Diversity, dynamics and trophic ecology of animal communities associated to Posidonia oceanica (L.) Delile macrophytodetrital accumulation: synthesis of a ten year study

Diversity, dynamics and trophic ecology of animal communities associated to

Posidonia oceanica (L.) Delile macrophytodetrital accumulation: synthesis of a

ten year study

v

Lepoint G.

_{, Borges A.V.}

_{, Champenois W.}

_{, Darchambeau F.}

_{, Dauby P.}

_{, Gobert S.}

_{, Mascart}

T.

_{, Michel L. N.}

_{, Remy F.}

_{, Sturaro N.}

_{and De Troch M.}

1. _{Laboratory of Oceanology (Ulg);} 2. _{Chemical Oceanography (Ulg);} 3. _{Diversity and Animal Systematics (Ulg), Belgium} 4. _{Marine Biology, (UGent), Belgium}

Introduction

Pictures of P. oceanica litter accumulation (10 m depth, Calvi Bay, Corsica, NW Mediterranean)

• 50-90 % P. oceanica biomass fuels detrital

pathway

• Large fraction is exported as dead leaves

• May form large litter accumulation in

shallow coastal areas

Objectives

• To determine litter distribution and composition (not shown)

• To characterize their physico-chemistry

• To characterize animal assemblage

• To study trophic web and trophic ecology

Work in progress since 2005 in Calvi Bay (Corsica) at STARESO marine station (ULg)

H₂S and other reduced compounds

L Sediment Water column PO₄,NH₄+ O₂

O

₂

O₂ PO₄, NH₄+ *Oxidation of reduced compounds (e.g. H₂S) *Nitrification *OM Degradation O₂ C_inorg Photosynthesis by epiphytes and drift plants C_inorg O₂ Nutrients Litter R e la ti v e a b u n d a n c e ( % ) 0 5 0 1 0 0 A r th r o p o d a A n n e lid a M o llu s c a E c h i n o d e r m a t a N e m e r te a P la ty h e lm in t h e s C h o r d a t a Gammarella fucicola = 40 % of individual number • Meiofauna dominated by Harpacticoid copepods

• Dominated by less than 10 species

• For both meiofauna and macrofauna:

• less diversity than in seagrass meadow

• but larger density (x 3 to x5)

• Main species tolerant to O₂ depletion

Gut contents species

Resemblance: D1 Euclidean distance

SPECIES GF GA MH PX AN GI HL IB SL LH NGU GSPP LN NS 2D Stress: 0,05 Increased Animal proportion Algal dominance Dead seagrass dominance Gammarella fucicola Melita hergensis Gammarus aequicauda Nototropis guttatus Nebalia strausi Athanas nitescens Palaemon xiphias

Fish juveniles and

Gobius sp. Galathea intermedia Gut Content Bittium reticulatum Stable isotopes • G. aequicauda • 15 – 20 % of animal density • 50-80 % assimilated C comes from dead

seagrass

• G. fucicola

• >40% of animal density

• 20 – 30% assimilated C comes from dead

seagrass

TAKE HOME MESSAGE

Posidonia litters, found everywhere and every time, are a main actor of the « DARK SIDE » of C cycle in seagrass meadows, represent a huge amount of exported carbon, host complex animal assemblages, less

diverse but more abundant than in the bed. This fauna consumes and assimilates seagrass carbon

Publications related

to this project

See also: Champenois & Borges. Limnology and Oceanography (2012), 57(1), 347-361

Faunal assemblage

Trophic web

-25 -20 -15 -10 -2 0 2 4 6 8 δ13_C δ 15 N Gf Ga Mh Ngu Ib Sl Ac An Px Pe Hl Ml Ln Lh Gi Ns Pspp Br Gspp Dead leaves Living leaves Epiphyte s/algae SPOM