dividing because of rigid ‘glass’ cell walls
= variable cell size in pop’

Question 23

how does microalgae reproduce sexually?

Answer 23

involves fusion of gametes. Greater genetic variation (size restitution in diatoms).
May involve fusion of identical motile cells (isogamy) of opposite mating types – as in some dinoflagellates and green algae - Chlamydomonas

Question 24

what is Conjugation in pennate diatoms to form auxospores like?

Answer 24

In pennate diatoms once minimum cell volume has been reached cells undergo conjugation
Cells come together and may either exchange protoplasts / 1/both cells donate protoplast = resting zygote.
Cells secrete mucilage & there is a proliferation of silicaeous frustule-like scales to form protective coat.

Question 25

what is Oogamous conjugation in centric diatoms to form resting spores like?

Answer 25

Centric diatoms are dioecious (separate sexes). Male cells produce uniflagellate sperm. Females produce eggs –internal or external protoplasts. Following fertilisation cells produce multi-layered (scaly) protective coats. Settle in sediments.

Question 26

what are resting spores?

Answer 26

specialised structures thick walls & abundant food reserves settle in sediements can survive w/out daylight

Question 27

what is axospore formation?

Answer 27

found in planktonic centric spp - Chaetoceros and Melosira produce resting type spores asexually cytoplasm aggregates & acquires thick ornamented wall Original frustule breaks up releasing these spores which sink into sediment.

Question 28

what are resting hypnospores in dinoflagellates?

Answer 28

Dinoflagellates produce gametes (may be isogamous or anisogamous). Following fusion they produce thick-walled resting spores (hypnospores) – often decorated with bifurcating strands. known from fossil record as hystrichospores

Question 29

what is diatom chemical ecology?

Answer 29

Gradual interaction of a clonal algal population with an environmental perturbation

Question 30

what is T0 of diatom chemical ecology?

Answer 30

perturbation has not reached the populations.

Question 31

what is T1 of diatom chemical ecology?

Answer 31

perturbation front reaches cells at borders = phenotypic response

Question 32

what is T2 of diatom chemical ecology?

Answer 32

responder cells produce & release chemical cue - conveys info on environmental change

Question 33

what is T3 of diatom chemical ecology?

Answer 33

cells not directly affected by perturbation recieve cue & enact phenotypic response to perurbation

Question 34

what is T4 of diatom chemical ecology?

Answer 34

perturbation front moves forward & reaches cells in pop' alerted by cue cells ready to respond to perturbation

Question 35

what is the evolution of pheremones from pre-existing hormones?

Answer 35

(a)hormone accidentally released into medium and conspecifics are unable to detect it. (b)receiver specializes to detect the hormone & to respond to it. (c)response of the receiver exerts selective pressure for specialization of producers.