Functional and structural responses of marine plankton food web to pyrene contamination

Abstract

The effects of single additions of pyrene (low, medium or high) on a natural marine plankton community are reported in this study. Direct and indirect effects on the function and structure of bacteria, phytoplankton and zooplankton communities were investigated using a food-web approach in a mesocosm. Phytoplankton communities suffered from direct effects of the exposure to pyrene and, after a lag-period of 2 d, so did the bacterial communities exposed to medium and high pyrene concentrations. Effects on the zooplankton community function were not as evident, mainly due to high variation in the measured prey uptake. Abundance of phytoplankton decreased, and the community composition changed in the exposed communities. The total phytoplankton community activity remained stable, resulting in high specific activity (activity per unit chlorophyll a), which could be interpreted as functional redundancy. However, we suggest that differences in nutrient availability between exposed and unexposed communities actually caused the indicated functional redundancy, as phytoplankton growth in control communities was nutrient limited during the experiment, whereas nutrient regeneration from the directly affected algae provided the exposed communities with better growth conditions. The system function, which integrates the functions of the 3 trophic levels, was affected at all 3 exposures during the first 5 d of the experiment. The change in system function suggests that PAHs (polyaromatic hydrocarbons) might be an important stress factor for pelagic systems, as a one-time exposure of a single compound changes the development of a pelagic community.

Plankton stress responses from PAH exposure and nutrient enrichment

“…The mesocosm experiment was carried out in the Isefjord, Denmark (average depth 5 to 7 m), for 12 d in April and May 2005 in a similar manner as described in Hjorth et al (2007). Twelve mesocosm bags (3 m 3 ) were established, creating 3 replicate mesocosms per experimental treatment.…”

“…The productivity can be bottom-up controlled, with abiotic conditions such as light, temperature and nutrients determining production rates, and where PAH exposure may affect primary producers more severely under these conditions. This was the case as determined by Hjorth et al (2007) who suggested phytoplankton are the most susceptible group, and declines in their biomass and/or activity lead to indirect effects in bacterial and zooplankton communities. On the other hand, a system can be top-down controlled where primary production is limited by predation from other trophic levels.…”

“…The PAH pyrene has a detrimental effect on plankton communities at concentrations close to 3.4 nmol l -1 (Hjorth et al 2007), which is the lower ecotoxicological assessment criteria (EAC) recommended by the Oslo Paris Commission (Bignert et al 2004). The same study implied that the type of response from plankton systems to PAH stress was coupled to the status of nutrients and availability of substrate in the system.…”

“…The same study implied that the type of response from plankton systems to PAH stress was coupled to the status of nutrients and availability of substrate in the system. If nutrients were scarce and limiting production, direct biological effects from pyrene exposure could be concealed in nutrient releases from indirect effects, and the strength of exposure of pyrene to higher trophic levels may also be linked to biomass concentrations (Hjorth et al 2007). To assess the extent to which stress from high nutrient loads compare and interact with the effects of PAHs on plankton communities, the present study was designed to test whether stress responses from plankton systems to pyrene exposure would be stronger if the initial nutrient status of the plankton community was high.…”

Do hydrocarbon and salinity disturbance affect marine meiofauna diversity and community structure?

“…These compounds are found in high concentrations in diesel fuel and other common hydrocarbon mixtures. Oil spills containing these compounds have been shown to drastically alter biodiversity in marine systems, ranging from large fish to planktonic communities (Incardona et al 2004, Hjorth et al 2007). …”