INTRODUCTION
The nation of Palau is situated in south-western Micronesia, and is noted for its beautiful coral reefs, despite being impacted by the worldwide bleaching event of 1998 (Bruno et al., Reference Bruno, Siddon, Witman, Colin and Toscano2001). Regardless of the overall good health of coral reefs, and a long history of coral reef research (Kawaguti, Reference Kawaguti and Kawaguti1940, Reference Kawaguti and Kawaguti1941, Reference Kawaguti and Kawaguti1942), very little is known about the species diversity of many groups of marine invertebrates in Palau, and no focused museum collection exists for this part of the world.
One such taxon for which almost no records from Palau exist are the zoanthids (Anthozoa: Hexacorallia: Zoantharia), an order of benthic cnidarians most closely related to the sea anemones (Fujii & Reimer, Reference Fujii and Reimer2011; Kayal et al., Reference Kayal, Roure, Philippe, Collins and Lavrov2013). Zoanthids are found in most marine environments, and some species are very common in shallow subtropical and tropical waters (Karlson, Reference Karlson1980; Irei et al., Reference Irei, Nozawa and Reimer2011). While recent research has reported on species diversity from several locations in the Pacific (e.g. Australia in Burnett et al., Reference Burnett, Benzie, Beardmore and Ryland1997; Galapagos in Reimer et al., Reference Reimer, Sinniger and Hickman2008), there are very little data from Micronesia in general (but see Paulay et al., Reference Paulay, Puglisi and Starmer2003), and Palau in particular (Colin, Reference Colin2009).
Within the zoanthids, the family Microzoanthidae Fujii & Reimer, Reference Fujii and Reimer2011 was recently described from specimens collected from numerous locations across the Pacific, including Okinawa, mainland Japan, Singapore, Thailand, Australia, and the Galapagos. Currently, there is only one genus and two species described in this family, Microzoanthus occultus Fujii & Reimer, Reference Fujii and Reimer2011 and M. kagerou Fujii & Reimer, Reference Fujii and Reimer2011. However, given the small size of individual polyps (diameter approximately 0.5 mm) and their cryptic habitat in cracks or on the undersides of coral rubble in shallow coral reefs, it has been speculated that these species may be widely distributed throughout the subtropical and tropical Pacific, and perhaps locally common (Fujii & Reimer, Reference Fujii and Reimer2011).
As part of a research project investigating the biodiversity of marine invertebrates in Palau, surveys were conducted to assess the biodiversity on zoanthids in Palau. Here, we report on one unexpected finding of Microzoanthidae from these surveys.
MATERIALS, METHODS AND RESULTS
During surveys of zoanthid diversity in Palau in December 2012 and March 2013, clusters of small colonial anthozoans (polyp diameter approximately 5 mm) were noticed in shaded areas on the sides of seawater outflow pipes at Palau Mariculture Development Center (Malakal Island, Koror; 7°19′43″N 134°27′1″E) (Figure 1A) and were the dominant benthos, far outnumbering the only other benthic organism observed (Aipstasia anemones). Detailed images, collection, and examination identified these to be the microzoanthid Microzoanthus kagerou, as polyps were clearly zoanthids with two rows of tentacles and sand encrustation, and had a white zigzagged pattern around the edge of oral discs with narrow stolons between polyps as is characteristic of this species (Figure 1B).
Specimens are currently housed at the Palau International Coral Reef Center (PICRC), Koror, under specimen number PICRC-SATREPS no.1. It is planned to deposit this specimen in the Belau National Museum, Koror once a marine invertebrate collection is established there in the near future.
Sampling locality of Microzoanthidae: (A) location of outflow pipes at Palau Mariculture Development Center (PMDC), Malakal Island, Koror. Arrows indicate areas of the outflow pipes where specimens were found; (B) Microzoanthus kagerou in situ at PMDC. Arrows indicate individual polyps. Scale bar: approximately 1 cm.
DISCUSSION
This is the first record of Microzoanthidae from Palau, and by extension in Micronesia. Previous reports exist for Japan, Singapore, Thailand, Australia, and the Galapagos (Reimer et al., Reference Reimer, Sinniger and Hickman2008, Reference Reimer, Obuchi, Irei, Fujii and Nozawa2011; Fujii & Reimer, Reference Fujii and Reimer2011), and other photographic evidence exists from Indonesia (Reimer & Hoeksema, unpublished data). This record helps to confirm the hypothesis put forward in the original description that Microzoanthidae are likely widespread throughout the Pacific (Fujii & Reimer, Reference Fujii and Reimer2011).
Azooxanthellate Microzoanthidae has previously been reported from shaded cracks and the undersides of coral rubble (Reimer et al., Reference Reimer, Sinniger and Hickman2008, Reference Reimer, Obuchi, Irei, Fujii and Nozawa2011; Fujii & Reimer, Reference Fujii and Reimer2011). This is the first report of their occurrence as a biofouling organism. However, based on their ecology, the presence of Microzoanthidae in outflow pipes was not unexpected as planktonivores can find outflow pipes to be potentially excellent sources of nutrition (e.g. O'Neill & MacNeill, Reference O'Neill and MacNeill1991). Outflow pipes are also safe from wave action and severe weather disturbances common in shallow reefs. It is interesting to note that, despite extensive searches during a zoanthid diversity survey of Palau by the first author in March 2013, no Microzoanthidae were found in coral reef environments.
Species in this family evidently prefer dark, shaded areas on reefs in small cracks or under rocks, in environments with high levels of current or waves, and outflow pipes fit well with this description. Future biodiversity surveys that include Microzoanthidae in their scope would be well served by checking outflow pipes of any seawater fisheries hatcheries.
ACKNOWLEDGEMENTS
This research was supported by the Science and Technology Research Partnership for Sustainable Development (SATREPS), ‘Project for sustainable management of coral reef and island ecosystems: responding to the threat of climate change' in Palau, funded by the Japan Science and Technology Agency (JST) and the Japan International Cooperation Agency (JICA) in cooperation with the Palau International Coral Reef Center (PICRC) and Palau Community College (PCC). Randa Jonathan at PICRC is thanked for logistical support. Two anonymous referees' comments greatly improved this manuscript. This is contribution Palau-SATREPS no.1.
