This thesis presents some aspects of the ecology of two highly abundant small marine teleost fishes belonging to the family Gobiidae Pomatoschistus minutus Pallas 1770 and Pomatoschistus lozanoi de Buen 1923. In spite of their high abundance in the coastal waters of western Europe these two entities were only recognised as separate species in the early 1970's, but had previously occasionally been described as separate subspecies or separate forms. In the shallow coastal zone densities of these animals can reach several per square meter of sea floor (corresponding to several gram Asfree Dry Weight per m2). The species are fast growing, mature within a year and are known to occur in the stomachs of a variety of piscivores. Therefore they can be expected to play an important role in the energy fluxes to higher trophic levels. In a first part (Chapter 1) a short introduction is given to the Gobiidae. In a second part (Chapters 2, 3 and 4) some basic studies are presented on the occurrence of P. minutus and P. lozanoi, their identification and their parasites. A third part (Chapters 5,6,7 and 8) considers the food resource use by P. lozanoi, the 24-hour feeding rhythm and daily ration of P. lozanoi, a report on a freeliving nematode occurring in P. minutus stomachs and the food resource use of P. minutus. In a fourth part (Chapter 9) the interaction between P. minutus and P. lozanoi is considered. In a fifth and final part (Chapter 10) the contribution of Pomatoschistus species to the annual food consumption of two abundant gadoids is discussed. This is followed by a statement on the implications of the results and by a predictive epilogue. After the references a short Appendix follows where the regressions, used for the calculation of prey weights, are presented. |
