Species in the family Lutjanidae (snappers) are important targets of fisheries around the world. Although the checkered snapper Lutjanus decussatus is distributed across the Indo-Pacific, little is known about the demographic parameters of this species. Thus, the age, growth, and length-weight relationship of the checkered snapper L. decussatus (family Lutjanidae) were investigated in an Okinawan coral reef. Alternate translucent and opaque zones were observed in all sectioned otoliths, with an opaque zone occurring at the edge of the otolith predominantly during the spawning season. The maximum ages of the male and female were 24 and 23 years, respectively. The von Bertalanffy growth parameters for the relationship between age and fork length (FL) were as follows:asymptotic mean FL (L∞)＝288.3mm, growth coefficient (k)＝0.09 year－1, and age when mean FL is 0 (t0)＝－12.0 years in males; L∞＝316.5mm, k＝0.08 year－1, and t0＝－12.1 year in females. In the case that the growth parameters were re-estimated using a fixed t0 value of 0, L∞＝256.1mm, and k＝0.54 year－1 in males; L∞＝274.4 mm, and k＝0.45 year－1 in females. L∞ was significantly greater in females than in males, but there were no significant inter-sexual differences in K or t0. The length-weight relationships for males and females were whole body weight (g)＝4.95×10－5 FL2.83 and 1.44×10－5 FL3.05, respectively. The present study is the first to demonstrate the age, growth, and length-weight relationship of L. decussatus, which would be useful biological information for the effective management of this species.
Diuron (DCMU; 3-(3,4-dichlorophenyl)-1,1-dimethylurea) concentrations were analyzed at 24 sites along shorelines of Ishigaki and Iriomote Islands in September 2019. The diuron concentrations ranged from <0.6 to 32 ng l-1. Slightly high concentrations of diuron as 32 and 19 ng l-1 were observed at a fishing port in Iriomote and a mooring point for boats in Ishigaki, respectively, implying contamination likely from antifouling paints of boats. A slightly high concentration (14 ng l-1) of diuron was also found in the estuary of Arakawa River in Ishigaki Island, which implies land sources. In Iriomote Island, diuron concentrations were low (≤1 ng l-1) at all sites except for the port site. These results indicate generally low levels (below toxic levels for organisms) of diuron contamination at least at the timing of the present study.
About 80 species of Acropora corals have been recorded in Japan to date. However, there are few information on its diversity in Amami-Oshima Island, which is located in the northern part of the central Ryukyu Islands. Multiple studies, including molecular work, have looked at the species diversity of Acropora in Japan, but many of them have not been effective in successful differentiation at the species. This is the first study reporting the species diversity and molecular phylogeny of the Acropora species in Amami-Oshima Island. We collected 89 Acropora specimens, including 26 species within reef lagoon in the southwestern area (Funakoshi) of the island. We recorded A. spathulata for the first time in Japan, and A. acuminata and A. papillare for the first time in the Amami Islands. For eight species that were uncommon or difficult to identify, we described their morphological characteristics. To infer the phylogenetic relationships between the Acropora species in Amami-Oshima Island and Japan, we also reconstructed the phylongey of the specimens using a mitochondrial putative control region including published DNA data from other Japanese specimens. The results showed that Acropora species were genetically separated into seven clades. As previously reported, A. hyacinthus and A. cytherea were highly polyphyletic; nonetheless, most species were included in specific clades. In combination with previously published ecological data, the present data allowed us to propose a new species grouping (eight groups) for 36 Japanese Acropora species, which have morphological, molecular phylogenetic, and ecological similarities. This grouping will help identify the species and understand the species diversity of Acropora until a formal taxonomic revision of the genus is conducted.