An incubation chamber for water column sampling: experimental trial with marine sponges in an IMTA system

One of the greatest challenges in in situ experimentation involves the difficulty of controlling environmental factors, which in the marine environment can vary drastically, such as marine currents that change the temperature, turbulence or water flow in the environment surrounding the organisms and therefore affect their metabolic processes. In this sense, in the last decades different designs of benthic chambers of all types have been developed to study sessile organisms in different substrates, but none to study them in the water column, as usually placed suspended on ropes in IMTA systems. In this work, a flexible incubation chamber has been designed to study the water column around sponges located in the Remedia Life IMTA system (southeastern Italy). For this purpose, domestic plastic vacuum bags have been modified by adding a tube with Luer-lock valve. Under water, sponge explants were added in their respective rearing modules. The chambers were hung in the long-lines already set up in the IMTA system at the same depth as the sponges present and were monitored for 4 h. During this period, four 50 mL samples were collected by syringe to estimate the bacterial load inside the chamber using flow cytometry. At the end of the experiment, the volume of each bag and parameters such as pH, dissolved oxygen and temperature were calculated. Bags without sponges and with dye served as controls for bacterial load and leakage, respectively. The design of the chambers proved to be successful, with an almost constant mean volume (11.51 ± 0.24 L) and no visible leakage of the contents. On the other hand, the syringe sampling system served to evidence the filtration capacity of the sponges, with final retention values up to 97%. Moreover, the possibility of working on the surface with the chambers still hermetic made it possible to use a multiparameter probe that showed a 30.38% (4.81 SE) reduction of dissolved oxygen in the presence of the sponges. All in all, the designed chambers can be used to study the environment associated with organisms in the water column, as in IMTA systems with vertical collectors, and thus better understand their true ecosystemic role.