We constructed a general relationship between prey concentration and absorption efficiency (AE; previously termed assimilation efficiency) in the cosmopolitan calanoid copepod Acartia tonsa. The relationships between observed AEs and prey concentrations developed differently on different prey species. While AEs decreased asymptotically with prey concentration on the cryptophyte Rhodomonas baltica, the chlorophyte Dunaliella tertiolecta generated a v-shaped response, whereas AEs remained constant on the diatom Thalassiosira weissflogii. We used these observations to develop a mechanistic gut model in which gut carbon concentrations depend on ingestion rate and either egestion rate or absorption rate. To investigate which rate was more important for AE, two different model modes were run: absorption was set to vary according to absorptive enzyme kinetics and egestion set to relate linearly to gut carbon concentration, or the contrary, egestion was set to vary according to enzyme kinetics and absorption set to relate linearly to gut concentration. This approach revealed that copepod carbon AE is controlled primarily by egestion rate kinetics and is independent of absorptive enzyme kinetics. Accordingly, we suggest a simplified regression model for the functional response of AE in pelagic copepods based solely on rates of ingestion and egestion.
Copepods, the largest group of pelagic grazers, are at risk from exposure to antifouling biocides. This study investigated the toxicity of the antifouling biocides 4,5-dichloro-2-octyl-1,2-thiazol-3(2H)-one (DCOIT), triphenylborane pyridine (TPBP) and 4-[1-(2,3-dimethylphenyl)ethyl]-1H-imidazole (medetomidine) to the copepod Acartia tonsa, using mortality and egg production as endpoints. The toxicity ranking for mortality was as follows: DCOIT (LC50 57 nmol l(-1)) = TPBP (LC50 56 nmol l(-1)) > medetomidine (LC50 241 nmol l(-1)). Egg production was more sensitive than mortality to TPBP (EC50 3.2 nmol l(-1)), while DCOIT and medetomidine inhibited egg production at roughly the same concentrations (72 and 186 nmol l(-1) respectively). Furthermore, TPBP seems to affect egg hatching directly which was not the case for DCOIT and medetomidine. DCOIT and medetomidine might pose an environmental risk as they have been reported to occur in different exposure scenarios or analytical surveys at concentrations only 2-3 times lower than the respective EC10. Reported environmental concentrations of TPBP are few but clearly lower than the EC10 values reported here, suggesting current risk of TPBP to copepods to be moderate.
Antifouling biocides are found in the marine ecosystem were they can affect non-target organisms. In this study the effects of five antifouling biocides on the settlement and growth of Ulva lactuca zoospores were investigated. The biocides investigated were copper (Cu(2+)), 4,5-dichloro-2-n-octyl-3(2H)-isothiazolone (DCOIT), triphenylborane pyridine (TPBP), tolylfluanid and medetomidine. Full concentration-response curves where determined for each compound. EC50 values were determined for copper, DCOIT, TPBP and tolylfluanid, all of which inhibited settlement and growth in a concentration dependent manner with the following toxicity ranking; tolylfluanid (EC50 80 nmol L(-1)) ~ DCOIT (EC50 83 nmol L(-1)) > TPBP (EC50 400 nmol L(-1)) > Cu(2+) (EC50 2,000 nmol L(-1)). Medetomidine inhibited settlement and growth only at the extreme concentration of 100,000 nmol L(-1) (93% effect). The low toxicity is possibly a consequence of a lack of receptors that medetomidine can bind to in the U. lactuca zoospores.
We measured ingestion rate (IR), egg production rate (EPR) and egg hatching success (EHS) at increasing prey concentrations and calculated egg production efficiency (EPE) and maintenance rate (MR) in the estuarine copepod Acartia tonsa fed three different algal diets. EPR and EHS were relatively more affected by prey species than by prey concentration. EPEs were constant among carbon concentrations (C) on a diet of Rhodomonas baltica (0.202 ± 0.055, mean ± SD) and Dunaliella tertiolecta (0.034 ± 0.015), but decreased significantly from 0.371 ± 0.062 (mean of two lowest prey concentrations) to 0.200 ± 0.019 at the highest concentration of Thalassiosira weissflogii. In general it seems that other requirements than C demand limit EPE and EHS in A. tonsa. The MR (IR when EPR = 0) was significantly higher on D. tertiolecta, which also yielded the lowest EPEs, and it seems that variations in maintenance requirements may have been instrumental in evoking EPE variations as well.
This paper presents a novel assay that allows a quick and robust assessment of the effects of biocides on the initial settling and establishment of marine photoautotrophic biofilms. The assay integrates the response of the multitude of indigenous fouling organisms, which overcomes a major limitation of existing assays which are largely limited to testing only lab-cultivatable species. The assay was evaluated using eight antifouling biocides, for which full concentration-response curves are presented. The efficacy ranking, based on EC 98 values from most to least efficacious compound is: copper pyrithione >TPBP >DCOIT >tolylfluanid >zinc pyrithione >medetomidine >copper (Cu 2+ ), while the ecotoxicological ranking (based on E C10 values) is irgarol, copper pyrithione >zinc pyrithione >TPBP >tolylfluanid >DCOIT >copper (Cu 2+ ) > medetomidine. The algaecide irgarol did not cause full inhibition. Instead the inhibition leveled out at 95% effect at 30 nmol l -1 , a concentration that was clearly lower than for any other of the tested biocides.
Keywords
In this paper a novel settlement and growth assay is presented that uses field-collected marine photoautotrophic biofilms as inoculum. The multitude of indigenous species that are the potential foulers aretherefore included in the assay, which overcomes the limitation of testing only those species that can be cultivated in the laboratory. The assay was evaluated using eight antifouling biocides. The methodological considerations are discussed thoroughly and full concentration response curves are presented for all testedbiocides. The efficacy ranking based on EC 98 values from the most to the least efficacious compound is as follows: copper pyrithione > TPBP > DCOIT > tolylfluanid > zinc pyrithione > medetomidine > copper (Cu 2+ ). The algaecide irgarol did not cause a full inhibition of settlement and growth but the inhibition leveled out at 95% already at 30 nmol l -1 , at a concentration that is clearly lower than for any other of the tested biocides.
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