Flow and polypide distribution in the cheilostome bryozoan Bugula and their inference in Archimedes

Abstract

Cilia‐generated flow in the absence of ambient current is directed from frontal to reverse sides of branches in Bugula turrita, B. turbinata, B. neritina, and B. stolonifera, whether axes of feeding lophophores are perpendicular to the basal plane of branches or are tilted toward distal ends of branches. Ambient current less than 5 cm per second interacts with cilia‐generated flow, but ambient flow of 15 cm per second destroys self‐generated colonial flow and severely hampers feeding. Polypides are located in the more distal, younger portions of colonies, in species with and without polypide recycling, whereas zooids in the more proximal, older portions are senesced. Presence of feeding polypides in distal but not in proximal portions of the larger spiralled colonies of B. turrita and B. turbinata results in downward, slightly radially directed flow through the colony. The colonial flow passes directly from one whorl to the next‐proximal so that water exits from low around the colony perimeter, and a proximally expanding conical stagnant zone occupies the interior of the colony. A substantial percentage of zooecia in distal whorls of well‐preserved Archimedes is filled by sediment and inferred to have been occupied by actively feeding polypides. whereas spar‐filled zooecia capped by terminal diaphragms were apparently senesced during the latter part of a colony's existence. The capped zooecia constitute an increasing percentage of the total in more proximal whorls. Generally similar colony form and inferred similarity in distribution of current‐generating polypides in spiralled colonies of Bugula and in Archimedes suggest that colony‐generated flow in Archimedes was similar to that in Bugula, passing downward and then outward, and only through the distal whorls of the colonies.

Form and metabolic scaling in colonial animals

“…It could also be imposed by self-shading resulting from three-dimensional colony growth and lack of feeding current integration that could potentially compensate for selfshading (processes that explain the surface area:volume scaling exponent predicted by the DEB model). Thus, both reprocessing of excurrents by zooids within the colony and flow diversion around the colony (Chamberlain and Graus, 1975;McKinney et al, 1986;Grünbaum, 1995) should contribute to self-shading.…”

Allometry of resource capture in colonial cnidarians and constraints on modular growth

“…Chamberlain & Graus (1975) found that water tended to flow around branching colonies rather than through it, resulting in stagnant water masses in the colony centre. Even when feeding currents are actively generated, as in the spiralled branching bryozoan Bugula , water drawn in from the top of the colony flows down and out, resulting in stagnant regions in the colony interior (McKinney et al 1986). Similarly, Grünbaum’s (1995) modelling efforts on the feeding currents in encrusting bryozoans reveal that flow is lowest at the colony centre and increases towards the colony periphery.…”

Effect of Zooid Spacing on Bryozoan Feeding Success: Is Competition or Facilitation More Important?

“…2). Food particles, which are generally phytoplankton, are transported to the mouth by a combination of mechanisms, including beat reversals of lateral cilia (Strathmann, 1973(Strathmann, , 1982, tentacle flicks (Borg, 1926;Bullivant, 1968a;Strathmann, 1973;Larsen and Riisgård, 2002), other behaviors involving the tentacles (Winston, 1978), and bulk flow (Bullivant, 1968a;Best and Thorpe, 1983;McKinney et al, 1986). Particle capture can be influenced by many factors such as temperature (Riisgård and Manríquez, 1997), particle concentration Thorpe, 1983, 1986b;Riisgård and Manríquez, 1997), presence of neighboring colonies (Okamura, 1984(Okamura, , 1985(Okamura, , 1988Best and Thorpe, 1986a, b), particle size (Okamura, 1987(Okamura, , 1990, and colony size (Okamura, 1984(Okamura, , 1985.…”