Larvae of uncommon caridean decapods in the German Bight: Species composition, distribution and abundance

Abstract

Typically, the most abundant group of shrimp larvae in the German Bight is formed by representatives of the family Crangonidae. Larvae of the remaining species have been largely ignored, and only scarce information concerning their ecology is available. Thus, the purpose of the present study was to determine the species composition, distribution and abundance of noncrangonid shrimp larvae in the German Bight in July 1990, after the mildest winter of the century. The material is based upon plankton samples collected at 77 stations, covering the entire German Bight. Eight species were identified, as well as larvae of Palaemonidae and Processa-juveniles. Processa nouveli holthuisi (53.0 %) and P. modica (31.3 %) were predominant in the collection. The distribution of the two species was clearly separated: the main concentration of P. nouveli holthuisi (peak concentration of 1.94 larvae per m 3) was confined to the northwest corner of the German Bight, while a majority of P. modica larvae (peak concentration of 0.54 larvae per m 3) occurred at the southwesterly stations. The spatial distribution of Caridion steveni and ]Zualus occultus around Helgoland indicates the presence of an adult population at the only rocky island in the study area. Other taxa, such as larvae of Palaemonidae and juvenile Pandalina brevirostris were collected exclusively in estuarine habitats. Based upon both the results of the present study and comparable data, we conclude that developmental stages of ten non-crangonid species, as well as representatives of Palaemonidae, can be expected to occur in the plankton of the German Bight. The extremely mild temperatures of the preceding winter may have been, in part, responsible for the relatively high densities of some taxa encountered during our plankton survey. We assume that warm winter temperatures favour the immigration, reproduction and survival of cold-sensitive species.

Larval Growth Patterns in the Aesop Shrimp Pandalus Montagui

“…The same effect was predicted to occur also in a spider crab species which releases its larvae in late winter (Anger, 1983). Scarcity of data from the plankton, however, precludes at present a comparison of predicted and observed patterns of larval development and recruitment in Aesop shrimp (Wehrtmann, 1989;Wehrtmann and Greve, 1995).…”

“…While the larval development of several other pandalid species has been extensively studied both in the laboratory and in the natural environment (e.g., Modin and Cox, 1967;Wickins, 1972;Haynes, 1976Haynes, , 1978Haynes, , 1979Haynes, , 1980Haynes, , 1983Haynes, , 1985Rothlisberg, 1979Rothlisberg, , 1980Stickney and Perkins, 1981;Wienberg, 1982a, b;Mikulich and Ivanov, 1983;Komai and Mizushima, 1993;Ouellet et al, 1995, and earlier papers cited therein), only incomplete morphological descriptions and a few growth data have become available for larval Aesop shrimp (Pike and Williamson, 1964; older literature cited therein). Possibly also as a consequence of identification difficulties caused by the lack of a detailed morphological description, only scarce data are available on the seasonal and local distribution patterns of larvae of P. montagui in the plankton (Thorson, 1946;Lebour, 1947;Rees, 1952;van der Baan et al, 1972;Lindley, 1987;Wehrtmann, 1989).…”