Are certain algae getting bad press? When is a lot of algae too much algae??

By Rodney Withall

The effects of algal blooms seem to frequently make news headlines. Whether we all pay attention to it or not, most of us have seen images of algal blooms from around the world and the problems that are associated with them. These can range from toxin production that contaminates our food supply, the formation or massive unsightly and inconvenient masses, or effects on the ecosystem community such as coral reefs.

Australian sailors training on a bed of algae at the Olympic sailing venue at Qingdao in China. (Photo: AFP)

An algal bloom is a rapid increase in the population of a particular (or multiple) species of algae. In recent years we’ve read about the effects of blooms; including toxin producing microscopic algae in the Atlantic that have closed the shellfish industry from Maine to Long Island, NY. In 2008, over 10,000 workers and 1000 boats were tasked with removing algae off the coast of Qingdao, China after a huge algal bloom formed at the sailing venue prior to the Beijing Olympics. At the same time, the first macroalgal blooms at Midway and Kure Atolls (the two northern-most atolls in the Papahānamokuākea Marine National Monument) were being reported by CRED divers. On this occasion, Boodlea composita, a bright green branched filamentous alga that forms dense spongy mats, was rapidly increasing and covering the shallow water reef lagoon habitats of these two atolls.

Boodlea composita surrounding a colony of Pocillopora meandrina at Kure atoll in 2009.

To most people, Boodlea blooms are viewed in negative light as they are thought to over-grow live coral colonies and block light penetration, however, even though this may be true in some cases, reports indicate that, in 2008, blooming Boodlea grew mostly over sand and rubble substrata. It should also be noted that some positive observations associated with Boodlea blooms can lead to a confounding situation and confusing assessment as to the real impacts and net outcome these blooms can have. Some of the positive observations include a larger abundance of juvenile fish being reported around dense Boodlea cover and Hawaiian Monk seals being observed resting on thick mats of Boodlea that wash ashore.

Since the initial observation of Boodlea blooms at Kure and Midway Atolls, scientists from the Coral Reef Ecosystem Division and other programs have been monitoring the increase or decline of Boodlea populations. I was fortunate enough to sail aboard the Hi`ialakai to both Kure and Midway atolls in September 2009 as part of a RAMP (Reef Assessment and Monitoring Program) cruise with the Papahānamokuākea Marine National Monument. We observed Boodlea distributions and densities that were not dissimilar to those reported the year prior in 2008, and visiting the Northwestern Hawaii Islands again this year is an opportunity to note distributional patterns for 2010.

A dense mat of Boodlea at a lagoon site in 2009.

A few days ago we observed and reported that Boodlea is also now blooming at the lagoon sites we surveyed at Pearl and Hermes, an atoll 81 nautical miles to the southeast of Midway. The density and distribution seemed considerable, however, the benthic team surveyed too few sites in the lagoon to map the extent of the distribution. These observations may represent the first scientific documentation of Boodlea blooming at Pearl and Hermes and may be further evidence that blooms are spreading throughout the archipelago.

Today was our second day of diving at Kure with sites from the forereef, backreef, and lagoon surveyed on each day. Although we have another day of reef assessment left at this atoll, our preliminary data and qualitative observations that we make while transiting from one site to another in the lagoon suggest that the severity of the Boodlea has declined at Kure. In witnessing this decline, I also noted evidence of Boodlea induced changes in the reef that were of particular interest to me.

Since Boodlea has the ability to over-grow or out-compete many coral species due to its more rapid growth rate, this species can quickly create a shading or light blocking effect, particularly surrounding or between the living portions of the coral Porites compressa. During Line Point Intercept surveys at one of our fairly shallow long-term lagoon monitoring sites yesterday, I noticed recently dead calcified red algae that normally thrive in light spectrums that are characteristic of dark shaded areas, under over-hangs or in much deeper water. All that remained of these delicate calcium depositing algae were their bleached-out white calcium carbonate crusts. I began to wonder if dense Boodlea mats once covered these portions of reef and were in fact creating conditions favorable for calcified red algal growth. Gently removing masses of spongy green algae soon answered my question. Yes!, I found healthy, thriving delicate calcified red algae underneath each piece of Boodlea that I removed. Considering that most calcified algae grow at and can deposit calcium carbonate more rapidly than most stony corals, I began to wonder if Boodlea blooms were actually helping a sinking atoll grow by creating more suitable habitat for coralline algal growth. Despite its bad reputation for over-growing coral in some places, it’s quite possible that there are great benefits that we don’t see upon initial superficial inspections.

Calcified red algae that typically grow in deep or dark shaded water were observed growing at shallow depths under dense sections of Boodlea at Kure in 2010.

Perhaps this served as a reminder to me that a good scientist has an objective mind rather than a judgmental one whom draws quick conclusions. It will be some time before we completely understand the net effect of Boodlea blooms at these atolls, but as for the blooming algae at the Olympic venue in Qingdao, well, I think I’ll plan to attend the London 2012 Olympics just in case their sailing venue has an algal bloom of comparable proportions.