Macroalgal community structure and composition in intertidal zone of Sarangan Beach, Gunungkidul, Indonesia

The intertidal zone of Sarangan Beach is characterized by rocky
substrates and it has high macroalgae biodiversity. However, based on
previous research, limited research was conducted at the location on the
changes of macroalgae community structure. This research aims to study the
structure and composition of macroalgae communities in the intertidal zone
of Sarangan Beach and the physicochemical factors that affect its growth.
Data was collected in September 2023, during the maximum low tide. The
data collection was done by systematic sampling method using 60 plots 1x1
m2. The physicochemical parameters were measured and observed i.e. water
and air temperature, pH, salinity, light intensity, and substrate type. The
results showed 23 species of macroalgae were found in the intertidal zone of
Sarangan Beach, consisting of 8 species of Chlorophyta, two species of
Phaeophyta, and 13 species of Rhodophyta. The highest abundance was
shown by Ulva lactuca, followed by Sargassum crassifolium and
Kappaphycus alvarezii, while the lowest was Gracilaria spinulosa. The
structure of the macroalgae community consists of moderate diversity
(H’=1.97) with high uniformity (E=0.63) and low dominance (C=0.27). This
is influenced by physicochemical parameters, especially water and air
temperature, pH, and substrate condition.