Ariake Bay has Japan’s biggest nori seaweed farming field in the innermost part and has suffered from environmental degradation since the late 1990s. To elucidate the seasonal patterns in the copepod community structure in the inner bay, we examined monthly plankton-net samples collected in the top 2-m layer at 11 stations for 5 years from April 2002 to March 2007. Of the 11 stations, 7 were at the high-turbidity site (HTS) representing the nori farming field and 4 in the offshore low-turbidity site (LTS) for comparison. The copepod community in the HTS was dominated almost year round by Oithona davisae, whose 5-year mean abundance of 203 ind. L⁻¹ comprised 84% of copepods and was more than double that in the LTS. O. davisae became extremely abundant in summer with the maximum monthly mean abundance in the HTS of 2756 ind. L⁻¹ and the maximum sample-specific abundance of 10116 ind. L⁻¹. The following predominant copepods in the HTS were Parvocalanus crassirostris in summer–autumn, Microsetella norvegica in summer, Acartia omorii in spring, and Paracalanus parvus s.l. irregularly. Possible causes for high abundance of O. davisae in the HTS are assumed to be sufficient food resources, water temperature over 21°C, and a wide salinity tolerance range of the species.

We investigated the growth, thermotolerance, and fatty acid composition of the green alga Desmodesmus sp., which was isolated from a freshwater puddle in Ibaraki, Japan. Incubation experiments on the isolated strain were performed at a range of temperatures (20–40°C) with continuous illumination (110 µmol photons m⁻² s⁻¹) and nutrient-replete medium. High specific growth rates of 1.14–1.62 day⁻¹ were observed at 20–35°C, but growth rates declined to 0.59 day⁻¹ at 40°C. Lipid contents were 13.2%–14.4% (% dry weight) at 20–35°C and increased to 21.3% at 40°C. Some microalgae are known to regulate membrane fluidity by changing their fatty acid compositions in response to changes in ambient temperature. We found that the major polyunsaturated fatty acid (PUFA; C18:3 ω3) of Desmodesmus sp. was negatively correlated with water temperature. By contrast, no significant relationship was identified between temperature and the ratio of saturated to unsaturated fatty acids. The negative relationship between ω3 PUFA composition and temperature was stronger among thermotolerant as opposed to non-thermotolerant microalgae. This suggests that thermotolerant Desmodesmus sp. can grow at high temperatures by altering its fatty acid composition to affect membrane fluidity.

Semi-terrestrial brachyuran sesarmid crabs are the most diverse and important faunal components of mangrove forest and temperate coastal communities worldwide. To establish a stable larval rearing method for understanding their larval developmental processes including molecular mechanisms of molting and metamorphosis, we examined the effects of diet on the survival and growth of three sesarmid crabs, Chiromantes haematocheir, Orisarma intermedium, and O. dehaani under larval development. Zoea of each species, immediately after hatching, were reared under different feeding conditions as follows: non-feeding; fed only nutrition-enriched rotifers; fed only Artemia (brine shrimp) nauplii; and fed a combination of both nutrition-enriched rotifers and brine shrimp. Larvae of each species survived almost to megalopa when they were fed both rotifer and brine shrimp, but all C. haematocheir larvae had died by zoeal stage 2 when they were only fed brine shrimp. Chiromantes haematocheir larvae could survive into the megalopa stage when fed only nutrition-enriched rotifer, whereas both O. dehaani and O. intermedium showed 50% or less survival and metamorphosis rates into megalopa. The duration of larval development and survival rates of the three crabs were shorter and higher, respectively, in the mixed feeding group (both rotifer and brine shrimp) than when only fed rotifer or brine shrimp. This study provides baseline knowledge of the interspecific variability in larval survival and duration under different diets for sympatric sesarmid crab species.

Globally, observations on marine species during marine heatwaves (MHWs) help outline the scope of the MHW’s possible biological effects. In line with this effort, this paper presents a 2020 MHW that coincided with a reported ‘tomato jellyfish’ (Crambione mastigophora Maas, 1903) bloom on 23 March 2020 in the Corong-Corong Bay of Palawan, Philippines. Detecting a moderate MHW from 21 March to 04 April 2020, the analysis of sea surface temperatures revealed that most areas surrounding the bloom site attained their peak positive anomalies on the same day as the reported bloom. Certain physical mechanisms present in the first quarter of 2020 may have played a role in the occurrence of both events: the presence of cyclonic eddies and parallel monsoonal winds alongshore can induce upwelling which promotes biological productivity in surface waters, while the observed weakening of winds have been associated with anomalous warming of the sea surface. Further studies are still highly recommended to determine the exact causes of the jellyfish bloom and what conditions make it more likely to happen during MHWs. However, if the C. mastigophora is hypothetically able to continually bloom amidst warming temperatures, the increasing trend of MHW frequency and intensity in the West Philippine Sea (where the reported bloom site is situated) may consequently yield more future co-occurrences. This paper aims to hopefully contribute to the existing knowledge of possible biological impacts associated with extreme marine events, especially in the Philippine context where both jellyfish blooms and MHWs are understudied.

Ghost crabs (genus Ocypode spp.) found on sandy beaches are susceptible with the loss of an ecotone, making them useful as indicators of anthropogenic alteration, such as seawall construction. On the sandy beaches of Sendai Bay on the Pacific coast of the Tohoku region of northern Japan, three Ocypode species have been sympatrically observed in recent years: O. stimpsoni, O. ceratophthalmus, and O. sinensis. However, these three Ocypode species only occur sympatrically from late summer to autumn, immediately after new recruitment. Since they are all juveniles at that period, it is difficult to identify them by morphological characteristics. Thus, we have developed a method for identifying these three Ocypode species. By using two restriction enzymes of AciI and BfaI, we can perform polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis on the 12S-rRNA region of the mitochondrial DNA. As a result, our PCR-RFLP analysis is able to identify all three Ocypode species. Therefore, this method will be a helpful tool for understanding population dynamics and evaluating the sandy beach ecosystem in cases where the three Ocypode species occur sympatrically but identification by morphological features is difficult.