Papers Published
Abstract:
We measured growth and survival in field enclosures of juvenile Rivulus marmoratus under a variety of biotic (effects of body mass and intraspecific density) and abiotic conditions (seasonal climatic changes, site-specific hypoxia). We also tested three different enclosure types, surface-floating buckets (0.021 m3), and tubes (0.006 m3) positioned at the surface or on the bottom. Growth rate was inversely correlated with wet body mass (between 6 and 42 mg) and density (1-16 fish/0.021 m3 enclosure). However, density did not affect survival. Growth was significantly lower in tubes placed on the bottom than at the surface. There were considerable differences in growth and survival among sites. This likely is due to differences in occurrence and persistence of hypoxic events. At the Catfish Creek location (a pool surrounded by black mangroves), the bottom was routinely hypoxic. At a shallow bay site, hypoxia was episodic: on the bottom at dawn (O2) < 2 mg/l occurred on nine of 48 days, with values < 1 mg/l on two of 48 days. Maximum growth rates (3.5-4%/day) were recorded in February to May, in comparison with lower values in December to January. However, low growth rates also occurred in the spring, probably caused by episodic hypoxia.