Early-life history processes in marine species

Larvae definition

The free-living stage between hatching and metamorphosis (typically with independent movement)

Larval pool

The total number of larvae produced (many die in this stage)

Primary larvae

Have cilia

Secondary larvae

Lack ciliated epithelium. Instead have setae

How are larvae similar

microscopic (<1-2mm), short-lived, typically in water column, most swim using cilia, poor swimmers but are transported long distances, most feed on phytoplankton and bacteria

Terminal addition hypothesis

the first animals were small pelagic forms similar to modern larvae, with adult bilaterian body plans evolved subsequently

Intercalation hypothesis

Adult bilaterian body plans evolved first and that larval body plans arose by interpolation of features into direct-developing ontogenies

Is the terminal addition hypothesis or the intercalation hypothesis more likely to have occurred

intercalation

Advantages of having a larval stage

Larvae eat different foods to adults which lessens competition, larvae can colonize new areas (reduces inbreeding), breaks pathogen and parasite cycles, avoid benthic predators during development

Evolution of reproductive larval niches

The ability of the larvae to feed on the plankton may have lessened the requirement of adults to provide reserves for the larvae or to produce large offspring. Leads to many smaller eggs rather than few larger ones

Disadvantages of larval form

Moving away from favorable parent habitat, vulnerability to planktonic predators, greater vulnerability to UV and chemical stress, chance of not finding place to metamorphosize

Planktotrophy

Complex larval morphology, small eggs, high fecundity (many offspring), long development, high mortality, high dispersal

Lecithotrophy

Simplified larval forms, large eggs, low fecundity (few offspring), short development, low mortality, low dispersal

Thorson’s rule

species producing planktonic larvae are rarer at higher latitude (cold regions less habitable)

Larval mortality rate is…

hard to estimate but extremely high

What percentage of larvae from the larval pool die per day

16%

Equation for recruitment

Causes of larval mortality

Predation, starvation/exhaustion, environmental, stranding/sinking

What percent of larvae are chemically defended

40-60%

What do most planktonic larvae feed on

Phytoplankton and bacteria

What percentage of planktonic larvae do not feed

<5%

Lecithotrophic larvae

Gain all of their nutrition from reserves in the egg and thus do not feed

Hydrosol feeding

Particulate food filtered or sieved by specialized feeding structures lost at settlement

How much do larvae eat per day

2-5 mL and 1,500-3,000 cells

Ideally, how many cells do larvae need to eat per day to survive

1,000 to 4,000 cells

How does temperature impact larval development

Low temps slow development rates, and higher temps quicken development rates

Kinds of Larval Transport

Mode of transportation (tides, currents, etc.)

Larval Dispersal

Distance larvae move

Connectivity

Dispersal can move larvae from one population to another, where they can settle and recruit

Benefits of larval dispersal

Easy to recolonize an area after local extinction, reduced likelihood of inbreeding, large geographic range, lower risk of extinction

Disadvantages of larval dispersal

Dispersal away from favorable parental habitat

How long do teleplanic larvae remain in the larval stage

Remain in larval state for many months (become large in size)

How long do actaplanic Larvae stay in larval stage

Remain in larval state from 1 week to 2 months (most temperate larvae) (coastal)

How long do anchiplanic stay in the larval stage

Stay in larval state for seconds to minutes

What is relationship between pelagic larval duration and dispersal distance?

The longer it takes for a larvae to mature and settle the farther it can travel

How far can anchiplanic larvae travel

Only a number of meters

How far can an actaplanic larvae travel

10Km or less

How far can Teleplanic larvae travel

10s-100sKm

What influences the larval experience

(nutrition, larval duration, metabolism) influences the energy and resources available for post-settlement juveniles (within generational)

What factors influence the adult stage of these species

(nutrition, environment) influences the energy and resources available for developmental stages (inter-generational)

What is the most vulnerable life history stage to environmental change

Larval stage

Reasons why larvae are highly vulnerable to env. change

Morphology: small, high surface areas

- Lack protective coverings

- Ectothermal

- Undergoing fast rates of development (i.e. embyos/larvae)

- Physiologically stressed

- Experience high mortality

- Development rates very sensitive to environmental conditions (temp, food)

What env. factors affect larval development the most

Temp & PH