September 15 2011,

The negative effects of iron in a reef ecosystem can easily be seen in the haunting image of a once pristine reef ecosystem turned into a dark mat of algae and microbes choking the colorful and diverse life off the reef. In a recent article in National Geographic, Enric Sala describes this “dark land of Mordor” he encountered when returning to remote Kingman Reef in the Pacific.

During the two-year span between when Sala last visited the thriving reef, something devastating had happened. Turns out a teak-hulled fishing vessel shipwrecked and was filled with items such as compressors, engines and other unidentifiable machinery high in iron that was slowly leeching out into the once iron-poor water creating a slow fertilization of reef-chocking algae.

According to a recent study published by The ISME Journal this month,  “reefs surrounding the shipwreck debris are characterized by high benthic cover of turf algae, macroalgae, cyanobacterial mats and corallimorphs, as well as particulate-laden, cloudy water. These sites also have very low coral and crustose coralline algal cover and are called black reefs because of the dark-colored benthic community and reduced clarity of the overlying water column.”

Pristine vs ‘black reefs’ on the Line Islands. Left column (top to bottom): Kingman Reef, Millennium Atoll, Malden Island (photos by Enric Sala). Right column (top to bottom): Black reef at Kingman, black reef at Millennium, and anchor chain killing corals at Jarvis Island (photos by Gareth Williams, David Obura and Mark Vermeij).

Even a more stark statement came from San Diego State University’s (SDSU) Linda Wegley, lead author of the study, “the black reefs show that a very small amount of some pollutant (in this case iron) can kill a large area of a pristine reef.”

So if this slowly-released iron from a shipwreck is killing a large reef, imagine what minute traces can do in the home reef aquarium. The hobby is filled with dreaded stories and pleas of help across the forums about algae outbreaks choking our contained systems and iron just may be one culprit we aren’t identifying or treating for.

Sure we bark about nutrient control and export and although it is difficult to test for iron in both fresh and saltwater, there are some steps you can take to reduce it in your system. The generic answer is to start at the source. Tap water can be a high source of iron and when you take steps to remove iron from your top off water it often can reduce outbreaks of dinoflagellates and other unwanted algae. Make sure you are using a quality RO/DI system and changing the filters and membranes on a regular basis.  Periodically use carbon and other water polishers like Clear Blue Pro or Purigen.

[via National Geographic]


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