The effect of water flow on growth and reproduction of celleporella hyalina (l.) (bryozoa : cheilostomata)

Abstract

Colonies of Celleporella hyalina (L.), settled on glass Petri dishes, were grown in the Menai Straits. Water flow over the colonies was either unrestricted or increasingly restricted by short and long funnels fitted over the Petri dishes. Under all conditions, colonies grew exponentially for the first few weeks, but then growth decelerated. Growth rate at standard size was minimal in winter (December-February). Restricted water flow enhanced growth during winter but retarded growth at other times. Colonies began sexual reproduction at a size of ≈57 autozooids, but at different ages depending on growth conditions. When colonies had accumulated 1000-2000 autozooids, the number of reproductive zooids (males plus females) per autozooid became asymptotic in the ratio of 1.0 : 2.0 : 3.6 in conditions of restricted, semi-restricted, and unrestricted water flow, respectively. The proportion of sexual zooids that were reproductively active was greater among colonies experiencing greater water flow and, for all treatments, was greatest in June and least in winter. The experimentally induced trends in growth and reproduction were reversed by translocating colonies from one regime of water flow to another. Colonies had lower budding rates when grown close to neighbouring colonies than when isolated, but the ratio of reproductive zooids to autozooids was similar in both treatments. Ratios of female to male zooids varied among colonies but with no clear relation to the experimental conditions, suggesting that relative investments in male and female functions are largely under genetic control. The life history of C. hyalina is well-suited to the ephemeral frondai tissue of Laminaria saccharina L. (Lamour), commonly used as a substratum in British waters. Early sexual maturity and sexual activity, concurrent with somatic growth, maximize average sexual output in the circumstances of unpredictable longevity. © 1987.