Honeycomb worm bioconstructions persist under combined human and wave-related disturbances

Marine bioconstructions and their ecological functions are increasingly threatened by compounded natural disturbances and direct and indirect impacts of anthropogenic activities. Through a manipulative experiment in the field, we assessed the response of intertidal biogenic patches built by the honeycomb worm, Sabellaria alveolata, to combined disturbances. Repeated battering events, simulating those associated with waves, were applied on intact or previously damaged bioconstructions, mimicking those impacted by harvesting of infaunal organisms. Descriptors of reef status, including the total patch size, the percentage cover of intact bioconstruction, tube density and diameter were examined as response variables to test two hypotheses: i) multiple disturbances would result in disproportionate effects on S. alveolata structures compared to isolate perturbations; ii) the structural stability of bioconstruction would be increasingly undermined by physical impacts with the increasing degree of reef damage from previous harvesting disturbance. When applied separately, intermediate intensity of harvesting and battering were associated with a larger size of S. alveolata patches compared to the unmanipulated control, while the cover of intact bioconstruction tended to decline over time in all experimental conditions. Such a reduction was particularly small under the high level of harvesting. The density and the diameter of sabellariid tubes were not significantly affected by any treatment. The difference between the effect of battering combined with each level of harvesting and the cumulative effect of each disturbance applied separately did not deviate from what would be expected by chance. Our findings highlight the ability of the examined bioconstructions to withstand and potentially thrive under compound disturbances, offering crucial insights for the implementation of sustainable conservation strategies in a threatened biogenic habitat.