This study was supported by the State Key Development Programs for Basic Research of China (2021YFC3100502).

The corals used for the present study were Seriatopora caliendrum, which are cultured in our lab. All the corals were kindly provided by the South China Sea Institute of Oceanology, University of Chinese Academy of Sciences.
1. Inspection and startup
NOTE: Each module must be tested for tightness and function individually before assembling the system. Deionized water should be used to test the module&#39;s tightness. Commercial details of all...

A Combined Micro-Device System for Promoting and Monitoring Coral Growth

<ol>
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V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coral+decline+threatens+fish+biodiversity+in+marine+reserves.">Coral decline threatens fish biodiversity in marine reserves.</a> Proceedings of the National Academy of Sciences of the United States of America. 101 (21), 8251-8253 (2004).</li><li>Hughes, T. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Global+warming+and+recurrent+mass+bleaching+of+corals.">Global warming and recurrent mass bleaching of corals.</a> Nature. 543 (7645), 373-377 (2017).</li><li>Carpenter, K. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=One-third+of+reef-building+corals+face+elevated+extinction+risk+from+climate+change+and+local+impacts.">One-third of reef-building corals face elevated extinction risk from climate change and local impacts.</a> Science. 321 (5888), 560-563 (2008).</li><li>Hughes, T. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatial+and+temporal+patterns+of+mass+bleaching+of+corals+in+the+Anthropocene.">Spatial and temporal patterns of mass bleaching of corals in the Anthropocene.</a> Science. 359 (6371), 80-83 (2018).</li><li>Albright, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reversal+of+ocean+acidification+enhances+net+coral+reef+calcification.">Reversal of ocean acidification enhances net coral reef calcification.</a> Nature. 531 (7594), 362-365 (2016).</li><li>Hoegh-Guldberg, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coral+reefs+under+rapid+climate+change+and+ocean+acidification.">Coral reefs under rapid climate change and ocean acidification.</a> Science. 318 (5857), 1737-1742 (2007).</li><li>Mason, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Decline+in+symbiont+densities+of+tropical+and+subtropical+scleractinian+corals+under+ocean+acidification.">Decline in symbiont densities of tropical and subtropical scleractinian corals under ocean acidification.</a> Coral Reefs. 37 (3), 945-953 (2018).</li><li>Prouty, N. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vulnerability+of+Coral+reefs+to+bioerosion+from+land-based+sources+of+pollution.">Vulnerability of Coral reefs to bioerosion from land-based sources of pollution.</a> Journal of Geophysical Research: Oceans. 122 (12), 9319-9331 (2017).</li><li>Heery, E. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Urban+coral+reefs:+Degradation+and+resilience+of+hard+coral+assemblages+in+coastal+cities+of+East+and+Southeast+Asia.">Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia.</a> Marine Pollution Bulletin. 135, 654-681 (2018).</li><li>Rosenberg, E., Koren, O., Reshef, L., Efrony, R., Zilber-Rosenberg, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+microorganisms+in+coral+health,+disease+and+evolution.">The role of microorganisms in coral health, disease and evolution.</a> Nature Reviews: Microbiology. 5 (5), 355-362 (2007).</li><li>Bui, V. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diversity+and+biogeography+of+coral+mucus-associated+bacterial+communities:+The+case+of+Acropora+formosa.">Diversity and biogeography of coral mucus-associated bacterial communities: The case of Acropora formosa.</a> Journal of Marine Science and Engineering. 11 (1), 74 (2023).</li><li>Hass, A. F., Smith, J. E., Thompson, M., Deheyn, D. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+reduced+dissolved+oxygen+concentrations+on+physiology+and+fluorescence+of+hermatypic+corals+and+benthic+algae.">Effects of reduced dissolved oxygen concentrations on physiology and fluorescence of hermatypic corals and benthic algae.</a> PeerJ. 2, 235 (2014).</li><li>Raj, K. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low+oxygen+levels+caused+by+Noctiluca+scintillans+bloom+kills+corals+in+Gulf+of+Mannar,+India.">Low oxygen levels caused by Noctiluca scintillans bloom kills corals in Gulf of Mannar, India.</a> Scientific Reports. 10 (1), 22133 (2020).</li><li>Luo, Y. S., Zhao, J. L., He, C. P., Lu, Z. H., Lu, X. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Miniaturized+platform+for+individual+coral+polyps+culture+and+monitoring.">Miniaturized platform for individual coral polyps culture and monitoring.</a> Micromachines. 11 (2), 127 (2020).</li><li>Pang, A. P., Luo, Y. S., He, C. P., Lu, Z. H., Lu, X. 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This coral culture system is designed to simulate and provide a relatively natural or customized microenvironment for corals to be transplanted into and survive. Meanwhile, as a self-developed equipment, this system needs to be reliable, user-friendly, and safe. For example, in terms of temperature control, the seawater temperature should be controlled appropriately based on the daily environmental circumstances. The system was tested by culturing the coral for 1 month, confirming the system's reliability.
<p class="...

The deterioration of coral reef ecosystems has been occurring worldwide over the past 70 years. Considering all the major coral areas across Central America1, Southeast Asia2,3,4,5,6, Australia7,8, and East Africa9, the global coverage of coral reefs has halved since the 1950s10. This mass loss of coral reefs has resulted in ecological and economic problems. For example, by tracing the presence/absence and abundance of all kinds of coral-dependent fishes for 8 years, researchers concluded that the coral decline has directly caused a substantial decrease in fish biodiversity and abundance in Papua New Guinea11. This result proved that the coral decline can not only undermine coral reef-based biological systems but also reduce fishery incomes.
Over decades of field surveys, including direct monitoring, remote sensing, and data comparison, the scientific community has identified several factors causing the mass coral decline. One major reason for the mass coral decline is coral bleaching caused by high seawater temperatures12,13. By combining bleaching and meteorological records, scientists have concluded that coral bleaching is happening more frequently in El Ni&#241;o-Southern Oscillation phases14. Another reason for the coral decline is ocean acidification. Owing to the increased CO2 concentration in both the atmosphere and seawater, calcium carbonate dissolves faster than before, causing downscale net coral reef calcification15. Indeed, it has been concluded that when the CO2 concentration in the atmosphere reaches above 500 ppm, tens of millions of people will suffer, and the coral reefs will be at risk of significant deterioration and symbiodinium detachment16,17. There are other factors that can also affect coral survival, such as inshore pollutants causing or accelerating coral decline. Researchers in Hawaii measured the carbon, oxygen, and nitrogen isotopes in corals, along with the dissolved inorganic carbonate and the related nutrients (NH4+, PO43-, NO2&#8722;, and NO3&#8722;), and concluded that pollution from the land magnified the coastal acidification and bioerosion of corals18. Further to pollution, urbanization also endangers coral survival and causes relatively low architectural complexity in corals, as revealed by a study on the coral survival status in Singapore, Jakarta, Hong Kong, and Okinawa. Thus, the impact of anthropogenic stressors and the superimposed effects of climate change are leading to widespread reduced biodiversity on coral reefs and an associated decline in coral ecological function and resilience19.
It should also be noted that a large number of microorganisms participate in the physiological functions of corals, including nitrogen fixation, chitin decomposition, the synthesis of organic compounds, and immunity20, and these microorganisms should, thus, be included when considering coral reef deterioration. In natural environments, such as coral reefs, many factors cause hypoxic or anoxic conditions, including insufficient water circulation, algal exudate, and algal overgrowth. This phenomenon negatively affects the population distributions of coral and coral-related microorganisms. For example, Vietnamese scientists found that in Nha Trang, Phu Quoc, and Ujung Gelam, bacterial composition in the coral Acropora Formosa could be affected by dissolved oxygen at different locations21. Researchers in the United States explored hypoxic or anoxia conditions in corals and found that algal exudates can mediate microbial activity, leading to localized hypoxic conditions, which may cause coral mortality in the direct vicinity. They also found that corals could tolerate reduced oxygen concentrations but only above a given threshold determined by a combination of the exposure time and oxygen concentration22. Researchers in India found that when Noctiluca scintillans algae bloomed, the dissolved oxygen decreased to 2 mg/L. Below this concentration, about 70% of Acropora montiporacan died because of hypoxic conditions23.
All the abovementioned facts and factors suggest that environmental change leads to the deterioration of coral reefs. To culture and study reef corals under certain conditions, it is important to accurately and comprehensively build up a controllable microscopic environment for reef corals to inhabit. Normally, scientists focus on temperature, light, water flow, and nutrients. However, other features, such as the dissolved oxygen concentration, microorganism abundance, and microorganism diversity in the seawater, are commonly ignored. To this end, our group has explored the possibility of applying small equipment to culture coral polyps in a relatively controlled environment24,25. In this work, we designed and built up a modular micro-device system for coral culture. This modular micro-device system can provide a controllable micro-environment in terms of the temperature, light spectrum, dissolved oxygen concentration, nutrients, and microorganisms, etc., and has the capacity for expansion and upgrade.
Modules and functions of the device 
The micro-device system was inspired by the Berlin system26, but no live rocks are used in the current system. As shown in Figure 1, the current system comprises six main modules, two brushless motor pumps, one gas pump, one flow-through UV lamp, one power supply, certain electronic control components, and the related wires and screws. The six main modules include a seawater store module (with an air pump and temperature sensor), a temperature control module, an algae purification module, a microbial purification module, an activated charcoal purification module, and a coral culture module.
Device architecture 
As shown in Figure 2 and Figure 3, the overall micro-device system can horizontally be divided into two compartments with a temperature control module in between. For safety reasons, all the seawater-containing modules and parts are placed in the left compartment, named the culture compartment. The other electronic parts are placed in the right compartment, named the electronic compartment. Both compartments are sealed or packaged within shells. The temperature control module is fixed in a divider plate in between. The shell of the culture compartment includes a baseboard and three screw-fixing plates. This design ensures compartment tightness and facilitates the operation of the system. Additionally, the tightness favors accurate temperature control. The shell of the electronic compartment includes a baseboard, two screw-fixing plates, and one front control panel.
Water circulation 
An inner and outer seawater circulation loop connected to the seawater store module was pre-designed. The inner circulation loop successfully connects the seawater store module, temperature control module, flow-through UV lamp, algae purification module, and microbial purification module. This circulation loop aims to provide suitable physiochemical and physiological seawater conditions for the corals, and no frequent maintenance is needed. The algae purification module contains Chaetomorpha algae, which absorbs the extra nutrients (nitrate and phosphate) in the water. The microbial purification module contains the bacterial culture substrate, which cultivates the microbiome to transfer nitrite and ammonium into nitrate for water purification. All these modules need to be replaced only under critical circumstances.
The outer circulation loop successively connects the seawater store module, coral culture module, and activated charcoal module. This circulation loop aims to provide light, tightness, water current, and high seawater quality to the corals. The seawater can be refreshed through a water inlet and a water outlet. Additives are added through a three-way valve, and the seawater sample can also be extracted from this valve for inspection. Air can be pumped in through an air inlet and discharged from an air outlet.
Electronic design 
A 220 V AC power supply with a switch and a fuse is used for the whole system. The input power is divided into four branches. The first branch goes to a 12 V DC power supply, which directly powers the heating panel, cooling panel, and cooling fan. This branch also indirectly powers two pumps and two lighting panels through a four-channel DC transformer. The second branch goes to a PID temperature controller. The third branch goes to an air pump power supply. The last branch connects to a UV lamp power supply. A solid-state relay connects the PID temperature controller and the cooling panel in the temperature control module. A regular relay is used to connect the PID temperature controller and the heating panel. The four-channel DC transformer converts the voltage to that required.
There are two control panels on the right part of the system. There are four switches and one controller for the UV lamp on the top panel, including a main power switch, a UV lamp power switch, an air pump switch, and a temperature control switch. The main power switch controls the 12 V power supply of the system.
A PID temperature controller, a cycle timer, a four-channel DC transformer, and a three-channel timer are on the front panel. The PID temperature controller adjusts the water temperature by controlling the heating and cooling panels in the temperature control module. The temperature control module only works when the inner circulation pump is working and the water is flowing past the temperature control module. The cycle timer is connected to the air pump power line. Its purpose is to assign the working time period to the air pump. There is a three-channel timer deployed in the electronic compartment too. This timer controls the work time period for the air pump, coral light, and algae light.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>12V DC power supply</td>
			<td>Delixi Electric Co., Ltd.</td>
			<td>CDKU-S150W</td>
			<td>12V12.5A</td>
		</tr>
		<tr>
			<td>3% hydrogen peroxide solution</td>
			<td>Shandong ANNJET High tech Disinfection Technology Co., Ltd</td>
			<td>NULL</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>75% ethanol solution</td>
			<td>Shandong ANNJET High tech Disinfection Technology Co., Ltd</td>
			<td>NULL</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Air pump</td>
			<td>Chongyoujia Supply Chain Management Co., Ltd.</td>
			<td>NHY-001</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Air sterilizing filter</td>
			<td>Beijing Capsid Filter Equipment Co., Ltd</td>
			<td>S593CSFTR-0.2H83SH83SN8-A</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Camera</td>
			<td>SONY</td>
			<td>&#913;7r4-ILCE-76M4A</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Coral nutrition solution</td>
			<td>Red Sea Aquatics Co., Ltd.</td>
			<td>22101</td>
			<td>Coral nutrition</td>
		</tr>
		<tr>
			<td>Coral pro salt (sea salt)</td>
			<td>Red Sea Aquatics Co., Ltd.</td>
			<td>R11231</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Cycle timer</td>
			<td>Leqing Shangjin Instrument Equipment Co., Ltd.</td>
			<td>CN102A</td>
			<td>220V version</td>
		</tr>
		<tr>
			<td>Double closed quick connector</td>
			<td>JOSOT Co., Ltd</td>
			<td>NL4-2103T</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Flow-through UV lamp</td>
			<td>Zhongshan Xinsheng Electronic technology Co., Ltd.</td>
			<td>211</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Four-channel transformer</td>
			<td>Dongguan Shanggushidai Electronic Technology Co., Ltd</td>
			<td>LM2596</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Macro lens</td>
			<td>SONY</td>
			<td>FE 90mm F2.8 Macro G OSS</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Microbiome source solution</td>
			<td>Guangzhou BIOZYM Microbial Technology Co., Ltd.</td>
			<td>303</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Mini-photo studio</td>
			<td>Shaoxing Shangyu Photography Equipment Factory</td>
			<td>CM-45</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>PID temperature controller</td>
			<td>Guangdong Dongqi&#160; Electric Co., Ltd.</td>
			<td>TE9-SC18W</td>
			<td>SSR version</td>
		</tr>
		<tr>
			<td>Pump (for water)</td>
			<td>Zhongxiang Pump Co., Ltd.</td>
			<td>ZX43D</td>
			<td>Seaswater version</td>
		</tr>
		<tr>
			<td>Pure water machine</td>
			<td>Kemflo&#160;(Nanjing) environmental technology Co, ltd</td>
			<td>kemflo A600</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Solid-state relay</td>
			<td>Delixi Electric Co., Ltd.</td>
			<td>DD25A</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Surface active agents</td>
			<td>Guangzhou Liby Group Co., Ltd.</td>
			<td>Libai detergent</td>
			<td>NULL</td>
		</tr>
		<tr>
			<td>Three-channel timer</td>
			<td>Leqing Changhong Intelligent Technology Co., Ltd.</td>
			<td>CHE325-3</td>
			<td>220V version</td>
		</tr>
		<tr>
			<td>Water sterilizing filter</td>
			<td>Beijing Capsid Filter Equipment Co., Ltd</td>
			<td>S593CSFTR-0.2H83SH83SN8-L</td>
			<td>NULL</td>
		</tr>
	</tbody>
</table>

an integrated micro-device system for coral growth and monitoring

Corals are fundamental organisms in marine and coastal ecosystems. With the advancement of coral protection research in recent years, precise control of the coral culture environment is highly in demand for coral conservation and study. Here, we developed a semi-closed coral culture micro-device system as a multi-functional platform, which can provide accurate and programmable temperature control, a sterile initial environment, long-term stable water quality, an adjustable dissolved oxygen concentration, and a customized light spectrum for corals. Owing to the modular design, the coral culture system can be upgraded or modified by installing desirable new modules or removing existing ones. Currently, under appropriate conditions and with proper system maintenance, the sample corals can survive for at least 30 days in a healthy state. Furthermore, due to the controllable and sterile initial environment, this coral culture system can support research into the symbiotic relationship between corals and associated microorganisms. Therefore, this micro-device system can be applied to monitor and investigate sea corals in a relatively quantitative manner.

Author Spotlight: Advancing Coral Culture - Creating a Semi-Quantitatively Controlled Microenvironment System to Counter Current Limitations 

An Integrated Micro-Device System for Coral Growth and Monitoring

The aim of our research is to develop an artificial microenvironment system for coral culture and study. The microenvironment in the micro-device system can at least be semi-quantitatively controlled. At the present, the existing equipment and the system used for coral culture lack precise control over temperature and other environmental factors.Additionally, these system are open, making them susceptible to contamination from an airborne substance. Our indoor coral culture system boasts a superior control accuracy, and the microbial tightness compared to other similar system or tanks. Additionally, our system is commercially cost-effective.Using this micro-device system, we can somehow customize the environmental parameters like temperature, strength, or metabolite concentration, which will make the coral study more quantitative and might promote the current coral research. We would like to know about longevity of corals in this artificial micro-device. Another important question that we want to address is how the artificially built-up system affects the growth process of corals in comparison to the nature environment.

Temperature control accuracy 
The system temperature is normally set to 23-28 &#176;C depending on the coral species. However, as one of the most important factors, temperature fluctuation can strongly affect coral survival. Hence, temperature control accuracy is a decisive factor for the coral culture system. A temperature sensor and an independent data collector with a temperature range from 9 &#176;C to 32 &#176;C can be used to test the temperature control accuracy in the coral culture module. W...

Watch this Scientific Journal Video about Advancing Coral Culture — Creating a Semi-Quantitatively Controlled Microenvironment System to Counter Current Limitations at JoVE.com

This protocol describes the development of a modular controllable micro-device system that can be applied for the long-term culturing and monitoring of sea corals.

Corals are fundamental organisms in marine and coastal ecosystems. With the advancement of coral protection research in recent years, precise control of ...