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NAYBAKKEN (CH1)
01/05/23 A.Alzaidan
BASIC FEATURES
Marine organisms produce larvae during their life cycles.
Larvae: independent morphologically different stages that develop from fertilized eggs and must undergo profound changes before assuming adult features.
Characteristics: smaller than adult stages of the species.
Important in the establishment and maintenance of many marine communities.
01/05/23 A.Alzaidan
BASIC FEATURES
According to Chia (1988) distribution and abundance of benthic invertebrates in a marine habitat are maintain by 4 factors:
o larval recruitment (= living & active larvae)o Migrationo asexual reproductiono mortality
01/05/23 A.Alzaidan
LARVAL TYPES & STRATEGIES
Pelagic and benthic adults produce various larval stages.
Benthic communities produce free-swimming larval stages in the water column before metamorphosing into benthic adults.
01/05/23 A.Alzaidan
Diverse Forms of Fish Larvae
01/05/23 A.Alzaidan
CRAB LARVAE
01/05/23 A.Alzaidan
Vance (1973) stated that there are 3 possible paths of development in
benthic invertebrates depending on amount of energy (yolk) available to
produce the young:1. Planktotrophic larvae2. Lecithotrophic larvae3. Non-pelagic larvae
LARVAL TYPES & STRATEGIES
01/05/23 A.Alzaidan
COMPARISON OF ADVANTAGES AND DISADVANTAGES OF EACH TYPE OF LARVAL DEVELOPMENT
LARVAL DEVELOPMENT
ADVANTAGEDISADVANTAGE
Planktotrophicproduce many eggs with little yolk = little energy
large number of youngwide dispersal due to spending long time as plankton
Dependent on plankton for nutritionIncreased chance of consumption by predators
Lecithotrophicproduce fewer eggs with more yolk= more energy
Spending less time in plankton less chance of being consumedNot dependent on plankton for food
Fewer eggs are produced fewer larvaeShorter time in plankton less dispersalLarger target for visual predators in the plankton
Non-pelagicProduce few eggs with large amount of yolk
Reducing plankton mortality to ZERO
Eggs undergo a long development then hatch as juveniles
Only few eggs produced dispersal is ZERO = no free-swimming larval stage
01/05/23 A.Alzaidan
1.Planktotrophic larvae Favored when:
planktonic food is predictable mortality is low dispersal necessary development time is short
Often seen in larger animals, organisms inhabiting rare
patches of habitat -- longer time to find appropriate habitat
01/05/23 A.Alzaidan
Nektonic planktotrophic
larvae
01/05/23 A.Alzaidan
Benthic Planktotrophic
larvae
01/05/23 A.Alzaidan
This specimen of a giant spider crab, Macroregonia
macrochira,
This ovigerous female was stationary on a large rock and carrying a large clutch of relatively small diameter eggs, which is typical of a
planktotrophic larval strategy.
01/05/23 A.Alzaidan
CRAB LARVAE
01/05/23 A.Alzaidan
2.Lecithotrophic larvae Favored when:
dispersal is necessary planktonic mortality is high
3. Nonpelagic or direct development Favored when (common in polar
regions) less reliable food source for
planktonic larvae perhaps greater selective pressure for
survival of those eggs that are produced
01/05/23 A.Alzaidan
Sea urchins are Benthic primitively
planktotrophic and only
secondarily (in polar regions)
do they adopt a lecithotrophic
life cycle.
01/05/23 A.Alzaidan
The planula larvae of the Sea Anemone can be either planktotrophic, which feed independently
, or lecithotrophic larvae, which means that they feed on
the yolk.
01/05/23 A.Alzaidan
Non-pelagic larval
development
01/05/23 A.Alzaidan
Catfish: Non-pelagic larvae
Female
Male to incubate
eggs
01/05/23 A.Alzaidan
Gafftopsail Catfish. The male of this Atlantic and Gulf Coast
sea catfish takes full responsibility for caring for the marble-like eggs after he has
fertilized them. How does he do this, in waters thick with predators?
By carrying them in his mouth -- as many as 55 eggs, each one an inch in diameter, for a
period estimated at six to eight weeks! As if that weren't
enough, he then may carry the young around as well, until
they double in size from their hatching length of two inches.
Catfish non-pelagic larval development
01/05/23 A.Alzaidan
Ecological PrinciplesThere are many hypotheses that explain under what
environmental conditions each of the 3 patterns would dominate, but they did not account for all the factors in the sea. Some include:
1. Thorson (1950): There is a latitude gradient in the proportions of the 3 larval types:
planktoptrophy common tropical marine organisms
lecithotrophy & non-pelagic: prevail as approaching polar latitudes.
01/05/23 A.Alzaidan
Ecological Principles
2.Obrebski (1979): the type of larval development should be predicted by the abundance of suitable substrates for development:
Organisms living in abundant habitats have less need for planktotrophic larvae (many habitats around) lecithotrophy & non-pelagic
Organisms inhabiting rare habitats have a need for planktotrophic larvae dispersal to search for the rare habitat
01/05/23 A.Alzaidan
Ecological Principles3. Underwood (1974) concluded that
energy considerations alone are not adequate to explain the 3 different development strategies proposed by Vance (1973):
many factors are important and determine the larval development
type.
01/05/23 A.Alzaidan
Ecological Principles3. Underwood (1974) concluded that energy considerations
alone are not adequate to explain the 3 different development strategies proposed by Vance (1973):
many factors are important and determine the larval development type.
Conclusion: There are many factors that work in determining larval development for each species, such factors must be balanced out and include:
energy allocation Dispersal relative abundance of microhabitat space longevity of adults competitive ability of adultsHence, some species alter their reproduction strategy
depending on the prevailing conditions.
01/05/23 A.Alzaidan
III.Settlement of larvae & metamorphosis
What mechanisms act in ensuring that the right larvae will settle and mature in the right place to keep the community going?
1. Preferences2. Stimuli
01/05/23 A.Alzaidan
III.Settlement of larvae & metamorphosis
1. Preferences larvae can 'test' the substrate many preferentially settle where there
are conspecifics can delay metamorphosis if haven't
found preferred habitat
01/05/23 A.Alzaidan
III.Settlement of larvae & metamorphosis
2. StimuliLight: (+)phototactic as early larvae; then
switch to (-) phototactic at end of larval period
PressureSalinityGravityfluid movement (tides, currents)chemical cues from organisms --
pheromones from food species, conspecifics, predators
01/05/23 A.Alzaidan