Marine Ecology Study Guide

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Marine Ecology Final Exam Review

Difference between broadcast spawners, brooders, direct developers, lecithotrophic and planktotrophic larvae

* Many marine organisms have a dispersal phase in their life history * Dispersal can occur as eggs, sperms, fertilized eggs, larvae, juveniles or adults * Many species only disperse as juveniles or adults

* Other species take advantage of high density of water to disperse during very early life stages: eggs/sperm/fertilized eggs/larvae
1. Broadcast spawners: parent release eggs/sperm/young fertilized eggs into water; developing young is on its own in the water column long time

2. Brooders: parent retains fertilized egg in body and releases young at a more developed stage; developing young spends less time in water column

3. Direct developers: parent retains fertilized egg in its body or in a large egg case until it hatches as a small version of an adult

* Larvae: independent, morphologically different stages developing from fertilized eggs and going through metamorphosis before reaching final adult stage.

* Are usually fundamentally unlike the adult stage morphologically, behaviorally, Physiologically

* Two basic types of larval production strategies:

1. Produce huge number of small eggs with little to no yolk that hatch quickly into feeding, free-swimming larvae: planktotrophic larvae 2. Produce smaller number of larger eggs with some yolk that hatch into non-feeding, free-swimming larvae: lecithotrophic larvae 3. In general, time in spent in plankton decreases as egg size increases

Pros and cons of different larval dispersal strategies; why all of them persist over time

* Planktotrophs:

Advantages:
1. Can produce more offspring with less parental investment (yolk) 2. Greater dispersal (longer time in water column)

Disadvantage:
1. Larvae might not find enough food in plankton
2. Long time in water column increase chances of predation

* Lecithotrophs

Advantages:
1. Less time in plankton reduces chances of predation
2. Get all nutrition from yolk: guaranteed food source

Disadvantage:
1. Fewer offspring produced per unit of parental energy
2. Larger eggs more of a target for visual predators
3. Shorter time in plankton = less dispersal

* Direct developers

Advantages:
1. Higher survivorship per capita

Disadvantage:
1. Only very few offspring produced per unit of parental energy 2. Zero dispersal in early life stage

* Nonpelagic development most common in polar waters, lecithotrophs in temperate waters, planktotrophy in tropics:

* Precise timing of planktonic larval release that’s necessary in polar waters too risky given very short time period of primary productivity; slow development b/c of cold water means larvae would be in water having to feed for a long time. * Where blooms last longer and water slightly warmer in temperate waters, lecithotrophy allows for dispersal and safe source of food. * Having feeding larvae in water for long periods is safer in tropics where there is a predictable, year-round supply of planktonic food; development also occurs faster b/c of warm water so don’t stay in water for too long.

* Small invertebrates are brooders (direct developers) more frequently than large ones:

* Small animals don’t have body space to produce huge numbers of eggs, so invest more in each fertilized embryo instead * Large animals can produce more eggs, but need to space them out to aerate them properly: selects for planktonic eggs/larvae to prevent suffocation

* Abundance of suitable habitat for next generation affects selection for dispersal:

* If suitable habitat is sparse and patchy, better to produce large numbers of widely dispersed larvae (planktotrophy) * Is suitable habitat is extremely common, dispersal is not as important...
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