Periphyton Ecology

Question 1

Define phytobenthos

Answer 1

• Surface-attached algal communities

–> These are algae that grow not in the open water but instead attached to surfaces

Question 2

Where do phytobenthos live generally

Answer 2

in relatively shallow areas with lots of sunlight - enough for them to actively photosynthesize

Question 3

What account for over 50% of the total productivity in shallow lakes, ponds, and streams

Answer 3

phytobenthos

Question 4

What is the littoral zone

Answer 4

this is the portion of submerged shoreline that receives adequate amounts of sunlight to support primary production –> phytobenthos in the littoral zone regulate primary production in most lakes and ponds making them important

Question 5

phytobenthic growth by filamentous green algae is greatest in what area of the littoral zone

Answer 5

• near the top of the littoral zone (epilimnion)
• in contrast cyanobacteria are more abundant in the lower level where there is not much sunlight because they can perform chromatic adaptation

Question 6

What type of phytobenthos are found on rocks

Answer 6

Epilithic

Question 7

What type of phytobenthos are found on submerged plants

Answer 7

Epiphyton

Question 8

What type of phytobenthos are found on submerged logs

Answer 8

Epixylon

Question 9

What type of phytobenthos are found on sediments

Answer 9

Epipelon

Question 10

What type of phytobenthos are found as floating clouds in the littoral zone

Answer 10

metaphyton

Question 11

The succession of species in phytobenthos is analogous to the succession of what

Answer 11

of plants on land

Question 12

Which species appear earlier in phytobenthos and are considered lower canopy species

Answer 12

penne diatoms are the first original colonists

Question 13

Describe the phytobenthos and the miniature forest analogy

Answer 13

• Algal competition for resources involves stalked and filamentous species (“trees”) being superior competitors for light –> these upper canopy species have better access to both light and nutrients
• In contrast, the small and short algae (“understory species”) are better positioned to compete for nutrients released from sediments )so they have more immediate access to nutrients coming from the sediments if they are living on them)

Question 14

What is a periphyton

Answer 14

• this is a term used to refer the an entire collective matrix with all the different organisms in it
• phytobenthic algae coexist with bacteria, fungi, and other microorganisms in a polysaccharide matrix collectively referred to as periphyton

–> so phytobenthos don’t just grow by themselves they are also hosted with other organisms

Question 15

Describe the understory algae in the periphyton

Answer 15

• periphyton is the phytobenthos and the other organisms

–> The understory algae are heterotrophic and capable of producing hydrolytic enzymes like phosphatase for retrieving organically bound nutrients

Question 16

What is the importance of the enzyme phosphatase in biofilms

Answer 16

• this helps cleave off phosphorous (a limiting nutrient) from organically bound molecules making it readily available for uptake by the different types of algae in the periphyton

Question 17

Describe the upper canopy algae in the periphyton

Answer 17

These tend to be more photoautotrophic and rely on dissolved nutrients from the water column –> the matrix has a lot of light attenuation so light availability is optimal at the top

Question 18

Describe the uptake gradients in the phytobenthos

Answer 18

• the autotrophic canopy species show a higher uptake of carbon dioxide than the understory species under both high and low light conditions –> upper canopy species tend to do well in terms of photosynthesis because they are very adapted to high light levels, while the ones in the understory live in perpetual shade
• the heterotrophic understory species show a relative higher uptake of labeled glucose (the don’t see as much light so their photosynthetic capabilities are not as great - they compensate by having a greater ability to absorb organic carbon C14-Glucose)

Question 19

Under conditions of light limitation, what kind of -trophy do phytobenthic species display

Answer 19

• they do photoorganotrophy - a type of heterotrophy
  -the uptake of extracellular organic carbon decouples light reactions from the Calvin cycle
• a net energy savings occurs as ATP and NADPH produced by light reactions are not required to fix carbon dioxide and produce sugars

–> a lot of the under story species are diatoms and they can optimize both photosynthesis and balance it with the uptake of carbon compounds in the environment and do photoorganotrophy - the heterotrophic diatoms will get their organic carbon by taking it up from direct absorption from the surrounding environments

Question 20

Describe the micro channels in periphyton

Answer 20

• grazing invertebrates and solar irradiance create microchannels through periphytic biofilms
• these microchannels are conduits for transfer of nutrients and hydrolytic enzymes, between bacteria, algae, and the open water column

–> so there is a lot of mucilaginous material in biofilm, there are often little gaps between the layers and these different crevices are conduits for different resources these species can use, a lot of different nutrient substrates come in ad get released
- so i is very biochemically active where there is transfer of all kinds of things including phosphatase

Question 21

describe the shade tolerant versus shade intolerant phytobenthos

Answer 21

• phytobenthos in shaded areas are more responsive to initial increases in light than are phytobenthos from more well lit areas
• shade tolerant phytobenthos from north facing lakeshores show photo inhibition at higher irradiances

(so the phytobenthos harvested at shaded sites, those species will respond quickly to low levels of light - their photosynthetic max goes up quickly - with increasing light the species from the shaded sites show evidence that they can’t tolerate it - so there is some form of photoinhibition)

Question 22

What is the effect of temperature on phytobenthic production

Answer 22

• moderate warming stimulates enzymatic rates, such as photosynthesis over respiration, resulting in a positive effect on net primary production
• however pronounced heating effects can suppress primary production and cause senescence of phytobenthos
  (so at extreme conditions there is suppression)

Question 23

Describe how grazers can disturb phytobenthos

Answer 23

• grazing has a lot to do with cell size, if large you are less edible to small species
• they understory species can only be grazed by certain types of highly efficient grazers like snails, the upper canopy species become more susceptible to different types of grazers

Question 24

What is the effect of snails in particular as grazers on phytobenthos

Answer 24

Snails are efficient removers of upper canopy and understory periphytic algae - this results in them having a more negative effect on total biomass

• there are some reports of stimulatory effects where moderate grazing pressure can remove detrital material and increase resource availability to periphyton

Question 25

What can occur from selective grazing effects on the upper canopy

Answer 25

• grazers tend to favor large upper canopy filamentous species and will reduce the amount of these species
• the understory species are left ungrazed and show an increase or stimulatory response in the presence of those same grazers - they are getting greater access to light and nutrients and so they are stimulated and compensate functionally for the loss of upper canopy species

Question 26

Where can phytobenthos account for >90% total production

Answer 26

in clear and shallow streams

–> phytobenthos are the primary source of organic carbon and elemental nutrients in autotrophic streams
- terrestrial inputs and periphytic bacteria fuel food webs in streams that are net heterotrophic ecosystems

Question 27

Describe how periphyton metabolism varies as a function of where they are in a stream

Answer 27

• in shaded headwaters, light limits the periphytic algal growth where photosynthesis: respiration < 1
• in larger streams, light and nutrient levels are optimal, stimulating periphytic algal photosynthesis over respiration (P>R)
• in larger rivers, turbid conditions suppress phytobenthos and limit phytoplankton production (P/R < 1) –> The ratio drops below 1 due to silt (here phytoplankton that can grow at the top of the water column can do better than the periphyton)