Temporal changes in community structure on a rocky shore in the Firth of Clyde

Hruby, Thomas (1977) Temporal changes in community structure on a rocky shore in the Firth of Clyde. PhD thesis, University of Glasgow.

Abstract

Temporal changes in the structure of a trophically simple community were investigated by monitoring the species diversity in disturbed and undisturbed algal populations on a rocky shore. The disturbance involved seasonally denuding transects from 3.04m to 1.89m above Lowest Astronomical Tide. Changes in populations were measured by calculating a coefficient of similarity between samples. Factors which could influence structure through their effects on colonization were investigated in field experiments and by culturing littoral, species in a simulated tidal regime. In an undisturbed transect extending between the littoral fringe and top of the eulittoral zone, from one to three separated population zones were identified, and the number of zones could change within six weeks. Changes in species diversity were large enough to indicate that the same piece of substratum was used by several species within a year. The vertical stratification in the top levels sampled was simple, and the dominant stratum was the algal crust. A canopy of seaweeds was poorly developed or absent. At these levels the stratification remained fairly constant with time, but in the lower levels sampled the relative amounts of substratum covered by a canopy, understory, and encrusting layer could change within a few weeks. When determined by the similarity coefficients, strips cleared in the spring took only 12-14 months to entirely recover, whereas those cleared in the late summer and autumn took 18-20 months. After clearing it took longer for an algal cover to develop at the higher levels on the shore, but the populations here came to resemble those in the undisturbed control sooner than did the ones in the bottom levels. It was found that the algal diversity settling under a canopy was significantly different from that settling on open substrata, and the populations in the lower levels came to resemble those in the control only after the full canopy of Fucus spiralis was re-established, and comparable to that in the lower levels of the control. of propagules, their distribution in the surface waters, the level on the shore, the nature of the algal canopy they must penetrate, and the environmental conditions prevailing immediately after settlement when the plants were found to be most vulnerable. Zonation appeared with the first populations colonizing cleared strips but it was different from that in undisturbed areas. The initial zonation was probably determined by the factors mentioned above, rather than by the tolerances of individual species or by competition. After the populations in cleared strips came to resemble those in the control, the zonation in both were essentially similar except for local differences resulting from patchiness. A very small scale patchiness not readily visible in the field was found to be caused by amphipod grazing.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Trevor A Norton
• Keywords: Biological oceanography
• Date of Award: 1977
• Depositing User: Enlighten Team
• Unique ID: glathesis:1977-73892
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 14 Jun 2019 08:56
• URI: https://theses.gla.ac.uk/id/eprint/73892