Use this URL to cite or link to this record in EThOS:
Title: Ecological studies of Littorina obtusata and Littorina mariae in Milford Haven
Author: Al-Hamadani, E. S. M.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1981
Availability of Full Text:
Access from EThOS:
The two species Littorina obtusata and Littorina mariae are sibling species of prosobranch gastropoda (Mollusca) of rocky intertidal habitats of N. West Europe. Their distribution in the study area seemed typical, with similar patterns relating shell colour polymorphism to wave exposure as previously seen elsewhere. L. obtusata was zoned on the middle and lower shore on its food plant Ascophyllum nodosum, while L. mariae was largely confined to Fucus serratus on the lower shore. Morphological comparisons revealed further criteria for separating difficult specimens. Detailed studies were made of egg and embryo size and development; also spawn characters and spawning season. Growth of both species in aquarium conditions was studied. Adult populations of L. obtusata had a stable, high density, whereas those of Lit. mariae had an unstable, low density. Density appeared to be controlled by predators. L. mariae survived high predator pressure on the lower shore by having a more concentrated spawning period and by breeding at a younger age (and smaller size) than L. obtusata. Adults of L. obtusata survive for 3 to 4 years to form the stable component; adult L. mariae are mainly predated in the summer of their first or second breeding season. An experiment demonstrated the better ability of L. mariae than L. obtusata to withstand water currents. Furthermore, the exposed shore morph (reticulata) of L. mariae withstand them better than the citrina morph (sheltered shores). Hatchlings of both species were more readily dislodged than adults which could help to explain the preponderance of the reticulata morph of L. mariae on exposed shores since the young winkles are cryptic in the undergrowth weeds, such as Gigartina stellata largely absent on sheltered shores. Collections of specimens of three related taxa were examined morphologically and by enzyme electrophoresis. It was concluded that "L. aestuarii" is an ecomorph of L. obtusata and "L. beensis" an ecomorph of L. mariae but L. palliata is a good species.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available