Life history and population dynamics of the opportunistic polychaete \u3ci\u3eCapitella\u3c/i\u3e sp. I in relation to sediment organic matter

Capitella sp. I is a deposit-feeding polychaete that occurs in estuarine and marine environments and that shows boom-bust population dynamics in response to organic pollution. A lifecycle experiment was carried out to quantify the relative importance of individual life-history traits for driving the dynamics of Capitella sp. I populations in response to changes in sediment organic matter concentrations. Individual-level effects were estimated as changes in survival, reproductive characteristics, and growth. Effects at the population-level were assessed by integrating the measured life-history traits in a simple 2-stage demographic model that was used to estimate the population growth rate (λ). Low organic content considerably impaired individual life-history traits and, as a consequence, λ. The results of the present study suggest that the minimum organic matter concentration for the maintenance, survival and growth of Capitella sp. I is 0.2 % TOM (total organic matter), and that sediments with \u3c 0.5 % TOM would not support Capitella sp. I reproduction. The change in λ in response to sediment organic concentration was primarily attributable to effects on time to first reproduction, which explained, on average, 47% of the variance in λ. Treatment effects on juvenile survival and fecundity explained, on average, 26 and 24 %, respectively, of the observed treatment effect on λ, whereas adult survival and time between broods together contributed about 3 % to the effect on λ. The threshold between population extinction and population increase was sharp, which suggests that relatively small changes in organic loading can have dramatic consequences for the population dynamics in this species

Consequences of a short pulse of pesticide exposure for survival and reproduction of \u3ci\u3eGammarus pulex\u3c/i\u3e

The aim of the present study was to examine the effects of a short and environmentally realistic pulse exposure of different life stages of the freshwater amphipod, Gammarus pulex, to the pyrethroid insecticide, esfenvalerate. We were particularly interested in determining the extent to which detectable effects on key life-history traits persisted following cessation of a brief exposure to this pesticide. Our results indicate that environmentally realistic exposure concentrations of this widely used insecticide can have a significant effect on the survival and reproduction of Gammarus pulex. Comparison of LC50 values indicates that G. pulex has a similar sensitivity to esfenvalerate as the standard test invertebrate, Daphnia magna and is more sensitive than other common stream invertebrates. Despite 100% survival during pulses of up to 2 μg l−1, mortality increased, in some cases markedly, following transfer to clean conditions. Pulse exposure to esfenvalerate at concentrations in the range 0.1–0.6 μg l−1 for as little as 1 h can have effects on G. pulex survival, pairing behavior, and reproductive output that can still be detected at least 2 weeks following the pulse. Reproductive traits were very sensitive to esfenvalerate, and exposure to 0.05 μg l−1 for 1 h led to immediate disruption of reproducing pairs, release of eggs or offspring from the brood pouch, and substantial delays in pair formation and subsequent reproduction following transfer to clean water. The kinds of effects on reproductive behavior observed in this study could potentially impact the population dynamics of G. pulex in the field. Whether such effects occur will depend on the frequency, duration, timing, and spatial extent of pesticide exposure in freshwater stream ecosystems, about which relatively little is known. Such information is essential if effects on non-target aquatic species are to be more accurately assessed

Toxicity and toxicokinetics of cadmium in \u3ci\u3eCapitella\u3c/i\u3e sp. I: Relative importance of water and sediment as routes of cadmium uptake

The importance of dissolved versus sediment-bound cadmium as uptake routes for the deposit-feeding polychaete Capitella species I and the toxicity and toxicokinetics of cadmium from these exposure routes were investigated. Effects were reported as changes in worm growth rate, egestion rate and allometry. Radioactive cadmium (109Cd) was used as a tracer to examine the uptake (5 d) and subsequent depuration (6 d) of cadmium. Both effects and kinetics were investigated in systems with and without sediment. Individual Capitella sp. I were exposed to (1) dissolved (i.e. –1). Worms in water-only treatments showed negative growth rates, which decreased linearly from –5 to –10% d–1 with increasing cadmium concentration. Cadmium had no detectable effect on egestion rate or growth in the presence of sediment in either sediment-bound only (ca 36% d–1) or porewater & sediment (ca 30% d–1) treatments. Cadmium exposure had no detectable effect on the allometric exponent (i. e. area-length relation) in any of the treatments; however, worms in water-only treatments were relatively thinner than in the 2 treatments with sediment. Worms in porewater & sediment treatments took up ca 50-fold more cadmium (ca 195 ng Cd worm–1) than worms in water-only treatments (3.9 ng Cd worm–1) during 5 d of exposure. Sediment-bound cadmium was calculated to contribute 95 % of the total amount taken up by feeding worms. Starving worms retained all of the cadmium during the subsequent depuration period (6 d), and exhibited an increased weight-specific body burden (μg Cd g–1 dry wt worm) due to shrinkage. In feeding worms, the decrease in weight-specific body burden was faster (T½ = 3 d) than the decrease in total body burden (μg Cd worm–1; T½ = 11 d), indicating that both active excretion and dilution of cadmium body burden as a result of growth contributed to the change in cadmium tissue concentration during the depuration period. Thus, our results indicate that in Capitella sp. I sediment-bound cadmium is the major route of uptake. We found that cadmium affects starving but not fed worms, despite the fact that fed worms took up considerably more cadmium than starving worms. Our results suggest that stress associated with food limitation increases the susceptibility of worms to cadmium stress

Toxicity and toxicokinetics of cadmium in \u3ci\u3eCapitella\u3c/i\u3e sp. I: Relative importance of water and sediment as routes of cadmium uptake

The importance of dissolved versus sediment-bound cadmium as uptake routes for the deposit-feeding polychaete Capitella species I and the toxicity and toxicokinetics of cadmium from these exposure routes were investigated. Effects were reported as changes in worm growth rate, egestion rate and allometry. Radioactive cadmium (109Cd) was used as a tracer to examine the uptake (5 d) and subsequent depuration (6 d) of cadmium. Both effects and kinetics were investigated in systems with and without sediment. Individual Capitella sp. I were exposed to (1) dissolved (i.e. –1). Worms in water-only treatments showed negative growth rates, which decreased linearly from –5 to –10% d–1 with increasing cadmium concentration. Cadmium had no detectable effect on egestion rate or growth in the presence of sediment in either sediment-bound only (ca 36% d–1) or porewater & sediment (ca 30% d–1) treatments. Cadmium exposure had no detectable effect on the allometric exponent (i. e. area-length relation) in any of the treatments; however, worms in water-only treatments were relatively thinner than in the 2 treatments with sediment. Worms in porewater & sediment treatments took up ca 50-fold more cadmium (ca 195 ng Cd worm–1) than worms in water-only treatments (3.9 ng Cd worm–1) during 5 d of exposure. Sediment-bound cadmium was calculated to contribute 95 % of the total amount taken up by feeding worms. Starving worms retained all of the cadmium during the subsequent depuration period (6 d), and exhibited an increased weight-specific body burden (μg Cd g–1 dry wt worm) due to shrinkage. In feeding worms, the decrease in weight-specific body burden was faster (T½ = 3 d) than the decrease in total body burden (μg Cd worm–1; T½ = 11 d), indicating that both active excretion and dilution of cadmium body burden as a result of growth contributed to the change in cadmium tissue concentration during the depuration period. Thus, our results indicate that in Capitella sp. I sediment-bound cadmium is the major route of uptake. We found that cadmium affects starving but not fed worms, despite the fact that fed worms took up considerably more cadmium than starving worms. Our results suggest that stress associated with food limitation increases the susceptibility of worms to cadmium stress

Individual physiological responses to environmental hypoxia and organic enrichment: Implications for early soft-bottom community succession

Infaunal inhabitants of coastal marine sediments occupy environments along a continuum from extremely food-rich, low-oxygen regions to food-poor habitats with relatively high levels of available oxygen. In organic-rich sediments, efficient utilization of available organic matter by deposit-feeding macrofauna may often be limited by the supply of oxygen. Specific feeding rate, growth, and production efficiency were measured on single individuals of the polychaete Capitella species 1 to determine whether previously measured declines in growth rates in response to hypoxia were due to decreased feeding, decreased conversion efficiency, or both. Under otherwise constant conditions, feeding rate was determined by the nitrogen content of the sediment, with a greater nitrogen content generally leading to higher specific feeding rates in a manner consistent with recent interpretations of optimal foraging theory. However, the relationship between feeding rate and growth was influenced by oxygen concentration such that in relatively nitrogen-poor sediment, greater growth rates were observed at the lower oxygen level. Simultaneous measurement of growth and feeding rates indicated that the effect of oxygen was due to a decrease in the efficiency with which ingested sediment was converted to tissue under low nitrogen, high oxygen conditions. We suggest that the decreased conversion rate of ingested sediment to body volume under the higher oxygen regime reflected an aerobic metabolic system poised to rapidly exploit available oxygen supplies. The physiological responses measured in our experiments are consistent with the classical faunal successional sequence occurring in a deposit following organic enrichment. When viewed temporally, these faunal changes parallel geochemical changes such that high organic matter, low oxygen conditions give way to higher oxygen levels and decreased concentrations of organic matter. Thus environmental conditions typically change toward those under which Capitella sp. 1 would be expected to perform most poorly. We suggest that an underlying physiological mechanism in Capitella spp. may strongly influence the early successional changes observed following the organic enrichment of soft-bottom benthic environments

Effects on the Function of Three Trophic Levels in Marine Plankton Communities under Stress from the Antifouling Compound Zinc Pyrithione

This study aimed to investigate functional responses of natural marine planktonic communities to stress from the antifouling compound zinc pyrithione (ZPT). Isotope labelling techniques (14C) were applied to study bacterial incorporation of leucine, photosynthetic activity of phytoplankton and grazing of labelled prey by zooplankton communities for 6 days after exposures to nominal concentrations of 0, 5, 25, 50 nM ZPT in a mesocosm experiment in Isefjord, Denmark. Significant direct effects were visible on chlorophyll α concentrations, which decreased in all exposed communities, to between 48 and 36% of control concentrations on Day 3, 1 day after the last exposure. Phytoplankton activities were also significantly affected on Day 3 with activities between 9 and 26% of control levels, as was zooplankton activities in the 25 and 50 nM exposures. In the 50 nM exposure the total community zooplankton activity was reduced to 25 ± 4%, and per individual to 46 ± 11% of control levels. Bacterial communities showed positive indirect effects with high activities (up to 183 ± 40%) due to higher amounts of available substrate from algal death. Pollution induced community tolerance analyses performed on phytoplankton and bacterial communities at the end of the experiment indicated a development of increased tolerance for phytoplankton in the 50 nM exposed communities, whereas there were no changes in tolerance in the bacterial communities. Multivariate analysis of the integrated functional response by the plankton communities revealed a significant difference (p \u3c 0.05) between exposed communities compared to controls in the first 3 days after last exposure and in the end of the experiment. The study provides evidence of diverse effects on the functions of marine plankton communities under stress from a pollutant. Direct effects lead to cascading indirect effects throughout the community, eventually causing different developments. Continuous exposure to ZPT could lead to severe long-term effects, causing more permanent changes in structure and function than observed here. The study demonstrates that it is possible to assess the functional effects of a stressor in a complex mesocosm system, and to determine effects in a complex plankton community, which were not predictable from laboratory studies