Phytoplankton Sampling Flashcards
Two gear types used to sample icthyoplankton
MOCNESS Net
(Multiple opening and closing net & environmental sensing system)
The Gulf VII plankton net
Explain how the Gulf VII plankton net works.
Towed from large vessel at high speed 6-7 knots.
Net encased in metal frame to protect.
Come at mouth reduces displacement and facilitates higher speed.
No bridle at mouth of net reducing gear avoidance.
How is MOCNESS NET used to sample icthyoplankton
Multiple opening and closing net & environmental sensing system.
Each net opens at different depths with different mesh sizes.
Formaldehyde
Most common fixing & preserving reagent.
Used at concentration of 4-5%.
Should be buffered to pH8
Formaldehyde sold as a 40% solution mixed w/ water -> formalin.
10% formalin
4% formaldehyde
Why do we process plankton samples
Plankton samples must be treated w/ preservative before longterm storage to prevent degradation, light damage etc.
Fixation & preservation should be carried out within 5 mins of collection
Advantages & disadvantages of formaldehyde
Cheap
Long lasting
Preserves pigmentation
Toxic
Makes tissues hard and brittle
Advantages & disadvantages of Lugols iodine
Adds weight to cells & help phytoplankton sink to bottom settling chamber.
Not very toxic.
Good preservative soft & hard tissues.
Breaks down in sunlight - must be stored in dark.
Can change pigmentation green to brown.
Lugol’s Iodine
10g iodine, 20g potassium iodide in 200 ml distilled water.
20ml glacial acetic acid added few days prior to use.
Why study icthyoplankton
Estimate abundance
Predict recruitment
Define stock boundaries
Understand recruitment processes
Investigate ecology
Elaborate on estimate abundance as a reason for studying icthyoplankton
Egg and larval surveys can be used to estimate size of stock based on its spawning production
(Independent of commercial fishery)
Elaborate on predict recruitment as a reason for studying icthyoplankton
Karbala and juvenile surveys provide an estimate of the size of a year class before it is available to fisheries
(Recruitment index)
Elaborate on ‘define stock boundaries’ as a reason for studying icthyoplankton
Concentrations of eggs and early life stages can be used to identify spawning locations.
Larval distributions can be used to define boundaries between stocks of same species and determine levels of stock mixing.
Elaborate on ‘understand recruitment processes’ as a reason for studying icthyoplankton
Info on abundance distribution and growth of early life stages in relation to environmental variables can provide insight into mechanisms driving recruitment variability.
Elaborate on ‘investigate ecology’ as a reason for studying icthyoplankton
Larval and juvenile surveys can provide information in the ecology of a species.
What can surveys of planktonic eggs and larvae be used to derive
Relative and absolute index of stock abundance.
B = P/RF
P - total egg production of stock
B - spawning stock biomass
R - proportion of the stock that are egg producing females
F - fecundity (no. Eggs produced per unit weight to female)
