High Mortality During Settlement Is a Population Bottleneck for a Tropical Surgeonfish

Abstract

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, Ͼ40,000 presettlement unicornfish, Naso unicornis entered our study area of ϳ1 km 2 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 ϳ61% 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.

Behavioural mediation of the costs and benefits of fast growth in a marine fish

“…Size-frequency distributions of Pomacentrus amboinensis that died and survived after 6 days at liberty on small patch reefs. species of fish and invertebrates immediately after settlement (Gosselin & Qian 1997;Doherty et al 2004;Almany & Webster 2006). This mortality was selective, preferentially removing the largest individuals, but did not appear to be linked to behaviour, as there were no significant differences between survivors and fish that died in risk taking or foraging behaviour, as measured by the average number of bites, swimming distance, the distance moved away from the coral and the mean number of chases.…”

“…Upon arrival in reef habitats from the plankton, young fishes face a very uncertain future. Naïve settlers are faced with a new suite of predators that consume the majority of arrivals, creating mortality bottlenecks (Doherty et al 2004;Almany & Webster 2006). Survival during juvenile life may not be a matter of chance, but can depend on the size and growth rate of individuals (Searcy & Sponaugle 2001;Vigliola & Meekan 2002;Hoey & McCormick 2004;Vigliola et al 2007;Gagliano et al 2007;.…”

Brain lateralization involved in visual recognition of conspecifics in coral reef fish at recruitment

“…Settling coral reef fish recruits are subjected to strong predation pressure. Up to 90% of newly settled fish are removed by predation during the first week postrecruitment (Doherty et al, 2004;Lecchini, Nakamura et al, 2007;Lecchini, Osenberg et al, 2007). Moreover, during the recruitment phase, reef fish juveniles are subjected to additional intra-and interspecific interactions compared to fish larvae in open ocean ecosystems (Barth et al, 2015;Lecchini & Galzin, 2003;Leis et al, 2011).…”

“…Moreover, during the recruitment phase, fish larvae are subjected to strong selective pressures to choose a suitable reef habitat that will facilitate survival and growth. Studies have documented up to 90% larval mortality in the first 7 days on the reef (Doherty et al, 2004;Lecchini, Osenberg, Shima, St Mary, & Galzin, 2007). Recruitment of new individuals is a critical process in the maintenance and recovery of marine communities (Lecchini & Galzin, 2003).…”

Causes of decoupling between larval supply and settlement and consequences for understanding recruitment and population connectivity

“…Recently, "larval supply" 4 has been used broadly to describe abundance of available propagules. Operationally, researchers 5 have measured larval supply as the number of planktonic larvae available near settlement sites 6 (e.g., Minchinton and Scheibling, 1991;Bertness et al, 1992;Miron et al, 1995;Sponaugle and 7 Cowen, 1996;Noda et al, 1998;Jeffery and Underwood, 2000;Doherty et al, 2004;Jonsson et 8 al., 2004;Todd et al, 2006;Beaulieu et al, 2009), and we use this definition here. Researchers 9 have used other terminology to refer to these available larvae (e.g., Porri et al, 2006).…”