Histochemistry and histology in planktonic ecophysiological processes determination in a temperate estuary (Mondego River estuary, Portugal)

Abstract

Zooplankton communities in temperate climates exhibit well documented seasonal variability. The reasons proposed to explain this kind of behaviour range from the effect of physical-chemical conditions (salinity, nutrients, temperature) growth rates, mortality, migration rates, food availability and predation. It is noticeable that the majority of the factors mentioned are external to the organisms, being environmental factors responsible for time dependent changes in zooplankton abundance. A question may arise from this conclusion, namely, "Could zooplankton blooms, in temperate climates, be mainly modelled by the internal physiological predispositions of the individual organisms?" Or, in a more "functional" formulation, "Could gonads be the baseline regulators of zooplankton abundance?". This study answers this pertinent question, assuming as a basic assumption that the reproductive potential of these organisms is constant, being controlled by extrinsic factors. For this purpose, histological and histochemical techniques were applied to the mysid Mesopodopsis slabberi, a key species in the Mondego River estuary, in order to establish a scale of gonadic development that would allow comparisons between high and low density periods. Histology reveals itself as the ideal base to establish a tool for the evaluation of the gonadic masses by allowing to calculate oocyte dimensions (trough biometry) and determine its maturity status through calculation of the N/C ratio and histochemical analysis (PAS and Tetrazonium reaction for proteins). Upon creation, validation and application of the formerly described tool, the most prominent result emerging from this study is the confirmation of the initial assumption: seasonal variability in zooplankton densities reflects advantageous or disadvantageous external factors acting over a latent reproductive potential. Moreover, this work confirms histology and histochemistry as valuable approaches to the determination of planktonic ecophysiological processes.

Seasonal and developmental variability of biochemical composition in Mesopodopsis zeylanica (Crustacea: Mysida) from Cochin estuary, India

“…This is apparently related to individual nutritional status and breeding cycle (Lehtonen, 1996;Pastorinho et al, 2003). In the present study M. zeylanica have shown relatively high values of biochemical composition during the monsoon period.…”

Biochemical Composition of Zooplankton of Khour Al-Zubair Port, Southern Iraq

“…Yousefian and Kideys (2003) found that the proteins decreased by 13.4% after 5 days of fasting, whereas the lipids decreased by 46.3%, where as, low sugars decreased by 24.5%. As for lipid changes, it is related to metabolism and reproductive strategy (Pastorinho, et al 2003).…”

Distribution, reproductive biology and biochemical composition of Rhopalophthalmus indicus (Crustacea: Mysida) from a tropical estuary (Cochin backwater) in India

“…This is apparently related to the individual's nutritional status and breeding cycle (Pastorinho et al, 2003). This is apparently related to the individual's nutritional status and breeding cycle (Pastorinho et al, 2003).…”