Littorina rudis (Maton) is the most widely distributed and variable British littorinid. The present study investigates the ecological adaptations which underlie its success in greatly differing habitats. Three contrasting shores, Greenhithe (polluted estuary), Landshipping (unpolluted estuary) and Newhaven (open coast) were studied between October 1972 and July 1975. Reproductive output differed markedly at each site. At Greenhithe large embryos were produced in small numbers, the opposite relationship existing at Newhaven. The Landshipping results, though less pronounced, resembled those from Greenhithe. Reciprocal transplants between Greenhithe and Landshipping provide tentative support for the view that these differences are genetic. There was no evidence that polluted estuarine conditions had ser= ious reproductive or other effects at Greenhithe. Significant embryonic abnormality was recorded, but at ecologically unimportant levels. Collections from additional shores suggested a more general relationship between embryo size and factors associated with shelter. Very high juvenile mortality occurred at each site,, and these reproductive differences are viewed as adaptive responses to prevailing causes of mortality. At Greenhithe and Landshipping these include crushing and desiccation, with possibly some predation by crabs at Landshipping. These factors would'favour larger, stronger hatchlings. At Newhaven, juvenile survival depends upon finding small crevices or empty barnacle shells in which to escape desiccation and wave buffeting. Here, production of numerous small hatchlings appears adaptive. As well as affecting reproductive characteristics, mortality patterns are suggested as a major cause of size structure variations within änd between populations. Individual growth and production rates are high at both estuarine sites, probably resulting from favourable conditions for feeding. Growth and production may be limited in.. exposure by the time available for feeding.
|Creators||Faller-Fritsch, Robert John|
|Publisher||King's College London (University of London)|
|Source Sets||Ethos UK|
|Type||Electronic Thesis or Dissertation|
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