Vermetid gastropods modify physical and chemical conditions above coral–algal interactions
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Interaction modifications can arise when a third species alters the physical and chemical environment within which two other species interact. On coral reefs, corals and algae commonly interact amid a suite of other species that may modify their interaction. Massive Porites coral and algal turfs often are covered by mucus nets cast by the vermetid gastropod, Ceraesignum maximum. Previously, vermetid mucus nets have been shown to have deleterious effects on corals. Here, we hypothesized that vermetids not only have direct effects on coral, but they also change the local physical and chemical environment establishing the potential for interaction modifications by intensifying the effects of algae on corals. To test this, we examined the effect of vermetids on physical and chemical aspects of the environments. We quantified light penetration, water flow, diffusive boundary layer (DBL) thickness, and oxygen concentrations in the presence and absence of vermetid nets. Vermetid nets did not affect light levels. Because we observed reduced water flow and increased DBL thickness in the presence of nets, we also expected to observe high oxygen concentration over coral surfaces. Instead, we observed no difference in oxygen concentrations in the presence of mucus nets. To explain the lower than expected oxygen concentrations, we hypothesize that nets decreased photosynthesis and/or increased respiration of corals and algae and their associated microbiota. This is the first study to explore mechanisms underlying the deleterious effects of vermetids on corals, and shows that vermetid mucus nets may modify coral–algal interactions by intensifying physical and chemical conditions.
KeywordsCeraesignum maximum Coral reefs Competition Interaction modification Physical and chemical conditions
We thank Robert Carpenter and Cal State Northridge for allowing the generous use of their flume. Thanks also to the UC Berkeley Richard B. Gump Marine Station and staff for support and facility use, J. Zill and E.A. Hamman for field assistance, M. Peil and B. Sipley for help with the light data, F. Ballantyne and C. Song for statistical insights, and J. Wares for comments on an earlier manuscript. This work was funded by NSF Grant OCE-1130359.
Author contribution statement
ALB and CWO conceived the ideas and experiments. ALB conducted the experiments for the lab and field water retention and oxygen studies. ALB and CWO did the fieldwork for the light experiment. ALB analyzed the data. ALB and CWO wrote the manuscript.
Compliance with ethical standards
All applicable institutional and/or national guidelines for the care and use of animals were followed.
Conflict of interest
We declare no conflicts of interest.
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