Image caption: The tank set-up at the Field Station with three treatments including: aquaria with a single crayfish dispersing Cladophora around the tank; algae suspended and dispersed by mild turbulence induced by a fin attached to a motor; and the control with no turbulence or crayfish, leaving a single mass of algae in one location in the tank.
Cladophora glomerata has long been viewed as a nuisance algal species throughout the Great Lakes. With increasing water clarity and altered benthic phosphorus availability, attributed to decades of ecosystem engineering by Ponto-Caspian dreissenid mussels, Cladophora is experiencing a resurgence. Cladophora attaches to hard substrates while growing but will eventually break from its holdfast as it ages (called sloughing). It can then be carried by waves and currents in the water-column, eventually settling in the benthos, washing up on shore or possibly being pulled into water-intakes and clogging infrastructure. Although significant work has gone into understanding its growth dynamics, a knowledge gap exists on what happens to Cladophora after it settles and begins to break down.
Throughout July, a 20-day decomposition experiment was performed at the Field Station using 25 aquaria to tease out the role of wave action and crayfish consumption on the breakdown process. To simulate the wave action, a machine moved a fin at a consistent, standard period within each aquarium receiving the abiotic treatment. Northern clearwater crayfish (Faxonius propinquus), a known consumer of Cladophora, was the biotic treatment. Controls were established as well as a combined treatment utilizing both biotic and abiotic contributors. Water samples were drawn from each aquarium at days 0, 10 and 20. These were sent to the National Center for Water Quality Research at Heidelberg University where a suite of tests was performed including measurement of soluble reactive phosphorus (SRP) and nitrogen. Initial and final Cladophora tissue was also collected, weighed, and tested for C:N:P as well as chlorphyll a pigment concentration in Dr. Pennuto’s aquatic ecology laboratory on campus.
While statistical analyses are ongoing, observational data through the experimental process has suggested interesting treatment effects. While crayfish have been reported to consume Cladophora in streams, this behavior has not been apparent in lakes. Throughout this experiment, the crayfish did not exhibit a significant change in mass with the presence or absence of Cladophora. However, distribution of the Cladophora within the enclosures containing crayfish appeared substantially different than enclosures containing only Cladophora. This may suggest that, although crayfish may not be actively consuming the detached algae, they may be contributing to its degradation through bioturbation of the detached mats of algae. Much as the way mechanical turbulence by waves serves to break apart algae masses, exposing surface area accessible to decomposers, the crayfish also break up and spread out the conglomerate of material. With this additional insight, combined with future statistical findings, we soon hope to better describe the contribution of natural processes to the reduction of nearshore nuisance algal biomass.
