Transcript Document

Larval Dispersal and Migration in the
Marine Environment
Chapter 5
From spawning to larvae…
Larval Ecology
Many marine animals reproduce by
spawning and then release offspring
into ocean waters. These young must
find food, protection, and a suitable
home.
Most marine communities are composed of species that reproduce
by producing various larval types. Therefore, an understanding of
larval ecology is central to understanding how such communities
persist.
• Larvae: independent morphologically different stages that develop from
fertilized eggs and must undergo a profound change before assuming adult
features.
•Settlement: when larvae fall out (leave) the water column, select habitat, and
undergo metamorphosis. This is usually brought on by cues from the
environment.
•Recruitment: The larvae that have (1) dispersed and settled, (2)
metamorphosed successfully, and (3) survived to be detected by the observer.
Larvae and adult of goose
neck barnacle species.
Hairy Triton and
its larval form
Palthyoa species larvae
Larvae and their adults
Sea star larvae and
and newly settled sea
star (juvenile)
Christmas Tree worm (polychate
worm species) and its larval form
Dispersal Types in Benthic
Species
• PLANKTOTROPHIC DISPERSAL - female produces
many (103 - 106) small eggs, larvae feed on plankton,
long dispersal time (weeks)
• LECITHOTROPHIC LARVAE - female produces
fewer eggs (102 - 103), larger, larvae live on yolk, short
dispersal time (hrs-days usually)
• DIRECT RELEASE - female lays eggs, or broods
young, juveniles released and crawl away
• Teleplanic Larvae: larvae that live in transoceanic
currents (are always planktotrophic larvae)
Lecithotrophic larva: tadpole larva of the
colonial ascidian Botryllus schlosseri
Planktotrophic larva of
snail Cymatium parthenopetum
teleplanic larva of an urchin
Veliger Larvae: a larval type
only found in Mollusks.
Torsion, twisting of the body
that produces the spiral shell,
is already taking place or will
very soon after hatching.
Many marine mollusks produce
veliger larvae, which are
lecithotrophic larvae. This type
of larvae is usually ready to
settle within days of hatching,
and is unique to mollusks.
Dispersing of larvae
PROBLEM OF SWIMMING LARVAE:
water motion carries them away from
appropriate habitats
Loss to offshore waters
Wind-driven
recruitment
onshore
Self-seeding
eddies
Longshore drift
Shore Population
Internal waves,
tidal bores
Some helping hands in dispersal
• Winds that wash larvae to shore
• Internal waves - bring material and
larvae to shore
• Eddies that concentrate larvae in spots
• Behavior – rising to the surface at certain
times of day, or with the rise of the tide.
Most larvae have some ability to control
the direction in which they disperse.
Estuarine larval adaptations - retention
Larvae rise on the flooding tide, sink to bottom on the
ebbing tide: results in retention of larvae within estuary
Estuarine larval adaptations - movement of
larvae to coastal waters, return of later stage
larvae
Blue crab, Callinectes sapidus
Recruitment of juvenile corals
Effect of local eddies on larval retention in a
patch reef on the Great Barrier Reef,
Australia
larva of coral
Distance from reef perimeter
Newly settled coral
Gamete production and larval life must often be timed precisely
to allow settlement and promote dispersal, to avoid being swept
from suitable habitat, and to counter predation. These factors
influence reproductive success (R in population models).
Planktonic
larval
stage
Post-settling stage
Examples of timing for Reproductive
Success:
a) larvae in intertidal areas that move at night are
selected for (avoid predation).
b) Grunion spawning on beaches; timed with
highest spring tides of Spring.
c) Coral reef damselfish lay eggs at dawn; larvae
hatch 4 sunsets later (avoid predation). Egg
production timed so that hatching is with the ebb
tide which sweeps larvae offshore (lowers
predation).
Settling problems of planktonic
larvae
• Presettling problems:
Starvation
Predation in plankton
Loss to inappropriate habitats
Settlement Cues
Larval settlement is an active choice, aided by chemical and
physical cues.
Photopositive and photonegative behaviors exist, sometimes within
same individual.
Almost all larvae prefer settlement sites with bacteria present.
Gregarious settling is where larvae settle on adults (oysters,
barnacles). (What are the costs and benefits??)
Larvae frequently use chemicals produced by other animals and
plants to determine settlement locations.
After all this, metamorphosis takes place and the animal becomes a
juvenile, and looks like a small adult).
Recruitment:
The larvae that have (1) dispersed and settled, (2)
metamorphosed successfully, and (3) survived to be
detected by the observer.
Larvae and adult of goose
neck barnacle species.
Why disperse when mortality is
thought be 90% or higher for most
species??
Biogeography and Function of Larval
Dispersal
Why disperse?
• High probability of local extinction; best
to export juveniles
• Spread your young (siblings) over a
variety of habitats; evens out the
probability of mortality
• Maybe it has nothing to do with dispersal
at all; just a feeding ground in the
plankton for larvae
Biogeography and function of larval ecology
 Most marine inverts have planktonic feeding larvae.
However, planktonic feeding larvae are rare in high latitudes (Fig.
5.28)
As you more South, planktonic feeding larvae dominant.
Allows species to invade new areas
Avoids crowding (areas where space is the limiting factor for
population growth).
The End