Recruitment to the reef
column spacer Recruitment to the reef: sexual reproduction
 
 

Spawning, larval development, & dispersal of larvae

 
This section deals with spawning, larval development, & dispersal of larvae in snails. The same topic for other reef organisms can be accessed via the icons. Other topics relating to recruitment, namely, SETTLEMENT & METAMORPHOSIS and SURVIVAL DURING EARLY LIFE, are found in their own sections. hot buttons for spawning/metamorphosis/dispersal section of BCCR website hot button for sponges section on spawning/metamorphosis/dispersal hot button for corals section on spawning/metamorphosis/dispersal hot button for snails section on spawning/metamorphosis/dispersal hot button for sea urchins & relatives section on spawning/metamorphosis/dispersal hot button for fishes section on spawning/metamorphosis/dispersal
 
 

Spawning, larval development, & dispersal of larvae: snails

 
 

photograph of milk conch
Most larger, shelled snails have separate sexes and copulation is the rule. After copulation, encapsulated eggs are deposited onto the substratum. These later hatch either to free-swimming larvae or to small juveniles depending upon species.

 

 

 

 

Milk conch Strombus costatus 2X. The prominent slit
on the left side of the shell allows clean water to flow
over the gill. The eyes in snails do not form images;
rather, they perceive only light/dark and movement

 

 
 
seahorse dive leader for BCCR website photograph of a queen conch taken from a video

This juvenile queen conch is disguised amongst the seaweeds, some of which it may be feeding on. As the camera approaches watch for the snail's eyes. As noted above, they are perceptive not to images but to light and shadows - Cozumel 2003

NOTE Strombus gigas

 
 

diagram of life cycle of a queen conch Strombus gigas
photograph of veliger larva of a snailQueen conchs Strombus gigas reproduce over a 4-6mo period in spring and summer. Sexes are separate. Copulation involves the male depositiing sperm in or near the female's vaginal opening with its penis. The eggs are fertilised as they emerge in a long mucousy string from the female's gonopore. The female uses her pointy-shaped operculum to fold the egg string back and forth on itself and, as this takes place, the egg string becomes coated (camouflaged?) with sand. The veliger larvae hatch after about a week and spend 4-5wk in the plankton before settling and metmorphosing. Like most invertebrate larvae, veligers are microscopic in size. They feed on phytoplankton by filtering the cells from the water with a double, ciliated velum (see photograph above). The beating cilia also provide propulsion. Settlement can be delayed for a few days or even weeks, but too long in the plankton can lead to death through lack of food, transport offshore by currents, and being eaten by predators. Davis 1998 Diss Abstr Int Part B: Sci Eng 59; Davis 2005 South Reg Aquat Center Publ No 7203. Black & white photographs courtesy Megan Davis & Leroy Creswell, and drawing courtesy Bonnie Bower-Dennis.



 

map showing current gyres spun off in the Gulf from the Florida CurrentRecruitment of queen conchs Strombus gigas in the Florida Keys depends upon upstream production in the Gulf of Mexico and transport of larvae in the Florida Current. Irregularities in this supply, perhaps by being caught up and held for too long in current gyres, may explain the poor recovery of queen-conch populations in the Florida Keys despite restrictions on their fishing since 1985. Lee & Williams 1999 Bull Mar Sci 64: 35.

NOTE circular current eddies or current vortices

 

 

Numbers within each gyre indicate potential months
of retainment. Survival of the larvae within a gyre
will be reciprocally related to the time spent
there. After more than a few weeks in the
plankton, mortality may become excessive

 
 

Sea hares Aplysia dactylomela occur sporadically throughout the Caribbean region. They are herbivorous, have good appetites, and eat prodigious amounts of green and red seaweeds. They are nocturnal and become active generally only in the latter part of the day. They locomote via lengthwise contractions of the foot musculature, known as pedal waves. When disturbed and in escape mode, they gallop off at high speed.

When not eating (or sometimes at the same time), they copulate. Sea hares are simultaneous hermaphrodites, meaning that each individual is reproductively mature as both sexes. Copulation involves at least 2 individuals, one on top of the other. The first one in line receives sperm while the photograph of copulating sea haressecond in line donates sperm. If more than 2 animals copulate, the first in the chain receives sperm, the last donates it, while the ones in-between do both. Copulation can last for many hours or days. Only the first individual in line can simultaneously feed and copulate. This is because the others' heads are buried between the large flaps on the upper surface of the individual in front, the flaps known as parapodia. Soon after the animals break off from copulation, they begin to deposit a long string of eggs. Photograph courtesy Anne Dupont, Florida.

 

Copulating Aplysia dactylomela in Florida 0.4X. If you
look carefully, you can see a thin line on the front
part of the body of each individual, sloping down
towards the mouth. This is the ciliated groove
along which the egg string is moved during spawning

 

photograph of spawn of sea hares AplysiaThe egg string or spawn of sea hares is sticky and is deposited in a tangled mass, often onto seaweeds. The string is gelatinous and carries many capsules along its length, each capsule containing 1-2 dozen eggs. Hatching to a veliger larva occurs in 7-10d. The spawn is coloured in accordance with the type of seaweed being eaten: yellowish for green seaweed foods, and shades of red for various red seaweed foods. If an individual changes abruptly from one type of seaweed to another, within 2-3d after the change a new colour appears. The colours may therefore be acting as camouflage. Brown coloration as shown in the photograph is from the colour of the shells of the developing veliger larvae. The brown colour thus signifies that the eggs are close to hatching. At this time, say, after about a week from being deposited, the egg string starts to break down, in part from microbial activity, thus assisting in the escape of the larvae. The larvae spend 3-4wk feeding in the plankton, then preferentially seek out certain red species of food algae, settle on them, and metamorphose to the juvenile stage.

NOTE refers to the mass of eggs or sperm emitted from fishes, amphibians, and many marine invertebrates. In most animals, single eggs are enclosed within a protective capsule. In sea hares, there may be 20 or more eggs in each capsule

 
 
photograph of sea hares in copulatory chain title for tail of some sea hares
 
cartoon 1 in series of mating sea hares
 
cartoon 2 in series of mating sea hares
 
cartoon 3 in series of mating sea hares
 
cartoon 4 in series of mating sea hares
 
cartoon 5 in series of mating sea hares
 
cartoon 6 in series of mating sea hares
 
cartoon 7 in series of mating sea hares
 
 

Your dive buddy asks you what was especially significant about the spawn mass that the sea hares crawled past. You think for a moment, then choose from the list below the answer that was most appropriate. CLICK HERE to see an explanation.

The spawn was fresh.

The sea hare that laid the top-most spawn had been eating green seaweeds.

Two or more different sea hares may have been involved in the laying.

The sea hare that laid the spawn first ate red seaweeds, then switched to green seaweeds a few days before depositing the mass.

 
  RETURN TO TOP