Maupiti on its way to becoming an atoll. Submerged reef appears in pale blue. Photo: NASA EARTH OBSERVATORY

South Pacific coral reef island formations have intrigued geologists: Fringing reefs, like Tahiti, have a shelf growing close to the island’s shore. Barrier reefs, like Bora Bora, are separated from the main island by a calm lagoon. An atoll displays as a ring of coral enclosing a lagoon with no center island. How reefs develop into these shapes over evolutionary time was explained by two hypotheses, one from Charles Darwin, the other by geologist Reginald Daly.

Darwin’s theory says that that fringing reefs, barrier reefs and atolls reflect different stages as an island sinks into the ocean floor: as the coral grows upward and the island sinks down, a fringing reef progresses to a barrier reef, and eventually to a signature atoll. This theory fails to explain all ocean islands we see today, such as the progression of Hawaiian Islands.

Daly argued that sea-level cycles were the key to understanding coral formations. Sea level drops during ice ages would expose reefs to increased wave energy and erode an island away. The coral would then regrow on submerged island platforms as sea level rose again as the ice melts.

Researches modeled the two scenarios separately and then together. By taking Darwin’s theory and adding in sea-level history based on geological evidence and paleoclimate data they were able to produce a coral-reef distribution that matched up well with the real-world observations.

More on the research at phys.org and geology.org

Start with the Right Water

The safest solution is to put the water through a purification process before it is added into any tank. The preferred method by most aquarists is a series filter system that combines reverse osmosis (RO) and deionization (DI). Reverse osmosis is the process of forcing a solvent (here, water) from a region of high solute (the impurities) concentration through a semipermeable membrane to a region of low solute concentration by applying pressure. The semipermeable membrane keeps the ions and compounds we don’t want on one side while allowing “pure” water to pass through. Deionization removes charged compounds by filtering the water through a deionizing resin. There are also sediment filters and activated carbon filters that are often used in conjunction with a RO/DI system to keep these parts operating properly. A typical water filtration system would filter water in this order:

• Sediment Filter: This does exactly what its name implies: filter sediment. Sediment can clog activated carbon filters and damage RO membranes.
• Activated Carbon: Primarily used to break down chlorine and chloramine and possibly other organic chemicals.
• Reverse Osmosis (RO): Purifies based on the size of molecules allowed through the membrane, the goal being allow water molecules through and anything larger stays behind. It does need to be noted that a number of compounds of concern to reef aquarist can pass through a reverse osmosis membrane to some extent: carbon dioxide (CO₂), ammonia (NH₃), hydrogen sulfide (H₂S) and silicic acid (Si(OH)₄). All of these should be trapped by the DI resins
• Deionization Resins (DI): These trap all charged molecules passing through, allowing just neutral (uncharged) molecules to pass through. The resin consists of porous beads that have fixed charges attached to them and different beads are used to bind cations (positive charge) and anions (negative charge).

There are many water filtration systems available for purchase that will produce purified water for use in your marine, reef, or fresh water tank. You may also be able to purchase RO/DI water from a local pet or aquarium retailer or similar source.

Mixing Saltwater

1. You will need a mixing container that holds at least 5 to 10 percent of the volume of water your display tank holds – i.e. if you have a 100 gallon tank, your container needs have the ability to hold at least 5 – 10 gallons. Old aquariums, clean storage containers, and new garbage cans are popular choices.

2. Next, fill the container with your RO/DI freshwater.

3. It’s a good practice to aerate RO water for 12-24 hours before mixing in the salt. This will help drive off excess CO2 so you get a proper pH and buffering capacity in your mixed seawater.

4. Follow the manufacturer’s instructions on your salt. You want to match the mixing tank salinity to that of your aquarium. Use a refractometer to measure the salinity and adjust accordingly. (Ideally, salinity should be 27 to 35 parts per thousand (ppt), or

5. Your freshly mixed seawater is very caustic and needs time to cure a minimum or 24 hours before it can be used in your aquarium. While it cures, use an airstone or powerhead in the water to circulate and aerate the mixture and put in a heater to make it match the water temperature of your display tank.

You spend a lot of time and money on your tank. Having extra saltwater ready to use provides extra insurance for those unforeseen accidents and the minimal investment in a container, powerhead, and heater is well worth the small cost and effort.

See our reef keeping chemistry article Salinity and Saltwater for more information.
References
1. http://water.epa.gov/drink/contaminants/index.cfm
2. http://reefkeeping.com/issues/2005-05/rhf/index.php#8

At the Smithsonian’s Tropical Research Institute in Panama, Andrew Sellers of the Smithsonian’s Tropical Research Institute is turning the lionfish invasion into an opportunity to study which Atlantic parasites are adopting the lionfish as a host. Believed to have been dumped into the Atlantic off southern Florida sometime around the late 1980s, this invasive is now found as far north as Virginia and south to Venezuela, and still spreading.

Because of their rapid spread they provide a good model for testing the theory that invasive species don’t do as well in the tropics as they do in temperate areas; stronger competition for food, predators and parasitism in the tropics may limit the success of an invasive species. More at Smithsonian Science

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