Stress Tolerance of an Invasive Alga, Grateloupia turuturu, and Studies of Bacterial Communities of Fucus spp. Along an Intertidal Stress Gradient

Maine’s intertidal zones are ecologically and economically important habitats that face new anthropogenic perturbations (e.g., invasive species introductions, commercial activities, climate change). For example, I discovered the invasive red alga Grateloupia turuturu for the first time in Maine (Damariscotta Estuary) in 2017, over 200 km north of its last known location. Coastal facilities often employ biosecurity protocols in an attempt to limit the spread of such invasive species, but their effectiveness against G. turuturu was unknown. This study examined susceptibility of G. turuturu and some native macroalgae (e.g., Mastocarpus stellatus, Palmaria palmata) to a common bleach-based biosecurity protocol (50 ppm free chlorine [bleach] for at least 2 hr). This procedure killed P. palmata, but neither M. stellatus nor G. turuturu died. Test strips that are widely used, and required in shellfish aquaculture by the Maine Department of Marine Resources, inaccurately measure free chlorine levels in seawater. Furthermore, bleach treatment likely triggered a previously unreported stress response in G. turuturu and altered its reproductive cycle; rather than releasing mature carpospores into the water, carpospores formed a callus-like mass in the cystocarp, which directly germinated into one new blade per cystocarp. I found that carpospores that were released from cultured blades germinated normally. Sporelings could survive subsequent bleach-treatment if they were covered by diatoms. Both G. turuturu and M. stellatus were susceptible to seawater heated to 60 degrees C for at least an hour. Based on these results, chlorination appears to be ineffective as a universal biosecurity method and another method should be used in conjunction with or to replace chlorination. Maine’s intertidal zones are often dominated by three Fucus congeners: F. spiralis (high zone), F. vesiculosus (mid-zone), and F. distichus subsp. edentatus (low zone). Some bacteria are vital to the health of their hosts, but it is unknown whether associated bacterial communities also follow zonation patterns caused by the sharp vertical gradients in abiotic and biotic stresses that affect their hosts. To investigate this, I surveyed the bacterial communities of Fucus spp. along the intertidal gradient. I also concurrently conducted a transplant experiment where individuals of F. vesiculosus were transplanted from the mid-zone to the high zone. Half of the transplants were kept wet to alleviate desiccation and thermal stress, while the other half experienced natural levels of environmental stress in the high intertidal zone. The bacterial communities of these transplants and procedural controls were analyzed after 2 weeks. Some bacteria possess traits that suggest their distributions were a response to the intertidal stress gradient. Furthermore, the microbial communities on transplants changed and became different from the microbiota of procedural controls. Interestingly, there was not a significant difference between microbiota of dry and watered transplants, suggesting another stress (e.g., light) may be important. Together, these studies provide novel insights the effects of stress (either ROS from bleach or environmentally generated ROS) on macroalgae in Maine