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 fishes. The same topic for other reef organisms can be accessed via the icons below. 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: fishes

 
 



Most or all reef-fishes produce pelagic larvae, and many of these hatch from eggs that float freely in the ocean. What follows is an account of early development in a jack mackerel Trachurus symmetricus, which is not a coral-reef fish, but has a similar pattern of development to a reef fish.

In coral-reef fishes, whether the adult inhabits open water or the sea bottom, the drifting larval phase is the chief means for disseminating the species to new habitats.

series showing developmental of a jack mackerel 1
 
"series showing developmental of a jack mackerel 2
series showing developmental of a jack mackerel 3
 
series showing developmental of a jack mackerel 4
series showing developmental of a jack mackerel 5
 
 

photograph of a terminal-phase male bluehead wrasse with its haremBluehead wrasse
Bluehead wrasses Thalassoma bifasciatum mostly begin life as females and, in this initial-phase stage, they mate with so-called terminal-phase males. The mating or spawning occurs in a quick flurry of movement above the reef crest and is completed in a few seconds. Some males are born as males, but the majority appears to be ones that transform from initial-phase females. The transformation involves not only changes in gonadal morphology and function, but also secondarily sexual changes in colour, size, and behaviour. Transformation occurs when an already-present terminal-phase male for whatever reason disappears, perhaps from being eaten or from dying of old age, and requires just a few days for completion.


A terminal-phase male bluehead wrasse Thalassoma bifasciatum tends his
harem, a task involving chasing off other competing males. The group here
is likely to be mostly female, but could include a male from birth 0.33X

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of wrasses taken from a video

"A terminal-phase bluehead wrasse associates loosely with groups of initial-stage females, and spawns with them dozens oftimes each day. The spawnings are just brief flurries in the open water accompanied by release of gametes. Let's see whether this one will do it...nope, just buzzes about " - Cayman Brac 2001

NOTE Thalassoma bifasciatum

 
 
drawing of bluehead wrasses in spawning behaviour


Studies using fluorescent dyes to simulate drift of spawned eggs show that bluehead wrasses tend to spawn during times of maximum current flow away from the reef. Hensley et al. 1994 Bull Mar Sci 54: 256; Appledorn et al. 1994 Bull Mar Sci 54: 271.

 

photograph of terminal-phase bluehead wrasses
Studies in St. Croix show that bluehead wrasses may migrate up to 1.5km daily each way to form large group-mating aggregations, spending up to 50min on each leg of the journey. Warner 1995 Envir Biol Fish 44: 337.
 
 

wrasses and chromises feed on the reef crestFertilisation success of bluehead wrasses in St. Croix is about 95%. This seems high, but reef fishes apparently average over 90%. A mature male wrasse is capable of spawning 30 or more times per day. Petersen et al. 2001 Behav Ecol 12: 237.

How many times does an average terminal-phase bluehead wrasse spawn in a lifetime? While you think about it, keep in mind that to reach the terminal-male phase the female stage has to be passed through, so the same individual will spawn eggs as an initial-phase female, then sperm as a terminal-phase male. One scientist estimates the total as 3500...500 as a female and 3000 as a male. Warner 1984 Evolution 38: 148.


Initial-phase bluehead wrasses and a
few blue chromises feed on planktonic
organisms above the reef face

 
  Fisheries scientists are always interested in statistics like these:
 
number 1 in a cartoon series on wrasse spawning number 2 in a cartoon series on wrasse spawning
 
number 3 in a cartoon series on wrasse spawning number 4 in a cartoon series on wrasse spawning
 
number 5 in a cartoon series on wrasse spawning number 6 in a cartoon series on wrasse spawning
 
number 7 in a cartoon series on wrasse spawning number 8 in a cartoon series on wrasse spawning
 
number 9 in a cartoon series on wrasse spawning number 10 in a cartoon series on wrasse spawning
 
 

During courting, the terminal-phase bluehead wrasse flits about, shows off his colours, touches the female, and eventually induces her to release a batch of eggs. He responds immediately with a cloud of sperm. His bright colours are a mixed blessing. In the one hand, they convey information to a female about his value as a mate, including the value of his mating site; on the other, they may attract predators. The question then arises as to what effect a predator might have on the courtship process. Would its presence slow down the mating process by distracting the participants, or would it go faster in order to decrease the risk?

graph showing courtship times of bluehead wrasses in the presence and absence of a predatorThis is tested by researchers on a reef in St. Croix by comparing courtship times of a male every 5min over a 90min period with an without (CONTROL) a nearby lurking "predator", in this case a preserved lizardfish in a clear plastic cylinder. Lizardfishes are known predators of wrasses.

Results show that a more wary female in the presence of a perceived predator requires significantly more courtship time. Data and ideas from Warner & Dill 2000 Behav Ecol 11: 444.

 
 

Sex change, coloration, and mating behaviour in other wrasses

 
photograph of yellowhead wrasse Halochoeres garnoti photograph of slippery dick Halichoeres bivittatus photograph of clown wrasse Halichoeres maculipinna
Yellowhead wrasse Halichoeres garnoti Slippery dick Halichoeres bivittatus Clown wrasse Halichoeres maculipinna
- all males are the same colour
- small males may interfere in the spawnings of large terminal-phase males
- sexes differ in coloring (dichromatic), but some overlapping
- mating groups are transient aggregations, no permanent territoriality
- spawn throughout year
- sexes differ in coloring (dichromatic)
- spawn throughout year
- some “streaking” observed (initial-phase males zip in to spawn together with terminal-phase male and spawning female)
 
photograph of creole wrasse Clepticus parrae photograph of Spanish hogfish Bodianus rufus Photograph of clown wrasse courtesy Carlos & Allison Estape, Islamorada, Florida
 

Warner & Robertson 1978 Smithsonian Institute Press, Washington No 254, 22pp.

NOTE with respect to the authors, who are clearly experts, this report is actually quite confusing for individuals who are new to the subject

Creole wrasse Clepticus parrae Spanish hogfish Bodianus rufus  
- sexes differ in coloring (dichromatic)
- spawn in large groups at throughout year
- no territoriality observed
- single colour for both sexes (monochromatic)
- males have permanent harems
- terminal-phase males control female spawning
 
 

photograph of Nassau groupers Epinephelus striatus at spawning site
Another species of Caribbean reef fishes that undertakes migrations to common spawning areas is the Nassau grouper Epinephelus striatus.  Use of standard and acoustic-telemetry tagging methods by researchers in Glover’s Reef, Belize shows that individuals of this otherwise solitary species will leave their usual shallow-water habitats during full-moon periods in winter and migrate to common spawning sites.  At the sites, which may require swims of many km, individuals spawn at depths of 20-100m.  Eggs are positively buoyant and reach the surface within a few hours, where they hatch to the larval stage.  Starr et al. 2007 343: 239. Photograph courtesy Enric Ballasteros, Spain.

NOTE  the authors comment that a main site on the northeastern point of Glover’s Reef that once hosted 15,000 groupers in 1975, is now reduced to less than 3000.  In 2002 the Belize Department of  Fisheries enacted a law to close off fishing on all historic and current spawning sites of groupers

 

Several Nassau groupers Epinephelus striatus
exhibit reproductive coloration at a
spawning site in Glover's Reef, Belize

 
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