Evidence of true succession in marine littoral associations
Cirino, Elizabeth Fahey
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A field test, designed to reveal the major aspects of the variations observed in marine littoral associations, was initiated in July, 1951, at Woods Hole, Massachusetts. This study consisted in the placing of wooden panels in the sea. Experiments based on two series of panels were outlined and so planned that the effects of tides, rhythmic reproduction, progressive variation, and cyclic variation could be segregated. One set of panels was floated vertically at a constant level and a second set was exposed so as to receive the full effects of the tides. Thus, both sets of panels were subjected to all the same features, operationally, except the tides. Panels were exposed in pairs each month and, of each pair exposed, one was left one month and the other was left two months. Thus, irregularities due to fortnightly reproduction were thought to be overcome. Other panels were exposed for varying periods of from three to twenty-four months. Panels removed for measurement and study were floated in a tray, photographed, and, when not returned to the sea, were dried out and saved. Each time a panel was removed, photographed, and measured, a collection of the biota present was made. The identity of these organisms was later confirmed in the laboratory. Observations were made at least once a week and sometimes more frequently; photographs were taken once a month. As a check on the effects, if any, of removing the experimental panels, as outlined above, control panels, left undisturbed for one year, were also set out. After exposure, panels were inspected frequently for evidence of settlement by marine organisms. Careful note was made of all variations. Irrespective of the time of exposure, the first visible change on wooden panels newly exposed to the sea at Woods Hole, Massachusetts, is the development of a scum. This scum, at first merely a thin coating imparting no more than a slickness to the surface, soon appears as a copious, thick, jelly-like mass. Although seemingly void of living organisms this material rapidly becomes associated with innumerable diatoms. Likewise, it is in this clear "gel" that the germlings of the Chlorophyceae, Rhodophyceae, and Phaeophyceae are first detected. Considering the data on all panels concerned, results show that there is a definite relationship between this incidence of microfouling and the subsequent successful invasion of macroscopic populants. The data also show the first macroscopic organisms to be species of the algae. Sessile animal forms do not become successful invaders, even when known to be breeding, until after a flourishing growth of algae has been established and an abundance of detritus is present. This investigation, continuing through August, 1954, further reveals: (1) variations in populants that are seasonal; (2) variations in populants that are annual; and (3) variations in populants that are neither seasonal nor annual and can be interpreted only in terms of a true succession. From the data it appears that much of the controversy, pertaining to the populating of newly exposed substrata, may be due to variation in the interpretation of experimental results, rather than converse data. Here we find support for the conclusions of earlier work that marine biota follow a definite sequence in populating intertidal transects and that variations in the biota do occur. However, it now seems probable that the simultaneous occurrence of variations in organisms due to seasonal progression and variations due to other causes, may have been instrumental in concealing the true nature of the complexities observed in marine littoral associations.
Thesis (Ph.D.)--Boston University
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