Carbon and nitrogen stable isotope turnover rates and diet–tissue discrimination in Florida manatees (Trichechus manatus latirostris)

Abstract

SUMMARYThe Florida manatee (Trichechus manatus latirostris) is a herbivorous marine mammal that occupies freshwater, estuarine and marine habitats. Despite being considered endangered, relatively little is known about its feeding ecology. The present study expands on previous work on manatee feeding ecology by providing critical baseline parameters for accurate isotopic data interpretation. Stable carbon and nitrogen isotope ratios were examined over a period of more than 1 year in the epidermis of rescued Florida manatees that were transitioning from a diet of aquatic forage to terrestrial forage (lettuce). The mean half-life for 13 C turnover was 53 and 59 days for skin from manatees rescued from coastal and riverine regions, respectively. The mean halflife for 15 N turnover was 27 and 58 days, respectively. Because of these slow turnover rates, carbon and nitrogen stable isotope analysis in manatee epidermis is useful in summarizing average dietary intake over a long period of time rather than assessing recent diet. In addition to turnover rate, a diet-tissue discrimination value of 2.8‰ for 13 C was calculated for long-term captive manatees on a lettuce diet. Determining both turnover rate and diet-tissue discrimination is essential in order to accurately interpret stable isotope data.

Feeding preferences of West Indian manatees in Florida, Belize, and Puerto Rico as indicated by stable isotope analysis

“…This pattern is consistent with findings in previous studies (e.g. Reich & Worthy 2006, Alves-Stanley & Worthy 2009). Aquatic plants incorporate carbon from the dissolved inorganic carbon (DIC) in the surrounding water into their tissues.…”

“…To accurately interpret isotopic results, it is important to know the diet -tissue discrimination value (the difference in isotope ratios between the diet and consumer tissue) as well as the turnover rate (the amount of time required to incorporate isotopes from the diet into the tissue). Previous studies have calculated or estimated diet -tissue discrimination values and turnover rates for carbon and nitrogen isotopes in manatee skin (Ames et al 1996, Reich & Worthy 2006, Alves-Stanley & Worthy 2009), allowing for more accurate interpretation of stable isotope data.…”

“…To accurately interpret isotopic results, it is important to know the diet -tissue discrimination value (the difference in isotope ratios between the diet and consumer tissue) as well as the turnover rate (the amount of time required to incorporate isotopes from the diet into the tissue). Previous studies have calculated or estimated diet -tissue discrimination values and turnover rates for carbon and nitrogen isotopes in manatee skin (Ames et al 1996, Reich & Worthy 2006, Alves-Stanley & Worthy 2009, allowing for more accurate interpretation of stable isotope data.The present study is the first to apply stable isotope analysis to Antillean manatees and further expands the assessment of the feeding ecology of Florida manatees. The objectives of this study were to (1) analyze δ 13 C and δ 15 N values in epidermal samples collected from free-ranging manatees in Florida, Belize, and Puerto Rico, (2) compare signatures in the skin to those of freshwater, estuarine, and marine vegetation within the presumed manatee diet, and (3) assess possible differences in feeding preferences by region, sex, age class, and season.…”

Isotope turnover rates and diet-tissue discrimination in skin ofex situBottlenose Dolphins (Tursiops truncatus)

“…Ramsay and Hobson, 1991;Ames et al, 1996;Walker et al, 1999;Kurle and Worthy, 2002;Yamamuro et al, 2004;Lee et al, 2005;Newsome et al, 2006;Reich and Worthy, 2006;Alves-Stanley and Worthy, 2009;Witteveen et al, 2011). Stable isotope analysis utilizes naturally occurring isotopes, such as those of nitrogen and carbon, which are passed from prey to consumer and are reflected in the consumer's tissues.…”

Stable isotopes of captive cetaceans (killer whales and bottlenose dolphins)

“…Nitrogen ( 15 N/ 14 N) and carbon ( 13 C/ 12 C) stable isotopes are used to denote a species' position within the food web and to trace the origin of trophic resources exploited by the species, respectively. Stable isotope analysis is especially advantageous when investigating the feeding ecology and habitat use of marine mammals, where it is often impossible to directly observe feeding or migratory behaviour (Alves-Stanley and Worthy, 2009;Newsome et al, 2010a), and provides information on assimilated foods (not just ingested foods) as well as time-integrated information (Dalerum and Angerbjörn, 2005). Moreover, the complex spatial, temporal and behavioural variation in trophic systems makes linking foraging behaviour to prey populations difficult (Kelly, 1996).…”