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Journal of Experimental Marine Biology and Ecology 242 1999 59–74
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Effects of two organochlorine compounds on hatching and viability of calanoid copepod eggs
a , a
a a
b ,1
J.A. Lindley , P. Donkin , S.V. Evans , C.L. George , K.F. Uil
a
Centre for Coastal and Marine Sciences , Plymouth Marine Laboratory, Prospect Place, The Hoe,
Plymouth PL 1 3DH, UK
b
Wageningen Agricultural University , Landbouwuniversiteit, Wageningen, The Netherlands
Received 21 May 1998; received in revised form 10 June 1999; accepted 28 June 1999
Abstract
Two organochlorine compounds, pentachlorophenol PCP, a respiratory uncoupler, and 1,2- dichlorobenzene DCB, a non-polar narcotic, were selected for experiments on their toxicity to
eggs of estuarine and neritic planktonic calanoid copepods. Experiments on freshly laid eggs in aqueous solutions of the toxicants showed that no viable nauplii of Eurytemora affinis or Acartia
bifilosa hatched from eggs incubated in initially saturated solutions and a reduced percentage of eggs hatched after temporary exposure | 16 h to saturated solutions. The percentage of eggs of
E
. affinis that hatched was reduced below control values in 5 and 10 saturated solutions with EC
concentration reducing the response by 50 estimated at 2.1 saturated solution of PCP
50
and 3.2 saturated DCB initial concentrations. Viability of nauplii was reduced at lower concentrations with estimated LC
concentration lethal to 50 of population values of 0.7
50
saturated PCP and 1.7 saturated DCB. Equivalent values for Acartia bifilosa were higher, with no reduction below control values in percentage hatch at 10 saturation and LC
values for
50
nauplii of 0.8 PCP and 14.2 DCB. The percentage of eggs of A . clausi that hatched when
incubated in sealed vials to eliminate loss of DCB through evaporation was not reduced in 10 saturated solutions but the estimated LC
was 2.0 saturation. In sediment exposed to a saturated
50
solution of DCB very high mortality occurred within 1 day.
1999 Elsevier Science B.V. All rights reserved.
Keywords : Calanoid eggs; Dichlorobenzene; Hatching; Nauplii; Pentachlorophenol; Viability
1. Introduction
Diaptomoid calanoid copepods, usually the dominant planktonic calanoids of neritic
Corresponding author.
1
Present address: Beltstraat 98a, 7512 AB Enschede, The Netherlands. 0022-0981 99 – see front matter
1999 Elsevier Science B.V. All rights reserved.
P I I : S 0 0 2 2 - 0 9 8 1 9 9 0 0 0 9 4 - 5
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.A. Lindley et al. J. Exp. Mar. Biol. Ecol. 242 1999 59 –74
and estuarine waters Lindley, 1997, produce eggs that may accumulate in the sediments. These eggs may remain dormant for periods far exceeding their normal
temperature dependent development times. The eggs include diapause eggs and delayed hatching eggs, the development of which is delayed by endogenous processes as well as
subitaneous eggs Marcus, 1996. The subitaneous eggs normally develop at temperature dependent rates but development of all types of egg may be delayed by unfavourable
environmental conditions for hatching, including the effects of burial in sediment. Anthropogenic contaminants and organic matter, the decay of which can cause anoxia
particularly where eutrophication occurs, also accumulate in coastal and estuarine sediments. Long et al. 1996, in experiments on sediments from 22 US estuaries, found
that sediments from 10.9 of the area and pore waters from 43 of the area were toxic. Reductions in viability of calanoid copepod eggs have been attributed to anoxia Uye et
al., 1984, to hydrogen sulphide Marcus et al., 1997 and to toxicants, for example rotenone Naess, 1991b. Zooplankton eggs can remain dormant in sediments, usually
for periods of days to months, but recent work has indicated that at least a proportion of eggs can remain viable over decades Marcus, 1996. There is potential for impact on
eggs in polluted sediment and hence on recruitment to the zooplankton through direct effects of accumulated toxicants and decay of organic matter or indirectly through
decreased bioturbation increasing anoxia and sulphide accumulation. Interspecific differences in susceptibility of the eggs or the hatching nauplii could result also in
changes in plankton community structure and species diversity. This investigation was undertaken to supplement existing information on effects of contaminants on estuarine
and neritic zooplankton eggs and to complement field studies on viability of eggs from estuaries with a range of histories of industrial and urban pollution Lindley et al., 1998
Two compounds were selected for experiments, pentachlorophenol PCP and 1,2- dichlorobenzene DCB. PCP is an extensively used biocide, which is on the UK Red
List of priority pollutants, in addition to EEC and US EPA priority lists. It has been detected in significant quantities in freshwater sediments in the USA Hoke et al., 1993,
in the Scheldt estuary, Netherlands van Zoest and van Eck, 1991 and in river and coastal monitoring programmes in the UK National Rivers Authority, 1995a,b,c. It is
very hydrophobic in its unionised form log n-octanol water partition coefficient, log K
5 5.12, so can readily be absorbed by sediments, and bioaccumulated,
ow
including into mitochondria where it uncouples respiration Mahler and Cordes, 1966. This mode of action provides a link with rotenone, another respiratory uncoupler, one of
the few other organic compounds known to reduce the viability of zooplankton eggs Naess, 1991b. The dichlorobenzenes are toxic by non-polar narcosis van Wezel et al.,
1996 and are more likely to partition into water. The 1,2-isomer was chosen for study since it is a liquid at the experimental temperatures, eliminating the possibility of crystal
formation during experiments at high concentrations. Its log K
is 3.38. 1,2-DCB
ow
occurs in sewage sludge Rogers et al., 1989a,b; Wang and Jones, 1994 and is a widespread contaminant of freshwater Hoke et al., 1993 and estuarine environments
Rogers et al., 1989a; van Zoest and van Eck, 1991. Aqueous solutions of these compounds were used in experiments on eggs laid by
females in the laboratory or in sacs attached to freshly caught females and on sediment known to contain eggs. The species used in the experiments were Eurytemora affinis, a
J .A. Lindley et al. J. Exp. Mar. Biol. Ecol. 242 1999 59 –74
61
mid-estuarine species, and Acartia spp., mainly A . bifilosa which overlaps with E. affinis
but is more abundant at higher salinities e.g., Collins and Williams, 1981. These species dominated our plankton samples from the Exe and Tamar estuaries. E
. affinis carries its eggs in a sac. Diapausing eggs are shed after a few days but eggs may reach
the sediment also following predation on the egg carrying females, which are more conspicuous to predators than those without egg sacs Webb and Weaver, 1988.
Conway et al. 1994 and Flinkman et al. 1994 found that the eggs of E . affinis remain
viable after passage through fish guts. Acartia spp. spawn freely and the eggs sink.
2. Methods
