Grazing impact and phenology of the freshwater sponge Ephydatia muelleri and the bryozoans Plumatella emarginata and Fredericella sultana under experimental warming

Abstract

1. Both the clearance rates (CR) and abundances of the freshwater sponge Ephydatia muelleri and the bryozoans Plumatella emarginata and Fredericella sultana were investigated from autumn to spring under different temperature regimes. The experiments were performed in bypass channels of the River Rhine (Cologne, Germany) in which temperature could be manipulated. 2. The impact of temperature increase on CRs depends upon the grazer: E. muelleri showed a clear increase in CRs with increasing temperature whereas P. emarginata was not significantly affected by experimental warming. 3. Distinct differences in food preference were found for the sponge (which is an efficient grazer of bacteria and small algae) and for the bryozoan P. emarginata (which feeds primarily on large algae, and with no significant grazing on bacteria). 4. In contrast to their temperature-related patterns in CR, respiration of both P. emarginata and E. muelleri increased with temperature between 19 and 32°C, suggesting that the risk of experiencing energy deficiency at high temperatures due to increased metabolic rates is particularly high for the bryozoan. 5. A temperature elevation of 3°C above the natural Rhine temperature resulted in a delay in the disappearance of active tissue and formation of resting stages for E. muelleri in autumn. This delay ranged from 8 (beginning of gemmulation) to 22 days (termination of gemmulation). In contrast, there was no distinct effect of warming on the disappearance of active zooids of the two bryozoan species in autumn. However, warming can positively affect the maintenance of active zooids during winter in F. sultana. In spring, the appearance of active zooids of P. emarginata was clearly stimulated by temperature elevations, whereas the hatching of both F. sultana and E. muelleri was hardly affected by warming. 6. The study demonstrated different patterns in the thermal ecology of the two freshwater bryozoans and the sponge in comparison to other filter feeders, particularly mussels. Such patterns need to be considered when predicting the impact of temperature on pelagic-benthic coupling in aquatic habitats.

Contribution of biofilm-dwelling consumers to pelagic-benthic coupling in a large river

“…Welker & Walz, 1998;Caraco, Cole & Strayer, 2006). Brown et al, 2005;Vohmann et al, 2009). However, as most evidence for the importance of bivalves in this context is indirect (e.g.…”

“…In addition to bivalves, several other benthic consumers of plankton exist in freshwaters (e.g. Brown et al, 2005;Vohmann et al, 2009). Among them, biofilm-dwelling consumers, i.e.…”

Identification of five bryozoan species in the Northern Mallee Pipeline, Australia

“…Plumatella emarginata is common throughout Europe, especially in lotic waters (Wood & Okamura 2005); this species has been reported from Britain (Harmer 1913), Wales (Thorpe & Mundy 1980), Ireland (Smyth 1994), Austria (Wo¨ss 2000), Italy (Tattichi & Pieroni 2005), Greece (Massard & Geimer 2008b), Germany (Gruhl et al 2009;Vohman et al 2009) and Serbia (Martinovic-Vitanovic et al 2010). Plumatella emarginata has also been reported from India (Shrivastava & Rao 1985), Israel (Massard et al 1992), Canada (Ricciardi & Reiswig 1994), New Zealand Smith & Batson 2005), USA (Callaghan & Karlson 2002) and Japan (Mukai et al 1990;.…”

Food selection by Plumatella geimermassardi Wood and Okamura, 2004 (Phylactolaemata, Bryozoa)

“…CRs were determined comparing concentration of solids before (pre-exposure) and after (post-exposure) polypides were collocated in the Petri dishes for 24 h. During this time frame specimens were fed and water cleared. The values were corrected for passive losses of suspended solids by sedimentation and by suspended organic matter degradation using control treatments containing only marsh water (Vohmann et al, 2009). Loss rates (R, h À1 ) were calculated by assuming exponential changes.…”

“…temperature, water velocity and salinity) (Okamura, 1987;Riisgård and Manriquez, 1997;Eckman and Okamura, 1998;Okamura and Partridge, 1999;Lisbjerg and Petersen, 2001;Pratt, 2008). However, CR of certain freshwater bryozoan species may be related only with food concentration (Vohmann et al, 2009).…”