Compared with the coral reef biota, the diversity of organisms inhabiting marine lakes is poorly known. Of just 14 publications describing the marine lakes, only two are taxonomic (Fautin & Fitt, 1991; Lipps & Langer, 1999). There has been no thorough description of the biodiversity of any marine lake although they likely contain many species new to science . The reasons for this are two-fold. First, the marine lakes likely facilitate founder events, allopatry, and novel selective regimes and, as such, are expected to harbor many endemic organisms. Second, the marine lakes are unexplored environments located in a relatively poorly explored part of the most biodiverse region of the world—the Indo-West Pacific—so, even if some species are not endemic to the marine lakes, there is still a high probability that they will be new to science.

Consistent with these expectations, researches in the marine lakes have found, among others, a new species of anemone (Fautin & Fitt, 1991), endemic jellyfishes (Hamner & Hauri, 1981), and sponges with novel biochemical properties (Reddy et al., 1997, 1998). Molecular analyses have revealed three distinct species of moon jellyfish in the marine lakes, coves, and lagoon around Palau (Dawson & Jacobs, 2001). Preliminary studies in the marine lakes by CRRF and collaborating taxonomists, undertaken as part of their contract with the National Cancer Institute, have found new species of ascidians in the marine lakes and recorded genera new to the Indo-Pacific (e.g. Cliothoosa and Desmanthus).

One of our major research endeavours currently underway is to catologue species diversity in a cross-section of the marine lakes, ranging from holomictic to meromictic, from the largest to one of the smallest, and from those that are geographically distant to those that are adjacent. They include lakes used by tourists, non-tourist 'reference' lakes, and lakes that are part of our long-term project monitoring climatic effects on lake populations. A major goal of this work is to increase the knowledge of patterns of biodiversity in Palau for application in the conservation and sustainable use of the marine lakes.