The tube-building polychaete Lanice conchilega has been thoroughly studied for the past few years. While it is classified as a reef builder, ecosystem engineer, its role in sediment dynamics in the benthos has fueled many discussions with contradictory results from a range of studies. Moreover, spatial fluctuations for those structures remain uncertain, raising questions as to the longevity of its engineering capacities due to its susceptibility to natural catastrophes. The present work set out to enlighten those controversial issues by posing the following to test: how physical properties of sand mason aggregations in combination with hydrodynamic forcing drive patch dynamics; how do reef patch boundaries evolve over time. Furthermore, the endeavor aimed at evaluating a promising methodology in the field of spatial ecology at fulfilling the second aforementioned goal, kite aerial photography. A flume experiment was executed testing the effects of patch height, tube presence, and tube nature in sediment stability, while monthly sampling campaigns (from January until May) acquired sets of aerial images from a sand flat in Boulogne-sur-mer (France), animal tube density values, and patch relative height transects. The images were treated and used to assemble mosaics of the site from which patch surface area were extracted for comparison, while separate testing was carried out with tube density and patch height transects. All data was compared statistically in search of trends through time and space. Results for the experiment show a clear difference between the effect of the presence of live animal tubes in sediment stability in comparison to their absence and the use of facsimile tubes, indicating that physical presence is not solely responsible for sediment stability. We propose that mucous substances secreted by patch fauna which differ from bare sediment and reef patches should be examined as a possible factor. Moreover, patch stability seem to be unaffected by patch height up to 9cm. Data from aerial surveys showed no significant differences despite density and patch height fluctuations. Density and patch height presented peaks toward May, which agrees with consulted literature for the period of recruitment. The event seems to not influence horizontal extension of patches. This combination of events points towards higher stability of reefs than previously conceded. |
