Behavioral and Physiological Responses of an Amphibious, Euryhaline Mangrove Fish to Acute Salinity Exposure
Amphibious fishes moving over land between aquatic habitats likely encounter abrupt changes in a number of environmental conditions, including salinity. This study characterized the 1) spatial heterogeneity in salinity in the mangrove forest habitat of the self-fertilizing, amphibious mangrove rivulus (Kryptolebias marmoratus), 2) metabolic cost and behavioral response to acute exposure to novel salinity, and 3) repeatability of individual responses to acute changes in salinity. In mangrove habitats on Long Caye, Belize, salinity varied widely over short distances from 20.9–41.7‰ over a 90 cm distance. In the lab, fish were exposed to an acute change in salinity of Δ10, 20, or 30‰. Oxygen consumption significantly decreased in response to a 10‰ decrease in salinity and increased when salinity was elevated by 30‰. Activity levels significantly increased with an increase in salinity (Δ20 and 30‰). Individuals showed repeatable differences in both oxygen consumption rates and activity levels. Together, our data show that K. marmoratus is highly responsive to abrupt increases in salinity. Thus, movements made by K. marmoratus between temporary pools in the mangrove forest will acutely alter behavior and possibly metabolism, with many potential ecological consequences.
Spatial distribution of crab burrows in Long Caye, Belize (December 2012). Salinity concentrations of each burrow are provided in parts per thousand, with high concentrations (hypersaline) in red and low concentrations (hyposaline) in blue. Distance in meters (m) is indicated by the scale bar.
Box plots displaying the influence of acute salinity change on oxygen consumption. A significant increase in SMR was observed in response to 45‰ (t = 3.46, P < 0.001), while exposure to 5‰ significantly decreased SMR (t = −3.19, P = 0.002). No significant change in SMR was observed in response to 35‰ (t = 0.371, P = 0.71). Control salinity was 15‰. Each box plot indicates the 25th, 50th (thickest line), and 75th percentiles. Whiskers on each box represent the 10th and 90th percentiles. All points falling outside the 10th and 90th percentiles are represented by individual data points. The red square in each box represents the mean for each treatment. 60 individuals were tested in control conditions and 20 individuals were placed in each treatment.
Box plots displaying the influence of acute osmotic shock on activity. Activity significantly increased in response to both hypersaline treatments (35‰: t = 2.985, P = 0.0035 and 45‰: t = 2.737, P = 0.0072). In hyposaline conditions, activity did not significantly change (t = −1.155, P = 0.25). Control salinity was 15‰. Each box plot indicates the 25th, 50th (thickest line), and 75th percentiles. Whiskers on each box represent the 10th and 90th percentiles. All points falling outside the 10th and 90th percentiles are represented by individual data points. The red square in each box represents the mean for each treatment. 60 individuals were tested in control conditions and 20 individuals were placed in each treatment.
Contributor Notes
Associate Editor: K. Martin.