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OCEANARIUM
Bryozoans on the move: adaptations to hard substrate-limitingtropical heterozoan carbonates (Banc d’Arguin, Mauritania)
André Klicpera & Paul D. Taylor & Hildegard Westphal
Received: 4 July 2014 /Revised: 30 September 2014 /Accepted: 7 October 2014# Senckenberg Gesellschaft für Naturforschung and Springer-Verlag Berlin Heidelberg 2014
The Banc d’Arguin off Mauritania hosts an extensive warm-water heterozoan carbonate factory that is unique in thepresent-day world. Tropical waters characterize this epiconti-nental gulf, which lacks photosymbiotic fauna because ofincreased nutrient levels, low water transparencies and dustfrom the Sahara. Dominated by eutrophic conditions, thisatypical carbonate system does not fit into commonly usedclassifications. However, in representing a depositional para-dox, the Banc d’Arguin serves as a modern analogue for thegeological record and future perspectives of marine environ-ments affected by eutrophication and desertification. Theheterozoan community is low in biodiversity because tropicalelements are suppressed by dysphotic conditions and partlyanoxic settings, a result of high primary productivity inducedby upwelling. Paucity of hard substrates and the hydrodynam-ic regime make this ecosystem particularly challenging formarine organisms. Profiteers are specialized suspensionfeeders, such as molluscs, balanids and bryozoans (Fig. 1a).
By forming free-living, semi-mobile colonies,cupuladriid bryozoans (e.g., Reussirella sp., Fig. 1b) arewell adapted to distinct niche habitats characterized bysandy substrates. Locomotion is made possible by usingsemi-rigid setae that act as legs. This adaptation enablescolonies to resurface if buried, as well as to move on orwithin the sediment (O’Dea et al. 2009). High populationdensities (> 500 colonies/m2) in Mauritanian sediments
Fig. 1 a Heterozoan carbonates form the Banc d’Arguin; b SEM imageof Reussirella sp.; c Mauritanian bryolith encrusted by Acanthodesiacommensale and occupied by pagurid crab (PC)
A. Klicpera (*) :H. WestphalLeibniz Center for Tropical Marine Ecology, Bremen, Germanye-mail: [email protected]
A. Klicperae-mail: [email protected]
P. D. TaylorDepartment of Earth Sciences, Natural History Museum, London,UK
Mar BiodivDOI 10.1007/s12526-014-0279-3
and similar occurrences reported from other mixedcarbonate-siliciclastic shelves off Florida, Brazil(Winston and Migotto 2005) and Ghana (Cook 1965)indicate that these interstitial bryozoans may be morecommon and of greater relevance than marine ecologistshave realized thus far.
Another extraordinary adaptation to environmentalconstraints is the symbiotic partnership between bryo-zoans (Acanthodesia commensale) and a hermit crab(Pseudopagurus granulimanus). This non-obligatory co-operation provides benefits to both symbiotic partners.As the bryozoan colony grows, it furnishes an ever-enlarging shelter for the growing hermit crab occupant(Fig. 1c). In exchange, the crab offers a hard substrateon which to settle, moves the colony to new feedinggrounds or protects it against hazards and endobioticbioerosion (Klicpera et al. 2013).
These new records from the Mauritanian Shelf highlightthat our perspective on subtidal sand communities deservesmore attention, and how such potential bioarchives can in-crease our understanding of environmental control factors.
References
Cook PL (1965) Notes on the Cupuladriidae (Cheilostomata, Anasca).Bull Br Mus Nat Hist Zool 13:153–187
Klicpera A et al (2013) Bryoliths constructed by bryozoans in symbioticassociations with hermit crabs in a tropical heterozoan carbonatesystem, Golfe d’Arguin, Mauritania. Mar Biodivers 43:429–444
O’Dea A et al (2009) Relation of form to life habit in free-livingcupuladriid bryozoans. Aquat Biol 7:1–18
Winston JE, Migotto AE (2005) A new encrusting interstitial marinefauna from Brazil. Invertebr Biol 124:79–87
Mar Biodiv
