The Physiological Impacts of Cultivating Mussels on a Kelp Farm: A Solution to Ocean Acidification?

Abstract

On shellfish farms, cultivated seaweed may remove sufficient amounts of CO2 to mitigate acidification at small spatial scales during peak primary production. This thesis investigates whether cultured sugar kelp, Saccharina latissima, creates favorable conditions for the blue mussel, Mytilus edulis. In a two-month field experiment, 1,200 one-year-old mussels and standardized recruitment substrata were deployed inside predator exclusion cages (3 replicates per site) at increasing distances from a kelp farm (0, 125, 180, 395m). Mussels cultivated within the kelp farm exhibited: 1) shells with significantly greater resistance to acute pressure (75%) and tolerance to force before breaking (5%), 2) greater shell thickness (27%) and density (88%), and 3) larger meat masses (28%). Further, mussels grown at an intermediate distances from the kelp farm contained significantly less CaCO3 and more demineralized protein matrix than those grown elsewhere. Despite higher rates of invertebrate recruitment inside the farm, biofouling of mussels was equivalent at each deployment distance, and mussel recruitment rates were negligible during the study period. An elliptic Fourier analysis suggests that stressed mussels have more variable and potentially less favorable shell morphology, but can otherwise maintain comparable shell length, width, and volume, relative to cocultivated mussels. The exact underlying mechanism of positive impacts to mussel production – amelioration of acidification or supplemental food from kelp detritus – is still under investigation. This study provides evidence that cocultivation offers a bio-efficient methodology for reducing marine calcifier stress, while simultaneously increasing mussel product quality.