- Die Wirkungen Extrem Niedriger Temperaturen
- Open Access
The effects of the cold winter of 1962/63 on the helgoland population ofBranchiostoma lanceolatum (Pallas)
© Biologischen Anstalt Helgoland 1964
1. Seawater temperatures at Helgoland were subnormal for six months during the winter of 1962/63 and fell to −1.3° C. Quantities of silt from the shores and estuaries of the mainland were released into the water when pack ice around the island melted in late February.
2. In a sample dredged from a ground near Helgoland in April, 1963, 40% of the lancelets consisted of isolated notochords. From comparison with a sample taken in November, 1962, it is estimated that at least 50% of the population died during the winter. The average number of animals per Van Veen grab fell from 6.9 before to 3.0 after the cold period.
3. None of the autumn settlement of newly metamorphosed animals survived, and there was a very high death rate estimated at 90% among the largest animals.
4. An analysis of activity in relation to temperature inBranchiostoma lanceolatum collected from Helgoland and Naples showed a temperature tolerance of 3° to 27° C in both populations with active swimming at temperatures of 10° to 20° C. There is no muscular movement below 3° C which is the lower limit of the normal winter temperature at Helgoland. It is suggested that the species is best adapted to Mediterranean conditions.
5. The pharyngeal mechanism cannot operate normally below 3° C and although it is considered unlikely that starvation was the primary cause of death, other effects of a reduced pharyngeal current may have proved lethal.
6. It is held that the depth to which lancelets of different sizes burrow into the substrate could account for differential mortality through cold.
- Cold Period
- Seawater Temperature
- Temperature Tolerance
- Active Swimming
- High Death