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 of

environmental stress caused by water pollution such as heavy metals, pesticides, but

as well by organic contamination. In the present study larvae from the side channels

of the Ciénaga Grande de Santa Marta were investigated. The chironomid community

of the channels are dominated by species of the genera Goeldichironomus and

Chironomus. All together 21 taxa were determined. The average proportion of mouthpart

deformities in all chironomid larvae was 21 percent. Incidents of mechanical abrasion

reached up to 59 percent. The highest frequency of abnormalities occurred in

Goeldichironomus carus in which more than 90 percent of all specimens were affected.

These numbers found here are fairly above average frequencies observed even at

polluted sites. Under natural conditions deformity frequencies are expected not to

exceed 8 percent. On the one hand, distinct concentrations of heavy metals originating

from 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 high

deformation rates like those found here. The most plausible explanation of these

contradictory findings assumes a non-detected synergism of several environmental

stressors. Possibly, the physical structure of the deposited sediments and a pronounced

nocturnal oxygen depletion owing to organic pollution contribute an important part to

the crucial processes on a small spatial scale. However, as far as no further investigative

efforts will be done the reason for this phenomenon of high deformity frequencies will

remain conspicuous but speculative to a large extent.