A stem-boring moth drives detritus production in SW Atlantic marshes

Boundary habitats are frequently hot spots for the production and flow of organic matter (OM) and exert strong effects on ecological processes in the habitats which they link. Salt marshes, which are boundary habitats occurring between the land and the sea, are important sources of OM for coastal habitats. Primary productivity and tides are among the main causes of OM production and export from salt marshes. By field sampling and experiments we found that the stem-boring moth Haimbachia sp. nov. substantially increases the production of detritus in salt marshes along the SW Atlantic coastline. The larvae of this moth enhance the natural mortality of Spartina alterniflora and S. densiflora by feeding inside the basal and middle portions of the stem tissue. The attacks of the moth larvae produce dead and debilitated stems that are more easily broken and transported by the tides than non-attacked stems. Because the moth-attack frequencies will vary geographically in response to variation in the physical environment, the amount of OM flow between habitats will also vary, resulting in a positive relationship between moth-attack frequencies and OM production on a regional scale. Our field and experimental results show that herbivory by this moth and tidal transport could be the main determinants of the production of Spartina macrodetritus in these marshes. A key finding based on this previously undescribed interaction is that biological interactions (i.e. the effects of herbivores) can change the permeability of boundary habitats by altering the OM flow between terrestrial and aquatic ecosystems.