Persistent occurrence of floating Ulva green tide in Hiroshima Bay, Japan: seasonal succession and growth patterns of Ulva pertusa and Ulva spp. (Chlorophyta, Ulvales)

Abstract

Since the late 1980's, a persistent green tide of floating Ulva without any clear seasonal fluctuation has occurred in Hiroshima Bay, Seto Inland Sea, Japan. We hypothesized that the persistence is due to the co-existence of Ulva species with different seasonal growth patterns, and monitored the seasonal composition and growth characteristics of the constituent Ulva within the green tide. Two morphological types of Ulva were identified, and one type, U. pertusa, was almost the sole constituent during winter and spring. The other type Ulva spp., which has marginal microscopic serrations on the thallus, was dominant during summer and autumn. Both Ulva showed the highest relative growth rate in early autumn, but growth of Ulva spp. was faster in summer than that of U. pertusa and inhibited in winter. U.pertusa had more eurythermal characteristics in which the growth rate remained relatively high in winter. Water temperature was the most correlated environmental variable for the seasonal growth of both Ulva types rather than light or nutrients, but more influential on Ulva spp. Recent increasing trend of ambient seawater temperature is considered to be favorable for the growth of both Ulva types and a causative factor of the green tide.

Species composition, diversity, and distribution of the genus Ulva along the coast of Jeju Island, Korea based on molecular phylogenetic analysis

“…procera , are predominant and widely distributed across the Jeju Island coast. Ulva australis is known to be the most common species involved not only macroalgal assemblages, but also green tides in Korea and also in Japan [41, 42]. This species is massively recruited during the late summer-autumn season and has sheet-like blades enabling high surface area [SA] to volume [V] ratio, which is favorable for absorbing inorganic nutrients in water columns [13].…”

Macroalgal blooms caused by marine nutrient changes resulting from human activities

“…Although macroalgal blooms may be attributed to multiple factors, including climate warming and marine acidification (Gao, Clare, Rose, & Caldwell, ), appropriate hydrographic events (Lavery, Lukatelich, & McComb, ), and even alien species immigration (Yabe et al, ; Yoshida, Uchimura, & Hiraoka, ), numerous studies still consider the primary factor associated with green tide formation to be marine eutrophication. The interpretation on the mechanism of green tide formation is based only on the fact that excess nutrients can stimulate rapid algal growth (Morten Foldager & Jens, ).…”

Polyphasic approach to a characteristic Ulva population from a limno-rheocrenic, mineral (chloride, sodium, sulphate) spring in the Siwa Oasis (Western Desert of Egypt)

“…The genus Ulva Linnaeus (Chlorophyta: Ulvales), including previously described taxa of the genus Enteromorpha Link (Hayden et al 2003;Shimada et al 2003), is known to be widely distributed in a variety of aquatic biotopes, i.e. marine coasts (e.g., Yoshida et al 2015;Phillips et al 2016 and references therein), estuaries (Shimada et al 2008;Hofmann et al 2010), brackish lakes (Malta et al 2002;Ogawa et al 2013), and also in rivers, channels, pools, and springs (e.g., Ichihara et al 2009;John et al 2011;Rybak 2015Rybak , 2016. The accurate delimitation of Ulva species is highly problematic due to their relatively simple morphotaxonomic structures (Mareš et al 2011;Rybak & Czerwoniec 2015).…”