SOME OBSERVATIONS OF BUCCAL DEFORMITIES IN CHIRONOMID LARVAE (DIPTERA: CHIRONOMIDAE) FROM THE CIÉNAGA GRANDE DE SANTA MARTA, COLOMBIA

The mouthpart deformities of chironomid larvae are considered as indicators ofenvironmental stress caused by water pollution such as heavy metals, pesticides, butas well by organic contamination. In the present study larvae from the side channelsof the Ciénaga Grande de Santa Marta were investigated. The chironomid communityof the channels are dominated by species of the genera Goeldichironomus andChironomus. All together 21 taxa were determined. The average proportion of mouthpartdeformities in all chironomid larvae was 21 percent. Incidents of mechanical abrasionreached up to 59 percent. The highest frequency of abnormalities occurred inGoeldichironomus carus in which more than 90 percent of all specimens were affected.These numbers found here are fairly above average frequencies observed even atpolluted sites. Under natural conditions deformity frequencies are expected not toexceed 8 percent. On the one hand, distinct concentrations of heavy metals originatingfrom Río Magdalena can be detected in the sediments of the channels. On the other,these concentrations do not reach the levels which are described as triggers of highdeformation rates like those found here. The most plausible explanation of thesecontradictory findings assumes a non-detected synergism of several environmentalstressors. Possibly, the physical structure of the deposited sediments and a pronouncednocturnal oxygen depletion owing to organic pollution contribute an important part tothe crucial processes on a small spatial scale. However, as far as no further investigativeefforts will be done the reason for this phenomenon of high deformity frequencies willremain conspicuous but speculative to a large extent.