Coral Reef Science:  Development Highlights

Habib Sekha

Effects of irradiance, flow, and colony pigmentation on the temperature microenvironment around corals: Implications for coral bleaching? Fabricius, Katharina E. Limnol. Oceanogr., 51(1), 2006, 30-37.


Experiments were conducted to determine the effects of colony pigmentation, irradiance, and flow on the temperature microenvironment that corals experience in shallow water. The warming of colony surfaces increased with increasing colony pigmentation (darker surfaces) and at high irradiance but was alleviated by higher water flow. Dark colonies were up to 1.5°C warmer than ambient seawater at high irradiance and slow flow. In contrast, very light colonies were similar in temperature to ambient water at all levels of flow and irradiance. The darkness of corals progressively increased along a gradient of decreasing water clarity from oligotrophic offshore reefs toward turbid high-nutrient reefs near the coast. The surface temperature of these darkly pigmented turbid-water corals was significantly greater than that of the paler corals in the clear-water environments at comparable seawater temperatures, light, and current conditions. The surface warming of darkly pigmented colonies in coastal environments is sufficiently high to exceed their bleaching threshold during warm, calm, and clear seawater conditions.


The above article suggests that darker-colored (brownish) corals might be susceptible to bleaching at a lower temperature than the more colorful (less brownish) corals. The explanation is that the darker corals absorb more heat (in the form of light) and get warmer compared to more colorful corals. It also suggests that water flow aids in lowering the temperature of the dark colored corals more towards the ambient water temperature. This is not surprising since a higher flow rate will facilitate a faster removal of heat.


Contribution of phytoplankton and bacterial cells to the measured alkalinity of seawater. Kim, Hyun-Cheol, Kitack Lee, and Wonyong Choi. Limnol. Oceanogr., 51(1), 2006, 331-338.


We report the first direct measurements of the contribution of phytoplankton and bacterial cells to the measured alkalinity of unfiltered seawater. Phytoplankton and bacterial cells suspended in seawater make a significant contribution to the measured alkalinity of unfiltered seawater; their contribution is probably next to that of borate ion in most seawater samples. This non-negligible contribution of particulate organic matter to the measured alkalinity is due largely to the presence of negatively charged surface groups on the phytoplankton and bacterial cells that react with protons during titration with hydrochloric acid. The contribution of organic particles to the measured alkalinity of unfiltered seawater could potentially be an important factor when evaluating the accuracy of presently available carbonate thermodynamic models using at-sea carbon system parameters that include measured alkalinity.


Sometimes hobbyists measure a high alkalinity when they start to cycle their tank with plenty of live rock. Often, that is not all true alkalinity but a significant part is caused by the presence of other things such as organics and bacteria blooms formed by the die-off and cycling processes. Just like the true alkalinity causing carbonate and bicarbonate, these organics can also neutralize acids.

Since alkalinity is measured by the amount of acid needed to more or less neutralize the previously mentioned compounds, these organics will show up as alkalinity in a test. This condition is known in aquarium situations and now scientists have demonstrated that even in often much cleaner natural seawater the floating bacteria and phytoplankton can show up as alkalinity because their outside surfaces can consume acid.

Eric Borneman

Allelopathy and Our Tanks:

While this is not a review of an article this month, a recent short thread developed on coral-list which is quoted below. I have edited the names of some for assumed anonymity and corrected a few typos in the post responses.

>>-----Original Message-----
From: ********

This is a picture of a coral a dog ate that developed progressive neurologic signs about two hours after the ingestion. The dog was ultimately euthanized because it was not breathing on its own, and the owners could not afford emergency care. I found some literature about corals that can have neurotoxins, specifically lophotoxins, and was wondering if it is possible that this could be one of those corals.

This particular coral was found on the beach in Jamaica and apparently is a leather consistency. Any ideas about what it might be would be helpful, and if it is possible, whether it could be a species that could be toxic as well as any information about coral toxins that you may have would be useful. Please feel free to forward the picture on if you know someone who might also be of assistance.<<

From: ******
Date: January 30, 2006 12:28:55 PM CST
Subject: [Coral-List] Toxic coral and a dog

Hi Coral listers,

Can anyone help determine the species of coral and whether it is toxic please? There is a link to the photo here:

From: ******
Date: January 30, 2006 6:43:40 PM CST
To: ******
Subject: Re: [Coral-List] Toxic coral and a dog

Dear Annie and Caroline: It is Briareum asbestinum, as Julian identified. We worked on the chemistry with Bill Fenical for many years, and it is not surprising that it is toxic enough to kill a dog. It's more surprising that the dog ate enough of what must have tasted very horrible to get a lethal dose. This species has high levels of chlorinated diterpenes, in addition to unidentified small proteins that might be in it. This species also has compounds in it that can trigger contact dermatitis and even respiratory issues for people who work with chemical extracts and dried samples of it regularly.

Below are some of our papers with Briareum; the most recent of these are available on my website.

Harvell, C. D., W. Fenical, V. Roussis, J. L. Ruesink, C. C. Griggs, C. H. Greene. 1993. Local and geographic variation in the defensive chemistry of a West Indian gorgonian coral (Briareum asbestinum). Marine Ecology Progress Series 93:165-173.

Harvell C. D., J. West, and C. C. Griggs. 1997. Chemical defense of embryos and larvae of a West Indian gorgonian coral, Briareum asbestinum. Invertebrate Reproduction and Development 30:239-246.

Jensen, P. R., C. D. Harvell, K. Wirtz, and W. Fenical. 1996. The incidence of anti-microbial activity among Caribbean gorgonians. Marine Biology 125:411-420.

Kim, K., P. D. Kim, A. P. Alker and C. D. Harvell. 2000. Antifungal properties of gorgonian corals. Marine Biology 137: 393-401

Editor's Notes:

Julian Sprung quickly responded with the identity of the coral. While Drew cited her works, there are others on the toxicity of this species, too. Recently, an aquarist asked me why he didn't see the effects of allelopathy in his tanks, and I responded that the effects might be subtle to severe and variable. This example is not unusual. The triple palytoxin poisoning of Anthony Calfo while propagating corals, the sensitization of people working with Goniopora, polychaete worms and zoanthids, all fit this pattern. I have written and repeatedly discussed during presentations regarding the potential seriousness of the toxins produced by most of the inhabitants in our tanks. My hands and arms bear dark spots of healing stings from working in my tanks on a nearly continuous basis. I preach to people to propagate soft corals outside their tank to avoid poisoning other things in the tank. The poisoning of the dog is a good example of the care that must be taken when dealing with the many species in our tanks - if not for our own safety, for those of children and pets who tend to put things in their mouths.

I thought the comment that Drew was surprised about a dog eating the gorgonian was odd. As dog owners can relate, I have seen them eat my cats' hairballs, feces, and all manner of what certainly cannot taste good. Cats find antifreeze palatable and are frequently poisoned by it. The toxicity of some of the novel compounds found in marine species can be among the most toxic on earth, lethal even in minute doses. So, I offer this story and warning to those who remove corals from their tanks, who leave corals on countertops while propagating them, who frequently handle marine livestock, and who have pets and children who could inadvertently become sick, or worse, from our own negligence and the nature of the species we take for granted in our tanks.

If you have any questions about this article or suggestions for future topics, please visit the respective author's forum on Reef Central (Eric Borneman's or Habib Sekha's).

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