High mortality during settlement is a population bottleneck for a tropical surgeonfish

Replenishment of benthic marine populations typically involves “settlement” from pelagic larval to benthic juvenile habitats. Mortality during this transition has been unknown because of the difficulty of measuring propagule supply in open water. For three weeks, we compared the nocturnal passage of presettlement fishes across the barrier reef encircling Moorea Island (French Polynesia) with the abundance of benthic recruits in the back-reef lagoon on the following morning. During this time, >40,000 presettlement unicornfish, Naso unicornis entered our study area of ∼1 km2 with half arriving on just two nights. Using coupled Beverton-Holt functions to describe the decay of each cohort, we were able to predict the daily abundance of recruits and their final age structure from the presettlement inputs. The best model estimated that ∼61% of the potential settlers were lost between their nocturnal arrival and the following morning, independent of cohort size. Postsettlement mortality was density dependent, varying between 9% and 20% per day. We attribute all mortality to predation and suggest that high risk associated with settlement has shaped colonization strategies. Because fishing targets the survivors of this population bottleneck, aquarium fisheries may be more sustainable when sourced from pelagic juveniles.

[1]  Peter Chesson,et al.  Rethinking ecological inference: density dependence in reef fishes , 2002 .

[2]  M. McCormick,et al.  Comparative study of metamorphosis in tropical reef fishes , 2002 .

[3]  Todd W. Anderson,et al.  Biodiversity, population regulation, and the stability of coral-reef fish communities , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[4]  G. Almany,et al.  Positive indirect effects in a coral reef fish community , 2002 .

[5]  J. Pineda,et al.  Semibalanusbalanoides in winter and spring: larval concentration, settlement, and substrate occupancy , 2002 .

[6]  M. Steele,et al.  Early postsettlement predation on three reef fishes: Effects on spatial patterns of recruitment , 2002 .

[7]  M. Webster.  Role of predators in the early post-settlement demography of coral-reef fishes , 2002, Oecologia.

[8]  M. Meekan,et al.  Size at hatching and planktonic growth determine post-settlement survivorship of a coral reef fish , 2002, Oecologia.

[9]  G. Lecaillon,et al.  Caging experiment to examine mortality during metamorphosis of coral reef fish larvae , 2001, Coral Reefs.

[10]  S. Sponaugle,et al.  SELECTIVE MORTALITY DURING THE LARVAL-JUVENILE TRANSITION IN TWO CORAL REEF FISHES , 2001 .

[11]  C W Osenberg,et al.  Quantifying the effects of multiple processes on local abundance: a cohort approach for open populations. , 1999, Ecology letters.

[12]  M. McCormick,et al.  Microstructure of settlement-marks in the otoliths of tropical reef fishes , 1999 .

[13]  M. Hixon.  Population dynamics of coral‐reef fishes: Controversial concepts and hypotheses , 1998 .

[14]  R. Scheibling,et al.  Role of early post-settlement mortality in recruitment of benthic marine invertebrates , 1997 .

[15]  M. Hixon,et al.  Synergistic predation, density dependence, and population regulation in marine fish , 1997 .

[16]  G. Sancho,et al.  Behavioral observations of an upcurrent reef colonization event by larval surgeonfish Ctenochaetus strigosus (Acanthuridae) , 1997 .

[17]  P. Qian,et al.  Juvenile mortality in benthic marine invertebrates , 1997 .

[18]  P. Qian,et al.  Early post-settlement mortality of an intertidal barnacle: a critical period for survival , 1996 .

[19]  Ransom A. Myers,et al.  Density-Dependent Juvenile Mortality in Marine Demersal Fish , 1993 .

[20]  L. Kaufman,et al.  A key phase in the recruitment dynamics of coral reef fishes: post-settlement transition , 1992, Environmental Biology of Fishes.

[21]  M. Fogarty,et al.  Recruitment variability and the dynamics of exploited marine populations. , 1991, Trends in ecology & evolution.

[22]  P. Sale,et al.  Early survivorship of juvenile coral reef fishes , 1988, Coral Reefs.

[23]  J. Roughgarden,et al.  Recruitment dynamics in complex life cycles. , 1988, Science.

[24]  P. Sale,et al.  Predation on juvenile coral reef fishes: an exclusion experiment , 2004, Coral Reefs.

[25]  C. Osenberg,et al.  CRYPTIC DENSITY DEPENDENCE: EFFECTS OF COVARIATION BETWEEN DENSITY AND SITE QUALITY IN REEF FISH , 2003 .

[26]  J. Bell,et al.  The use of wild-caught juveniles in coastal aquaculture and its application to coral reef fishes. , 2002 .

[27]  B. Bolker,et al.  MANAGEMENT AT A DIFFERENT SCALE: MARINE ORNAMENTALS AND LOCAL PROCESSES , 2002 .

[28]  Todd W. Anderson,et al.  PREDATOR RESPONSES, PREY REFUGES, AND DENSITY‐DEPENDENT MORTALITY OF A MARINE FISH , 2001 .

[29]  M. McCormick.  Delayed metamorphosis of a tropical reef fish (Acanthurus triostegus): a field experiment , 1999 .

[30]  A. Lo-Yat,et al.  Colonization of Reef Fishes at Moorea Island, French Polynesia: Temporal and Spatial Variation of the Larval Flux , 1996 .

[31]  A. Fowler,et al.  Variation in the relationship between otolith weight and age: implications for the estimation of age of two tropical damselfish (Pomacentrus moluccensis and P. wardi) , 1995 .

[32]  R. Galzin,et al.  Colonization patterns of reef fish larvae to the lagoon at Moorea Island, French Polynesia , 1993 .

[33]  Peter Doherty,et al.  A comparison of towed nets, purse seine, and light-aggregation devices for sampling larvae and pelagic juveniles of coral reef fishes , 1993 .

[34]  M. Meekan,et al.  Larval supply: a good predictor of recruitment of three species of reef fish (Pomacentridae) , 1992 .