<div><p>Response of larval behavior to high pCO2<br />
To determine the position of P. damicornis larvae in the seawater in response to high pCO2, larvae were transferred from collection containers to UV-transparent acrylic tubes (UV-T, ACRYLITE Colorless 0070 GT, Evonik Industries, New Jersey, USA) and incubated in situ at two depths, which centered the tubes vertically at ~ 0.3 m (July 2016) or ~ 3.3 m (August 2016). The tubes had a wall thickness of 6 mm, were 68-cm long with an inner diameter of 4.5 cm, and were sealed at either end with UV-T acrylic caps. A 6-mm hole was drilled in the top cap so the tubes could be filled with seawater; the hole was later covered with vinyl electrical tape. While the objective was to completely fill the tubes with seawater, in most cases small bubbles were introduced during the filling process and combined when the tubes were positioned vertically to create an air gap of ≤ 1-cm height at the top of the tube. The acrylic in these tubes transmitted ~ 92% of ultraviolet radiation (UV-R) (280–400 nm), ensuring larvae were exposed to ecologically relevant light conditions for shallow seawater. Previous studies of the vertical movement of P. damicornis larvae in acrylic tubes, as well as preliminary observations of larval behavior used in the present study, show that larvae of P. damicornis exposed to ambient seawater generally aggregate either in the top or bottom 0–2 cm of tubes regardless of light conditions (i.e., light versus dark). Therefore, the vertically-oriented tubes were marked into two sections for the purpose of scoring the larvae by position: an upper section (21-cm length) and lower section (47-cm length), since we reasoned it would be unlikely that the larvae would accumulate in the center of the tubes. Of the larvae found in the lower section, 83–88% were located in the bottom 23 cm of the tube, which suggested that the greater size of the lower scoring section in the tubes did not upwardly bias estimates of larvae scored as moving downward.</p>
<p>Eight tubes were used for each experiment, during which four were filled with ambient (~ 400 µatm pCO2) seawater, and four with treatment (~ 1000 µatm pCO2) seawater that simulated the elevated pCO2 conditions predicted under a pessimistic scenario of human activity to occur by 2100 (RCP6.0). Once tubes were filled with seawater, 50 larvae were haphazardly selected from the larval stock obtained by pooling larvae released that morning from maternal colonies, and added using a Pasteur pipette through the 6-mm hole in the cap of the tube. The hole was sealed when the tubes were stocked with larvae. Each tube was carefully inverted to gently mix the 50 larvae, so each trial began with the larvae scattered along the length of the tube. Although the pelagic larval duration (PLD) of P. damicornis can be > 100 d, their larvae commonly settle ≤ 24 h following release, and therefore, the present incubations were designed to last 12 h starting at 08:00 hrs.</p>
<p>After the tubes were stocked with larvae on the shore, they were transported by a snorkeler to an adjacent fringing reef and suspended vertically, with the midpoint of the tubes at a median depth (MD) of either ~ 0.34 m (July) or 3.34 m (August) (hereafter referred to as 0.3 and 3.3-m MD) (Fig. 1). The median depth was recorded at the middle of the vertically oriented tubes, thus the depth range for the 0.3 m MD tubes extended from the surface to 0.68 m, and from 3 – 3.68 m for the 3.3 m MD tubes. To maintain this configuration, the tubes were attached to a weight at 5-m depth, and a float was used to keep them suspended vertically. While it is not possible to exclude an effect of time (July versus August) in confounding the contrast of depth, experimental conditions were kept virtually identical between months to reduce temporal bias. Tubes were stocked with larvae shortly after sunrise, and were installed on the reef within 30 minutes of filling at ~ 07:30 hrs. Thereafter, the vertical position of the larvae was scored every 4 hours starting at 08:00 hrs (initial) and finishing at ~19:30–20:00 hrs (sunset); the tubes were removed from the water at 08:00 hrs the following day and the larvae processed for lipid content (described below). At each census, the position of the larvae in the tubes was scored as the number of larvae in either the top or bottom sections of the tube. Tubes were not evaluated at night because of logistical constraints associated with nighttime snorkeling. The percentage of the total number of larvae present in the tubes at the time of each sampling was calculated for the top section of the tubes and used as the response variable to evaluate the effects of the treatments (depth and pCO2).</p>
<p>Statistical analysis<br />
Statistical analyses were conducted using SYSTAT Version 11 software (Systat Software, San Jose, CA). A two-factor RM ANOVA was used to compare the effects of depth and pCO2 on larval position in the tubes, with time of day as the RM factor and arcsine-transformed values of the percentage of larvae found in the top of each tube as the dependent variable. Differences in lipid content of larvae were evaluated using a two-sample t-test to compare the effect of pCO2 on total lipid between depths, and a Kruskal-Wallis non-parametric test (due to violations of normality in the data) to compare lipid content after pCO2 incubations regardless of month. Assumptions of normality and homogeneity of variance for the RM-ANOVA were assessed through graphical analyses of the residuals.</p>
<p> </p></div>
Larval positioning in acrylic tubes describing the behavior of coral larvae in high pCO2 within shallow tropical reefs in Okinawa, Japan from 2016-07 to 2016-08
<div><p>Twelve colonies of Pocillopora damicornis (Linnaeus 1758) were collected in July and August 2016 from ~ 1-m depth on a patch reef on the northwest shore of Okinawa (26°40’18.24” N, 127°53’4.78” E). Colonies were collected prior to expected larval release in Okinawa in July and August (S. Harii, unpublished data on the study site), with peak release occurring ~ 7 days after the new moon.</p>
<p>Following collection, colonies were transferred to Sesoko Station, part of the Tropical Biosphere Research Center University of the Ryukyus, where they were incubated outdoors in individual containers exposed to natural irradiance in flow-through seawater. Ambient seawater was pumped at 3.0 L min-1 (AC Flowmeter, Tokyo Keiso Co., Japan) from 4–5 m depth and stored in two 10 L reservoirs. Air was bubbled constantly in to the reservoirs at 3.0 L min-1 to maintain ambient seawater pCO2 (i.e., the control conditions). Seawater temperature was measured hourly at 1–2-m depth near the collection site prior to, and during, the experiment (HOBO Pro v2, Onset Computer Corporation, USA), and was 29.9 ± 0.2°C (mean ± SE, n = 45 days), with a daily minimum of 28.3°C and daily maximum of 31.8°C (R. Prasetia & S. Harii, unpublished data) that reflects summertime diurnal warming in this location. Temperature in the containers holding the corals was maintained within this range during the experiment (29.8 ± < 0.2°C, mean ± SE, n = 31) using a chiller (ZR-130E, Zensui, Japan).</p>
<p>Planulae released from P. damicornis during the first quarter moon of July and August were collected at ~ 05:00 hrs following their release at ~ 03:00 hrs, using containers lined with 110 µm plankton mesh. As larvae from P. damicornis are physiologically dissimilar among days of release, larvae were collected from the inferred day of peak release and pooled among colonies releasing larvae on this day. Larvae from July and August were used to test the effects of pCO2 (two levels) and depths (two levels) on larval behavior, and the experiment was conducted in two parts. The first part (July 2016) tested the effects of two pCO2 regimes on larval behavior with the tubes positioned with their upper opening adjacent to the air-water interface of the seawater (hereafter “shallow” tubes), and the second part (August 2016) tested the effects of the same two pCO2 regimes on larval behavior with the tubes positioned with their upper opening ~3–4 m below the surface (hereafter “deep” tubes).</p></div>
larvae count
<div><p>BCO-DMO Processing Notes:</p>
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<li>added conventional header with dataset name, PI name, version date</li>
<li>modified parameter names to conform with BCO-DMO naming conventions</li>
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751013
larvae count
2018-12-06T13:01:53-05:00
2018-12-06T13:01:53-05:00
2023-07-07T16:10:26-04:00
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Larval positioning in acrylic tubes describing the behavior of coral larvae in high pCO2 within shallow tropical reefs in Okinawa, Japan from 2016-07 to 2016-08
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Bergman, J., Edmunds, P. J. (2018) Larval positioning in acrylic tubes describing the behavior of coral larvae in high pCO2 within shallow tropical reefs in Okinawa, Japan from 2016-07 to 2016-08. Biological and Chemical Oceanography Data Management Office (BCO-DMO). (Version 1) Version Date 2018-12-07 [if applicable, indicate subset used]. http://lod.bco-dmo.org/id/dataset/751013 [access date]
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