Studies on Holkham salts hole : an isolated salt water community with relict features

Alcock, Barry R. (1982). Studies on Holkham salts hole : an isolated salt water community with relict features. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000de10

Abstract

There is at Holkham, North Norfolk, a marine pond which supports a fauna thought to be principally a relict from the time when it was part of an estuarine tideway, two hundred and fifty years ago.

Studies have been carried out on the hydrology and hydrography of this pond, known locally as the Salts Hole. The nature of the substratum,changes in salinity, temperature and other physical variables have been assessed and from these it has been possible to establish that conditions within the pond are remarkably stable.

The fauna is reviewed and its relationship to other brackish water ponds discussed.

Experiments designed to produce response surfaces have been carried out for three crustacean species, Idotea chelipes, Gammarus duebeni and Praunus flexuosus. These describe how changes in salinity, temperature and oxygen concentration influence survival of both adults and juveniles. Populations drawn from the surrounding marshes of Holkham Bay have been compared to those of the pond,, The response surface centres of the Salts Hole populations correlate more closely with the conditions prevailing in the pond, than do the Bay populations.

Electrophoresis of Malate dehydrogenase and Leucine aminopeptidase isozymes was performed for the same three species of crustaceans. The Salts Hole populations contain fewer alleles and show significantly higher levels of genetic divergence. Several hypotheses relating genetic polymorphism. and environmental conditions have been examined.The findings support Valentine's hypothesis of trophic resource stability and Stenseth's interpretation of the Red Queen hypothesis, predicting that fewer species are found in the pond than in the surrounding salt-marshes.

The relative contributions of random genetic drift and selection are discussed and conclusions are drawn that the Salts Hole populations,despite their relatively short period of isolation and small numbers, have been subjected to the effects of selection.