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Stable isotope ratios suggest limited trophic importance of seagrasses for invertebrate consumers from Malagasy tropical polyspecific seagrass meadows
Michel, Loïc; Wang, Haolin; Frederich, Bruno et al.
2015Zoology 2015
Editorial reviewed
 

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Keywords :
seagrass; food web; stable isotopes; madagascar; anthropogenic impacts
Abstract :
[en] Polyspecific seagrass meadows are of critical ecological importance in tropical coastal zones. These ecosystems provide a wide range of socio-economical services to local populations. Meadows however undergo multiple threats linked to human activities (increased nutrient input, overfishing, invertebrate overharvesting, etc.). It is currently difficult to assess how seagrass meadows could respond to anthropogenic impacts due to poor knowledge of their functional ecology. Here, stable isotope ratios of carbon, nitrogen and sulfur were used to unravel trophic interactions ruling the food webs associated to seagrass beds of the Toliara Great Reef (SW Madagascar). The contributions of various potential food items (sediment-associated and suspended particulate organic matter, plankton, leaves, roots and epiphytes of 7 seagrasses and thalli of 7 dominant macroalgae) to the diet of 20 invertebrate taxa (one sea urchin, 2 sea stars, 2 sea cucumbers, 5 gastropods including one sea hare, one bivalve, 2 amphipods, one leptostracan, one cumacean 2 hermit crabs and 3 shrimps) were assessed using a Bayesian stable isotope mixing model. Model outputs revealed that important trophic diversity existed among the invertebrate assemblage. In some groups (e.g. hermit crabs and amphipods), resource use by morphologically and taxonomically close taxa was markedly different. Many of the dominant taxa heavily relied on macroalgae for their nutrition. On the other hand, few species apparently consumed seagrass tissues. Moreover, when they did, seagrass generally accounted for a minor portion of the diet only. Overall, our results suggest that seagrass grazing in meadows of the Toliara Great Reef could be lower than in other tropical areas. These discrepancies could be linked with seasonal variation in resource availability or with eutrophication. Higher nutrient load is indeed known to cause ecosystem phase shifts and it may induce diet shift to algivory in some invertebrate consumers.
Research center :
MARE - Centre Interfacultaire de Recherches en Océanologie - ULiège
Disciplines :
Aquatic sciences & oceanology
Environmental sciences & ecology
Zoology
Author, co-author :
Michel, Loïc  ;  Université de Liège > Département de Biologie, Ecologie et Evolution > Océanologie
Wang, Haolin
Frederich, Bruno  ;  Université de Liège > Département de Biologie, Ecologie et Evolution > Morphologie fonctionnelle et évolutive
Lavitra, Thierry;  Instituts d'Halieutique et de Sciences Marine de Tuléar (Madagascar) > Polyaquaculture Unit
Lepoint, Gilles  ;  Université de Liège > Département de Biologie, Ecologie et Evolution > Océanologie
Language :
English
Title :
Stable isotope ratios suggest limited trophic importance of seagrasses for invertebrate consumers from Malagasy tropical polyspecific seagrass meadows
Publication date :
09 October 2015
Event name :
Zoology 2015
Event organizer :
Royal Dutch Zoological Society
University of Amsterdam
Royal Belgian Zoological Society
Event place :
Amsterdam, Netherlands
Event date :
08 & 09/10/2015
Audience :
International
Peer reviewed :
Editorial reviewed
Funders :
F.R.S.-FNRS - Fonds de la Recherche Scientifique [BE]
Available on ORBi :
since 07 October 2015

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