DOI: 10.5061/dryad.zgmsbcc93
title: Lunar rhythms in growth of larval fish

description: Growth and survival of larval fishes is highly variable and unpredictable.
 Our limited understanding of this variation constrains our ability to
 forecast population dynamics and effectively manage fisheries. Here we
 show that daily growth rates of a coral reef fish (the sixbar wrasse,
 Thalassoma hardwicke) are strongly lunar-periodic and predicted by the
 timing of nocturnal brightness: growth was maximized when the first half
 of the night was dark and the second half of the night was bright. Cloud
 cover that obscured moonlight facilitated a ‘natural experiment’, and
 confirmed the effect of moonlight on growth. We suggest that
 lunar-periodic growth may be attributable to light-mediated suppression of
 diel vertical migrations of predators and prey. Accounting for such
 effects will improve our capacity to predict the future dynamics of marine
 populations, especially in response to climate-driven changes in nocturnal
 cloud cover and intensification of artificial light, which could lead to
 population declines by reducing larval survival and growth.
 EndDryadContent
description: Methods of data collection and processing are described in the
 following publications: "Reproductive
 phenology across the lunar cycle: parental decisions, offspring responses,
 and consequences for reef fish" (Ecology,
 https://doi.org/10.1002/ecy.3086) "Lunar rhythms
 in growth of larval fish growth" (Proceedings B,
 doi:10.1098/rspb.2020.2609)
description: <strong>Data</strong> 
 <strong>Full data set (thalassoma-hardwicke-otolith-growth
 increments.csv)</strong> contains 46 variables and 40517
 rows<strong>.</strong>  Each row gives information relating to
 a given otolith growth increment of a given individual.  Some fields
 contain missing values because data do not exist or fields are not
 applicable for some observations (these are denoted by ‘NA’). 
 <strong>fish.id</strong> is a unique identifier for
 each fish; <strong>bag.id</strong> is an identifier of sample
 grouping ("batch number") for otolith
 reading; <strong>stage</strong> is the ontogenetic stage of
 each fish (settler, juvenile, or
 adult); <strong>increment</strong> identifies otolith growth
 increment (1=first visible growth increment near the otolith
 core); <strong>larval.age</strong> is an estimate of age (days
 since egg fertilisation) of a fish at increment formation (= increment +
 2); <strong>pld</strong> is the pelagic larval duration
 (number of increments before the settlement
 mark);  <strong>post.set.age</strong> is the number of
 increments between the settlement mark and the otolith outer
 edge; <strong>total.age</strong> is the sum of pld and
 post.set.age; <strong>days.prior.to.set </strong>is the number
 of increments remaining until settlement; <b>date</b> is the
 calendar date of increment formation;<b>  birth.date </b>is
 the calendar date corresponding to egg fertilisation<b>;
 set.date</b> is the calendar date corresponding to the night of
 settlement<b>; incr.width </b>is the measured width of a
 growth increment (in microns)<b>; radius.width </b>is the
 measured distance from the otolith core to the focal increment (in
 microns)<b>; radius.min<i> </i></b>is the measured
 width of the first growth increment (in microns)<b>;
 total.otolith.radius</b> is the width of the otolith from the core
 to the outer edge of the otolith (measured along the postrostral axis, in
 microns); <b>post.set.tot.incr</b>  is the cumulative width of
 post-settlement growth increments (microns);
 <b>ave.post.set.GR</b> is estimated as:
 post.set.tot.incr<b>/</b><strong>post.set.age;
 </strong><b>site</b> is an acronym defining
 the location the site (within the lagoon of Moorea, French Polynesia)
 where the fish was collected; <b>reef </b>is a numerical
 identifier of the focal reef where the fish was collected (missing values
 indicate the fish was not collected focal reefs)<b>; fresh.tl
 </b>is the measured total length of the fish at capture (in mm);
 <b>etoh.tl.est </b>is the estimated total length of the fish
 at capture, accounting for shrinkage following preservation in ethanol
 (estimated based on a relationship derived from a subset of samples; units
 = mm); <b>etoh.tl </b>is the total length of the fish at
 capture (measured after preservation in ethanol, in mm); <b>fresh.sl
 </b>is the measured standard length of the fish at capture (in mm);
 <b>etoh.sl </b>is the standard length of the fish at capture
 (measured after preservation in ethanol, in mm); <b>fresh.mass
 </b>is the measured weight of the fish (settlers and juveniles only)
 after capture (in g); <b>etoh.mass </b>is the weight of the
 fish (settlers and juveniles only) at capture (measured after preservation
 in ethanol, in g); <b>date.collected </b>is the calendar date
 of collection (adults only); <b>weight </b>is the measured
 weight of the fish (adults only) after capture (in g); <b>liver
 </b>is the measured weight of the dissected liver tissue (adults
 only) after capture (in g); <b>gonads </b>is the measured
 weight of the dissected gonadal tissue (adults only) after capture (in g);
 <b>gender </b>is the identified sex (adults only);
 <b>lunar.month </b>is the lunar month of increment formation
 (Brown lunation number); <b>lunar.day </b>is the lunar day of
 increment formation (a 29.53d cycle; 0 = ‘new moon’);
 <b>lunar.day.bin </b>is binned lunar days (bin size = 2);
 <b>lunar.phase.precise </b>identifies the precise dates of
 four lunar phases (new moon, first quarter, full moon, last quarter;  NA
 appears for dates not falling precisely on these phases)<b>;
 lunar.phase.category.centered</b> estimates the lunar phase of
 increment formation where phase is centered on lunar.phase.precise;
 <b>lunar.phase.category.centered.month </b>adjusts Brown
 lunation number corresponding to lunar.phase.category.centered;
 <b>lunar.phase.category.start </b>estimates the lunar phase of
 increment formation where phase is starts on lunar.phase.precise;
 <b>time.moonrise </b>indicates local time of moonrise;
 <b>time.moonset </b>indicates local time of moonset;
 <b>time.moonrise.1 </b>indicates local time of moonrise;
 <b>time.meridian.passing </b>indicates local time of moon
 passing the meridian; <b>distance.from.earth.km </b>indicates
 the distance from the moon to Earth (km); <b>illumination
 </b>indicates the proportion of the lunar disc that is illuminated
 (1 = ’full moon’); <b>cloud.cover.airs.nighttime.3x3
 </b>indicates the proportion of the night sky (in a 3degx3deg box
 centered on Moorea, French Polynesia) that is obscured by cloud
 cover <strong>Ancillary data
 sets required to replicate Fig 2a and Fig 3:</strong> 
 
 <strong>moonlight_ancillary_fig_2a.csv</strong> contains
 3 variables and 390 observations (no missing values).  <b>lunar.day
 </b>is the lunar day within the lunar cycle (a 29.53d cycle; 0 =
 ‘new moon’); <strong>order</strong> represents an hour of the
 night to facilitate plotting of the y-axis in Fig 2a (12 = 18:00, 11 =
 19:00, 10 = 20:00 ... 6 = midnight ... 0 = 06:00 the following
 morning); <strong>illum</strong> indicates the proportion of
 the lunar disc that is illuminated (1 = ’full moon’) 
 <strong>moonlight_ancillary_fig_3.csv</strong> contains 5
 variables and 209 observations (no missing
 values).  <strong>date</strong> is the calendar
 date; <b>lunar.month </b>is the lunar month (Brown lunation
 number); <b>lunar.day </b>is the lunar day within the lunar
 cycle (a 29.53d cycle; 0 = ‘new
 moon’); <strong>proportion.first.half </strong>is the
 proportion of the first half of the night (from 18:00-23:59) when the moon
 is above the
 horizon; <strong>proportion.second.half </strong>is the
 proportion of the second half of the night (from 0:00-06:00) when the moon
 is above the horizon. <strong>R
 Code</strong> 
 <strong>R_code_for_analyses_and_figures_for_lunar_rhythms_paper.txt</strong> gives all R code to replicate analyses and figures presented in "'Lunar rhythms in larval fish growth", with annotations.