Recruitment to the reef
column spacer Recruitment
 
 

Sexual reproduction: settlement & metamorphosis

 

Recruitment in sexually reproducing animals involves 3 main topics: 1) spawning, larval development, and dispersal of larvae, 2) settlement and metamorphosis, and 3) survival during early life.  The second topic is considered in this section.  The other recruitment topics are accessible via the icons.

Settlement & metamorphosis in sexually reproducing animals is considered here for fishes, while information on a few selected INVERTEBRATES can be found in its own section.

title for recruitement to the reef part of BCCR hot-button icon for linking to the topic of spawning, larval development, & dispersal of larvae in BCCR hot-button icon for linking to the topic of settlement & metamorphosis during early life in BCCR hot-button icon for linking to the topic of survival during early life in BCCR hot button for survival during early life in BCCR
 
 

Sexual reproduction: settlement & metamorphosis: fishes

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of seagrass area with juvenile fishes taken from a video

"Settlement of larval fishes from the plankton may be initiated by state of the moon, time of tides, type of substrate, and other factors. Seagrass areas, perhaps for the protection offered the young fishes, are often preferred settling areas. Here are some young surgeonfishes and chromises sheltering under a shallow dock area" - Little Cayman 2003

NOTE Acanthurus bahianus

NOTE Chromis sp.

 
 

photograph of adult 3-spot damselfish amongst the corals
Larvae of coral-reef fishes tend to settle in response to localised habitat features. For example, 3-spot damselfishes recruit almost exclusively to living corals on the reef slope and, in so doing, minimise competition with other damselfish species that prefer shallow, rocky areas on the reef crest.

 

 

 

 

Adult 3-spot damselfish Stegastes
planifrons
amongst some corals 0.5X

 

drawing of 3-spot damselfish settling to the reef faceA 3-spot damselfish Stegastes planifrons spends several weeks in the plankton, feeding and growing. The process of settlement and metamorphosis to the juvenile stage takes several days or weeks.

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs photograph of patch reef taken from a video

This video principally shows an older juvenile 3-spot damselfish swimming around in its algal garden, but note the presence of 2 other juveniles, both considerably younger, and smaller in size. The older individual is starting to darken to the adult colours, a process that may take several weeks to complete - St. Thomas 2007

NOTE Stegastes planifrons

 
 

Recruitment of larval fishes may not be to the first part of the reef encountered.  Studies in St. Croix show that recruitment of ocean surgeonfishes is photograph of surgeonfish feedinggreater to the back-reef zone than to the fore-reef zone or to photograph of ocean surgeonfishesseagrass beds, a result initially of settlement-choice by the larvae, but later modified by survival-affecting factors such as food supply and predator density. The surgeonfish larvae spend about 40-60d in the plankton before settling at a size of 4mm. Risk 1997 Mar Ecol Progr Ser 161: 51.



Juvenile ocean surgeonfishes Acanthurus bahianus
feeding on algae in the back-reef area 0.5X 

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a sergeant-major fish taken from a video

"Colorful sergeant-majors are found as adults virtually everywhere on the reef, but the juveniles tend to recruit to seagrass beds and mangrove areas. Like other pomacentrids, they seem always to be on the move. Let's follow this one for a bit." - Aruba 2004

NOTE Abudefduf saxatilis

 
  photo composite of sergeant-majors
Studies in Panama show that juvenile sergeant-majors preferentially recruit to shallow intertidal-fringe areas of the reef, while the adults frequent deeper areas.  Larval life is completed after 2-3wk at a size of about 1cm. The larvae are planktivorous, and eat copepods and other small crustaceans.  Robertson 1988 Proc 6th Intern Coral Reef Sympos 2: 839; DeLoach 1999 Reef Fish Behavior New World Publ, Florida.
 

During their pelagic life, larval fishes may be carried long distances in currents, and it is in this way that new areas are colonised. In reef systems with umap of Barbados showing predominant water currentsnidirectional currents, as in Barbados (see map, upstream events therefore tend to regulate the supply of recruits.

monthly data on larval-fish abundance in BarbadosLight-trap collections on the west coast of Barbados in springtime provide data on potential larval settlement (see graph on Right). Note the predominant peaks in the latter part of each of the 3 months shown, indicating that the larval fishes are active in inshore waters and are in settling mode.

The authors of the study note that settlement of fishes is greater on the N-S ends of the island in comparison to the sides, likely owing to splitting of the currents on either side. Additionally, settlement of larval fishes is greater at spring tides than at neap tides. The high tides during springs is associated with strongest onshore tidal transport. Settlement is also greater during night than daytime, possibly because predators hunt less effectively during nighttime. Sponaugle & Cowan 1996 Mar Ecol Progr Ser 133: 13.

 
 

What about the lunar cycle? It appears from the graph that settlement is on a monthly (28d) cycle, but exactly what part of the moon's cycle? Think about which phase of the moon might be associated with greatest settlement of larval fishes, then CLICK HERE for explanations. Sponaugle & Cowan 1996 Mar Ecol Progr Ser 133: 13.

Full.

Neap (waning moon).

New.

Neap (waxing moon).

 
 

Other than vision, what other sensory cues might be important in helping a larval fish to find a suitable site during settlement?

Taste/olfaction: while taste is unlikely to be important, olfaction or smell certainly is. This could provide sensory information over considerable distance. Some scientists even propose that reef fishes may imprint to the characteristic odours of a reef during embryonic or early larval stages, thus promoting retention of the larvae in a certain reef locality, and additionally providing the potential for long-distance navigation. However, the notion of staying around their original reef of "birth" seems to argue against the evolutionary value of having a pelagic phase at all (for its dispersal value), and trans-oceanic navigation by smell would seem unlikely.photograph of species of damselfishes

Sound/vibration: a fish's ear can hear sounds, but its function is mainly for acceleration and balance perception. Sounds or vibrations that could be used by a larval fish for navigation, such as surf beating on a shore, are readily perceived by the fish's lateral line system. The reef edge is a noisy place and sounds travel well underwater. Experiments on damselfish and other coral-fish larvae indicate that they can navigate to a sound source from 65m distance, but the potential is likely much greater than this - perhaps even up to many kilometers. Leis et al. 2003 J Fish Biol 63: 724.

NOTE salmon are known to imprint to the chemical signature of a certain spawning stream or channel where they hatched and spent some time as youngsters (alevin, fry, parr), before reaching the smolt stage and entering the ocean. They use this information to return to their original spawning stream - probably not during their oceanic navigation, but once they reach the shallower regions of the continental shelf

 

Bicolor damselfish Stegastes partitus (above) and juvenile yellowtail
damselfish Microspathodon chrysurus swim about the reef 0.5X

 
  RETURN TO TOP
   
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