Marine ecology Lecture 14: Recruitment and dispersal

Concept of patterns

“Everything residing in the ocean that does not have the ability to outswim the current has to follow the flow”

The eggs, larvae, or juveniles of many, if not most marine animal species have a stage at which they can be transported in ocean currents

Dispersal

How far do larvae disperse?

What proportion of larvae stay local?

Scale matters: annual, ecological, decadal and evolutionary scales may yield different results

What is a metapopulation?

A group of spatially separated populations of the same species that interact through occasional dispersal, effectively creating a “population of populations

What is “open” and “closed”

The degrees to which particular population is “open” to recruitment from outside is fundamental to its ecology and conservation

• but some populations are closed

Larval connectivity

Process of dispersing and then surviving to enter the adult reproductive population (=recruitment) at the destination location

Measures of Recruitment & Connectivity (migration)

Direct observations: Recruitment

• Ecological time scale population dynamics

Population genetic: similarity

• population structure: evolutionary time scale migration rates and metapopulation structure

Bio-physical models

• predictions of all measures at all time scales

Major factors influencing larval dispersal, settlement, and recruitment

Reproductive effort Fecundity environment

Larval duration Hydrological conditions and geographic distance

Environment chemicals cue biotic interactions

Biotic interactions sedimentation environment (local scale)

Fecundity and overall larval production

Cases in which fecundity is depressed

• bleached/ stressed colonies

• young

• over-grazed

Cases in which total production is depressed

• disturbed populations (storms, bleaching, destructive fishing)

• Young (recovering population)

Larval duration Hydrological conditions, geographic distance

Brooded larvae will have a low number of settling and a low dispersal distance

Broadcast will have a high dispersal distance and high larval settling

Do dispersing larvae behave as passive particles?

No. ocean currents have a strong influence on where the larvae end up. They also have sensory cues responding to light, chemical signals. A major factor is habitat selection

Recruitment: Biotic interactions sedimentation environment

Most settlement in preferred locations, but some in others

Strong growth in fused colonies, greatest coral cover