Biological control of incrusting organisms and sediments in Chilean oyster cultures

The oyster culture has the incrusting organism as problem for production, in this context, it evaluated as biological control against incrusting organism and sediments the introduction of gastropod Tegula atra (Lesson, 1830) in Chilean oysters (Triostrea chilensis Phillippi, 1844) cultures in conditions of starvation presence and absence located in floating cages and bottom cultures. The predation and mechanic effect on T. atra grazing generated a decreasing in seven days of 19.8% and 13.7% of incrusting organisms in cage culture and bottom sediments by effects of gastropods without starvation respectively. Whereas it had a decrease of 12.6% and 11.4% of incrusting organisms in cage culture and bottom sediments by effects of gastropods with starvation respectively. The incrusting organism removed were mainly algae, colonial ascidia, polychaeta, bryozoan and small crustaceans.

Investigation on Suitable Spat Collectiors and Culture Sites for Edible Oyster in the Coast of Bay of Bengal, Bangladesh

Potential spat collectors and suitable culture sites were investigated for the development of edible oyster culture from June to December 2019 at three study sites (Moheshkhali, the Jeti of Nuniarchora, and Sonadia) of Cox’s Bazar coast of Bangladesh. Four types of collectors such as oyster shell, earthen pot, kortal (windowpane oyster shell) and tiles were investigated. On site sampling of water quality parameters and number of spats on each collector were done at 15-days interval following standard methods. Results indicated insignificant difference (P > 0.05) in temperature, salinity, dissolved oxygen and pH, while significant difference (P < 0.05) in total dissolved solids, total suspended solids and Chl-a content of the water among the study locations. However, these parameters were in suitable range for growth and spawning of oyster. Results also indicated spat recruitment was significantly influenced by the types of collectors and study locations with significantly (P < 0.05) higher spat were recruited in Tiles. Tiles were also found to facilitate with an advantage of recycling of this collector. The location in interaction with polluting materials such as total dissolved solids and total suspended solids had a significant effect on spat recruitment rate and therefore, Sonadia was the most suitable location for spat recruitment. This study site can also be used as a suitable location for the development of oyster culture in the cost of Bay of Bengal, Bangladesh based on its environmental characteristics. Bangladesh J. Zool. 49 (2): 257-265, 2021

Monitoring oyster culture rafts and seagrass meadows in Nagatsura-ura Lagoon, Sanriku Coast, Japan before and after the 2011 tsunami by remote sensing: their recoveries implying the sustainable development of coastal waters

Background Coastal ecosystems are blue infrastructures that support coastal resources and also aquaculture. Seagrass meadows, one of coastal ecosystems, provide substrates for epiphytic diatoms, which are food resources for cultured filter feeder organisms. Highly intensive coastal aquaculture degrades coastal environments to decrease seagrass meadows. Therefore, efficient aquaculture management and conservation of seagrass meadows are necessary for the sustainable development of coastal waters. In ria-type bays, non-feeding aquaculture of filter feeders such as oysters, scallops, and ascidians are actively practiced along the Sanriku Coast, Japan. Before the 2011 Great East Japan Earthquake, the over-deployment of oyster culture facilities polluted the bottom environment and formed an hypoxic bottom water layer due to the organic excrements from cultured oysters. The tsunami in 2011 devastated the aquaculture facilities and seagrass meadows along the Sanriku Coast. We mapped the oyster culture rafts and seagrass meadows in Nagatsura-ura Lagoon, Sanriku Coast before and after the tsunami and monitored those and environments after the tsunami by field surveys. Methods We conducted field surveys and monitored the environmental parameters in Nagatsura-ura Lagoon every month since 2014. We used high-resolution satellite remote sensing images to map oyster culture rafts and seagrass meadows at irregular time intervals from 2006 to 2019 in order to assess their distribution. In 2019, we also used an unmanned aerial vehicle to analyze the spatial variability of the position and the number of ropes suspending oyster clumps beneath the rafts. Results In 2013, the number and distribution of the oyster culture rafts had been completely restored to the pre-tsunami conditions. The mean area of culture raft increased after the tsunami, and ropes suspending oyster clumps attached to a raft in wider space. Experienced local fishermen also developed a method to attach less ropes to a raft, which was applied to half of the oyster culture rafts to improve oyster growth. The area of seagrass meadows has been expanding since 2013. Although the lagoon had experienced frequent oyster mass mortality events in summer before the tsunami, these events have not occurred since 2011. The 2011 earthquake and tsunami deepened the sill depth and widened the entrance to enhance water exchange and improve water quality in the lagoon. These changes brought the expansion of seagrass meadows and reduction of mass mortality events to allow sustainable oyster culture in the lagoon. Mapping and monitoring of seagrass meadows and aquaculture facilities via satellite remote sensing can provide clear visualization of their temporal changes. This can in turn facilitate effective aquaculture management and conservation of coastal ecosystems, which are crucial for the sustainable development of coastal waters.

An Estimation of Fish Biomass and Attached Organisms beneath Oyster Rafts in Hiroshima Bay, Japan

Hiroshima Bays is top production approximately 60% of oyster production in Japan. For cultivate of oyster, fishermen use hanging rafts. A thousand of raft is hanging during 2-3 years in the bay. Large-scale oyster culture may change the ecosystem structure and material cycles in the bay through the filtration of particulate matter by oysters and other associated animals. This study described the community structure of marine organisme in terms of fishes surrounding and animal attached on oyster rafts. Field observation was carried out from 2016 to 2019 at oyster farming in Hiroshima Bay. Oyster production and provisioning for the fish habitat were also evaluated by placing underwater video cameras beneath oyster culture rafts. The result showed that black seabream was high biomass and oyster it shelf was bigger bioyster for animal attached on oyster raft. The number of individual, mussel is most abundance of animal attach on oyster raft with ratio 9:1 than number of oyster. Maintaining oyster culture is important not only for maintaining oyster production, but also for maintaining fish production by enhancing material cycles through the paths in the food chains of Hiroshima Bay under oligotrophic conditions.

Variation in environmental characteristics of waters among Amazon coast oyster culture units

ABSTRACT Oyster culture has benefited traditional coastal communities along the Amazon macrotidal mangrove coast of Pará state in Brazil since 2006. Currently, seven oyster culture units in five municipalities are expanding production, but with no environmental monitoring, which is important for the control of the impacts of oyster culture on waters as well as for oyster management and conservation. Seasonal variation in environmental characteristics of the water was evaluated at all oyster culture units in Pará, from September to November 2013 (dry season) and February to April 2014 (wet season), to generate baseline data to evaluate future impacts and aid strategic planning, such as diversifying seed production. Salinity, dissolved oxygen, pH, oxidation-reduction potential, depth, temperature, and chlorophyll-a concentration were measured during flooding and ebbing tides, and compared between seasons and among culture units using uni- and multivariate statistics. All variables were significantly higher in the dry season, except depth, which was significantly greater in the wet season. Mean salinity, which varied from 2.4 to 46, explained most of the variation among culture units in relation to season, sampling date within each season and tidal state. However, dissolved oxygen, pH and depth were also important. Oyster culture units in Pará may be suitable for sustainable harvesting of seed/spat from the wild (lower salinity and pH), or for on-growing (higher salinity, higher pH, and greater depth). Seasonal variation is sufficient to allow both activities at most units at appropriate times of the year, which would help increase oyster production in Pará.

Oyster culture (Crassostrea lugubris) in Lang Co Lagoon, Vietnam.

Grow-out culture of oyster (Crassostrea lugubris) is developing spontaneously at Lang Co lagoon (Thua Thien Hue province). Various culture systems are used: culture on cement block stakes as a holdfast connected to a trellis, culture in a small cage hanging on a trellis, culture on wooden stakes (bamboo or cajeput stakes), culture on rubber tyres, and culture on stones. The culture depth differs depending on the culture style: about 4-6 m on a trellis and 1.5-2 m on wooden stakes and on stones. The chosen substrate is muddy bottom or muddy sand. The salinity of the culture area is 4-5‰ in the rainy season and 27-30‰ in the dry season. Oyster seed is collected from the wild, two times per year: in April and July. The culture duration is prolonged, at about 10-12 months. The commercial size of oyster is 9-11 cm long and about 200 g per piece. The price of commercial oyster is VND 5,000 kg-1 (about US$ 0.30 kg-1).