Larvae of Decapod Crustacea from the Adriatic Sea
Abstract
A preliminary study of the larvae of decapod crustacea from the Adriatic Sea is made on the basis of a series of collections from Mljet (Gonoturska) from February 1952 to March 1953. Almost simultaneous collections taken from the lake Mljet (Vrbovačka) and Dubrovnik (Sv. Andrija) and some other stations in the Adriatic Sea are also made use of for the sake of comparison.
The systematics, seasonal and zonal distribution of 60 species of decapod larvae are given.
From a systematic study of the larval stages, it may be observed that
the larval stages of some species recorded from the warm Adriatic Sea are larger than the corresponding stages of the same species collected
from the cold waters of the North Sea, Danish coasts and Plymouth area
and are found to be further advanced in development, even from the time of hatching from the egg.
The number of species of decapod larvae is greater than found
in similar collections from the cold waters of the North Sea and Danish coasts.
The number of species as well as the number of individuals of decapod larvae is greater in the collections nearer the shore than at the stations away from the shore.
The maximum number of larvae occurs within 50 m.
Judging from the occurrence of larvae in the collections, two main breeding seasons are observed in the sea - one in summer and the other in winter, the winter maximum being formed by the sporadic occurrence of crab zoeae and early larval stages of Sergestes spp.
The hatching period of most larvae seems to agree with that in the Mediterranean Sea and is earlier by 4-6 weeks, than in the North Atlantic.
The occurrence of the larvae in the lake Mljet almost coincides with that in the sea outside, but the larval maximum (the number of species as well as individuals) in the lake is found to be earlier than in the sea by about one month, probably because of the quick heating of the water by the onset of spring, which induces the spawning of the species.
Larvae of no endemic species are found in the lake.
Only a single maximum of larvae (May) is found in the lake, mainly because of the absence of the larvae of Penaeidea, which are found to breed in the sea during the winter months.
The larvae of each species has a depth preference.
The general trend in diurnal migration of larvae agrees with the accepted views on vertical distribution namely the concentrating of most species near the surface during dusk and travelling back to their optimum intensity of light during day time.
