Name: Quantifying Artemia Nauplii Density Pre- and Post-Feeding of Pocillopora acuta
Uploaded: 2023-06-23T14:45:00
Description: Watch this Scientific Journal Video about Quantifying Artemia Nauplii Density Pre- and Post-Feeding of Pocillopora acuta at JoVE.com

quantifying artemia nauplii density pre- and post-feeding of pocillopora acuta

Ex Situ Culture of &lt;em&gt;Pocillopora acuta&lt;/em&gt; and Effective Feeding Techniques

Many coral reef ecosystems globally are being lost and degraded as a result of high-temperature stress driven by climate change1,2. Coral bleaching (i.e., the breakdown of the coral-algal symbiosis3) was considered relatively rare in the past4 but is now occurring more frequently5, with annual bleaching expected to occur in many regions by&#160;mid to late century6,7. This shortening of the interim period between bleaching events can limit the capacity for reef resilience8. The direct impacts of high-temperature stress on coral colonies (e.g., tissue damage9; energy depletion10) are intrinsically linked to indirect impacts at the reef-scale level, of which a reduction in reproductive/recruitment capacity is of particular concern11. This has spurred a range of applied research exploring, for example, the active in situ enhancement of recruitment (e.g., reef seeding12), new technologies for scaling-up coral restoration13, and the simulation of reproductive cues to induce reproduction in ex situ systems14. Complementary to these active interventions are the recent recognition of the advantages of heterotrophic feeding in corals under high-temperature stress15 and the exploration of the role that food provision may play in reproduction16.
Heterotrophic feeding is known to influence the performance of corals17 and has been specifically linked to increased coral growth18,19, as well as thermal resistance and resilience20,21. Yet, the benefits of heterotrophy are not ubiquitous among coral species22 and can differ based on the type of food being consumed23, as well as the level of light exposure24. In the context of coral reproduction, heterotrophic feeding has shown variable results, with observations of higher25 as well as lower26 reproductive capacity following heterotrophic feeding being reported. The influence of heterotrophic feeding on coral reproduction across a spectrum of temperatures is rarely assessed, yet in the temperate coral Cladocora caespitosa, heterotrophy was found to be more important for reproduction under lower temperature conditions27. A better understanding of the role of temperature and feeding on reproductive output is likely needed to determine whether specific reefs (e.g., reefs associated with high food availability28) possess a higher capacity for recruitment under climate change.
Similar to reproductive output, the effect of temperature and feeding on reproductive timing in corals remains relatively understudied, despite the synchronization of reproduction with abiotic/biotic conditions being an important consideration for recruitment success in a warming ocean29. Warmer temperatures have been shown to result in earlier reproduction in coral thermal conditioning studies conducted in the lab30, and this has also been observed in corals collected from natural reefs across seasons31. Yet, interestingly the opposite trend was recently observed in fed corals cultured over the course of 1 year in an ex situ flow-through system (i.e., reproduction occurred earlier in the lunar cycle at cooler winter temperatures and later in the lunar cycle at warmer summer temperatures)32. This contrasting result suggests that reproductive timing may stray from typical patterns under conditions associated with abundant energetic resources.
Long-term controlled experiments under different temperature scenarios could contribute to a better understanding of the influence of heterotrophy on reproduction in scleractinian corals. Maintaining reproducing coral colonies under ex situ conditions for multiple reproductive cycles, however, can be challenging (but see previous research32,33). Herein, straightforward and effective techniques for the active feeding (food source: Artemia nauplii) and long-term culture of a brooding coral (Pocillopora acuta) in a flow-through aquaculture system are described; yet, it should be noted that all the techniques described can also be used in recirculating aquaculture systems. To demonstrate these techniques, a preliminary comparison of the reproductive output and timing of coral colonies held at 24 &#176;C and 28 &#176;C under &#34;fed&#34; and &#34;unfed&#34; treatments was conducted. These temperatures were chosen to approximate seawater temperatures in winter and summer, respectively, in southern Taiwan30,34; a higher temperature was not chosen because the promotion of long-term ex situ culture, rather than testing coral response to thermal stress, was a primary goal of this experiment. Further, the density of Artemia nauplii before and after the feeding sessions was quantified&#160;to compare the feasibility of heterotrophic feeding at both temperature treatments.
Specifically, 24 colonies of P. acuta (mean total linear extension &#177; standard deviation: 21.3 cm &#177; 2.8 cm) were obtained from flow-through tanks at the research facilities of the National Museum of Marine Biology &#38; Aquarium, southern Taiwan. Pocillopora&#8203;&#160;acuta is a common coral species that possesses both a broadcast spawning, but&#160;typically brooding reproductive strategy35,36. The parent colonies of these corals were originally collected from the Outlet reef (21.931&#176;E, 120.745&#176;N) approximately 2 years earlier for another experiment32. Consequently, the coral colonies used in the present experiment had been reared for their entire lives under ex situ culture conditions; specifically, the colonies were exposed to ambient temperature and a 12 h:12 h light: dark cycle at 250 &#181;mol quanta m&#8722;2&#183;s&#8722;1 and were fed Artemia nauplii twice per week. We recognize that this long-term ex situ culture could have affected how the colonies responded to the treatment conditions in this experiment. We, therefore, would like to emphasize that the primary aim here is to illustrate how the described techniques can be effectively used to culture corals ex situ by demonstrating an applied example wherein the effects of temperature and feeding on coral reproduction were assessed.
Coral colonies were evenly distributed across six flow-through system culture tanks (tank interior length x width x height: 175 cm x 62 cm x 72 cm; tank light regime: 12 h:12h light:dark cycle at 250 &#181;mol quanta m&#8722;2&#183;s&#8722;1) (Figure 1A). The temperature in three of the tanks was set at 28 &#176;C, and the temperature in the other three tanks was set at 24 &#176;C; each tank had a logger that recorded the temperature every 10 min (see the Table of Materials). The temperature was independently controlled in each tank using chillers and heaters, and water circulation was maintained using flow motors (see the Table of Materials). Half of the colonies in each tank (n = 2 colonies/tank) were fed Artemia nauplii twice per week, while the other colonies were not fed. Each feeding session was 4 h in duration and was conducted in two independent temperature-specific feeding tanks. During feeding, all the colonies were moved into the feeding tanks, including the unfed colonies, to standardize the potential stress effect of moving the colonies between the tanks. The colonies in the fed and unfed treatments were positioned in their own compartment using a meshed frame within the temperature-specific feeding tanks so that only the colonies in the fed condition received food. The coral reproductive output and timing were assessed for each colony daily at 09:00 A.M. by counting the number of larvae that had been released into the larval collection containers overnight.

Author Spotlight: Advancing Coral Research by Exploring Climate Change Resistance, Ex Situ Aquaculture, and Reproduction Strategies 

Effective Techniques for the Feeding and Ex Situ Culture of a Brooding Scleractinian Coral, Pocillopora acuta

Our lab is interested in understanding climate change, resistance, and resilience in coral and exploring ex-situ aquaculture's role. Specifically, we aim to cultivate coral in a lab that can be used for restoration and research efforts. Over the past few years, we have seen major advances in coral ex-situ aquaculture, including being able to induce reproduction, as well as complete the entire coral life cycle in both broadcast spawning and brooding corals.Maintaining the long-term reproduction of brooding corals in the lab is usually quite challenging, with reproduction typically stopping after a few months. However, we found that if we culture the colonies together in mesocosm tanks and provide them with supplemental food, they can continue to produce larvae each month. In general, we have a good understanding of how feeding and temperature independently affect coral reproduction, but their interactive effects remain relatively understudied.For example, heterotrophy may have different benefits, or limitations at warmer compared to cooler temperatures. Using the protocols that we have described, we can effectively feed and culture the colonies long-term in X2 aquaculture systems, and can ultimately track the reproduction at the colony level to help infer the influence of heterotrophy on reproduction, and recruitment in a warming ocean.

Watch this Scientific Journal Video about Quantifying Artemia Nauplii Density Pre- and Post-Feeding of Pocillopora acuta at JoVE.com

Quantifying Artemia Nauplii Density Pre- and Post-Feeding of Pocillopora acuta

To quantify Artemia Nauplii used for coral feeding experiments, collect the samples at two time points. At each time point, use three syringes to collect 20 milliliters of water from the feeding container's surface, middle layer, and bottom layer. Transfer the collected water sample into individual 500-milliliter beakers.Next, add 180 milliliters of hot water, approximately 60 degrees Celsius, to the beaker to achieve a 1 to 10 dilution. Add two milliliters of water sample from the beaker into each well of a six-well plate. Next, using a stereo microscope, set to 6.5 times magnification.Count the number of Artemia Nauplii in each well. Density measurements of Artemia Nauplii before and after coral feeding sessions showed that the initial assessment at T0 showed no difference in both temperature treatments. After two and four weeks of culture, the Artemia Nauplii density was lower after feeding in both temperature treatments.There was no difference in the pre-feeding density between temperature treatments, or the post-feeding density between temperature treatments at any of the three time points assessed.

quantifying-artemia-nauplii-density-pre-post-feeding-pocillopora

Research

JoVE Journal

Biology

Climate change is affecting the survival, growth, and recruitment of corals globally, with large-scale shifts in abundance and community composition expected in reef ecosystems over the next several decades. Recognition of this reef degradation has prompted a range of novel research- and restoration-based active interventions. Ex situ aquaculture can play a supporting role through the establishment of robust coral culture protocols (e.g., to improve health and reproduction in long-term experiments) and through the provision of a consistent broodstock supply (e.g., for use in restoration projects). Here, simple techniques for the feeding and ex situ culture of brooding scleractinian corals are outlined using the common and well-studied coral, Pocillopora acuta, as an example. To demonstrate this approach, coral colonies were exposed to different temperatures (24 &#176;C vs. 28 &#176;C) and feeding treatments (fed vs. unfed) and the reproductive output and timing, as well as the feasibility of feeding Artemia nauplii to corals at both temperatures, was compared. Reproductive output showed high variation across colonies, with differing trends observed between the temperature treatments; at 24 &#176;C, fed colonies produced more larvae than unfed colonies, but the opposite was found in colonies cultured at 28 &#176;C. All colonies reproduced before the full moon, and differences in reproductive timing were only found between unfed colonies in the 28 &#176;C treatment and fed colonies in the 24 &#176;C treatment (mean lunar day of reproduction &#177; standard deviation: 6.5 &#177; 2.5 and 11.1 &#177; 2.6, respectively). The coral colonies fed efficiently on Artemia nauplii at both treatment temperatures. These proposed feeding and culture techniques focus on the reduction of coral stress and the promotion of reproductive longevity in a cost-effective and customizable manner, with versatile applicability in both flow-through and recirculating aquaculture systems.

Climate change is impacting coral reef ecosystems globally. Corals sourced from ex situ aquaculture systems can help support restoration and research efforts. Herein, feeding and coral culture techniques that can be used to promote the long-term maintenance of brooding scleractinian corals ex situ are outlined.

Climate change is affecting the survival, growth, and recruitment of corals globally, with large-scale shifts in abundance and community composition ...

Hanging Pocillopora acuta Colonies in Ex Situ Aquaculture Tanks

Begin by positioning a notched bar, also called a hanging bar, across the culture tank for hanging the coral colonies in place. Put the coral colony between the two large loops, ensuring the loops are positioned securely around the colony for stable hanging in water. Hook the smaller top loop of the fishing line into a notch on the hanging bar.

Feeding Pocillopora acuta with Artemia Nauplii

Feeding  Pocillopora acuta with  Artemia Nauplii  

Collect two liters of seawater from an independent feeding tank and pour it into an Artemia hatching container. Next, connect an air pump to the tubing connected to the bottom of the hatching container, and let it run for approximately 10 minutes before adding the Artemia cysts. While waiting, measure eight grams of Artemia cysts using a weighing balance.After 10 minutes, pour the measured Artemia cysts into the hatching container. Next, prepare the feeding tank by placing the feeding container into it, ensuring the top remains above the water surface. Connect the outer portion of the feeding container's corner tubing to an air pump that supplies air to the bubble stones to ensure proper water circulation during feeding.To enrich Artemia Nauplii, add 1.5 milliliters of enrichment diet to the hatching container two hours before the desired feeding time. After two hours, turn off the valve supplying air to the hatching container. After placing a light source at the base of the hatching container, cover it with a cardboard box to exclude ambient light.Allow the light to attract Artemia Nauplii to the bottom of the container for five minutes to separate live Artemia Nauplii from empty shells. After five minutes, remove the box and light source. Place a three liter measuring jug beneath the hatching container.Detach the tubing from the hatching container, allowing the Artemia Nauplii and seawater solution to flow into the jug and collect one liter of the solution within close proximity to the feeding tank. Pour the Artemia Nauplii and seawater solution through a 100 micrometer strainer to separate them from the sea water. Then rinse the Artemia Nauplii inside the strainer twice with water from the feeding tank.Place the strainer into the feeding tank to unload the Artemia Nauplii. Next, stir the water in the tank to evenly distribute the Nauplii throughout the tank. Move each hanging bar with the attached coral colonies from the culture tank to the feeding tank.Ensure the hanging bar is securely positioned across the top of the feeding tank. Remove the coral colonies after the four hour feeding session by taking the hanging bars out of the feeding tank. Thoroughly rinse each coral with sea water from the respective culture tanks.To remove residual Artemia Nauplii, place the hanging bars with the attached corals back into their respective culture tanks.

Pocillopora acuta Larvae Collection and Enumeration from Culture Tank

Immerse a larvae collection container completely into a culture tank. Next, submerge the coral colony into the larvae container, ensuring both remain under water. Then hook the handle of the larvae collection container onto the hanging bar.The following morning, unhook the fishing line from the hanging bar, and carefully remove one colony from its larvae collection container. Immediately, place the colony back into the culture tank. Next, remove the larvae collection container from the tank and place it on top of the measuring jug.Apply moderate pressure on the cap using one finger, and unscrew it. Transfer water from the measuring jug into a bowl. Manually, count the larvae in the bowl, using a three-milliliter pipette to transfer them to a 50-milliliter tube.This method enabled the evaluation of the reproductive output of Pocillopora acuta colonies under different temperature and feeding treatments. Colonies cultured at 28 degrees Celsius, released more larvae when unfed than when fed. But the opposite trend was found in colonies cultured at 24 degrees Celsius, whereby the fed colonies produced more larvae than the unfed colonies.Reproduction in all the colonies occurred before the full moon. The mean lunar day of larva release ranged from lunar day 6.5 to lunar day 11.1. However, a significant difference among treatments was only observed between the unfed, 28-degrees-Celsius colonies, which produced earlier in the lunar cycle, and the fed, 24-degrees-Celsius colonies, which produced later in the lunar cycle.