Search

Water-soluble marine natural products are interesting as they generally do not penetrate into the cells but exhibit biological activities through cell surface receptors, ion channels, and glycans. Some molecules, however, interact with cell membrane and disrupt it. In this review, discovery, structures, and biological activities of water-soluble marine natural heterocyclic molecules are summarized with special emphasis on their biological activity and functions.

Water-soluble marine natural products are interesting as they generally do not penetrate into the cells but exhibit biological activities through cell surface receptors, ion channels, and glycans. Some molecules, however, interact with cell membrane and disrupt it. In this review, discovery, structures, and biological activities of water-soluble marine natural heterocyclic molecules are summarized with special emphasis on their biological activity and functions.

To properly assess risk, an animal must focus its attention on relevant external stimuli; however, attention can be reallocated when distracting stimuli are present. This reallocation of attention may interfere with an individual's ability to effectively assess risk and may impede its response. Multiple stimuli presented together can have additive effects as distractors, and these include stimuli in different modalities. Although changes in noise and water flow are detectable by some bivalves, this has not been studied in the context of risk assessment or distraction. We experimentally exposed giant clams (Tridacna maxima) to changes in water particle movement through underwater sound (motorboat noise) and increased water flow to determine whether these stimuli, individually or together, modified risk assessment or caused distraction. We found that clams responded to sound, flow, and their combination by increasing frequency of mantle retractions (a potential anti-predator response) when exposed to a stimulus. Sound alone did not change risk assessment in either the latency to close or to reemerge following closure. However, when exposed to both stimuli simultaneously, clams increased their latency to close. We suggest that clams perceive sound and flow in an additive way, and are thus distracted. Interestingly, and uniquely, clams discriminate these multimodal stimuli through a single sensory modality. For sessile clams, anthropogenic noise is detectable, yet unavoidable, suggesting that they be especially vulnerable to marine noise pollution.

To properly assess risk, an animal must focus its attention on relevant external stimuli; however, attention can be reallocated when distracting stimuli are present. This reallocation of attention may interfere with an individual's ability to effectively assess risk and may impede its response. Multiple stimuli presented together can have additive effects as distractors, and these include stimuli in different modalities. Although changes in noise and water flow are detectable by some bivalves, this has not been studied in the context of risk assessment or distraction. We experimentally exposed giant clams (Tridacna maxima) to changes in water particle movement through underwater sound (motorboat noise) and increased water flow to determine whether these stimuli, individually or together, modified risk assessment or caused distraction. We found that clams responded to sound, flow, and their combination by increasing frequency of mantle retractions (a potential anti-predator response) when exposed to a stimulus. Sound alone did not change risk assessment in either the latency to close or to reemerge following closure. However, when exposed to both stimuli simultaneously, clams increased their latency to close. We suggest that clams perceive sound and flow in an additive way, and are thus distracted. Interestingly, and uniquely, clams discriminate these multimodal stimuli through a single sensory modality. For sessile clams, anthropogenic noise is detectable, yet unavoidable, suggesting that they be especially vulnerable to marine noise pollution.

The cyanobacteriosponge Terpios hoshinota has been reported throughout the Indo-Pacific including the Great Barrier Reef, Australia. The species encrusts live coral, giant clams, and other benthos and can be a threat to benthic communities on coral reefs. The Kimberley region of Western Australia has some of the least impacted reefs globally. We report for the first time the presence of T. hoshinota in the eastern Indian Ocean on Kimberley inshore coral reefs. Given its invasive potential, reef health surveys should include this species, and monitoring approaches developed to audit the remote Kimberley for this and other invasive species.

To validate the usability of the giant clam shell as a recorder of short-term environmental changes such as typhoons, we collected a live Tridacna maxima from Okinotori Island, Japan, on 15 June 2006. Growth increment thickness, stable isotope ratio (O-18(shell), C-13(shell)), and the barium/calcium ratio (Ba/Ca) in the T.maxima shell sample were measured and compared to Okinotori Island instrumental environmental data. In the outer layer of the shell sample, there were 3656 growth increments per year, as estimated by the O-18(shell) profile compared with sea surface temperature. The growth increments in the specimen were formed daily, and thus, we can determine the date of the sampling points of O-18(shell), C-13(shell) and the Ba/Ca ratio by counting growth increments. After typhoon approach, there is a decrease in increment thickness and some disturbed growth increments. The positive peaks in the shell Ba/Ca ratio and O-18(shell) corresponded to lower sea surface temperature caused by typhoons. These results indicated that the microstructural and geochemical record in Tridacna maxima shells could be useful for detecting past typhoon events.

To validate the usability of the giant clam shell as a recorder of short-term environmental changes such as typhoons, we collected a live Tridacna maxima from Okinotori Island, Japan, on 15 June 2006. Growth increment thickness, stable isotope ratio (O-18(shell), C-13(shell)), and the barium/calcium ratio (Ba/Ca) in the T.maxima shell sample were measured and compared to Okinotori Island instrumental environmental data. In the outer layer of the shell sample, there were 3656 growth increments per year, as estimated by the O-18(shell) profile compared with sea surface temperature. The growth increments in the specimen were formed daily, and thus, we can determine the date of the sampling points of O-18(shell), C-13(shell) and the Ba/Ca ratio by counting growth increments. After typhoon approach, there is a decrease in increment thickness and some disturbed growth increments. The positive peaks in the shell Ba/Ca ratio and O-18(shell) corresponded to lower sea surface temperature caused by typhoons. These results indicated that the microstructural and geochemical record in Tridacna maxima shells could be useful for detecting past typhoon events.

Giant clams are in symbiotic relationship with the photosynthesizing zooxanthellae and dwell in the shallow coral reefs of the Indo-Pacific region where they may be exposed to fluctuating salinities during high levels of precipitation. This study evaluated the effects of reduced salinities (18, 25, and 35‰ as control) on the rates of photosynthesis and respiration in juvenile Tridacna gigas for 14 days. At 18‰, total mortality was recorded after day 4, so no photosynthetic measurements were subsequently conducted for this treatment. However, results showed no significant differences in the photosynthetic rates among treatments. Respiration rates were significantly increased at both low salinities resulting in low Pg/R ratios. After 14 days of exposure, photosynthetic parameters at 25‰ were not significantly different from the control which suggests that juvenile T. gigas may be able to acclimate to osmotic stress and adjust its photophysiology following reductions in salinity of up to 25‰. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

Giant clams are in symbiotic relationship with the photosynthesizing zooxanthellae and dwell in the shallow coral reefs of the Indo-Pacific region where they may be exposed to fluctuating salinities during high levels of precipitation. This study evaluated the effects of reduced salinities (18, 25, and 35‰ as control) on the rates of photosynthesis and respiration in juvenile Tridacna gigas for 14 days. At 18‰, total mortality was recorded after day 4, so no photosynthetic measurements were subsequently conducted for this treatment. However, results showed no significant differences in the photosynthetic rates among treatments. Respiration rates were significantly increased at both low salinities resulting in low Pg/R ratios. After 14 days of exposure, photosynthetic parameters at 25‰ were not significantly different from the control which suggests that juvenile T. gigas may be able to acclimate to osmotic stress and adjust its photophysiology following reductions in salinity of up to 25‰. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

Giant clams are in symbiotic relationship with the photosynthesizing zooxanthellae and dwell in the shallow coral reefs of the Indo-Pacific region where they may be exposed to fluctuating salinities during high levels of precipitation. This study evaluated the effects of reduced salinities (18, 25, and 35‰ as control) on the rates of photosynthesis and respiration in juvenile Tridacna gigas for 14 days. At 18‰, total mortality was recorded after day 4, so no photosynthetic measurements were subsequently conducted for this treatment. However, results showed no significant differences in the photosynthetic rates among treatments. Respiration rates were significantly increased at both low salinities resulting in low Pg/R ratios. After 14 days of exposure, photosynthetic parameters at 25‰ were not significantly different from the control which suggests that juvenile T. gigas may be able to acclimate to osmotic stress and adjust its photophysiology following reductions in salinity of up to 25‰. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

Monitoring gonadmaturation for protandrous and functional hermaphrodite species such as the giant clamTridacna maxima is difficult due to the juxtaposition and relative proportion ofmale and female tissues in the gonad [gonadal sex ratio (GSR)]. Here, the relevance of the widely used gonadosomatic index (GSI) as proxy of giant clam gonad maturation is tested with a large dataset (n = 265). Gonadosomatic index is compared with other indices, namely the proportion of the male part harboring spermatozoids, the proportion of empty oocyte follicles, the mean oocyte diameter, and the oocyte elongation. At gonad scale, high index variability highlighted partial spawning. At individual scale, male and female maturation proxies were contrasted, showing either asynchronous emissions of male and female gametes or contrasted spermatogenesis and oogenesis duration. The GSI was mostly driven by the number and diameter of oocytes and therefore it is recommended here as primary proxy for female maturity. Except for the oocyte elongation, all indices were affected by the GSR, which ruled out drawing conclusions at population scale. These results highlight the need for maturation stage proxies that are optimized for functional hermaphrodite species.

Monitoring gonadmaturation for protandrous and functional hermaphrodite species such as the giant clamTridacna maxima is difficult due to the juxtaposition and relative proportion ofmale and female tissues in the gonad [gonadal sex ratio (GSR)]. Here, the relevance of the widely used gonadosomatic index (GSI) as proxy of giant clam gonad maturation is tested with a large dataset (n = 265). Gonadosomatic index is compared with other indices, namely the proportion of the male part harboring spermatozoids, the proportion of empty oocyte follicles, the mean oocyte diameter, and the oocyte elongation. At gonad scale, high index variability highlighted partial spawning. At individual scale, male and female maturation proxies were contrasted, showing either asynchronous emissions of male and female gametes or contrasted spermatogenesis and oogenesis duration. The GSI was mostly driven by the number and diameter of oocytes and therefore it is recommended here as primary proxy for female maturity. Except for the oocyte elongation, all indices were affected by the GSR, which ruled out drawing conclusions at population scale. These results highlight the need for maturation stage proxies that are optimized for functional hermaphrodite species.

Monitoring gonadmaturation for protandrous and functional hermaphrodite species such as the giant clamTridacna maxima is difficult due to the juxtaposition and relative proportion ofmale and female tissues in the gonad [gonadal sex ratio (GSR)]. Here, the relevance of the widely used gonadosomatic index (GSI) as proxy of giant clam gonad maturation is tested with a large dataset (n = 265). Gonadosomatic index is compared with other indices, namely the proportion of the male part harboring spermatozoids, the proportion of empty oocyte follicles, the mean oocyte diameter, and the oocyte elongation. At gonad scale, high index variability highlighted partial spawning. At individual scale, male and female maturation proxies were contrasted, showing either asynchronous emissions of male and female gametes or contrasted spermatogenesis and oogenesis duration. The GSI was mostly driven by the number and diameter of oocytes and therefore it is recommended here as primary proxy for female maturity. Except for the oocyte elongation, all indices were affected by the GSR, which ruled out drawing conclusions at population scale. These results highlight the need for maturation stage proxies that are optimized for functional hermaphrodite species.

The Aquaculture Department of the Southeast Asian Fisheries Development Center (SEAFDEC/AQD) started its Stock Enhancement Program more than a decade ago with the first stock enhancement initiative on the mud crab Scylla spp. funded by the European Commission. This was followed by another stock enhancement program in 2005 supported by the Government of Japan Trust Fund. In preparation for its implementation, a Regional Technical Consultation on Stock Enhancement of Species Under International Concern was convened in Iloilo City, Philippines in July 2005 to identify species for stock enhancement. During the meeting, seahorses Hippocampus spp., giant clam Tridacna gigas, abalone Haliotis asinina, and sea cucumbers Holothuria spp. were among the priority species for stock enhancement work. Stock enhancement, restocking and ranching are management approaches involving the release of wild or hatchery-bred organisms to enhance, conserve or restore fisheries. This paper reports SEAFDEC/AQD release activities and some of the release strategies that have been established for mud crabs, giant clams and abalone.

To restore the diminishing population of the giant clam Tridacna gigas in Sagay Marine Reserve (SMR), Negros Occidental, central Philippines, two size classes [8- and 10-cm shell length (SL)] of hatchery-bred T. gigas were reared in an adjacent ocean nursery for restocking to Carbin Reef later upon reaching grow-out size of ≥20 cm SL. Growth rates did not significantly differ for both sizes and were on average 0.67 cm month−1. However, survival after 382 days of rearing T. gigas was significantly higher in the 10-cm SL clams than the 8-cm SL clams (96 and 83%, respectively). For future restocking projects, the use of 8-cm SL clams is recommended because the lower survival of this size class is compensated by its cheaper price. While rearing the clams to attain grow-out size, the population of wild clams (Family Tridacnidae) in Carbin Reef was assessed using ten 50 × 2-m belt transects. Four species of tridacnid clams have been recorded: Hippopus hippopus, Tridacna crocea, T. maxima>, and T. squamosa. T. crocea comprised 12.5–93.9% of all the clams observed in all ten transects. There was a significant difference in clam density between species (ANOVA, F = 6.94, P < 0.001), with T. crocea having the highest density. Living T. gigas were absent, but presence of dead shells was indicative of its presence in the reef in the past. It can be expected that the release of hatchery-bred T. gigas juveniles in Carbin Reef could provide future breeders that will repopulate this reef and the adjacent reef communities.

Giant clams (Tridacnidae; Bivalvia) are described as important framework builders on coral reefs in the Indo-Pacific region. They are phototrophic as they are associated with primary producing zooxanthellae. Populations are low due to over-exploitation and most species are now endangered in many areas. Also the general degradation of coral reef habitats and marine pollution related disturbances are threatening local giant clam populations. The aim of my thesis is to provide information of physiological and ecological requirements of giant clams to improve the management of these species. By using mainly physiological methods and lethality tests, the responses to anthropogenic stress and natural disturbance were studied. In Paper I, the effect of elevated temperature was tested for in three different species of clams in order to rank the relative sensitivity. Using the end-point production to respiration ratio (Pg/R), we concluded Hippopus hippopus to be the most sensitive species. Paper II compares two different methods measuring copper stress on the photosynthetic efficiency. It was evident that fluorescence measurements and whole animal physiology gave different results. In Paper III Tridacna gigas were transplanted to sites with increased turbidity due to human activities during 6 months. Clearly, the actual growth rate decreased compared to a “clean” site. The clams from turbid waters on the other hand developed a somewhat higher tolerance to copper exposure. Tridacna gigas larvae were exposed to a combination of copper and low salinity in Paper IV, and it was shown that reduced salinity increases mortality, and synergistic effects were obvious. In Paper V and Paper VI effects of oil pollution on juveniles and larvae were studied. Juvenile clams displayed a reduction in the Energy Balance Equation due to reduced filter feeding and absorption efficiency. The larval stage had low tolerance to benzo[a]pyrene, and there was a negative trend in settlement success. Ov