Have you ever surfed off Kailua Beach? Or next to the Mokes off Lanikai? I haven’t yet had the pleasure, but I find it interesting that without reefs, many surf breaks wouldn’t exist. There would be nothing special underwater for the waves to pause on and curl over. Reefs are also are a kind of underwater speed bump for storms, providing some protection for the island against severe weather, but that’s all small potatoes compared to the other stuff reefs do!
25% of all marine species live in coral reefs, reefs worldwide feed over 500 million people (30 million of which have no other source of food), and the net annual benefit of Hawaii’s coral ecosystems has been estimated at 360 million dollars.
You’ve seen pieces of coral washed up on Kailua Beach, maybe bought some in stores at some point, but what exactly is coral? With a quick glance through a face mask one might assume that corals are plants or rocks, but corals are actually colonies of individual animals called polyps. An entire coral reef starts with just one polyp. “One polyp, singing in the darkness, all it takes is one polyp!” (Barry Manilow, anyone?)
Corals are female, male, or both. Regardless of their gender, they can reproduce both sexually and asexually. In an asexual budding, a new polyp is produced right next to its parent polyp and remains there, living and adding to the existing reef structure. In other words: with most species, one coral is an original polyp cloned over and over!
When corals reproduce sexually, they release eggs, sperm, or a package of both into the water. This is a highly synchronized event; it happens on a specific night during a certain phase of the moon, and each species releases its gametes during specific hours. This synchronization allows for more potential pairings between matching gametes, which creates more coral polyps and the potential for new reefs. Faaaantastic!
After drifting from its parents for a while and managing to avoid all the predators who would like to make a meal of it, sexually produced polyps settle . . . somewhere. Gee, sounds like my life. (Okay, not completely, but I had to say it!) Using chemical elements from the surrounding water, the polyp builds an outer limestone skeleton, into which it withdraws during the day. A reef hosts more predators during daylight hours, so it is safer for the polyp to take the night shift.
At night, the coral polyp rouses itself and, looking very much like a miniature sea anemone, reaches out small stinging tentacles to capture and eat plankton floating by. But that plankton only gives most corals 2% of the energy needed to live. Where does the rest come from?
Hydroelectricity?
Um, no.
Corals have a symbiotic relationship with certain types of algae called zooxanthellae (“zoh-oh-zan-THEH-lay”). The algae live inside the coral tissue that encases the limestone skeleton, and they spend the day photosynthesizing--transforming sunlight into energy--for themselves and the coral. In turn, the algae receive compounds from the coral needed for their photosynthesis and have a relatively safe place to stay. Algae give corals their color, and coral with algae can grow up to three times faster than coral without. Corals around Oahu can grow, tops, 1.3 inches per year.
It is important to keep in mind that in order for this relationship to work--for the algae to be comfortable living within their particular coral in its particular location--certain water conditions must be met. I’m a renter too, so I get it. The surrounding ocean’s temperature, light levels, and pH must remain within a certain range.
Most corals thrive in shallower waters, as sunlight is more accessible there. Pollution can cut down on the amount of sunlight available for photosynthesis. In Kailua, the storm water pollution entering Kaelepulu Stream (and subsequently Kailua Bay) has likely been lessened because of the new rain garden and repaving installed just across from Buzz’s Steakhouse.
Another threat to coral health is the human touch. The leading coral photographer and teacher Keoki Stender requests on his website “Take care to avoid touching live coral; their delicate flesh may be injured if pressed (even lightly) against the razor-sharp skeleton, allowing infection or algae to take hold, weakening and potentially killing the colony.” Mahalo to you for caring for what sustains us!
My thanks to the coral researchers and educators cited below who contributed to today’s column information. We shall continue our coralline journey next month when you, Dear Readers, can look forward to climate change! I bet you’ve never heard that before . . . be well!
Jury, C. (2012, October). Coral Adaptation to Hotter, More Acidic Oceans. Hanauma Bay Education Program Lecture Series. Lecture conducted from Hanauma Bay, Honolulu, HI.
Chaston, K. (2012, October). Managing Coral Reefs from Reef to Ridge. Hanauma Bay Education Program Lecture Series. Lecture conducted from Hanauma Bay, Honolulu, HI.
Walton, M. (2012, October). Coral Disease in Oahu’s Marine Life Conservation Districts. Hanauma Bay Education Program Lecture Series. Lecture conducted from Hanauma Bay, Honolulu, HI.
Silbiger, N. (2012, October). Bioerosion of Coral Reefs. Hanauma Bay Education Program Lecture Series. Lecture conducted from Hanauma Bay, Honolulu, HI.
Carrier, S. (2013, January). Perceptions of Coastal Resource Managers in Hawaii: The Current Situation and Outlook for the Future. Hanauma Bay Education Program Lecture Series. Lecture conducted from Hanauma Bay, Honolulu, HI.
Holmes, M. (Producer). (2001). Coral Seas. [Television series episode]. In A. Fothergill (Series Producer), The Blue Planet: Seas of Life. London: BBC.
The above column was originally posted in March of 2013, in the online newsletter kailua411.com. It was reprinted here with permission from the publisher. The newsletter is no longer online. The reef photo was taken in November of 2016, off Papawai Point in Maui.