Naoko Morimoto

Phenotypic Plasticity and Sexual Dimorphism in Size at Post-Juvenile Metamorphosis: Common-Garden Rearing of an Intertidal Gastropod With Determinate Growth

Proximate factors of the intraspecific variation in molluscan shell morphology have long received attention in biology. The intertidal gastropod Monetaria annulus (Mollusca; Gastropoda; Cypraeidae) is particularly suitable for the study of variation in body size, because this species is a determinate grower in the sense that soft-body size shows no further increase after the juvenile stage. Cross-sectional field surveys on post-juvenile individuals have indicated that the mean body size varies widely among populations and is larger in females than in males within populations. To examine whether these patterns are due to genetic differences, we conducted a common-garden rearing experiment with juvenile individuals collected from two populations on Okinawa Island. After adjusting for among-individual differences in initial degree of development, statistical analyses revealed that this species exhibits female-biased sexual size dimorphism mediated by a longer development time rather than by faster growth rates in females. Although wild individuals show a remarkable size difference between populations, no size difference was found between the populations in the individuals reared in a common-garden condition. This result suggests that the among-population size difference does not have a genetic basis and is caused by phenotypic plasticity based on environmental heterogeneity among habitats.

Phosphorus as a driver of nitrogen limitation and sustained eutrophic conditions in Bolinao and Anda, Philippines, a mariculture-impacted tropical coastal area.

The dynamics of nitrogen (N) and phosphorus (P) was studied in mariculture areas around Bolinao and Anda, Philippines to examine its possible link to recurring algal blooms, hypoxia and fish kills. They occur despite regulation on number of fish farm structures in Bolinao to improve water quality after 2002, following a massive fish kill in the area. Based on spatiotemporal surveys, coastal waters remained eutrophic a decade after imposing regulation, primarily due to decomposition of uneaten and undigested feeds, and fish excretions. Relative to Redfield ratio (16), these materials are enriched in P, resulting in low N/P ratios (~6.6) of regenerated nutrients. Dissolved inorganic P (DIP) in the water reached 4μM during the dry season, likely exacerbated by increase in fish farm structures in Anda. DIP enrichment created an N-limited condition that is highly susceptible to sporadic algal blooms whenever N is supplied from freshwater during the wet season.

Water-Quality Variables across Sekisei Reef, A Large Reef Complex in Southwestern Japan.

Abstract: At Sekisei Reef in southwestern Japan (24° N), coral cover dramatically decreased in the mid-1980s, probably due to a population outbreak of the coral predator Acanthaster planci. Coral communities subsequently recovered well outside the semiclosed lagoon, but recovery has been poor inside it. Hence, water-quality degradation including eutrophication has been a concern inside the lagoon. In addition, temporal variation in eutrophication parameters is common among high-latitude coral reefs, resulting in difficulties in evaluating them. Therefore, to address these issues, we monitored temperature, salinity, turbidity, chlorophyll-a, NO x -N (NO3-N + NO2-N), and NH4-N concentrations year-round across the lagoon at Sekisei Reef. Turbidity and NO x -N concentration increased with increasing wind velocity, suggesting that variation in turbidity and NO x -N concentrations was attributed to resuspension of bottom sediments, and NO x -N release through regeneration processes of micro-organisms from the sediments and reef frameworks, respectively. In contrast, variation in chlorophyll- a and NH4-N concentrations appears to be mainly controlled by the seasonality of temperature and irradiance. Long retention time of seawater inside the lagoon seems to have enhanced NH4-N assimilation and increase of phytoplankton during summer. Inside the lagoon, turbidity, NO x -N, and summer chlorophyll-a concentrations were higher, and variation in temperature was larger than outside it. Although water quality appears not to be seriously degraded, multiple effects of these water-quality variables might have negatively affected recovery of coral communities inside the lagoon. Recent expansion of land use on nearby islands might have contributed to water-quality degradation inside the lagoon.

Atmospheric Deposition of Reactive Nitrogen as a Regional-Scale Eutrophication Stress on the Coral Reef Ecosystem

Long-range transport and deposition of atmospheric pollutants from mid-latitude industrial regions to low-latitude seas have the potential to degrade coral reefs. We investigated the atmospheric wet deposition of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) to coral reef sites around the Ishigaki and Iriomote Islands in the subtropical western North Pacific. The deposition rate of DIN was higher in autumn and winter than in summer. The annual N deposition was 3–8 times higher than rates previously observed at subtropical North Atlantic reef sites and was almost as large as the cyanobacterial N2 fixation rate previously estimated for Ishigaki reefs. A backward trajectory analysis of an air mass suggested that the dominant remote emission source for atmospheric nitrate in winter was coastal industrial areas in continental China. A comparison with previous reports suggested that the influence of transboundary pollution on the N budget at the study site had significantly increased during the first decade of the twenty-first century.