AGING IN MODULAR ORGANISMS: ECOLOGY OF ZOOID SENESCENCE IN STEGINOPORELLA SP. (BRYOZOA; CHEILOSTOMATA)

¹ Department of Zoology, University of Washington, Seattle, WA 98195, Discovery Bay Marine Laboratory, Discovery Bay, Jamaica W.I.
² Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, MD 21218, Discovery Bay Marine Laboratory, Discovery Bay, Jamaica W.I.

The modular construction of clonal plants and animals can lead to physiological deterioration of some clonal components independent of the age or size of the clone as a whole. As a result, senescence does not invariably lead to death (as is the case for solitary organisms), but rather to a patchwork of colony areas exhibiting differing degrees of modular deterioration. In Jamaican cryptic reef environments, older zooids of the cheilostome bryozoan Steginoporella sp. exhibit deterioration in feeding and regenerative abilities, are more heavily fouled by epibionts, and contain more stored metabolic waste products when compared to younger zooids. In particular, slower regeneration of broken colony margins in proximal sections allows other encrusting species, which are normally overgrown by the vigorous distal sections of Steginoporella sp., to overgrow senescent sections. Thus, although Steginoporella sp. is the most abundant bryozoan in Jamaican cryptic reef environments, it can occupy space only ephemerally. Evidence suggests that in Steginoporella sp. and ecologically similar species, the disadvantages of proximal senescence are offset by increased translocation of energy or nutrients to vigorously growing distal colony sections.

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