Changes of Heart Rate and Lipid Composition in Mytilus Edulis and Modiolus Modiolus Caused by Crude Oil Pollution and Low Salinity Effects

Abstract

Blue mussels, Mytilus edulis, inhabiting tidal zones, are naturally exposed to fluctuating environmental conditions (e.g., fluctuations in temperature and salinities), while horse mussels, Modiolus modiolus, live under relatively invariable shelf water conditions. The present investigation tested the hypothesis: blue mussels, in comparison to horse mussels, have an increased ability to tolerate the stress of pollution combined with low salinity. To assess the response of blue mussels and horse mussels to oil pollution at seawater salinities of 25 psu (normal) and 15 psu (low), we used a combination of heart rate and lipid composition as physiological and biochemical indicators, respectively. A sharp decrease in heart rate as well as important fluctuations in cardiac activity was observed under all oil concentrations. Modifications in the concentrations of the main membrane lipid classes (phosphatidylcholine, phosphatidylethanolamine, and cholesterol) and storage lipids (primarily triacylglycerols) in response to different crude oil concentrations were time- and dose-dependent. Both chosen indicators showed a high sensitivity to crude oil contamination. Furthermore, both bivalve species showed similar responses to oil pollution, suggesting a universal mechanism for biochemical adaptation to crude oil pollution.

Keywords: cardiac activity; cholesterol; mussel; oil pollution; phospholipids; triacylglycerols.

Figure 1

A scheme of the experimental design.

Figure 2

(A) Heart rate change in blue mussels under 25 psu salinity; (B) Heart rate change in blue mussels under 15 psu; (C) Heart rate change in horse mussels under 25 psu salinity (with no oil (grey line) and under exposure to low (L), medium (M), and high (H) crude oil concentrations: thin black line, thick black line, and dotted black line, respectively; the arrow points to the time of pollution water added). Each point represents the mean of seven individuals; error bars are a standard error.

Figure 3

Lipid classes levels (A) and ratios (B) in the gills of horse mussels under low (L), medium (M), and high (H) crude oil concentrations. Values are means ± standard error (n = 5). * significant results in comparison with initial level; 1, 3—significant results in comparison with the first and third days of exposure. Differences were estimated by the nonparametric Kruskal–Wallis test, p < 0.05.

Figure 4

Lipid classes levels (A) and ratios (B) in the digestive glands of horse mussels under low (L), medium (M), and high (H) crude oil concentrations. Values are means ± standard error (n = 5). * significant results in comparison with initial level; 1, 3—significant results in comparison with first and third days of exposure. Differences were estimated by the nonparametric Kruskal–Wallis test, p < 0.05.

Figure 5

PEA/PC ratio in gills (A–C) and digestive glands (D–F) of horse mussels and blue mussels under low (L), medium (M), and high (H) crude oil concentrations. Values are means ± standard error (n = 5). * significant results in comparison with initial level; 1, 3—significant results in comparison with first and third days of exposure. Differences were estimated by the nonparametric Kruskal–Wallis test, p < 0.05 + significant differences between mussels acclimated to 15 and 25 psu were estimated by the nonparametric Mann–Whitney U test, p < 0.05.

Figure 6

The content of some minor phospholipids and lysophosphatidylcholine (LPC) in gills (A,C,E) and digestive glands (B,D,F) of horse mussels (A,B) and blue mussels (C,D) low salinity; (E,F) normal salinity) under low (L), medium (M), and high (H) crude oil concentrations. Values are means ± standard error (n = 5). * significant results in comparison with initial level; 1, 3—significant results in comparison with first and third days of exposure. Differences were estimated by the nonparametric Kruskal–Wallis test, p < 0.05 + significant differences between mussels acclimated to 15 and 25 psu were estimated by the nonparametric Mann–Whitney U test, p < 0.05.