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The effects of mound building ants on soil and vegetation have been described worldwide; however, few studies have explored their effects in salt marsh communities. Here, we studied the effects of the black fire ant Solenopsis richteri on the cordgrass Spartina densiflora in a southwestern Atlantic salt marsh. We found that S. richteri nests are more abundant in the high marsh than in the low marsh and in the terrestrial environment. Sediment characteristics were examined in the above-ground and below-ground portions of nests, and in the surrounding soil apart from them. Nests’ sediment had lower organic matter content, lower bulk density and higher pH values than the non-nest soil. These differences were in general more marked in the above-ground portion of nests. Grain size distribution was biased towards coarser grain particles in nests, with the smallest particles being more abundant in the non-nest soil. Ammonium content was higher in the nests than in the non-nest soil, despite nitrate and dissolved inorganic nitrogen were not different. Phosphate content was higher in the below-ground portion than in the above-ground portion of nests. Samplings and transplant experiments showed that plants growing in contact with mounds grew longer, had wider stems and higher root biomass than plants apart from mounds. These results indicate that by affecting sediment characteristics, ants indirectly and positively affect plants condition, with potential cascading up effects on community structure and dynamics. Because mounds are relocated every ~3.5 months, bioturbation impacts may extend over time through the whole high marsh, highlighting the role that black fire ants may have in the ecology of southwestern Atlantic marshes. |
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