lecture 15 (macroalgal ecology)

Question 1

periphyton

Answer 1

complex mixture of microalgae, bacteria and fungi, held together in mucilaginous matrix and attached to substrate

Question 2

seaweed

Answer 2

macroalgae, typically attached to substrates

Question 3

phytoplankton

Answer 3

unicellular, colonial, filamentous chain-forming algae, floating or swimming weakly

Question 4

describe in a diagram the fate of macroalgal PP in a food web

Answer 4

10% is consumed by herbivores directly, 90% enters detrital food web.
solar energy goes into macrophytic production. this goes into DOM, POC, debris, and herbivores grazing these live plants. from there, debris is eaten by debris feeders and beach strandings, where it becomes feces and is taken up by bacteria. POC is taken up by bacteria and filter feeders (filterfeeders produce feces which is again taken up by bacteria). DOM is taken up by bacteria, which is taken up by protozoa. bacteria and protozoa are taken up by filter feeders

Question 5

what factors effect vertical zonation of macroalgae?

Answer 5

water motion/wave action, tides, desiccation resistance, salinity, nutrients, light availability, type of substrate, herbivory, pathogens, interspecific competition etc.

Question 6

emersed

Answer 6

exposed to air

Question 7

immersed

Answer 7

covered by seawater

Question 8

define the three nearly universal intertidal zones

Answer 8

1. uppermost black strip of highly desiccant tolerant cyanobacteria, marine lichen and littorinid snails
2. intermediate zone of various seaweeds with barnacles and limpets
3. a lowermost zone inhabited by laminarialean brown algae or corals

Question 9

name 3 effects of exposure to air on seaweeds

Answer 9

loss of source of nutrients
desiccation
damaging levels of solar radiation

Question 10

name 2 effects of immersion on seaweeds

Answer 10

reduced irradience levels
subjected to stressful mechanical forces of wave action

Question 11

in regards to seaweeds, what is a a boundary layer and under what conditions of water movement is it better established?

Answer 11

it is thicker and better established under still waters. A diffusive barrier to movement of dissolved nutrients into algae (slower nutrient uptake and slower growth rates)

Question 12

pros and cons of water movement for seaweeds

Answer 12

pros: thins the boundary layer, increases nutrient uptake and growth rates, removes sessile animals that compete for attachment space, disperse fronds, reduces self-shading
cons: high mechanical forces which cause damage and removal. shear stress on macroalgal surfaces, causing drag forces proportional to velocity of water squared.

Question 13

what are the 4 main components of macroalgal adaptations that dissipate effects of drag force?

Answer 13

elasticity in tension (stretchiness), in bending (flexibility), torsion (twisting), breaking strain (strength)

Question 14

describe blade adaptations of sublittoral kelp nereocystis living in sheltered and energetic environments

Answer 14

in energetic environments: smooth, narrow blades which bundle together to streamline profile (reducing drag force, but self shading)
in sheltered environments: wider, ruffled blades (increasing turbulence to reduce boundary layer, but can tear at high flow rates)

Question 15

what are some seaweed adaptations to irradiance in the intertidal?

Answer 15

photoinhibition under high light stress (closing photosynthetic reaction centers), protective compounds such as beta-carotene and aromatic amino acids

Question 16

what are some seaweed adaptations to irradiance in the subtidal?

Answer 16

body structure for optimal light absorbance, increase in light harvesting accessory pigments (phycoerythrin, fucoxanthin, etc.)
reallocation of stored reserve materials and dark C assimilation

Question 17

what is photoinhibition?

Answer 17

depression of photosynthetic activity and photo-oxidation of chlorophyll. closing photosynthetic reaction centers.

Question 18

what are the effects of decreasing and increasing salinity on seaweeds?

Answer 18

increasing lowers external water potential. causes plasmolysis (upake of ions, water loss, synthesis of osmotically active compounds)
decreasing increases external water potential. increases uptake of water by seaweeds, increasing cell volume and turgor pressure. loss of ions and organic solutes leading to osmotic adjustments

Question 19

what are the effects of decreasing and increasing air exposure on seaweeds?

Answer 19

exposure to air results in dehydration, increase in cellular solute concentrations, loss of ability to take up dissolved nutrients (water loss dependent on seaweed surface and volume)
desiccation can help keep fungus from decaying seaweed hosts.
decay if not exposed periodically to air in some species

Question 20

what factors influence nutrient uptake in macroalgae and why?

Answer 20

influenced by irradiance, temperature, water motion, desiccation and age.
too little irradiance, cant photosynthesize, wont take up as much
need water motion to bring nutrients up
when out of water, can’t absorb nutrients
different speeds of uptake with age/temp

Question 21

describe the main physical and biological factors that affect kelp communities

Answer 21

disturbance (storms)
behavioural changes in herbivores
competition for light
grazing pressures (eg. sea urchins, abalone, limpets)

Question 22

where are kelp forests most commonly found in the worlds oceans?

Answer 22

most common in coastal areas. more in pacific than atlantic

Question 23

explain how storms can influence kelp-urchin interactions and favour development of barrens

Answer 23

storms can remove kelps, creating barrens. urchins rove the sea floor, eating new recruits and maintaining barrens

Question 24

Describe with labeled diagrams the effects of changes in carnivores and herbivores on kelp forest density over time

Answer 24

with decreases in herbivores: recruitment of several kelp species. nereocystis is upper canopy which dies back every year. eventually perennial laminaria will dominate, shading out other seaweeds
(initial increase in diversity, eventual monoculture due to lack of disturbance)
decreases in carnivores: increased herbivore biomass and intensity, decreased kelp cover (creates barens)