Many studies have proved the importance of hard substrata in marine ecosystems as numerous organisms depend on hard substrata because of its structural and functional heterogeneity. With the increase of artificial hard substrata, it is essential to understand understanding the community composition of these ecosystems. For example, with the increase of wind farms in the Belgian part of the North Sea (BPNS) accurate sampling of hard substrata fouling communities including rare and non-indigenous species is important. This study focuses on the qualification and quantification of the efficiency and accuracy of hard substrate sampling methods. From previous studies, the airlift suction sampler was found to be the most efficient method to sample hard substrata epifauna as the quadrat techniques underestimate the species density (loss of individuals during sampling). For this study, the efficiency and feasibility of three airlift devices with different tube diameter – 5,80 cm; 4,46 cm and 2,81 cm- was tested at three levels: (1) species and taxon density, (2) diversity, and (3) community structure. Samples were collected from concrete blocks outside the Revellata bay located on the western coast of Corsica. Randomly, five replicates were collected from the horizontal and vertical surfaces of the concrete blocks using different airlift diameters. A total of 2903 ind. m-2 spread over 147 species was identified. Only hard substratum related species were collected with the airlift devices. No matter which airlift device, the mean surface density are considerably higher in samples collected from the horizontal surface (4003 ind. m-2) than the samples collected from the vertical surface (2489 ind. m-2). The latter difference might be related to loss of sampling material on the vertical surface and less on the difference in community structure between both surfaces as no significant difference in algae cover was observed. The impact of the three different airlift diameter devices showed no statistically significant difference in density, diversity and community structure. No significant difference does not necessarily means no difference as significance is also depending on the intrinsic variability and hence degree of replication. This study showed that all three airlift diameters were accurate in sampling hard substrata. From a practical point of view, the medium-sized airlift device is more easily to operate at certain depth as the small-sized airlift device has the risk of clogging depending on the hard substrata coverage while the large-sized airlift device is more difficult to operate. |
