Study goal: to determine the cause of death of those Chthamalus that settle below the mhwn. Methods

Connell, Joseph H. 1961. The Influence of Interspecific Competition and Other Factors on the Distribution of the Barnacle Chthamalus stellatus. Ecology. 42:710-23.

Summary

This is one of the earliest studies demonstrating the complexities of competition in the field.

Study organisms:

Chthamalus stellatus: the “upper” barnacle species. Adults occur between the Mean High Water of Neap and Spring tides (MHWN and MHWS respectively). Although juveniles settle down to the Mean Tide Level (MTL), few survive below the MHWN level.

Balanus balanoides: the “lower” barnacle species. Adults occur from mean low water of spring tides to region between MHWN and MHWS. Above MHWN it occurs with Chthamalus for a short distance. Predation by the snail Thais lapillus is among the most imp. causes of mortality and the snail preferentially feeds on Balanus over Chthamalus.
Study goal: to determine the cause of death of those Chthamalus that settle below the MHWN.
Methods: Measured the survival of Chthamalus with and without interspecific competition, with or without predation by Thais lapillus, and at different depths in the water column.
Results:

Effect of Competition

1. 
   Chthamalus is tolerant of much greater immersion than it normally encounters (translation: it could live deeper in the water column than it is found)
   

2. 
   Intraspecific comp. in Chthamalus rarely leads to mortality
   
3. 
   Interspecific comp. between Chthamalus and Balanus is an important cause of death for Chthamalus.
   
4. 
   After a year of crowding, the relative proportions of Chthamalus and Balanus remained constant, but Balanus grew faster and taller, occupied a greater proportion of the surface area and, presumably, had a higher biomass.
   
5. 
   Seasonal variations in the growth rate of Balanus corresponded to changes in mortality rate of Chthamalus.
   
6. 
   “For all of these observations it appears that the poor survival of Chthamalus below MHWN is a result mainly of crowding by dense populations of faster growing Balanus.
   

Effect of Predation:

“At upper levels mortality is greater inside the cage, at lower levels greater outside. Densities of Thais tend to be greater at and below MTL so that this trend in mortality rates of Chthamalus may be ascribed to an increase in predation by Thais at lower levels”

Much of the mortality of Chthamalus growing intermingles with Balanus was a result of crowding…”It therefore seemed reasonable to take the difference between the mortality rates of Chthamalus with and without Balanus as an index of the degree of competition between the species.”
Background, putting it in context:

Connell’s paper marked one of the first times that field experiments were used to examine the interaction between environment and competitive outcomes. Unlike the earlier work by Gause (1932) where uniform a experimental environment lead to the extinction of one spp, Connell’s field experiments demonstrated how a diverse environment with complex interacting factors could result in coexistence of competing spp. These experiments and other by Connell laid the groundwork for subsequent field experiments examining biotic interactions along physical gradients.

Connell’s 1975 synthetic overview asserted that ecologists needed to be more rigorous in what they accepted as “evidence” supporting competition as the central mechanism determining community structure. This resulted in more experimental investigations of competition, more balanced views on factors determining community structure, and increased appreciation of the complexities of community interactions and thus increased difficulties in making generalizations about community patterns.

Good background to the Connell paper in the section intro in Foundations (above is all taken from there)