It is critical to understand the potential impacts of climate and anthropogenic changes on oyster resources in order to better adapt and manage for long-term sustainability. These studies demonstrate that high water temperatures (> 30☌) and low salinities (< 5 psu) negatively impact oyster growth and survival, and that high temperatures alone may negatively impact market-sized oysters. In higher salinity tanks (15 psu), only market-sized oysters held at 32☌ experienced significant mortality (> 60%). The results demonstrate that the optimal combination of temperature. In contrast, at 5 psu, temperature significantly affected the mortality rate all size class oysters experienced greater than 50% mortality at 32☌, and less than 40% mortality at 25☌. Using long-term (1988 to 2015) monitoring data from Louisiana's public oyster reefs, we develop regionally specific models of temperature- and salinity-driven mortality (sack oysters only) and growth for spat (<25 mm), seed (2575 mm), and sack (>75 mm) oyster size classes.Regardless of temperature, seed and market oysters held in low salinity tanks (salinity = 1 psu) experienced 100% mortality within seven days. Oysters were placed in 18 tanks in a fully crossed temperature (25☌, 32☌) by salinity (1, 5, 15 psu) study with 3 replicates, and repeated twice for each oyster size class. To explicitly examine oyster responses to extreme low salinity and high temperature combinations, a series of laboratory studies were conducted. Regardless of size class, oysters at the lowest salinity site (annual mean = 4.8 psu) experienced significantly higher mortality and lower growth than oysters located in higher salinity sites (annual means = 11.1 and 13.0 psu) furthermore, all oysters in open bags at the two higher salinity sites experienced higher mortality, likely due to predation. Beginning in 2011, the Sea Grant Oyster Hatchery on Grand Isle, LA and the Louisiana Department of Wildlife and Fisheries (LDWF) collaborated to test the survival of hatchery-produced spat and hatchery-produced larvae deployed on public oyster grounds and cultch plant sites. Growth and mortality were recorded monthly. In 20, hatchery-produced oysters were placed in open and closed bags at three sites in Breton Sound, LA, along a salinity gradient which typically ranges from 5 to 20 psu. Using lab and field studies, this project quantified the combined effects of extremely low salinities (30☌) on growth and survival of spat, seed, and market-sized oysters. Mortality varied considerably both between and within bays. On average oysters died over a period of 18 days. Mortalities started at the end of May and continued until early August, peaking in early July. Little is known explicitly about how low salinity and high temperature combinations affect spat ( 75 mm) oyster growth and mortality. Batch mortality averaged 37 (1865 quartiles) but showed a bimodal distribution (half the batches had mortality less than 45). Changes in the timing and interaction of seasonal high temperatures and low salinities as predicted by climate change models could dramatically alter oyster population dynamics.
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