Abstract
Marine organism are often kept, cultured, and experimented on in running seawater aquaria. However, surprisingly little attention is given to the nutrient composition of the water flowing through these systems, which is generally assumed to equal in situ conditions, but may change due to the presence of biofouling organisms. Significantly lower bacterial abundances and higher inorganic nitrogen species (nitrate, nitrite, and ammonium) were measured in aquarium water when biofouling organisms were present within a 7-year old inlet pipe feeding a tropical reef running seawater aquaria system, compared with aquarium water fed by a new, biofouling-free inlet pipe. These water quality changes are indicative of the feeding activity and waste production of the suspension- and filter-feeding communities found in the old pipe, which included sponges, bivalves, barnacles, and ascidians. To illustrate the physiological consequences of these water quality changes on a model organism kept in the aquaria system, we investigated the influence of the presence and absence of the biofouling community on the functioning of the filter-feeding sponge Halisarca caerulea, by determining its choanocyte (filter cell) proliferation rates. We found a 34% increase in choanocyte proliferation rates following the replacement of the inlet pipe (i.e., removal of the biofouling community). This indicates that the physiological functioning of the sponge was compromised due to suboptimal food conditions within the aquarium resulting from the presence of the biofouling organisms in the inlet pipe. This study has implications for the husbandry and performance of experiments with marine organisms in running seawater aquaria systems. Inlet pipes should be checked regularly, and replaced if necessary, in order to avoid excessive biofouling and to approach in situ water quality.
Highlights
Running seawater aquaria are frequently used to study the physiology of marine organisms under controlled, ex situ condition (e.g., Wilkerson & Muscatine, 1984; Enrıquez, Mendez & Prieto, 2005; Anthony et al, 2008; Duckworth & Peterson, 2013)
The concentration of ammonium increased from the entrance of the old inlet pipe to the flow-through aquaria, but did not significantly increase along the length of the old pipe, and no significant difference was observed in the concentration of phosphate along the length of the old pipe
Bacterial abundance in the flow-through aquaria supplied by the new inlet pipe was lower (5.9 ± 0.2 × 105 mL−1, Fig. 2A) compared to the abundance at the reef entrance of the new inlet pipe (7.0 ± 0.1 × 105 mL−1)
Summary
Running seawater aquaria are frequently used to study the physiology of marine organisms under controlled, ex situ condition (e.g., Wilkerson & Muscatine, 1984; Enrıquez, Mendez & Prieto, 2005; Anthony et al, 2008; Duckworth & Peterson, 2013). In the experimental design and set-up of such studies, ambient physical abiotic factors, such as light, temperature, and water flow are given the most attention since these are well known to deviate from in situ conditions. The extent to which changes in water quality occur within running seawater aquaria and the potential effect of this on the physiology of experimental marine organisms remains largely unknown. The motivation for the present study was a large discrepancy in the number of proliferative cells measured in the sponge Halisarca caerulea (Porifera: Demospongiae) during two distinct fieldwork periods of several months, using the same running seawater aquaria system and identical methodology. The low bacterial abundances observed in our running seawater aquaria could point toward suboptimal nutritional conditions and may explain the compromised physiology of our experimental organisms
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