Estuaries are the interface between freshwater systems and the sea, with clearly
recognizable changes in the distribution of organisms along various environmental
gradients from riverine to fully marine conditions. This thesis studied ecological
processes affecting the distribution of marine species along estuarine gradients using
both field and laboratory experiments with barnacles as a tractable model system.
Elminius modestus Darwin, Semibalanus balanoides Linneaus, Chthamalus montagui
Southward are the most common barnacle species found in the intertidal of British
estuaries. Surveys performed in the Plym and the Yealm Estuaries revealed that E.
modestus occurred furthest up estuaries and was dominant along most of their length,
with the exception of sites closest to the sea; C. montagui had the most restricted degree
of penetration up-estuary; and S. balanoides occurred at low abundances, with limits of
penetration located between those of C. montagui and E. modestus. Transplants of adult
specimens to sites along the marine-to-freshwater gradient revealed that E. modestus
was better adapted to environmental conditions found in inner areas of the estuaries than
C. montagui and S. balanoides. Survival of the latter two species was negatively
correlated with deposition of silt and decreasing salinity. Laboratory experiments
showed that, in contrast to the other two species, E. modestus was highly tolerant to
burial by silt. A comparison of observed distributions along the gradients with
survivability showed that C. montagui was able to survive in areas where adults were
absent, indicating that early life cycle stages were a potential limiting factor to the
distribution of this species. Examination of patterns of cyprid settlement and
recruitment to the benthic phase reinforced the suggestion that pre-settlement processes
contribute to restrictions in the distribution of both C. montagui and S. balanoides. The
abundance of these species, post-settlement, was also affected by physico-chemical
conditions in the upper estuary. Pre-settlement processes did not limit the distribution of
E. modestus and post-settlement processes appeared to be more important in limiting its
abundance at sites closest to the sea.
Date of Award | 2007 |
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Original language | English |
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Awarding Institution | |
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PRE- AND POST-SETTLEMENT PROCESSES INFLUENCING THE DISTRIBUTION OF BARNACLES ALONG ESTUARINE GRADIENTS
GOMES FILHO, J. G. F. (Author). 2007
Student thesis: PhD