Influence of the water-soluble fraction of petroleum on photosynthesis and chemical defenses in two sympatric seaweeds

In this work, we aimed to evaluate the effect of the water-soluble fraction (WSF) of petroleum on the photosynthesis and chemical defenses of two sympatric members of the brown algal family Dictyotaceae, Dictyota caribaea and Stypopodium zonale. The algae were cultivated in incubator chambers for 8 days in flasks containing the WSF or seawater as a control laboratory cultivation. Measurements of chlorophyll fluorescence revealed distinct responses between the two species. Stypopodium zonale was less tolerant than D. caribaea as shown by a more intense diminishing of the potential quantum yield of photosystem II (Fv/Fm) as well as by the reduction of the intrinsic photosynthetic capacity observed in parameters obtained from the rapid light curves. Feeding experiments revealed that the WSF reduced strongly the palatability of the lipophilic extracts from both algae to the herbivore crab Pachygrapsus transversus (Gibbes). The analyses of the chemical profiles from these extracts by chromatographic techniques showed that the effect of the WSF on secondary metabolites production could only be observed in D. caribaea. Our results indicated that these sympatric species showed distinct tolerances to the WSF where S. zonale was more sensitive than D. caribaea. On the other hand, both species responded to the WSF with a more deterrent behavior to herbivory. Possible ecological consequences are discussed.