Recovery capacity of the invasive colonial bryozoan Membranipora membranacea from damage: effects of temperature, location, and magnitude of damage

Abstract

The survival and reproduction of individual or small groups of modules affords colonial organisms a great regenerative capacity. Consequently, modular loss due to fragmentation or senescence may not necessarily lead to colony mortality. This study (1) examines in situ partial mortality for colonies of the invasive bryozoan Membranipora membranacea in Nova Scotia by quantifying the location, magnitude, and timing of partial mortality for colonies growing on kelp (Saccharina latissima) in the field, and (2) estimates the effects of temperature (5–20 °C), and location and magnitude of modular loss on the recovery capacity of experimentally damaged colonies in the laboratory. In situ zooid mortality was substantial, with 50–100 % of colonies experiencing some level of partial mortality by the end of the growing season. Colonies with damage to older centrally located zooids maintained their capacity for growth and recovery, while colonies where younger peripheral zooids were removed showed no sign of recovery, and often experienced further loss of zooids. The effect of temperature depended on the location of colony damage, with increasing temperature resulting in increased loss of zooids for peripherally damaged colonies, but having no effect on the recovery of colonies with damage to central zooids. Variation in colony recovery may be related to the age distribution and reproductive maturity of zooids within a colony. Alteration of resource allocation between sexual and asexual reproduction may be adaptive in that it maximizes lifetime fitness in response to localized partial mortality.