Abstract
Soft bottom macrobenthic communities were studied seasonally in three coastal ponds (Marinello ponds, Italy) at increasing distances from a gull (Larus michahellis) colony to investigate the effect of seabird-induced eutrophication (i.e. guanotrophication) on macrobenthic fauna. We hypothesized that enhanced nutrient concentration and organic load caused by guano input significantly alter the trophic and sedimentological condition of ponds, affecting benthic fauna through a bottom-up control. The influence of a set of environmental features on macrobenthic assemblages was also tested. Overall, the lowest macrobenthic abundances and functional group diversity were found in deeper sites, especially in the pond characterised by severe guanotrophication, where the higher disturbance resulted in a decline in suspension feeders and carnivores in favour of deposit feeders. An increase in opportunistic/tolerant taxa (e.g. chironomid larvae and paraonids) and totally azoic sediments were also found as an effect of the harshest environmental conditions, resulting in a very poor ecological status. We conclude that macrobenthic assemblages of the Marinello coastal system display high spatial variability due to a synergistic effect of trophic status and the geomorphological features of the ponds. The macrobenthic response to guanotrophication, which was a clear decrease in abundance, diversity and trophic functional groups, was associated with the typical response to severe eutrophication, magnified by the geomorphological features.
Highlights
Fluxes of nutrients are of paramount importance in ecological systems due to the implications for primary production, trophic structure and biodiversity [1]
The guanotrophic pond, VE, showed a quite diverse taxa composition in the shore site and a marked dominance of chironomid larvae in the bottom site
The most abundant taxa in the guanotrophic pond, were the small gastropod H. ventrosa, which showed a marked, not significant, peak at the shore site, during summer (Fig. 3 i) and chironomid larvae with the highest densities in both sites (Fig. 3 k)
Summary
Fluxes of nutrients are of paramount importance in ecological systems due to the implications for primary production, trophic structure and biodiversity [1]. Through their activities and movements, seabirds, which commonly use coastal ecosystems as nesting sites or corridors, release a large mass of nutrients and contaminants contained mainly in guano [2,3,4,5] and may directly and/or indirectly affect the functionality of these systems. Where bird abundance is very high [14, 15] and/or the systems are small and with scarce water renewal, such as coastal ponds and lagoons [4], the avian-induced nutrient enrichment can be magnified leading undesirable effects on the whole ecosystem, to severe eutrophication, here- the term guanotrophication [16]
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