In Micronesia, snapping shrimps occurred in endolithic habitats that were previously unknown or poorly described. Alpheus malleodigitus lived in tunnel systems in massive and branching species of Porites. Systems up to 232 mm long were recognized as bands of dead coral,
up to 35 mm wide, punctuated by circular ports. Dead zones contained algal turfs and debris. Some ports were surrounded by live coral. At Malakal, Palau, up to 80% of the massive Porites colonies had tunnel systems. A. obesomanus occurred in tunnels in Millepora platyphylla
in Guam, Palau, and Pohnpei and in Heliopora coerulea in Palau and Pohnpei, but not in Guam. In Millepora, tunnels were characterized by zones of dead coral having several ports and covered by coralline algae and Millepora regrowth. At Guam up to 95% of the colonies surveyed
had shrimp tunnels. In Heliopora, ports marking younger systems were individually surrounded by small zones of dead coral whereas older systems had several ports per zone. Dead zones contained debris and filamentous and coralline algae. In all three corals, some systems were markedly
depressed below the usual coral surface. At Guam, A. idiocheles occupied sub-hemispherical galleries in an intertidal erosion bench. Galleries in the study area numbered up to 45/m2 and averaged about 15 cm3 in volume. A gallery was usually inhabited by a male-female
pair of shrimp.
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