Investigating the relative roles of physical and biological factors in determining community structure across gradients of emersion and wave exposure in the rocky shore intertidal has been one of the principal areas of interest in marine ecology. However, the way in which the role of these factors changes over large latitudinal scales across European shores has not been quantitatively assessed. Using a large scale survey across the European coastline changes in community structure from a local to a European scale were assessed in a quantitative manner, with particular focus on the dominant primary producers, fucoid macroalgae, and key grazers, patellid limpets. Following this quantitative descriptive approach, key controlling processes that ultimately could lead to alterations in the community structure and energy flow between ecosystems were also explored. The large scale survey gave a broad scale quantitative description of major functional intertidal groups over a latitudinal gradient from northern Scotland to southern Portugal (Chapter 2). This descriptive work explicitly operated at a very coarse scale of resolution to essentially differentiate between algal dominated and sessile invertebrate dominated assemblages. In describing latitudinal patterns, a key confounding variable, wave exposure, was addressed by independently categorising shores into three categories according to the I / degree of wave action. This was achieved using a GIS model based on wave fetch. The quantification of patterns of biomass and percentage cover over latitudinal scales resulted in the development of a database for different intertidal functional groups covering a large area of the European rocky intertidal, which can be used by future studies for temporal comparisons and evaluation of the effects of possible climatic alterations. The survey showed a decline in total fucoid biomass and percentage cover in the Portuguese region, but little variation over the extent of the British Isles. The expected corresponding increase in filter feeder cover was not obvious and an increase in Patella grazer density and biomass in Portugal was not found. A number of targeted field experiments and collections were undertaken in Wales and Portugal to ascertain the causal factors leading to the observed gradient in algal-animal balance in the intertidal over a European scale. A factorial experiment (Chapter 3) was undertaken in the field to determine the interactive effect of grazing pressure and physical environment (shade and moisture) on patterns offucoid recruitment. Amelioration of the physical environment did not improve recruitment at either geographical region, while grazing pressure was found to be an important process regulating fucoid recruitment only on northern European shores. Adult algal characteristics, specifically stress levels (Chapter 4) and reproductive capacity (Chapter 5), were assessed, through experimental work, to determine their contribution to latitudinal scale patterns. The results showed that stress levels (measured as photosynthetic resilience) increase in fucoid populations when they were subjected to physical conditions characteristic of a summer day in Portugal, with specimens not being able to fully recover even after a 16 hour recovery period. Environmental conditions in southern regions were also found to promote fucoid populations with lower numbers of receptacles and lower reproductive tissue biomass, which indicates reduced reproductive capacity. Using the data collected and conclusions about patterns and processes from the experiments undertaken during the PhD, changes in algal productivity and filter feeder abundance were discussed, while predicting energy flow from and to the coastal environment at local and large geographical scales. The work demonstrates the importance of undertaking quantitative surveys over large scales whilst controlling for key confounding variables. Whilst many of the patterns expected from previous qualitative descriptions and quantitative work undertaken at local scales were verified, there were important unexpected outcomes. In addition, experimental work undertaken in different geographical regions has provided some insight into key processes determining large scale patterns.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:569559 |
| Date | January 2012 |
| Creators | Ferreira, Joao Luis Gomes |
| Publisher | Bangor University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://research.bangor.ac.uk/portal/en/theses/latitudinal-and-climatic-driven-changes-in-local-patterns-of-intertidal-macroalgae--implications-for-biodiversity-and-ecosystem-functioning(2925385d-de37-4383-baa4-3c4f842f753e).html |
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