Responses of mangrove and salt marsh in Corpus Christi Bay after the Feb. 2021 hard freezes

Since the last freeze in 1989, populations of black mangroves (Avicennia germinans) have rapidly increased throughout coastal Texas. Some sites are dense shrub thickets that reduce light penetration, lowering salt marsh abundance; large-scale ecological regime shifts along segments of the Texas coast. Two consecu- tive nights of below-freezing temperatures in Feb. 2021 provided an opportunity to study the effects of a catastrophic disturbance on the regime shift in Corpus Christi Bay. The freeze caused substantial adult Avi- cennia mortality. We are using observational data to test two hypotheses: 1) that recovery of mangroves will be faster on Mustang Island than on Ward Island because Mustang is nearer the Gulf of Mexico which may provide for more mangrove propagule colonizers from locations outside the bay and also may have been a little warmer due to thermal buffering by the Gulf. We established paired 3x3 m plots on each Island near the seaward edge of the intertidal vegetation and 5-10 m further inland. We quantified shrub mortality, survivor resprouting, seedling recruitment, and marsh cover by species. Data from October 2021 shows that there was adult shrub recovery via epicormic resprouting (34% on Mustang and 13% for Ward) and seedling recruitment in all plots, while marsh cover expanded in most plots possibly because of mangrove canopy reduction. Nine months post freeze Ward had mean = 1.16 (2.6 SD) total seedlings per m2 and Mustang had a mean = 40.8 (22.8 SD) seedlings. In 2019, Ward had a mean = 5 (1.1 SD) seedlings per m2 and Mustang had a mean = 4.3(1.1 SD) seedlings per m2.