Food habits of the farmer damselfishStegastes nigricansinferred by stomach content, stable isotope, and fatty acid composition analyses

Abstract

This content has not been published or submitted for publication elsewhere in any language, and all authors have contributed significantly, and are in agreement with the content of the manuscript. 2 AbstractThe territorial damselfish, Stegastes nigricans, maintains algal farms by excluding invading herbivores and weeding unpalatable algae from its territories. In Okinawa, Japan, S. nigricans farms are exclusively dominated by Polysiphonia sp., a highly digestible filamentous rhodophyte. This study was aimed at determining the diet of S.nigricans in Okinawa and its dependency on these almost-monoculture algal farms based on stomach contents and chemical analyses. Stomach content analyses revealed that all available food items in the algal farms (i.e., algae, benthic animal inhabitants, trapped detritus) were contained in fish stomachs, but amorphous organic matter accounted for 68% of the contents. Therefore, carbon and nitrogen stable isotope ratios and fatty acid (FA) compositions were analyzed to trace items actually assimilated in their bodies. Stable isotope analyses showed that benthic animals were an important food source even for this farmer fish. Two essential FAs (EFA), 20:4n6 and 20:5n3, which are produced only by rhodophytes among available food items, were rich in the muscle tissue of S. nigricans as well as in algal mats and detritus, suggesting that algal mats contribute EFAs to S. nigricans directly and indirectly through the food web. In conclusion, S. nigricans ingested algal mats, detritus and benthic animals maintained within its farm. Algae and detritus were original sources of EFAs, and benthic animals, which were much more abundant in the farms than in outside territories, provided a nitrogen-rich dietary source for the fish.

Resource use of two damselfishes, Stegastes planifrons and Stegastes adustus, on Guadeloupean reefs (Lesser Antilles): Inference from stomach content and stable isotope analysis

“…Calculations were performed on each food source and the fractionations obtained were then averaged in each situation. We found similar fractionation factors for the four situations, and these values were in agreement with previous studies on Stegastes (Hata and Umezawa, 2011;Mill et al, 2007). Due to their similarity, we used mean C and N fractionation factors (± 95% CI) for the four mixing models: Δ 13 C = 1.6 ± 0.5‰ for carbon and Δ 15 N = 5.1 ± 0.4‰ for nitrogen.…”

“…However, the comparison of their trophic niches has received little attention, in contrast to damselfishes in other regions (Frédérich et al, 2009;Hata and Umezawa, 2011;Ho et al, 2009).…”

Farming behaviour of reef fishes increases the prevalence of coral disease associated microbes and black band disease

“…It is likely that S. nigricans has a less diverse assemblage of turf algae because they cultivate a thick mat of Polysiphonia sp. (figure 1), a highly filamentous turf that readily retains detritus and is one of the main food sources of Stegastes [64][65][66][67][68]. When cultivated to reach high densities, such as inside S. nigricans's territories, Polysiphonia sp.…”

Intra- and interspecific challenges modulate cortisol but not androgen levels in a year-round territorial damselfish

“…This sexually monomorphic damselfish holds solitary year-round territories in small colonies within coral reefs (Karino and Kuwamura, 1997). They live from the algae growing in their territory, which both sexes fiercely defend against any species that passes (Ceccarelli, 2004;Hata and Umezawa, 2011). As long as animals are not reproductively active (females spawn in male territories), the territory serves similar functions in males and females, and both intra-and interspecific intrusions may convey a similar threat.…”

“…This prediction is in line with the recently proposed 'finite state machine' theory, which emphasizes that Intra-and interspecific challenges modulate cortisol but not androgen levels in a year-round territorial damselfish , 1997). They live from the algae growing in their territory, which both sexes fiercely defend against any species that passes (Ceccarelli, 2004;Hata and Umezawa, 2011). As long as animals are not reproductively active (females spawn in male territories), the territory serves similar functions in males and females, and both intra-and interspecific intrusions may convey a similar threat.…”