Research by marine biologists from Wageningen University has shown that feeding on zooplankton by scleractinian corals has been greatly underestimated.
|A first report: Pocillopora eydouxi spawning in Hawai’i, and other observations|
|Written by Dana Riddle and Sara Peck|
Dana Riddle and Sara Peck report about Pocillopora eydouxi (Milne-Edwards and Haime, 1860) spawning in Hawai'i. This is the first documented Hawaiian spawning of this unique Indo-Pacific species.
Figure 1: The Antler Coral (Pocillopora eydouxi) in shallow water at Kahalu’u Beach Park, Big Island of Hawai’i (photograph courtesy of Bo Parda).
Pocillopora eydouxi (Milne-Edwards & Haime, 1860)
Pocillopora eydouxi (pronounced ey-dew-eye), often called the Antler Coral, has a wide geographical distribution with colonies reported on the west coast of Central and South America, Hawaii, the Indo-Pacific Ocean, western Pacific and the Red Sea (Veron, 2000).
These corals are often found in environments exposed to strong wave action or water currents. The skeletal structures of another Pocillopora (meandrina) inhabiting the same environments as P. eydouxi are very dense with high tensile strength (Rogers, 2001) and are more resistant to breakage than other corals examined (such as Porites lobata, Porites compressa, and Montipora capitata – now M. verrucosa).
Wave action is often associated with shallow water, and P. eydouxi can often be found in water at a depth of less than 0.3 meter (~1 foot, although this species occurs at much deeper depths as well). However, living in very shallow water would necessitate that these corals’ symbiotic algae ( zooxanthellae) are tolerant of warmer water, high light and ultraviolet radiation. P. eydouxi colonies in American Samoa are known to contain Symbiodinium (zooxanthellae) belonging to Clade D, which is known to be more heat resistant than many other clades (Smith et al., 2008). LaJeunesse et al. (2004) report that shallow-water P. eydouxi colonies in Hawai’i, the central Great Barrier Reef (Feather Reef), Okinawa, Japan and the eastern Pacific (Panama) all contain zooxanthellae of Clade C1c. Simple observations suggest that Clade C1c is tolerant of environmental extremes seen in the waters of Hawai’i.
To our knowledge, the spawning behaviour of P. eydouxi has never been documented. Observations providing the following data were made at the Kahalu’u Beach Park located on the west (leeward) side of the Big Island of Hawai’i on June 9th and 10th, 2009 by Bo and Jamie Pardau (the spawning event of June 9th was also observed by Riddle). Based on these limited observations, we offer the following.
Figure 2: Spawning time of P. eydouxi relative to moon phase, based on limited observations. Note that spawning time is similar to that of P. meandrina, which spawns at full moon as well (Riddle & Peck, 2009).
P. eydouxi spawns in June at ~0645 hours, which is about 1 hour after the ‘official’ sunrise time of 0549 (in our case, sunrise occurs later because the volcanic summits to the east of Kona block the sun). This species is hermaphroditic, and spawn collected from one colony was capable of ‘selfing’ (self-fertilization). Interestingly, the same colony spawned two days in a row (June 9th and 10th, two and three days after the full moon, respectivelym see Figure 2). Low tide occurred at 0950 hours on the 9th, and 1027 hours on the 10th – (3.08 hours and 3.7 hours, respectively, after the spawning events). A single colony was observed spawning and based upon this observation, we report P. eydouxi is sexually mature at a diameter of about 35 cm (~14 inches). Growth rates for P. eydouxi (at Barber’s Point, Oahu, Hawai’i) averaged 4.6 cm (~1.8 inches) per year (Kolinski, 2007). Assuming 35 cm is the minimum size at which P. eydouxi reproduces, this means this species is sexually mature in 7-8 years (this number will be refined as more data are collected).
Note that Bentis et al. (2000) report a growth rate of P. eydouxi near Johnston Atoll of ~5 cm (2.02 inches) per year. In surveyed areas in Hawaii, adult colonies rarely exceed 100 cm (40 inches) in diameter (Kolinski, 2007) or 90 cm (36 inches) in height (Gulko, 1998).
"Pocillopora eydouxi is hermaphroditic, and spawn collected from one colony was capable of selfing."
In the laboratory we made further observations, many of which were surprisingly similar to previous reports of spawning by another Pocilloporid – P. meandrina. Oocytes (eggs) contain zooxanthellae that are obtained from the parent colony (vertical transmission). Eggs are small even for corals – 80 microns or less, and in the laboratory under conditions of no water movement, are negatively buoyant.
Spawning of Pocillopora meandrina, a closely related species, in Hawai'i (video: Denise Ulrich).
Planula larvae are apparent within 24 hours after the spawning event. These do not contain any of the green fluorescent proteins (GFPs) which would make recruits visible as fluorescent dots when viewed under ultraviolet or blue light. Attempts to induce settlement of planula larvae did not meet with success, however they were maintained in captivity for about 9 days after the spawning event.
Identification of P. eydouxi
Pocillopora species can be difficult to distinguish from one another. Certainly, environmental factors (particularly water motion) can influence the morphology of the skeleton. Colonies can be rather compact where wave action is intense (such as that in the introductory photograph) but grow in the shape of an antler in calmer water. In addition, it is possible that hybridisation amongst species can blur the traits generally considered characteristic of a species. Geographical partitioning can produce endemic species. However, two sources (Gulko, 1998; Conruyt et al., 1997) report the presence of columellae within the calyx to be a defining feature of P. eydouxi (figure 3).
Figure 3: Detail of skeletal structures. The presence of columellae in some corallites suggests this animal is P. eydouxi (photograph by Dana Riddle).
Conclusions and other observations
Our limited observations are offered as an initial report only. We will continue with our efforts and will offer updates as they become available.
The spawning habits of P. eydouxi in Hawaii are very similar to those of Pocillopora meandrina.
These similarities exist:
As with P. meandrina, the environmental triggers for eydouxi spawning are poorly understood. Temperature could play a part, as well as the amount of solar insolation, moon phase and others. We obviously have a lot to learn, but knowledge of reproductive timing is a critical first step in deciphering the mysteries surrounding the habits of this animal. Veron (2000) suggests inter-breeding among some Pocillopora species is possible, and it is an interesting thought that simultaneous spawning of P. meandrina and P. eydouxi might result in hybrids.
Growth rates reported for P. eydouxi by Kolinski (2007) and Bentis et al. (2007) are remarkably similar for central Pacific P. eydouxi corals. Growth rates of about 5 cm (2 inches) per year were reported in both locales.
P. eydouxi has the traits of an r-strategist: They are sexually mature at a relatively young age, have high fecundity, display opportunistic colonisation, have a relatively short lifespan, and so on. This coral is adept at exploiting harsh environments.
While Smith et al. (2008) report American Samoan P. eydouxi to contain Clade D zooxanthellae, LaJeunesse et al. (2004) found specimens from Hawai’i, the Great Barrier Reef, eastern Pacific and Japan to contain Clade C1c. Since Pocilloporids are generally thought to obtain zooxanthellae from the parent colony, this suggests several possibilities:
1. P. eydouxi could consist of two or more groups with different distinct zooxanthellae populations;
2. These corals simultaneously harbour more than one zooxanthellae clade (with one or more clade populations falling below the detection limit of current research instruments);
3. Pocillopora species have a high fidelity to a particular clade until pressured to obtain another type (switching from vertical transmission to horizontal acquisition).
"Knowledge of reproductive timing is a critical first step in deciphering the mysteries surrounding the habits of this animal."
P. eydouxi possesses exceptional skeletal strength and is probably similar to that found in its close relative P. meandrina. Rogers (2001) calculated that a force of 25 Megapascals (~3,625 pounds per square inch) is required to break P. meandrina’s skeleton.
The ReefWatchers along the west coast of the Island of Hawai’i have a rather unique opportunity to document the early life history of this common species. We are preparing to gather more information and further our understanding of P. eydouxi’s early life stages.
Special thanks to Bo and Jamie Pardau for their unusual dedication and hard work. As difficult as it is for some to believe, getting up before sunrise in Hawai’i and plunging into seawater cooled by the night air can be a real challenge!
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Conruyt, N., G. Faure, G. Ancel, J. Le Renard, M. Guillaume, O. Naim, N. Gravier-Bonnet, and D. Grosser, 1997. A knowledge base for corals of the Mascarene Archipelago: genus Pocillopora. Proc. 8th Int. Coral Reef Symp., Panama. 2: 1549-1554
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Hirose, M., R. Kinzie III, and M. Hidaka, 2000. Early development of zooxanthellae-containing eggs of the corals Pocillopora verrucosa and P. eydouxi with special reference to the distribution of zooxanthellae. Biol. Bull., 199:68-75.
Kolinski, S., 2007. Recovery projections for the scleractinian corals injured in the M/V Cape Flattery incident, Oahu, Hawaii, 2005. National Marine Fisheries Service.
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Rogers, K., 2001. A quantitative evaluation of trampling effects on Hawai’i’s coral reefs. Master’s Thesis, University of Hawai’i.
Smith, L., H. Wirsbing, A. Baker and C. Birkeland, 2008. Environmental versus genetic influences on growth rates of the corals Pocillopora eydouxi and Porites lobata (Anthozoa: Scleractinia). Pac. Sci., 62, 1:57-69.
Veron, J.E.N., 2000. Corals of the World. Australian Institute of Marine Science, Townsville. 1382 pp.