NAYBAKKEN (CH1)

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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.

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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

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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.

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Diverse Forms of Fish Larvae

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CRAB LARVAE

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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

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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

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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

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Nektonic planktotrophic

larvae

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Benthic Planktotrophic

larvae

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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.

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CRAB LARVAE

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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

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Sea urchins are Benthic primitively

planktotrophic and only

secondarily (in polar regions)

do they adopt a lecithotrophic

life cycle.

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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. 

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Non-pelagic larval

development

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Catfish: Non-pelagic larvae

Female

Male to incubate

eggs

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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

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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.

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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

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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.

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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.

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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

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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

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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

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