Physiological differences in the growth of Sargassum horneri between the germling and adult stages

Thermal Tolerance May Slow, But Not Prevent, the Spread of Sargassumhorneri (Phaeophyceae) along the California, USA and Baja California, MEX Coastline

“…This pattern was consistent across all irradiance and nutrient combinations, which suggests that low survival and recruitment of young S. horneri may slow its latitudinal spread north of Point Conception, CA, USA where minimum temperatures below 10°C are regularly observed in the coastal zone Estes 2006, Edwards 2019). Moreover, S. horneri exhibits a much wider range of temperature tolerances (1-28°C) in its native habitat (Umezaki 1984, Komatsu et al 2014), but our results align with studies from South Korea by Choi et al (2008) who found S. horneri germlings grew more slowly at 10°C than in warmer temperatures. Whether limited temperature tolerance in California is the result of reduced genetic diversity and/or a specific S. horneri genotype that invaded the region during a single introduction event from one source locality in the Seto Inland Sea of Japan (Aguilar-Rosas et al 2007, Miller et al 2007, Uwai et al 2009) is currently not known, but worthy of further investigation.…”

“…Whether these populations will become established and lead to further spread is unknown, but given S. horneri's broad latitudinal range (approx. 33-45°N) observed along the coast of Japan (Komatsu et al 2014), and the widespread emerging invasive populations along the coasts of northeastern China, South Korea, and Taiwan (Yoshida 1983, Umezaki 1984, Uchida 1993, Nanba 1995, Choi et al 2008, Pang et al 2008, Yoshikawa et al 2014, Kim et al 2016, Lin et al 2017, we believe it is possible. Short-timescale events, such as favorable recruitment windows, may be equally as important as longer-timescale events like El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO).…”

“…Immediately to the south, average ocean temperatures can range between about 18°C (e.g., from Bahia Tortugas to Asuncion) to almost 23°C (e.g., from La Bocana to Punta Abreojos), with maximum temperatures ranging between 25°C to almost 30°C (Sicard-Gonzalez et al 2012). Given that Choi et al (2008) and Lin et al (2017) observed total mortality at 28-30°C, S. horneri's southward spread along Baja California may have slowed due to high ocean temperatures. However, it is important to note that minimum ocean TABLE 3.…”

“…comm.). While this species has been the subject of several studies in its native range along the coast of Japan and in invaded habitats in northeast China, South Korea, and Taiwan (e.g., Yoshida 1983, Umezaki 1984, Uchida 1993, Nanba 1995, Choi et al 2008, Pang et al 2008, Yoshikawa et al 2014, Kim et al 2016, Lin et al 2017, little is known about its ecology in the invaded regions of the California and Baja California coast. For instance, S. horneri occurs in a broad range of temperatures (1-28°C) in its native habitat (Umezaki 1984, Komatsu et al 2014, but it appears to occur within a much narrower temperature range of about 12 to 20°C in California and Baja California (Cruz-Trejo et al 2009, Miller and Engle 2009, Riosmena-Rodr ıguez et al 2012, Marks et al 2015, which may be critical to regulating its continued northward and southward spread.…”

“…Early life stages of marine macroalgae often respond differently to variation in environmental conditions than their macroscopic adults (Matson and Edwards 2007, Choi et al 2008, Cie and Edwards 2008, Harley et al 2012, Shukla and Edwards 2017, Liesner et al 2020, suggesting that it is critical to consider the entire life cycle when investigating ecological constraints. Often, early life stages have narrower light, temperature, or nutrient tolerances (Matson and Edwards 2007, Cie and Edwards 2008, Carney and Edwards 2010, Fejtek et al 2011.…”