L9 - Zooplankton 1 Flashcards
Define
‘Plankton’
“To Drift”
Thus
‘Zooplankton’ = Animal drifitng
‘Phyoplankton’ = Plant drifitng
Why should we care?
Very important between algae and fish..
Experiment
- Resovoir having trouble with algal blooms (lots of phytoplankton)
- Big numbers of introduced Perch predating on zooplankton
- Feb 2007: 4000 Perch removed
- Feb 2008: 4500 Perch removed
- Zooplankton number sky rocketed in absence of Perch.
- Zooplankton smashed the Algae and reduced/controlled algae blooms.
Three major groups of Zooplankton
Rotifers } Phylum Rotifer
Cladocera } Crustaceans
Copepods } Crustaceans
ROTIFERS
‘Smallest of animals in the world, 900-1200 cells’
Kingdom Animalia - True animals
Multicellular, heterotrophs
ROTIFER DEFINED: ‘WHEEL BEARER’
Have little cilia on their heads which beat one after the other, they are used for swimming and creating feeding currents by sucking algae up towards the head.
Rotifera: General characteristics
Two distinctive features
1. Muscular pharynx - called the mastax, containing a hardened set of jaws called the trophi.
2. Corona: Ciliated head region for swimming and feeding
Most feed on algae and bacteria.
Some predatory, feed on other Rotifers and crustaceans.
What are these?
Rotifer ‘Trophi’
‘Hardened jaws used to chew up food’
Rotifer general characteristics
3. Hardened lorica (armour) - others can be soft bodied
Most species benthic or periphytic (75%)
- Spines form to reduce sinking rate and also for protection from predation
Rotifer general characteristics
(Typical of rock, soil and plant dwelling Rotifers)
Body plan of benthic Rotifers considered “typical”
-Long foot and toes, pedal glands.
Adaptations for pelagic life; planktonic rotifers commonly have:
a) Suspension processes or swimming organs
e. g., spines, movable fins
b) General reduction in size and weight, lose foot
c) Attachment of eggs to body or vivipary
FIN/SPINE ADAPTATIONS
Used when stopped to create drag in the water collumn and reduce the rate at which you sink.
Open water Rotifer carry eggs and they hatch in the water collumn, they can drop eggs but it means the young will sink and have to expened lots of energy to make their way back up the water collumn.
ROTIFER LIFE CYCLE
- Reproduction of rotifers by cyclical parthenogenesis
2 PHASES
A: PARTHENOGENESIS (a sexual)
Specifically where a mother produces an egg and a genetically identical daughter hatches from egg.
B: SEXUAL REPRODUCTION
Mostly by Parthenogenesis in the absence of males
Parthenogenetic females are diploid and give rise to diploid daughters using eggs.
Rotifera: Life cycle
Following environmental cues, males are produced and sexual reproduction occurs
- Occurs during good conditions (not stressed)
Females produce haploid eggs - by meiosis
- Unfertilised eggs turn into males - haploid
- Fertilised eggs produce resting eggs - diploid
Males (haploid) are present for only a brief period
- Extremely small, do not feed, short lived
- Produce sperm by mitosis
What are haploid and diploid cells?
A diploid cell is a cell that contains two sets of chromosomes. This is double the haploid chromosome number. … Gametes are haploid cells. During sexual reproduction, gametes (sperm and egg cells) fuse at fertilization to form a diploid zygote. The zygote develops into a diploid organism.
Rotifera: Life Cycle
Diapause = suspended development
Eutely = Possesing all cells upon hatching
Trichocerca (Rotifer)
Big spine out the back reduces rate it drifts down water collumn
Carrying egg on back
Spine punctures algae and can move along filamentous algae and suck the insides out.
Conochilus (Rotifer)
Usually found in cleaner lakes
Lives in a colony of approx 20 Conochilus banded together
By having a ball like this its more efficent to suck algae in as a group than individually.
Floscularia (Rotifer)
Sessile Rotifer, builds a little house for protection and the cilia ropes in drifting algae.
Rotifer: Distribtuion and Dynamics
Rotifer distribution and diversity largely based on trophic state of lakes.
Oligotrophic = Conochilus efficent at getting algae in low concentrations
Eutrophic = Brachionas (bacteria feeder)
Different species adapt dependant on trophic state
Rotifera: Distributions and dynamics
Rotifers show seasonal changes in abundance and composition
Temperature most important
Species can be divided into:
Cold stenotherms: Develop populations in winter and early spring
Warm stenotherms: Develop populations in summer
NZ is a series of islands in the middle of a big ocean meaning we have a mild oceanic climate, not to hot in summer, not to cold in winter. Lakes are fundamentally different to those over seas.
Below graph is based on a typical lake in the Northern hemispher of our latitude.
Summer very hot with thermocline (stratified)
Autumn (holomixus)
Winter holomixus
PTO for NZ graph
Our lakes get no way near as cold as overseas lakes
Not cold enough for lakes to freeze over
Smaller diversity of zooplankton due to fairly stable state of lakes
Better studied as they are efficent filter feeders.
Clean up algae from lakes relatively quickly - high aethetic and ecological value.
Each Cladocera adapted for respective environment.
Cladocera: General Characteristics
In common with other Crustacea
- 2 sets of antennae
(one big one small, one used for swimming and other for ?)
- Biramous (branched) limbs
- Body enclosed in carapace
(legs enclosed in carapace, legs filter algae)
- Laterally compressed
Can measure distance between setae, gap size indicates what kind of algae and size they are filtering out.
Mostly female population
Environmental cues produce Males
