Ecobiology of horseshoe crab in Brebes, Northern Coast of Java: Preliminary study

Horseshoe crabs are known as living fossils and three species are found in Indonesia where all of them are being protected. The research aimed to assess ecology, species composition, and biological aspects in Brebes estuary. The research was conducted in August and October 2017 in Brebes Estuary. Samples were caught using local fishermen and experimental gears. Parameters of water quality were observed insitu and substrate was analyzed in the laboratory. The horseshoe crabs were measured morphologically, their stomach and eggs were taken to be analyzed in the laboratory. Total specimens of horseshoe crabs were 33 individuals ( Tachypleusgigas=8 ; Carsinoscorpius rotundicauda=25). T. gigas has 16.3-22.6 cm of prosomal width and 216.1-717.0 gram of weight. C. rotundicauda has 11.2-14.5 cm of prosomal width and 96.0-275.5 gram of weight. Stations with a muddy sand substrate (silt >50%) have the highest number of captured horseshoe crabs. Food habits of T. gigas are macrophytes and detritus while C. rotundicauda are macrophytes, molluscs, annelids, and coral. Niche breadth of C. rotundicauda were wider than T. gigas . High niche overlap value between T. gigas and C. rotundicauda indicates high competition in utilizing food sources. The fecundity of C. rotundicauda was higher than T. gigas but the egg diameter of C. rotundicauda smaller than T. gigas .