Distribution of artisanal fishing gears with impacts on sedimentation and benthic macroinvertebrate assemblages in Songkhla Lake, the largest lagoon in Thailand.

The present study investigated the distribution and diversity of stationary fishing gears in Songkhla Lake and assessed the effects of the most abundant gear in the lake, the standing trap, on sedimentation and the abundance of benthic macroinvertebrates. Our survey revealed that six types of fishing gear were used: standing traps, fyke nets, fish aggregating devices, seabass net cages, small traps and stationary lift nets. The type of fishing gear used depended on the depth of water. The density of installed standing traps reached a maximum of 357 traps/km2, which was the highest density of any fishing gear installed on the lake. They were mainly set in the middle part of the lake, where the water was less than 2 m deep. Sedimentation was examined inside and outside the areas influenced by standing traps. Sediment samples were collected with sediment traps in the northeast and southwest monsoon seasons. Sedimentation rates inside and outside the areas influenced by standing traps differed at some sites but the pattern was not consistent across seasons. Sedimentation rates were higher in the northeast monsoon season with the average rate 1132.32 ± 43.73 (mean ± SE) g m-2day-1 when precipitation and run-off were higher and 323.98 ± 10.68 g m-2day-1 in the southwest monsoon or dry season. Moreover, the proportion of finer clay particles was greater in the sediment from the areas influenced by traps. Benthic macroinvertebrate communities between the two areas were different. A bivalve, Potamocorbula sp., which dominated benthic macroinvertebrate assemblages, had a higher abundance in areas influenced by traps. The effects of stationary fishing gears on sedimentation and benthic macroinvertebrates highlighted in this study suggest that the long-term deployment of these gears may affect food chain dynamics in this lagoon system. Ultimately, a proper regulation of the use of these gears may be needed.

The role of monsoon-driven oceanographic variability in recruitment patterns of key intertidal space occupiers on tropical rocky shores on the west coast of Thailand, Indian Ocean.

We investigated the influences of oceanographic variables on recruitment patterns of the acorn barnacle Chthamalus malayensis and the rock oyster Saccostrea cuccullata, key space occupiers on tropical intertidal rocky shores. Recruitment data and nearshore environmental variables were obtained at spatial (regional and local) and temporal (monthly) scales on the west coast of Thailand. The relationship between the recruitment of each species and combinations of environmental variables was modeled. The climate of the study sites is influenced by the southwest and northeast monsoons of the Indochinese monsoon system. Observations showed that recruitment of both species and oceanographic variables exhibited differences at either local scale or monthly scale or both. Recruitment of both species was positively related to temperature, while barnacle recruitment was negatively related to salinity, but oyster recruitment was positively related to salinity. Barnacles showed a greater rate of recruitment when south-westerly onshore winds predominated during the southwest monsoon season, while the influence of wind patterns on rock oyster recruitment was not clear. Differential larval delivery regulated by monsoon-driven currents is, therefore, a potential determinant of barnacle recruitment. Our study highlights the roles of monsoon-influenced oceanographic processes as predictors of recruitment patterns of intertidal species in a tropical system. Supplementary Information: The online version contains supplementary material available at 10.1007/s10750-023-05256-w.

Role of the Sea Urchin Stomopneustes variolaris (Lamarck, 1816) Pits as a Habitat for Epilithic Macroinvertebrates on a Tropical Intertidal Rocky Shore.

Many sea urchin species excavate pits in sedimentary rock, transforming primary rocky substrates into sea urchins' pits. These pits are not only used as their home but seem to harbor a distinct assemblage of organisms. We investigated small-scale spatial variation in community of macroinvertebrates by comparing community composition of epilithic macroinvertebrates between those found on unmodified rocky substrate, inside pits occupied by rock-boring sea urchin Stomopneustes variolaris (Lamarck, 1816), and unoccupied pits, on an intertidal rocky shore in southern Thailand. Size structures of macroinvertebrates were compared between pits and analyses were performed to investigate whether the use of habitat depends on availability of space, or biological interactions between sea urchins and other macroinvertebrates. Size structure of the most abundant mobile fauna, top shells Trochus radiatus Gmelin, 1791, were also analyzed to assess whether they exhibit ontogenetic changes in habitat use. Although a few species were found in all habitat types, community compositions were different. Chitons and limpets were found exclusively on unmodified substrate; whereas relatively large-sized gastropods inhabited unoccupied pits, and occupied pits harbored small-sized crustacean and gastropod species. Generally, in occupied pits, small-sized faunas were more abundant than larger faunas, suggesting that sea urchin's body may function as a biogenic structure providing refugia for small-sized individuals. In unoccupied pits volume of all macroinvertebrates increased as available space increased. This was not observed in occupied pits, where disturbances due to sea urchin's activities may be more important in determining habitat use.