Lecture 7-bottom up control of zooplankton

Question 1

what is the difference between bottom up and top down control?

Answer 1

Bottom up control: controlled by food sources lower down the train
Top down control: controlled by predators higher up the food chain

Question 2

where are metazooplankton commonly found in aquatic environments? why?

Answer 2

• metazooplankton are commonly found at the deep chlorophyll maxima
• this is because algae are positioned at this point, near the thermocline. They are her to acquire maximum nutrients etc, and as metazooplankton predate them, it benefits then to be located in the same region

Question 3

explain the seasonal distribution in algae?

Answer 3

-in winter there is little abundance due to sunlight being a limiting factor for photosynthesis. the increase in light intensity in spring causes the formation of spring blooms,-in summer overpredation by zooplankton causes the formation of a clearwater phase. algae recover in later summer, undergoing a second summer bloom

Question 4

explain the edibleness of the spring bloom

Answer 4

• the spring bloom is composed of edible algae species, such as:
• phytoflagellates
• chlorophytes
• centric diatoms

Question 5

explain the edibleness of the summer bloom

Answer 5

• begins with edible species, but growth is limited by phosphorous
• diamtoms become the dominating species due to their ability to tolerate low p conditions
• as diatoms require silica to make their glass casing, silica becomes limiting
• these are then replaced by cyanobacteria, which are very efficient at nutrient utilization and are NON EDIBLE
• in autumn diatoms and flagellates appear in low number (as stratification is over)

Question 6

what happens to metazooplankton in the winter famine?

Answer 6

• cladocerans and rotifers produce by sexual reproduction due to resource scarcity
• copepods go into diapause

Question 7

what triggers the end of copepod diapause?

Answer 7

• food concentration
• food quality
• temperature

Question 8

what is threshold density?

Answer 8

the lowest available food concentration required to produce a positive population growth. This determines when cladoceran EPHIPPIUMS hatch

Question 9

how does threshold density relate to growth rate?

Answer 9

-the greater the organisms threshold density, the greater the growth rate

Question 10

what happens to organisms with high threshold densities during times of famine?

Answer 10

-theyre the first to disappear

Question 11

what is the wakeup order of rotifer, cladocerans and copepods?

Answer 11

rotifers and copepods wake up together, then cladocerans

Question 12

why do copepods wake up early?

Answer 12

because they have six stages of nauplis growth, they must wake up early to acquire food and avoid being out competed

Question 13

how does rotifer “wake up” relate to algae type?

Answer 13

-rotifers have a very low threshold density for edible algae species. but a high one for inedible species

Question 14

which metazooplnakton is active in the spring bloom?

Answer 14

-cladocerans

Question 15

explain the feeding of the two dominant cladoceran types in the spring bloom

Answer 15

-both bosmina and daphnia hatch in may, but the lower threshold density of bosmina means that they hatch later. bosmina eat phytoflagellates, and when these become limiting daphnia becomes the limiting form. daphnia have no carry capacity for resources, so overgraze algae and cause the clearwater phase

Question 16

what happens to metazooplnakton in the clear water phase?

Answer 16

cladocerans +rotifers: large species die off of cladocerans

• rotifer populations still increase slowly
  copepods: use lipid reserves as a food source to avoid die off

Question 17

describe claodceran species populations during feast 2 in the peg model

Answer 17

two types of cladocerans:

• left overs, who survived the famine
• newly hatched species, including: Ceriodaphnia, Diaphanosoma and Chydorus
• newly hatched species can consume cyanobacteria

Question 18

describe copepod species populations during feast 2 in the peg model

Answer 18

• high correlation with algae abundance, suggesting that they are the dominant grazers
• populations are now mature
• can consume cyanobacteria (typically non-edible algae)

Question 19

describe rotifer species populations during feast 2 in the peg model

Answer 19

-activity is completely temperature dependant

they preferentially predate cilliates over algae, giving them a poor correlation to algae populations

Question 20

why do cladocerans switch from large genera to small genera from the spring feast- summer famine?

Answer 20

• starvation

- fish predation

Question 21

what are the two main problems of the peg model?

Answer 21

• no mention of indirect feeding

- bacteria and protezoa not included

Question 22

explain algae and bacteria correlation in the BACTERIA INITIATED CASCADE MODEL

Answer 22

-as bacteria feed on algae waste products (DOC), population is closely correlated to the increase/decreases of algae populations

Question 23

what organisms feed on bacteria in the clearwater phase? why?

Answer 23

• ALL metazoplankton (copepods,cladocerans,rotifers)
  -protezoa
  because algae is limiting

Question 24

what is the other food source for zooplankton in the clear water phase?

Answer 24

-protezoa

Question 25

explain flagellate and cilliate distribution over the peg model?

Answer 25

• as they are a food source for bacteria when algae are limiting, population changes are closely related to those of bacteria.
• however cilliate populations do not increase during the summer feast as they are over predated by rotifers (who choose to not eat the non-edible algae)