Long-term study on seasonal changes in floristic composition and structure of marine macroalgal communities along the coast of Northern Taiwan, southern East China Sea

This study presents a long-term study (9 years) on seasonal changes in the marine macroalgal flora of Northern Taiwan in the southern East China Sea, from 2007 to 2015. Both spatial and temporal variations in the marine flora at six sites in the intertidal and subtidal zones were investigated. A total of 178 macroalgal species belonging to 4 phyla, 6 classes, 26 orders, 50 families, and 108 genera, were identified. The top five most abundant species were Ulva lactuca [Mean ± SD coverage (MC): 5.75 ± 9.44%], Pterocladiella capillacea (4.7 ± 4.76%), Marginisporum aberrans (2.49 ± 3.04%), Gelidium elegans (2.46 ± 4.05%), and Chondracanthus intermedius (1.58 ± 2.85%), accounting for 16.9% of the total macroalgal coverage. Non-metric multidimensional scaling analysis of all data revealed that the macroalgal assemblages fluctuated seasonally, with proportions of dominant species in the two habitats showing seasonal succession that was influenced by interplay of waters of the China Coastal Current from the west and the Kuroshio Current from the east. The physical differences of water depth and substrate in the intertidal and subtidal sites appeared to be an influential factor affecting the macroalgal composition. Cluster and index of seaweed importance analyses revealed the relative importance of certain species based on coverage and occurrence frequencies without requirements of other time-consuming measurements. Statistical analyses indicated significant variations in macroalgal assemblages among different sampling months. The macroalgal coverage and species richness have noticeably decreased during 2014–2015. Whether or not this phenomenon is a consequence of increasing seawater temperature needs further investigation.