Modeling marine ecosystems is a complex undertaking, requiring considerable planning, monitoring, and maintenance to simulate the different environments on display and to establish and maintain the right balance of living organisms. The equipment used to maintain the model ecosystem aquaria controls everything from the chemistry and clarity of the water, using biological, chemical, and mechanical filters, to the temperature and the amount of light each aquarium receives.
Following is a brief description of most of the equipment used to simulate the physical and chemical conditions of the model ecosystems and what goes into selecting, collecting, and caring for specimens. These are the secrets behind the Smithsonian Marine Ecosystems Exhibit...the Secrets of SMEE!
The most important life support system employed at the exhibit is the one used to control the buildup of inorganic nitrogen and phosphorus, which is excreted by all aquatic animals. In the small controlled environments of our model ecosystems, inorganic nitrogen in the form of ammonia and nitrites can quickly reach toxic levels, while elevated nitrates (which can also reach toxic levels) and phosphates are often associated with algae blooms. In natural waters, these nutrients are maintained at nearly undetectable levels by organisms like seagrasses, phytoplankton, algae, and to a lesser extent certain specialized bacteria.
Over 20 years ago, Smithsonian scientists led by Dr. Walter Adey, developed a biological process which utilizes naturally occurring turf or hair algae to control nitrogen and phosphorus levels. The process called algal turf scrubbers or ATS, takes advantage of the photosynthetic capabilities of algae which need nitrogen and phosphorus to grow. Water from the aquarium is constantly circulated over brightly illuminated shallow trays of fast growing turf algae grown in the absence of herbivores. Excess nutrients are removed from the system by routinely harvesting the excess algae, as seen in the photograph to the right. In addition to maintaining naturally low levels of nitrogen and phosphorus, other advantages of using ATS filtration include the night-time production of oxygen and the removal of carbon dioxide. In keeping with the Exhibit's philosophy of modeling nature, ATS are the primary means of removing excess nutrients. top
Chemical filters are used to limit the buildup of organic compounds in the model ecosystem aquaria. However, chemical filters are used sparingly because they remove compounds which are nutrients for some organisms.
Activated carbon (charcoal) filters are used to remove compounds that discolor the water. The best example is the brown colored water typical of our Mangrove Ecosystem. The brown color is caused by compounds called tannins, which leach out of the fallen mangrove leaves. However, the most common reason for using activated carbon filters is to limit the buildup of yellow plant pigments in the other model ecosystems, especially the coral reef. In addition to giving the water an unnatural appearance, these plant pigments can significantly reduce the amount of light penetrating the water. Each model ecosystem is designed to accept an activated carbon filter, but only the Coral Reef Model Ecosystem uses a filter on a regular basis to simulate clear extremely low nutrient tropical waters.
Foam fractionators or protein skimmers are better suited for removing organic compounds produced by animals such as mucus and those specialized compounds produced for chemical defense. All but the Mangrove Model Ecosystem are equipped with protein skimmers. top
Mechanical filters called bag filters are used to remove suspended solids from the water, but like chemical filters, are used sparingly to minimize their impact on organisms. All of the model ecosystem aquaria were designed with a bag filter plumbed in-line, although the actual filter bag, (which is available in a variety of mesh sizes), is only installed when necessary. Typically, a mechanical filter is only used for as long as it takes to clear cloudy water, which is usually less than a day. Although unusual, the water might become cloudy if the bottom gets seriously stirred up by tank inhabitants or staff. However unlikely, excess nutrients (which might be released by a decaying specimen) can fertilize a bacterial or phytoplankton bloom. top
The sun emits an intense broad spectrum of light energy, some of which plants and other photosynthetic organisms are able to use to make their own food. As a result, nearly all of the earth's ecosystems are fueled by sunlight and the photosynthetic organisms that use it. Unfortunately for us trying to simulate ecosystems, not all photosynthetic organisms utilize the same color(s) of light for photosynthesis. For example, red algae use mostly blue light, green algae red light, and brown algae use yellow and/or green light. As a result, not only do the model ecosystem's artificial lights have to be intense, they must also emit a broad spectrum of light.
The daylight spectrum metal halide lights used at the exhibit are bright, but not nearly as bright as the sun. To help make up for this deficiency, the lights, which are all on timers, are set to stay on for up to 15 hours. It also helps that most photosynthetic organisms can live at a variety of depths/light levels and are able to adapt to lower levels of light.
In an effort to simulate the tropical sun, the Coral Reef model ecosystem is the brightest tank with eight 1,000 watt lights. At the other extreme is the unlit deepwater Oculina Bank Model Ecosystem. top
The building's air conditioning system works well enough to keep the temperatures of all but two of the model ecosystems within acceptable limits (between 72 °F and 88 °F.) The intense, hot lights used on the Coral Reef Model Ecosystem require two, 1 HP in-line water chillers to keep the temperature between 76 °F and 81 °F. The 1/2 HP in-line water chiller on the Oculina Bank model ecosystem is used to help simulate the cooler temperatures typical of that habitat. While the temperature of the Oculina Bank reefs can be as low as 50 °F and as high as 75 °F depending on the time of year, our exhibit is maintained at around 70 °F. top
Water is constantly on the move in most marine ecosystems. Tides, currents, and waves provide a constant supply of fresh nutrients, food, and oxygen, while they carry away excess nutrients and decaying matter. At the exhibit, this critical function is simulated by water pumps and mechanical systems which work to simulate wave action, as well as a tidal cycle on the Mangrove Model Ecosystem. top
The salinity of the ocean usually remains very close to 35.4 parts per thousand (ppt). Whereas, salinity readings taken in an estuary like the Indian River Lagoon can vary greatly within a single day, depending on the location, tide and the amount of freshwater runoff. The target salinity of the exhibit's three oceanic model ecosystems is 35.4 ppt +/- 1 ppt. The target salinity of the exhibit's three IRL model ecosystems was arbitrarily set at 25 ppt +/- 3 ppt.
Left unchecked, all of the model ecosystems would experience a gradual increase in salinity due to evaporation. To offset this, all but one of the model ecosystems is equipped with a system that automatically makes up for evaporation by adding buffered freshwater which has been purified with a reverse osmosis/deionization system. top
In traditionally managed aquaria, it is usually necessary to perform routine water exchanges to help limit the buildup of potentially toxic nutrients (usually nitrates.) Even though the algae filters used on the model ecosystem aquaria make routine water exchanges unnecessary, each model ecosystem still receives a 10% to 20% water exchange annually.
These water exchanges are primarily used as a means of replenishing rare nutrients and other compounds which might have been taken up by organisms, or to remove accumulated detritus and/or loose algae. In nature, detritus and loose algae are dislodged and slowly transported to the deep sea by tides, storms, and currents.
The saltwater used at the exhibit is pumped out from the intake canal of the St. Lucie Nuclear Power Plant on South Hutchinson Island. The water source is approximately ¼-mile off the beach. The raw seawater is pumped into two plastic tanks mounted on a converted boat trailer, and transported back to the exhibit. It is processed through a large diatomaceous earth filter to remove suspended particles, plankton, and most potential pathogens and pumped into a 475-gallon storage tank located on the second floor of the exhibit. The water is covered and vigorously aerated. top
Identifying, selecting, and acquiring the proper specimens for the model ecosystems is an exceedingly difficult task, with many things to consider: Will a specimen fill a necessary niche to help keep the model ecosystem in balance? Is the specimen representative of a particular habitat? Will it be visible and/or interesting to watch? Is it likely to eat its tankmates, or destroy the habitat? Will it find enough to eat in the model ecosystem and/or can it be fed? And, does it have a good chance of surviving in captivity?
Aggressive predators such as sharks, groupers, snappers, jacks, eels, barracudas, and octopi are usually avoided because they are too disruptive. Occasionally, a very small snapper, grouper, or barracuda might be added, but they usually have to be removed after several weeks because they are extremely aggressive eaters and grow very quickly. Some species are excluded because of their destructive habits or because we cannot properly feed them. For example, juvenile food shrimp (Penaeid shrimp), which can be abundant in seagrass beds, are usually avoided because they uproot seagrasses in search of food. top
In order to make the exhibit aquaria more appealing to the public, all of the model ecosystems contain more organisms than their limited habitats can support. And obviously, exhibit inhabitants cannot relocate after they have exhausted the resources in one location. As a result, it is necessary to supplement the food webs of all of the model ecosystems.
Specimens targeted for supplemental feedings receive a wide variety of whole and commercially prepared frozen and freeze-dried foods, and some are even fed live foods. A feeding schedule tracks all feedings as to when, what, and how much is fed to each model ecosystem. The exhibit's fishes receive the most attention with two feedings a day. Additional feedings target the exhibit's crustaceans, corals, anemones, and miscellaneous invertebrates.
Many corals and other attached invertebrates feed on plankton. Unfortunately, the combination of too many potential predators and very limited environments make it is impossible to sustain enough plankton for these organisms. To supplement the diet of plankton feeding species, Artemia nauplii (baby brine shrimp) are cultured and regularly added to some of the model ecosystems. The Coral Reef Model Ecosystem receives nauplii every day and the Oculina Reef display receives Artemia nauplii every other day. The Seagrass display also receives nauplii less frequently.
It is also necessary to add live grass shrimp to the Seagrass Model Ecosystem on a regular basis, primarily for the slow-moving seahorses and pipefish. top
In an effort to ensure that all mechanical systems used to simulate the different environments are working properly, exhibit staff spend a good portion of the day monitoring the chemical and physical parameters, and checking and servicing the necessary life support equipment. top
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