1. Water quality - primarily maintained by algal turf scrubbers, mats of algae that replenish oxygen and remove carbon dioxide and wastes. Trace elements are also added daily. A range of parameters are tested regularly.

2. Sunlight (energy) - reproduced by metal halide lighting that closely simulates the spectrum and intensity of natural sunlight.

3. Waves - produced by dumping buckets, distributing clean, oxygenated water throughout the systems and washing away sediments. These waves distribute water already in the systems, since no outside currents bring in fresh, new water.

4. Artemia Feeding System and Plankton Refugium - provide brine shrimp and invertebrate larva to system that serves as a plankton source.

5. Tides (Maine systems only) - synchronized motors and pumps produce high and low tides (spring and neap), allowing us to maintain the various intertidal organisms characteristic of Maine ecosystems.

6. Heaters and Chillers - designed to keep temperatures in the optimal ranges and prevent large temperature fluctuations stressful to the organisms.

7. Water Replacement System - makes up for water lost during evaporation, a problem endemic to this artificial setting. Keeps salinity in balance and within an optimal range. Also a source of new water for the systems.

8. Organisms - eat and be eaten. A wide diversity of organisms are displayed, with most of them producing or consuming their food from within the system. Some organisms, such as the top predators (squirrelfish in reef and pollock in Maine), must be fed daily.















The algal turf scrubbers are the principle means of filtration for the model ecosystems. They rely on plant photosynthesis to keep nutrient levels low and dissolved oxygen and pH levels high. Located on the balcony, each scrubber is a large box containing 2 wave buckets, 2 mesh screens, and 4 drains. They work rather simply. Water pumped from the tanks to the algal turf scrubbers collects in the wave buckets. When the wave buckets become full, they tip over, generating waves across the scrubber box. The waves pass over the mesh screens, on which algae is cultivated in thick mats. During photosynthesis, the algae remove, or "scrub", excess nutrients and carbon dioxide from the water. At the same time they give off oxygen as a byproduct. Powerful lights over the scrubbers simulate the natural sunlight the algae need to complete this process. The clean, oxygenated water then flows down the drains and is reintroduced to the system by way of the wave generator. The algal turfs grow rapidly and need weekly harvesting.

The algal turf scrubber system is an extremely effective method of recreating the natural chemical state of water. The water quality of the systems is maintained through plant photosynthesis, just as it would be in nature.

For the reef system, four scrubbers are used to maintain nutrient levels within an acceptable range. Only one scrubber is used for the Maine system. This is because nutrient levels are much lower in a Caribbean coral reef ecosystem than a rocky shore ecosystem.



Marine plants acquire energy from natural sunlight that, through a process called photosynthesis, they can convert into chemical energy, or food. Because plants are the only organisms with the ability to produce their own food, other organisms usually get their food, either directly or indirectly, from plants. That is why plants are the base of many food webs.

Because the model ecosystems do not receive natural sunlight, it has to be reproduced. This requires reproducing the two most important characteristics of natural sunlight, spectrum and intensity. Spectrum refers to the specific wavelengths, or colors, emitted by a particular light.

Each color is a different wavelength, and different marine plants use different wavelengths more efficiently. Intensity refers to the brightness of the light.

The overall health of the model ecosystems depends greatly on how accurately the lighting system duplicates natural sunlight. Otherwise, the algae are not able to photosynthesize, which means they cannot provide food and clean water for each system. Also, the corals are not able to thrive, since the single-celled algae that live symbiotically in their tissues cannot photosynthesize either. Lighting is very important to all the organisms in the ecosystems, not just the plants.



Both tanks have a wave generator, the large box that sits above the deep end of the tanks that is the source of wave generation for the system. It comprises two wavebuckets similar to those in the scrubbers, boxes with angled fronts and hinged ends that tip over when they are full with water and produce waves. These waves help distribute food, nutrients, and gases throughout the system. They distribute the clean, oxygenated water from the scrubbers.

Water is fed to the wave generator via PVC lines from the refugia and scrubbers. Because the wavebuckets are different sizes, they dump at different intervals. This is done to control the force of the waves produced. The waves travel the length of the tank and are diffused by the wavecatcher in the reef tank and the intertidal area in the Maine tank, so as not to produce a counter-wave. The reef wavecatcher is the reservoir at the backreef end of the tank that contains the pump intakes.



Water from the tanks is pumped to the refugia, scrubbers, and heat exchangers upstairs by 10, 20 or 50 gpm (gallon per minute) pumps through PVC lines. In the reef tank water is pumped from the wavecatcher; in the Maine tank it is pumped from the deep end. All water re-enters the tank by way of the wave generator.



The refugia are essentially holding tanks - isolated, protected places to house organisms that either need special care or are better off in a separate tank. Often new collections are stored here until they can gradually be introduced into the tank. The reef refugia also serve other purposes. Because certain organisms are isolated in the reef refugia, they can reproduce and disperse their larva without high predation. This larva is then carried downstairs and dispersed throughout the main tank, where it becomes a plankton source. The refugia also trap sediment and particulates from the water in their angled bottoms.

There are two reef refugia and one Maine refuge.



The deionized water system consists of several large canisters, which remove certain ions and impurities from tap water. The water is further polished as it passes through the smaller canisters above the sink. The deionized water is stored in the box that sits in the sink. Calcium hydroxide is added to the water in the box to help increase pH and provide various invertebrates with enough calcium to build their skeletons or shells.



Water flows from the wavecatcher to the sensor box via two siphon hoses. As a result, the water level in the sensor box is the same as the water level in the wavecatcher. The probe in the sensor box hangs at the level at which the water level should be kept. This probe senses when the water level is low and turns on the Masterflex pump. Deionized freshwater from the plexiglass box in the sink is then pumped into the wave generator to bring up the water level. Once the water level reaches the probe, the pump is turned off, until the level drops again. Most water loss is due to evaporation.



Artemia, also known as brine shrimp or sea monkeys, are cultivated in the laboratory to be fed to all four tanks. They hatch from eggs or cysts after an incubation period of approximately 24 hours. Certain conditions are required for cultivation, such as a salinity between 15 and 30 ppt, a temperature around 25 C, and the presence of aeration. For this system, the Artemia are incubated in jugs of seawater aerated by air pumps. The jugs are then fed alternately to the tanks. The Artemia represent a source of zooplankton for the systems. Zooplankton are small floating or weakly swimming animals abundant in marine waters. They are consumed either directly or indirectly by many marine organisms and therefore are an integral part of the food chain. In the wild, plankton are introduced to an ecosystem by waves, currents, and tides. In this coral reef system, Artemia are added automatically at night.



At about midnight each night, the Artemia Feeding System comes on. The system involves a jug that sits above the reef tank next to the wavemaker and a solenoid valve controlled by two timers. One timer opens the solenoid valve (release valve), and the second timer controls how long the valve stays open. The Artemia enter the system at the fore-reef end and are dispersed by the waves. Artemia is added by hand to the other three tanks.



Water is pumped upstairs to the heat exchangers to be either heated or chilled.


Salinity and Specific Gravity

For all practical purposes, salinity is defined as the total amount of salts dissolved in water. We use an instrument called a hydrometer to determine the salinity. Hydrometers measure specific gravity, which represents a ratio of the density of seawater to the density of an equal amount of distilled freshwater. Because warm water is less dense than cold water, specific gravity readings are affected by temperature. The specific gravity reading from the hydrometer is used, along with the water temperature, to calculate salinity.

The major cause for salinity fluctuation in the systems is due to evaporation. To compensate for this water loss, seawater is added if the salinity is too low, deionized freshwater is added if the salinity is too high.


Nitrite/Nitrate levels are tested with an instrument called an autoanalyzer. Nitrite/Nitrate are the bypoducts of biological processes (waste production, for example), inorganic substances dissolved in seawater. The animals excrete ammonia, which is toxic. Certain bacteria convert ammonia into nitrite and then nitrate. The algae in the tank and scrubbers use them, other nutrients, and light to photosynthesize (produce their own food), thereby reducing nitrite/nitrate levels in the system. This is important because wild coral reefs inhabit waters low in nutrients.

This level is yet another factor of a coral reef ecosystem that must be replicated in this model. Increased nitrite/nitrate levels may result from overfeeding (food rots uneaten in tank), overcrowding of organisms (too many organisms producing waste), or reduced efficiency of the algal turf scrubbers (photoperiod is too short, too many amphipods grazing the algae off the screens). If nitrite/nitrate levels get too low, the scrubber algae may be returned to the system (they are locked up in the algae), after being dried, weighed, and recorded.

Dissolved Oxygen

Because marine organisms take in oxygen from the water, the amount of oxygen dissolved in the water is very important. Without enough dissolved oxygen (DO) we would not be able to sustain the large biological load that we do. The amount of oxygen that can be dissolved in water depends upon the temperature and salinity of the water. As the temperature and salinity increase, the amount of oxygen that can be dissolved decreases.

There are two ways oxygen can enter water. One, atmospheric oxygen can enter water through the air-water surface interface. Two, and probably most important for our system, plants release oxygen into the water as a by-product of photosynthesis. Throughout the day the algae in the tank are releasing oxygen, throughout the night the algae in the scrubbers are releasing oxygen. This way DO levels remain high on a constant basis. Sometimes the water becomes saturated with oxygen and no more can be dissolved. When that happens tiny air bubbles can be seen streaming off the plants.



pH, short for "Power of Hydrogen," is the measure of how acidic or basic water is, based on the amounts of hydrogen ions (H+) and hydroxyl ions (OH-) present. Water is acidic when more hydrogen ions are present and basic when more hydroxyl ions are present. pH is measured on a scale from 1 to 14, with 1 being the most acidic and 14 being the most basic. A pH of 7 is neutral, meaning that there is an equal number of H+ and OH- ions present.

Two factors that greatly influence the pH level are dissolved carbon dioxide (CO2) and organic acids. The accumulation of both of these cause the pH level to decrease. The algae in the tank and scrubbers remove CO2 from the water and use it during photosynthesis, thereby lowering CO2 levels and maintaining pH both day and night. Maintaining a pH level of at least 8.0 is important for coral growth and overall health.