Abundance, edge effect, and seasonality of fauna in mixed-species seagrass meadows in southwest Sulawesi, Indonesia

Abstract

Motile fauna species in two mixed-species seagrass meadows with different canopy structure were studied on an uninhabited island in the Spermonde Archipelago, Sulawesi, Indonesia. The main focus of the study was to assess the edge effect and seasonal abundance of macrobenthic invertebrates. Fish and infauna densities were determined as well. Fauna was counted using permanent transects (macrobenthic invertebrates), visual census (fish species), and sediment cores (infauna). Both meadows had a comparable distribution of motile fauna species with polychaetes (35% of total abundance), bivalves (27%) and sipunculids (25%) accounting for the largest part of the total faunal abundance. The closed canopy meadow (high seagrass leaf biomass) had an overall higher faunal abundance compared with the open canopy meadow (low seagrass leaf biomass) (1133 vs. 751 individuals m⁻²). Although infauna abundance was comparable between the meadows, macrobenthic invertebrates (crustaceans, echinoderms, and molluscs) and fishes were more abundant in the closed canopy meadow, with only a few individual species more abundant in the open canopy meadow. The effect of distance from the meadow edge on macrobenthic invertebrate abundance was significant, with higher abundances towards the interior of the seagrass meadows, but for fish abundance no significant differences were found. Effects of seasonality (rainy vs. dry season) on macrobenthic invertebrate abundance were only significant for molluscs. We concluded that macrobenthic invertebrate abundance was most influenced by seagrass canopy structure, followed by meadow edge effects, and least by seasonality. Comparisons of faunal abundance in seagrass meadows need thus to include information on these three variables.

Keywords:

• Fish
• infauna
• macrobenthos
• seagrass–fauna interactions
• tropical seagrasses

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

We thank Piet Nienhuis, Christian Mulder and both anonymous reviewers for comments on the manuscript, Alfian Noor for administrative arrangements in Indonesia, and Klaas Strating, Marjolein Pijnappels, and Saido for assistance with sampling. This research was funded by NWO-WOTRO grant W86-168, Schure-Beijerinck-Popping grant SBP/JK/2005-44 and the Department of Environmental Science, Radboud University Nijmegen.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark