In 2014, a huge sized box jellyfish specimen was caught during a fishing trawl in off-shore waters near Karachi, Pakistan. While taking photographs the specimen broke into pieces due to its own weight but at least its size hinted to its identity as a member of one of three Carybdeida families: Alatinidae Gershwin, 2005 (genera Alatina Gershwin, 2005 or Keesingia Gershwin, 2014), Carukiidae Bentlage et al., 2010 (genus Morbakka Gershwin, 2008) or Tamoyidae Haeckel, 1880 (genus Tamoya Müller, 1859). After sampling six more specimens off Sonmiani, Pakistan, morphological observation of the diagnostic features was possible and all these specimens were identified to belong to the family Alatinidae, precisely the genus Alatina. There are only 7 accepted Alatina species but up to now only one possesses a bell size this big. This report presents the occurrence of the alatiniid jellyfish, Alatina grandis (Agassiz & Mayer, 1902), officially recorded for the first time from waters off the coast of Pakistan in the northern Arabian Sea and the rediscovery of specimens from this region in the collection of the ‘John Murray’ Expedition 1933–34 of the Natural History Museum in London.
Marine dinoflagellates synthesize ultraviolet absorbing compounds, such as mycosporine-like amino acids (MAAs), at high ultraviolet radiation (UVR) to protect from UVR damage. Short-term responses (360 min) of MAAs and absorption of UVR between 310 nm to 360 nm (a[310–360]) to UVR were examined in the dinoflagellate Prorocentrum micans to confirm reproducibility even at relatively low doses of UVR (UVB: 0.76 W m−2 in 320–340 nm) and (UVA: 0.84 W m−2 in 340–400 nm). By using a low dose of UVR there was no apparent bleaching of cells and it was possible to normalize MAA concentration with chlorophyll a concentration (Chl a). At the beginning of the exposure experiment, MAAs primarily consisted of shinorine (58.5%), palythine (30.2%), mycosporine-glycine (7.0%), palythene (2.6%), and porphyra-334 (1.7%). Net change in the Chl a specific MAA concentration (δMAAs) was estimated as the difference in Chl a specific MAA concentrations between the experiments with photosynthetically active radiation (PAR in 400–700 nm) and PAR+UVR (320–700 nm). The responses to either PAR or PAR+UVR were composed of two phases: the first was shorter than approximately 90 min, and the second included the subsequent phases. The initial temporal change during the first phase in δMAAs (0.031 nmol MAAs [mol Chl a]−1 min−1) consisted of an increase in the four primary MAAs, shinorine, porphyra-334, mycosporine-glycine, and palythene (0.049 nmol MAAs [mol Chl a]−1 min−1), and a decrease in one secondary MAA, palythine (−0.018 nmol MAA [mol Chl a]−1 min−1). Although the temporal increase in δMAAs was limited, a possible main route of MAA transformation had mycosporine-glycine and porphyra-334 as the primary precursors of a sequential series of conversions, by which the cells accumulated shinorine and palythene, possibly at the expense of palythine. The increased MAAs enhanced a(310–360). The cells appear to achieve MAA transformation with an increase in total MAAs to protect from UVR damage.
We investigated the nucleic acid ratio (RNA/DNA) as a proxy for starvation in copepods collected from coastal and pelagic sites across the North Pacific Ocean. While RNA/DNA ratios were variable among copepod species and their life stages, lower ratios were found for the copepods collected from the Kuroshio region compared to ones from the western subarctic site of the North Pacific Ocean. Log-transformed RNA/DNA ratios showed a negative correlation to log-transformed mean temperature in the sampling layer and a positive correlation to log-transformed chlorophyll a concentrations. Copepod incubation experiments demonstrated that RNA/DNA ratios significantly declined after exposure to starvation and the decline was greater for the copepods collected from the subtropical sites compared with those from the subarctic. However, no significant decline was found for some species and stages accumulating lipids. These findings suggest that copepod RNA/DNA ratios are associated with food availability but are not sensitive to starvation for some copepods accumulating lipids.
The burrowing ocypodoid crab Macrophthalmusjaponicus, a major bioturbator on Japanese tidal flats, is classified as a “regenerator”, that reworks the sediment without changing sediment grain distribution. We examined the effects of M. japonicus on abiotic and biotic sediment characteristics through crab exclusion experiments conducted on two adjacent tidal flats in the Tama River, Tokyo Bay, Japan, in 2012 and 2013. Although sediment organic matter content and water content were significantly higher in the exclusion treatment than in the control treatment, the silt-clay content did not differ significantly between them. Microphytobenthos (MPB) biomass was affected negatively by M. japonicus feeding, which caused in a high turnover ratio. The experimental results indicated that M. japonicus decreased MPB biomass and maintained high primary production without changing the sediment grain size distribution. This suggests that “regenerators” affect mudflat abiotic and biotic sediment characteristics in a different manner from other types of bioturbators.
Laboratory experiments were conducted to examine how the bivalve Trapezium liratum, originating from a population in the Ariake Sea, responds to decreases in salinity in cold and warm waters. After the ambient salinity had been decreased from ≈34 psu to 0–27 psu, 90 to 96% of the specimens survived for >120 h at both 12 and 24°C. When the ambient salinity was decreased to <5 psu the specimens continued to close their valves for 140 h at both temperatures. The percentages of specimens closing their valves, together with clearance and respiration rates, were in general lower for specimens with the ambient salinity more sharply decreased, regardless of water temperature. These results suggest that T. liratum can tolerate a rapid decrease in salinity by closing their valves to decrease water intake.
The moonsnail Laguncula pulchella (Naticidae, formerly known as Euspira fortunei) is an invasive species that has had a negative impact on the Manila clam (Ruditapes philippinarum) population in northern Japan. In southern Japan, few records of L. pulchella exist; furthermore, the knowledge concerning the ecology of this organism is currently limited. Unexpectedly, we found many L. pulchella individuals in the Misuji River estuary, located in Hiroshima in southern Japan, during May 2015. We conducted a field survey on the density and body size of L. pulchella at a tidal flat in the Misuji River estuary (Site H) and compared those to L. pulchella in Matsukawaura Lagoon, located in Fukushima in northern Japan (Site F). The adult population of L. pulchella in a clam fishing ground (40,500 m2) at Site H was estimated to be 2,048 individuals in 2015. Densities of both surfaced individuals and egg collars of L. pulchella were lower at Site H than at Site F. Sizes of L. pulchella individuals and their egg collars as well as the somatic weight of the individuals at Site H were significantly smaller than those at Site F. These results suggest that the biological characteristics of L. pulchella largely differ between the two sites.
A new species of “cydippid” ctenophore, Pukia ohtsukai sp. nov., is described from material collected in Nishino-omote Port, Tanegashima Island, Japan. It can be distinguished from the only other member of the genus by the presence of perradial canals, lack of bilateral diverticula beneath the comb plates, a lower number of comb plates per comb row (19–21), the presence of black pigment patches at the oral ends of the comb rows and around the statocyst, and by the length of the pole plate, which extends only to the aboral tips of the comb rows.
A doliolid species belonging to the genus Paradoliopsis was photographed by an Autonomous Visual Plankton Recorder (AVPR) off the eastern seaboard of Japan in October 2014 at 493–512 m depth. Two Paradoliopsis gonozooids were also captured on the video record of the ROV Crambon at 372–373 m depth during the same cruise. This is the first record of this genus from the Pacific Ocean, and although it resembles the sole described species in this genus, P. harbisoni Godeaux, 1996, some aspects of its morphology suggest it may be an as-yet-undescribed species.
Instances of predation and scavenging of jellyfish (pelagic Scyphozoa, Hydrozoa and Ctenophora) by benthic invertebrates are reviewed and presented. Sea anemones and decapod crabs are widespread as well as common predators or scavengers of jellyfish. Dead or dying jellyfish are also preyed upon by species of Echinodermata.
Two Saccostrea oysters (S. glomerata and S. cucullata) are considered to be protandric hermaphrodites based on indirect observations. However, no other information is available on the sexual systems of Saccostrea oysters and the potential for bi-directional sex change has not previously been reported in them. Therefore, the present study was undertaken to investigate the sexual systems of S. kegaki and S. mordax in western Japan, utilizing field sampling and in situ experiments. In the field sampling, shell length (SL) and sex were determined during the reproductive season of these oysters (June–October) in 2012. Then, sex change was directly observed between 2013 and 2016 by determining the sex of individuals through gonadal biopsy, re-attaching the individuals in the field, collecting the survivors in the following year, and determining their sex by dissection. In both species, the proportion of males decreased with increasing SL, although the SL of males and females greatly overlapped. Direct observations showed that both male-to-female and female-to-male sex change occurred. Thus, our results indicated that both Saccostrea species tend to be protandric, but have the ability to change sex in both directions under natural conditions.