Current Research


Currently I am investigating the effect of an amphidromous life-history strategy on the persistence of metapopulations of tropical freshwater gobies. Amphidromy refers to a type of diadromy where juveniles and adults live and breed in freshwater while the larval stage is completed in marine waters.  Amphidromous species often exist in metapopulations that are comprised of semi-isolated adult sub-populations (streams) that only achieve connectivity via larval dispersal in marine waters and the subsequent post-larval recruitment back to fresh water. This pelagic larval stage lasts on average from 65 to 266 days for sicydiine gobies depending on the species.

Specifically, my research is focused on the dispersal capability of the larvae of two Sicydiine gobies (Stiphodon pelewensis and Stiphodon caeruleus) while in marine waters around the island of Pohnpei, Micronesia. S. caeruleus is endemic to Micronesia, having only been reported from the islands of Pohnpei and Kosrae.  S. cf. elegans exhibits a more widespread distribution, putatively ranging throughout much of Oceania.  These reported distributions are in contrast to their mean pelagic larval duration (PLD), which is longer for S. caeruleus (88.6 days) than for S. pelewensis (65.8 days)

Once the marine larval stage is complete, amphidromous gobies tend to gather at the mouth of fresh water streams.  It is believed that entering this low salinity environment triggers morphological changes, primarily to the shape of the head and orientation of the mouth, as they begin their juvenile life-history stage.  The post-larval juveniles often recruit into the rivers en mass with pulses of large schools of fish swimming upstream toward their adult habitat.  For many species the preferred adult habitats are only found in the upper reaches of streams and rivers, which on volcanic islands may require
climbing up to 600 m above sea level in a matter of only 10s of kilometers.  These rivers are typically fast flowing over rocky substrate and often have a number of waterfalls between the mouth and the headwaters.  Juvenile amphidromous gobies are very well adapted to climb even the tallest of waterfalls, some as high as 100 m.  Using their specialized ventral fins, which have evolved into a circular suction-cup like appendage on their abdomen, they are able to stick to the shear face of most moist surfaces.  With an undulating motion these young gobies inch their way up and over these vertical barriers and reach preferred adult habitats in a matter of days to weeks, depending on the species.

A waterfall on the Ngardmar River,

Palau 2009


An adult river goby (Stiphodon pelewensis) in the Senipehn River, Ponape, Micronesia - 2009

Using small specialized spears, Joe Hall and Sunny Brenneman snorkel a river in Palau to collect goby specimens - 2009

Click to see a video of a rock climbing goby!