Habitat associations of fish-parasitic gnathiid isopods in a shallow reef system in the central Philippines
Gnathiid isopods are among the most common ectoparasitic organisms infesting marine fishes in benthic marine environments, and are best known in coral reef ecosystems. These micropredators are ecologically important, as they can impact their hosts directly through blood loss and tissue damage, and indirectly by transmitting blood parasites. Their abundance, and thus expected impact on hosts, varies greatly over multiple spatial scales. Most studies on gnathiids in coral reef systems have been conducted in the Caribbean and on the Great Barrier Reef, Australia, with few studies conducted in the heart of marine biodiversity, the “Coral Triangle”. This is the first field study of gnathiid ecology in the Philippines. The primary goals of this study were to characterize substrate associations and diel activity patterns of gnathiids in shallow reef areas. Gnathiid larvae were found to infest at least 28 species of hosts and were found in both seagrass and reef habitats. Within reef habitat, there was a significant difference in gnathiid abundance among coral reef substrates. Gnathiid larvae were most abundant in coral rubble substrates and least abundant on live hard coral. This is in spite of host abundance (fish) being greater near live coral. More and larger-sized gnathiids were collected from dusk to dawn compared to daytime, and gnathiids were able to find hosts using non-visual sensory cues. Our results are, thus, consistent with previous studies in the Caribbean.
KeywordsEctoparasite Micropredator Coral reef Coral Triangle Diel activity
The authors thank the late Mayor Emmanuel Diputado, the Department of Agriculture and the Bantay Dagat of the Sibulan Municipality for logistic support and permitting access to the marine sanctuary of Agan-an. We also thank the director, Dr. Hilconida P. Calumpong, Dr. Janet S. Estacion, Dr. Rene A. Abesamis, and the staff of Silliman University Institute for Environmental and Marine Sciences for assistance and use of lab space. We thank Dianne Mira Yap, Danielle Mark Fukuda, Jean Asuncion Utzurrum, Floramae Joyce Neri, Denzyl Divinagracia, Persie Mark Sienes, and Mary Shodipo for the field assistance. Finally, we thank Dioscoro Inocencio, Rafael Ceriales, Andres B. Tubat, Paseo Tubat, and Jose G. Somoza Sr. for fish collections and field support, and Nico J. Smit for assistance with gnathiid species identification. This work was funded in part by the US National Science Foundation (OCE-1536794, PC Sikkel, PI).
Compliance with ethical standards
The use and care of animals used in this study was approved by the Arkansas State University Institutional Animal Care and Use Committee (IACUC) protocol number 778227-1. All other applicable international, national, and institutional guidelines for the care and use of animals were followed.
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