PALAU — BAYER AND HARRT-ROFEN 499 



continued our homeward trip with one of the prize catches of the 

 expedition — some tiny black-and-yellow fishes little more than an inch 

 in length. 



In practically any protected sandy area of the lagoon we could ex- 

 pect to find the unusual partnership of shrimps and fishes that we 

 first observed at If aluk Atoll in 1953. We were delighted to find this 

 association at Palau in such shallow water and in such abundance 

 that we could observe it closely and collect the animals in numbers. 

 At Palau, two kinds of alpheid shrimps and at least four kinds of 

 gobies live together with identical habits. 



Each pair of shrimps excavates its own burrow and then plays 

 host to a pair of fishes. The fishes sit just outside the mouth of the 

 shrimp burrow (pi. 14, fig. 1) while the shrimps repair and deepen 

 it, bringing load after load of sand to the surface on their large claws, 

 bulldozer-fashion. But should any danger threaten, the gobies dart 

 down the hole in a trice, tumbling the shrimps over in their haste. 

 From this activity the shrimps detect that something is amiss and 

 cease digging until the gobies regain their composure and their usual 

 position on the front doorstep. Whether this inadvertent warning 

 is the only benefit derived by the shrimps from the association we are 

 unable to say at present. It seems probable that the gobies obtain, 

 in addition to shelter, an occasional banquet at the expense of their 

 hosts, since one of the specimens collected was stuffed with larval 

 crustaceans — probably the young of the shrimps whose home it had 

 shared. 



There is still much to be learned about these and various other rarely 

 observed biological associations, and it will take patient observation, 

 study, and experimentation in the field before we know the exact 

 nature of the relationship between the partners and how it may have 

 developed. 



THE OUTER REEFS 



The outer reefs have an entirely different appearance from the 

 lagoon reefs of Iwayama Bay and the staghorn coral thickets of the 

 shallow passes. On the west side of the archipelago the reefs are 

 barriers, but on the east they are fringing reefs that follow the land 

 closely, with an offshore barrier in only a few places. Whether barrier 

 or fringing reefs, they are bathed with the always clean water of the 

 open sea and pounded by its sometimes thunderous surf. Different 

 and stronger corals live in these exposed situations, and a whole new 

 population of fishes swims among their branches. The surgeonfishes, 

 butterflyfishes, and wrasses that live here are for the most part 

 peculiar to this zone of churning, turbulent water. Few species of 

 the quiet lagoon waters are hardy enough to adapt to this rigorous 

 environment. Sharks and barracudas in particular prefer this region, 



