Pelagic larval duration and settlement size of a reef fish are spatially consistent, but post-settlement growth varies at the reef scale

Abstract

Recent research has demonstrated that, despite a pelagic larval stage, many coral reef fishes disperse over relatively small distances, leading to well-connected populations on scales of 0-30 km. Although variation in key biological characteristics has been explored on the scale of 100-1000 s of km, it has rarely been explored at the scale relevant to actual larval dispersal and population connectivity on ecological timescales. In this study, we surveyed the habitat and collected specimens (n = 447) of juvenile butterflyfish, Chaetodon vagabundus, at nine sites along an 80-km stretch of coastline in the central Philippines to identify variation in key life history parameters at a spatial scale relevant to population connectivity. Mean pelagic larval duration (PLD) was 24.03 d (SE = 0.16 d), and settlement size was estimated to be 20.54 mm total length (TL; SE = 0.61 mm). Both traits were spatially consistent, although this PLD is considerably shorter than that reported elsewhere. In contrast, post-settlement daily growth rates, calculated from otolith increment widths from 1 to 50 d post-settlement, varied strongly across the study region. Elevated growth rates were associated with rocky habitats that this species is known to recruit to, but were strongly negatively correlated with macroalgal cover and exhibited negative density dependence with conspecific juveniles. Larger animals had lower early (first 50 d postsettlement) growth rates than smaller animals, even after accounting for seasonal variation in growth rates. Both VBGF and Gompertz models provided good fits to postsettlement size-at-age data (n = 447 fish), but the VBGF's estimate of asymptotic length (L ? = 168 mm) was more consistent with field observations of maximum fish length. Our findings indicate that larval characteristics are consistent at the spatial scale at which populations are likely well connected, but that site-level biological differences develop post-settlement, most likely as a result of key differences in quality of recruitment habitat.

Reef-fish larval dispersal patterns validate no-take marine reserve network connectivity that links human communities

“…Third, the study does not provide any insights into population connectivity beyond the first few months of the juvenile stage (i.e., up to adulthood). The fates of recruits are likely to vary across sites given local ecological conditions (Leahy et al 2015), thus modifying the strength of population connections suggested by larval dispersal. However, determining patterns of full demographic connectivity was beyond the scope of this study.…”

“…Chaetodon vagabundus (vagabond butterflyfish, Family Chaetodontidae) has a pelagic larval duration (PLD) of about 3 to 4 weeks (Leahy et al 2015), similar to a wide range of reef-fish species in the Indo-Pacific (Lester and Ruttenberg 2005). Adults of the species are territorial mid-water spawners that form strong pair bonds (Tanaka 1992).…”

“…Transverse cross-sections of the left sagittal otoliths of juvenile fish in the accepted parentage assignments were prepared and interpreted as per Leahy et al (2015). PLD was estimated by counting the daily rings between the centrum and the settlement mark and adding one day to approximate the duration of the egg stage in butterflyfish (Leis 1989).…”

Rehabilitation of coral reefs through removal of macroalgae: state of knowledge and considerations for management and implementation

“…Established macroalgal beds can be highly persistent due to positive feedbacks that inhibit grazing and the settlement, growth, and survival of other reef organisms, including corals (Hoey & Bellwood ; Dell et al ) and some fishes (Leahy et al ). Large stands of upright macroalgae have been shown to discourage entry of herbivorous fishes, positively reinforcing macroalgal dominance (Hoey & Bellwood ).…”

“…The allelochemicals can directly influence coral fitness through physiological deterioration of coral tissues (Rasher & Hay 2010;Rasher et al 2011), the inhibition of coral recruitment (Bulleri et al 2018), and by shifting associated microbial communities to predispose them to bleaching, infection, and mortality (Pantos et al 2003;Bourne et al 2009). Established macroalgal beds can be highly persistent due to positive feedbacks that inhibit grazing and the settlement, growth, and survival of other reef organisms, including corals (Hoey & Bellwood 2011;Dell et al 2016) and some fishes (Leahy et al 2015). Large stands of upright macroalgae have been shown to discourage entry of herbivorous fishes, positively reinforcing macroalgal dominance (Hoey & Bellwood 2011).…”