MEPS 486:237-245 (2013)  -  DOI: https://doi.org/10.3354/meps10370

ABSTRACT: The considerable quantities of dead wood in the intertidal zone of mature mangrove forests are tunnelled by bivalves of the family Teredinidae. When the surface of heavily tunnelled wood is broken open, cryptofauna are able to use tunnels as refuges. In this study, the exploitation of this niche during low tide by the dartfish Parioglossus interruptus was investigated. The majority of tunnels offer a close fit falling within the range of typical dartfish diameters. The fish found within wood tended to be smaller than fish found swimming between mangrove roots at high tide. Dartfish were found in tunnelled wood even where it was emersed for over 11 h d^-1, but favoured wood in the lower intertidal. Within the wood, daytime thermal maxima were reduced by 6.5°C compared with adjacent tidepools. Wind-tunnel observations indicated that this lowering could be due to evaporative cooling. However, dartfish were found to be notably tolerant of high temperatures, with a critical thermal maximum that exceeded temperatures reached in tunnelled wood and pools. Nonetheless, such tolerance may impose a metabolic cost that would be reduced by occupying tunnels. Teredinid tunnels are also likely to give dartfish protection from desiccation and predation. During high-tide, free-swimming dartfish were observed to favour areas of Rhizophora roots over open creeks. In aquaria, fish swam actively during the day, but took refuge in teredinid tunnels at night. Sampling of wood at low tide and direct observations at high tide indicate that a substantial proportion of the dartfish population takes refuge in wood during low tide. Thus, teredinid-tunnelled wood is a key low-tide refuge especially for younger fish, which would otherwise be exposed to predators. This study provides an example of a mechanism whereby mangrove forests support intertidal biodiversity.

KEY WORDS: Teredinidae · Cryptofauna · Niche-creation · Mangrove wood · Thermal tolerance