The ecology of the marine lakes offers fascinating opportunities for research because they harbor marine species in an unusually enclosed situation. The marine lakes have all of the components of other marine ecosystems—allochthanous input, primary production, competition, predation, mutualism, nutrient export, etc.—but greatly reduced in complexity and scale. Each of the salt lakes presents an unique natural experiment in the organization of food webs—the interdependence of life forms (Hamner, 1982). Moreover, the marine lakes allow us to study firsthand the ecological and other consequences of allopatric evolution in marine taxa, an opportunity that is not guaranteed elsewhere. However, semi-enclosed estuaries do have many of the properties of marine lakes, and some of the properties of more open marine ecosystems. Consequently, estuaries provide the conceptual and experimental links that help integrate model marine lake ecosystems with the "real world" of oceanographers.

Regarding the ecology of the marine lakes, our principal undertaking at this time is the continuation and extension of a monitoring program begun in December 1998, in reaction to massive changes in the marine lakes precipitated by the severe 1997/98 El Niño/La Niña (ENSO) event (CRRF Tech. Rep. 2, [301 KB, PDF]). The severity of the event raised awareness worldwide of the potentially dire repercussions of climate change. Subsequent events have emphasized the fact that marine lakes are fragile, dynamic ecosystems, susceptible to climatic perturbations. For example:

Jellyfish Lake (Ongeim’l Tketau), Mecherchar. In 1998, the previously perennial population of endemic golden jellyfish medusae, Mastigias sp., disappeared from Jellyfish Lake. This event, which had important socio-economic repercussions (see below), likely was due to atypically high water temperatures (up to 35°C) that inhibited strobilation of new medusae and bleached Mastigias sp. polyps (Dawson et al., 2001;see the jellyfish life-cycle). In addition, moon-jellyfish, Aurelia sp., and endemic anemone, Entacmaea medusivora, populations became smaller than usual and/or individuals looked unhealthy (e.g. inverted bells/polyps and other deformations) although neither population disappeared. The Mastigias population took approximately 1.5 years to recover and since has been subjected to at least two massive dysoxic events which killed all polyps and other benthic fauna and flora below approximately 10 meters (Dawson et al., unpubl. data), indicating continued disturbance of the ecosystem.

Goby Lake, Koror. The endemic population of Mastigias sp. medusae in Goby Lake was decimated by the ENSO perturbation (Dawson et al., 2001). However, a strobilation event in November 1998 prevented the complete loss of medusae. Other biota in Goby Lake also were affected detrimentally, for example, the green alga, Caulerpa sertularioides, experienced a dramatic die-back. These changes also were coincident with unusually warm and salty waters. In late-summer 2001, Goby Lake, like Ongeim'l Tketau, suffered a massive dysoxic event which dramatically reduced the abundance of Mastigias in the lake and coincided with the absence of an as yet unidentified hydromedusa that usually is abundant in the lake.

Lake 10, Urukthapel. The abundances of the green alga, Caulerpa serrulata, and many species of sponges were reduced dramatically; at least one new species of sponge was extirpated. The diverse sponge fauna was replaced by an almost monotypic mussel bed. These changes also were associated with warmer and saltier waters. Notably, in summer 1999, Lake 10 became fully mixed (holomictic) in contrast to its usual meromictic state (Hamner & Hamner, 1998).