6^th International Symposium on Ecohydraulics: bridging the gap between hydraulics and biology - Chrischurch, Februar 18^th-23^th, 2007.

Oral presentation : Impact of ship-induced waves on benthic invertebrates colonising littoral habitats. Garcia XF, Gabel F, Hochmuth H, Brauns M, Sukhodolov A, Pusch M.

Abstract

Ship-induced waves disturb benthic invertebrate assemblages inhabiting the littoral zones of lakes and rivers, resulting in low abundance and species diversity in boat-wash zones. However, the factors influencing the degree of dislodgment of invertebrates by waves were never addressed nor quantified.

In this study, we investigated in an experimental wave channel, if the structural complexity of the littoral habitats may reduce the adverse effect of ship-induced waves on benthic invertebrates.

Three different substrate-types (sand, reeds and roots) were combined with six levels of degradation to provide seven habitats with contrasted levels of structural complexity, as quantified using the Frontier's fractal geometry method. Five benthic invertebrate species (Bithynia tentaculata, Calopteryx splendens, Cloeon dipterum, Dikerogammarus villosus, Laccophilus hyalinus) were exposed to waves of increasing strengths (shear stress range: 4.3-21.9 dyn/cm2) in each habitat.

Benthic invertebrates exposed to waves of increasing shear stress were least detached in root habitats. The overall detachment rate of species was significantly higher in habitats with low structural complexity (r=0.73, p<0.01) in the following sequence: sand, low reed density, high reed density, degraded and non-degraded root bunch. However, a species-specific response to habitat-type was also observed, as species-specific fixing or hiding capabilities matched habitat-specific physical characteristics. The detachment rates were positively correlated (r=0.88, p<0.05) with the dissipation of the kinetic energy of the waves due to habitat complexity. Hence, complex-shaped habitats like tree-roots provide the best sheltering conditions against hydraulic disturbances, because they combine refuges availability and maximal dissipation of the kinetic energy. As a consequence, the negative effects of boat traffic on littoral invertebrate assemblages is drastically increased as soon as complex littoral habitats like tree-roots or dense reed belts are degraded and disappear by frequent exposition to wave action or other human impacts.

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