Patterns of bioconstruction in the cheilostome bryozoan Schizoporella errata:the influence of hydrodynamics and associated biota

Abstract

In the region of La Spezia (Ligurian Sea, Italy), the bryozoan Schzoporella errata forms sizeable buildups, termed 'giant colonies' or 'compound colonies' by previous investigators. Buildups were encrusting (up to 40 cm wide) with flat or bumpy surfaces in an exposed site, and erect (more than 20 cm high) branching anastornosed structures in a semi-exposed and in a sheltered site. The buildup architecture was significantly different in the 3 sites, with hlgher vertical development and number of branches per dm2 in the sheltered site. The internal structure of the buildups was also different: densely packed, extensive laminated sheets developed in the sheltered site; loosely packed, concentric sheets alternating with small cavities filled with sediment and shells of associated organisms were found in the semi-exposed and exposed sites. Functional groups could be recognised among the biota associated with S. errata buildups. The constructional pattern was interpreted as resulting from both interactions with other organisms and hydrodynamic conditions. While in the exposed site S. errata showed no vertical growth, in the sheltered site soft-bodied erect organisms formed the frame around which S. errata deposited a multilayered structure, which eventually caused the death and disappearance of the immured organisms. Breakage of branch tips by episodic disturbance and repeated binding through a complex array of budding patterns by S. errata resulted in tall buildups which preserved no trace of the soft-bodied organisms. Because of the role they played, these may therefore be defined as 'ghost frame-builders'. KEY WORDS: Bryozoa. Bioconstruction. Growth forms. Hydrodynamics. Associated biota. Mediterranean Sea

The macrofauna associated with the bryozoan <i>Schizoporella unicornis</i> in southeastern Brazil

“…Other common boring taxa included sipunculans and bivalves of the genera Lithophaga, Petricola and Gastrochaena (Morton, 1983). These organisms may occur mainly in the basal parts of the colonies, where dead layers accumulate (e.g., Cocito et al 2000). These results contrast with those of Hutch- (Hutchings, 1981).…”

“…The role of bryozoan colonies as habitats was described mainly in temperate systems (Stebbing, 1971;Gordon, 1972;Bradstock and Gordon, 1983;Maluquer, 1985;Conradi and Cervera, 1995;Ferdeghini and Cocito, 1999;Cocito et al, 2000), with fewer work on tropical or subtropical regions (Lindberg and Stanton, 1988;Mantelatto and SouzaCarey, 1998). The bryozoan Schizoporella errata (Walters) generally forms massive colonies with variously shaped branches, determined from interactions with other organisms and hydrodynamic conditions Ferdeghini et al, 2000).…”

“…However, the influence of water movement on the trophic structure of assemblages associated with either biogenic or artificial substrata has received less attention (e.g., Dittman, 1990;Whorff et al, 1995). Colonial organisms such as corals, bryozoans, and some polychaetes and molluscs can develop rigid three-dimensional colonies, increasing the available secondary substrata in sublittoral systems (Gore et al, 1978;Bradstock and Gordon, 1983;Lewis and Snelgrove, 1990;Safriel and Ben-Eliahu, 1991;Nalesso et al, 1995;Cocito et al, 2000). These colonies are used by boring or dwelling species such as polychaetes, molluscs, crustaceans, and echinoderms, which make small galleries or use the available internal space both to hide from predators and to forage on debris and small invertebrates (McCloskey, 1970;Gordon, 1972;Safriel and BenEliahu, 1991;Porras et al, 1996).…”

Bioconstruction and biodiversity: their mutual influence

“…In the NW Mediterranean, several bryozoan species form monospecific structures of which the associated biota has been analysed: 'Pentapora fascialis reef' (Cocito et al, 1998;Ferdeghini and Cocito, 1999), 'Cellaria salicornioides meadow' (McKinney and Jaklin, 2000), 'Schizoporella errata buildups' (Cocito et al, 2000). Many other cases of constructions made by bryozoans interacting with other organisms have been described but information on faunal composition is not always available.…”

“…Other erect, non-skeletal to poorly skeletonized organisms, usually smaller than constructors, act as 'bafflers' reducing current velocity on the framework surface, enhancing sediment deposition and cavity filling within the framework. Because of their poor skeletonisation, sometime bafflers can remain within the framework in their original position after death (Cocito et al, 2000). If soft-bodied, bafflers can disappear after complete overgrowth by encrusting animals with mineralised skeletons (Pouyet, 1971;Taylor, 1990).…”