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Vol. 52, 2013
Palythoa zoanthid
‘barrens’ in Okinawa: examination of possible environmental causes
Sung-Yin
Yang*, Carine Bourgeois, Carey Denise Ashworth and James Davis Reimer
Graduate
School of Engineering and Science, University of the Ryukyus, 1 Senbaru
Nishihara, Okinawa 903-0213, Japan
Abstract
Background: Coral reefs are among
the most diversified ecosystems in the world, but suffer from
anthropogenic and natural disturbances, often causing a shift from
coral to algal (or other benthic groups) dominated ecosystems. Linking
benthic communities’ information with water quality data is urgently
needed to understand current and future changes in benthic dominance.
This research examined possible environmental causes on the abundance
of the zoanthid Palythoa tuberculosa on Okinawa Island in
southern Japan. Various water parameters (temperature, dissolved
oxygen, salinity, pH, particulate organic matter, chlorophyll a, NO2-N, NO3-N,
PO4-P, NH4-N, and the distance to the river
mouth) were recorded along with benthic community composition at eight
locations.
Results: Turf algae, coralline algae, or sand,
rubble and rock dominated most locations in this survey. Coral coverage
was moderate (10% to 40%). P.
tuberculosa was generally low in abundance, but common at
Mizugama (9% of the benthic community) and Oku (25%). Water parameters
varied among sites. Salinity was the only parameter correlated with the
abundance of Palythoa (R2 a = 0.47). P. tuberculosa had a positive
relationship with the presence of coralline algae, Pocillopora, Goniastrea, and Porites, and had negative
correlation with turf algae and other invertebrates.
Conclusions: Likely no single
parameter is related to the coverage of P. tuberculosa on Okinawa Island.
Nutrients were found at low concentrations at the sites, and may
explain why there was no strong relationship observed between P. tuberculosa and nutrients. Based
on these first results, further long-term monitoring combined with the
collection of additional environmental data and benthic surveys are
needed to better explain the abundance of P. tuberculosa. Such data would be
particularly helpful to understand how reef organisms will interact
with their environment under scenarios of future climate change.
Key words: Water parameters; Reef benthic
community; Phase shift; Zoanthid.
*Correspondence: E-mail: likefh@gmail.com
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