Acid-iron waste as a factor affecting the distribution and abundance of zooplankton in the New York Bight: I. Laboratory studies on the effects of acid waste on copepods

Abstract

Laboratory experiments were conducted using three species of copepods to study the effects acid-iron wastes might have on zooplankton. Individuals of Calanus finmarchicus, Temora longicornis and Pseudocalanus sp. were maintained in bottles containing varying dilutions of acid wastes in sea water or control sea water solutions for 24 to 48 hours to examine survival of adults exposed to high concentrations of waste. They were also maintained for time periods up to 18 days to ascertain effects on reproduction and survival of young. In addition, individuals of C. finmarchicus were transferred through a series of increasing dilutions of acid wastes and into filtered sea water to simulate the short-term effects of acid waste concentrations in the wake of a discharging barge. Substantial mortality of adults of the above three copepods occurred at concentrations of acid waste producing pH's of approximately 6·5 and lower. However, this mortality is not indicative of mortality in the field as these concentrations and pH values exist for only a short time (less than 3 min) due to rapid mixing of the acid waste with sea water. Individuals maintained in buffered acid wastes of comparable dilutions showed no mortality, while individuals maintained in test media using sulfuric acid in place of acid waste showed high mortalities at pH's of 5·5 or less. Thus, acidity of test solutions may be a principal cause of copepod mortality rather than some toxic component of the waste material. Inhibition of reproduction and deleterious effects on survival of young were observed in experiments of 18 days duration at concentrations of acid wastes which do not in fact persist for such periods on the acid grounds. No mortality was observed when C. finmarchicus was transferred through acid waste dilutions with pH values and time periods comparable to those they would encounter on the acid grounds during discharge of acid wastes. Acid waste discharges, therefore, did not appear to be responsible for the large variations in zooplankton biomass previously observed in the survey area since mortality of species due to short term exposure to high concentrations of waste appears small and little effect on adults or larval forms at great dilutions could be demonstrated. Although the average biomass from the acid grounds was 30% less than that from the adjacent control area, this difference could not be directly linked to the toxicity of acid-iron waste. The spatial pattern of biomass variations and the results from the initial laboratory toxicity studies suggested the difference was probably due to a transitory large scale patchiness of zooplankton. We have conducted further laboratory studies on the effects of acid wastes on copepod species that occur in the area where acid waste is discharged. The results of these experiments are reported here. We have also counted the zooplankton samples collected at the time of our synoptic field sampling survey of the acid waste dumping site and a nearby control area. The analysis of these data and the implications to the observed distribution of zooplankton biomass and to monitoring studies are presented in the succeeding paper (Wiebe et al., 1973).