In the Oueme River, a lowland river in Benin, Africa, artificial ponds constructed in the floodplain (whedos) are colonized during the high-water period by a presumably random sample of fishes from the river channel. As water slowly recedes from the floodplain, fishes are isolated in whedos until they are harvested near the end of the dry season. I surveyed fishes in whedos and adjacent main-channel and floodplain habitats during two low-water (2008 and 2009) and one falling-water (2010-2011) periods, and measured a suite of physicochemical variables including dissolved oxygen, temperature, specific conductivity, and percent cover of aquatic vegetation in the falling-water period to investigate if fish assemblage structure of whedos resulted from stochastic or deterministic processes. I also investigated food web structure of whedos by analyzing carbon (delta13C) and nitrogen (delta15N) stable isotope ratios of fish and primary producer tissue samples, and samples of net primary production, soluble reactive phosphorus (SRP), NH4+, NO2-, and NO3- collected during the falling-water period. Whedos were covered with dense growth of aquatic vegetation, and dissolved oxygen concentrations were lower in whedos compared to a natural floodplain depression and the main channel. Multivariate analyses revealed that habitat types were distinct with regard to fish assemblage structure and abiotic conditions. Assemblages in whedos and natural floodplain depressions were differentiated from those of the river channel, with the floodplain habitats being dominated by piscivorous fishes that tolerate aquatic hypoxia. These results indicate that fish assemblage structure of whedos was influenced by deterministic processes during the falling- and low-water periods when these water bodies were isolated. Floodplain habitats were more nutrient-rich than the river channel, and whedos were net heterotrophic. Microphytobenthos and C3 macrophytes accounted for a large fraction of fish biomass in whedos, compared with the river channel, which was mainly supported by seston. Whedo food webs had fewer trophic transfers compared to the food web of the river channel.

Global climate change has become an increasing source of concern due to the recent build-up of greenhouses gases in the atmosphere. The rocky intertidal zone, as the interface between land and sea, is particularly vulnerable to climate change. Many inhabitants of the intertidal zone are sessile and thus experience both terrestrial and aquatic lifestyles at low and high tides, respectively. When emersed at low tide, organisms experience a number of abiotic stresses including heat stress, desiccation stress, and low oxygen availability. Most intertidal organisms have evolved from marine animals and respire most efficiently in water. Barnacles are one such type of intertidal organism. At low tide barnacles face a tradeoff between access to oxygen and loss of water through evaporation. In this study, individuals of the species Balanus glandula, a common intertidal barnacle, were exposed to temperatures of 16°C, 24°C, 30°C, and 35°C for four hours in simulated low tide to determine when aerial respiration occurred. Oxygen levels were measured over the four hours of the exposure and oxygen consumption rates were calculated. Oxygen consumption occurred at all temperatures studied, but the rates at different temperatures were not significantly different from each other. The results showed that barnacles can conduct aerial respiration over the entire course of the low tide exposure despite the risk of desiccation. This indicates that ATP demand remains substantial throughout the low tide and that resorting to anaerobic respiration is not sufficient to meet metabolic needs during low tide exposure.