The behavior of sympatric sea urchin species across an ecosystem state gradient.

Background: In temperate macroalgal forests, sea urchins are considered as a keystone species due to their grazing ability. Given their potential to shape benthic communities, we monitored the habitat use by three sympatric sea urchin species and compared their behaviors in a vegetated habitat (VH) and an adjacent isoyake habitat (IH). Methods: We monitored the environmental conditions and sea urchin density along deep and shallow transects of the VH and IH for over a year. The benthic rugosity at both sites were also surveyed. A mark-recapture experiment was conducted on the two most abundant sea urchins, Diadema setosum and Heliocidaris crassispina, to elucidate sea urchin movement patterns and group dynamics. Results: We found that exposure to waves was highest at the VH while the IH was sheltered. The deep IH experienced the least amount of light due to high turbidity. Water temperature patterns were similar across sites. The VH benthic topography was more rugose compared to the smoother and silt-covered IH substate. Peak macroalgal bloom occurred three months earlier in IH, but macroalgae persisted longer at the shallow VH. Among the sympatric sea urchins, H. crassispina was most abundant at the shallow VH and was observed in pits and crevices. The most abundant across IH and in the deep VH was D. setosum, preferring either crevices or free-living, depending on hydrodynamic conditions. The least abundant species was D. savignyi, and most often observed in crevices. Small and medium sea urchins were most often observed at the IH site, whereas larger sea urchins were more likely observed at the VH. The mark-recapture study showed that D. setosum was found to displace further at the IH, and H. crassispina was more sedentary. Additionally, D. setosum was always observed in groups, whereas H. crassispina was always solitary. Discussion: The behaviors of sympatric urchins, Diadema savignyi, D. setosum and H. crassispina, differed in response to changes in the benthic environment and physical conditions. Sea urchin displacement increased when rugosity and wave action were low. Habitat preference shifted to crevices in seasons with high wave action. In general, the mark-recapture experiment showed that sea urchins displaced further at night.

Global kelp forest restoration: past lessons, present status, and future directions.

Kelp forest ecosystems and their associated ecosystem services are declining around the world. In response, marine managers are working to restore and counteract these declines. Kelp restoration first started in the 1700s in Japan and since then has spread across the globe. Restoration efforts, however, have been largely disconnected, with varying methodologies trialled by different actors in different countries. Moreover, a small subset of these efforts are 'afforestation', which focuses on creating new kelp habitat, as opposed to restoring kelp where it previously existed. To distil lessons learned over the last 300 years of kelp restoration, we review the history of kelp restoration (including afforestation) around the world and synthesise the results of 259 documented restoration attempts spanning from 1957 to 2020, across 16 countries, five languages, and multiple user groups. Our results show that kelp restoration projects have increased in frequency, have employed 10 different methodologies and targeted 17 different kelp genera. Of these projects, the majority have been led by academics (62%), have been conducted at sizes of less than 1 ha (80%) and took place over time spans of less than 2 years. We show that projects are most successful when they are located near existing kelp forests. Further, disturbance events such as sea-urchin grazing are identified as regular causes of project failure. Costs for restoration are historically high, averaging hundreds of thousands of dollars per hectare, therefore we explore avenues to reduce these costs and suggest financial and legal pathways for scaling up future restoration efforts. One key suggestion is the creation of a living database which serves as a platform for recording restoration projects, showcasing and/or re-analysing existing data, and providing updated information. Our work establishes the groundwork to provide adaptive and relevant recommendations on best practices for kelp restoration projects today and into the future.

Geographic Variations in the Toxin Profile of the Xanthid Crab Zosimus aeneus in a Single Reef on Ishigaki Island, Okinawa, Japan.

Toxic crabs of the family Xanthidae contain saxitoxins (STXs) and/or tetrodotoxin (TTX), but the toxin ratio differs depending on their habitat. In the present study, to clarify within reef variations in the toxin profile of xanthid crabs, we collected specimens of the toxic xanthid crab Zosimus aeneus and their sampling location within a single reef (Yoshihara reef) on Ishigaki Island, Okinawa Prefecture, Japan, in 2018 and 2019. The STXs/TTX content within the appendages and viscera or stomach contents of each specimen was determined by instrumental analyses. Our findings revealed the existence of three zones in Yoshihara reef; one in which many individuals accumulate extremely high concentrations of STXs (northwestern part of the reef; NW zone), another in which individuals generally have small amounts of TTX but little STXs (central part of the reef; CTR zone), and a third in which individuals generally exhibit intermediate characteristics (southeastern part of the reef; SE zone). Furthermore, light microscopic observations of the stomach contents of crab specimens collected from the NW and CTR zones revealed that ascidian spicules of the genus Lissoclinum were dominant in the NW zone, whereas those of the genus Trididemnum were dominant in the CTR zone. Although the toxicity of these ascidians is unknown, Lissoclinum ascidians are considered good candidate source organisms of STXs harbored by toxic xanthid crabs.

Potential oxygen consumption and community composition of sediment bacteria in a seasonally hypoxic enclosed bay.

The dynamics of potential oxygen consumption at the sediment surface in a seasonally hypoxic bay were monitored monthly by applying a tetrazolium dye (2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride [INT]) reduction assay to intact sediment core samples for two consecutive years (2012-2013). Based on the empirically determined correlation between INT reduction (INT-formazan formation) and actual oxygen consumption of sediment samples, we inferred the relative contribution of biological and non-biological (chemical) processes to the potential whole oxygen consumption in the collected sediment samples. It was demonstrated that both potentials consistently increased and reached a maximum during summer hypoxia in each year. For samples collected in 2012, amplicon sequence variants (ASVs) of the bacterial 16S rRNA genes derived from the sediment surface revealed a sharp increase in the relative abundance of sulfate reducing bacteria toward hypoxia. In addition, a notable shift in other bacterial compositions was observed before and after the INT assay incubation. It was Arcobacter (Arcobacteraceae, Campylobacteria), a putative sulfur-oxidizing bacterial genus, that increased markedly during the assay period in the summer samples. These findings have implications not only for members of Delta- and Gammaproteobacteria that are consistently responsible for the consumption of dissolved oxygen (DO) year-round in the sediment, but also for those that might grow rapidly in response to episodic DO supply on the sediment surface during midst of seasonal hypoxia.

Storage capacity for phosphorus during growth and maturation in a brown alga Sargassum macrocarpum.

Improved coastal management has decreased anthropogenic nutrient input over the past few decades, leading to phosphorus depletion. It has been hypothesized that phosphorus depletion in coastal environments leads to declines in macroalgae abundance. Perennial canopy-forming temperate macroalgae can experience the effects of limited phosphorus availability during seasonal phosphorus depletion periods. When nutrients are sufficient, they are stored in algal tissues after luxury uptake and are available to support growth during phosphorus-depleted conditions. Cultivation of mature and actively growing juvenile brown alga (Sargassum macrocarpum) under different nutrient conditions provided individuals with different tissue nutrient concentrations. The maximum photosynthetic rates of these individuals were examined under nutrient-depleted conditions to evaluate "storage capacity", which we defined as the amount of stored phosphorus that can support maximum growth. Maximum photosynthetic rate was used as a proxy for maximum growth rates. The experiments revealed that growth rates of juveniles increased when stored phosphorus content was high. In contrast, the maximum growth rates tended not to increase with an increase in stored phosphorus content in mature individuals. The phosphorus storage capacities for juvenile and mature individuals were approximately 19 and more than 16 weeks, respectively, suggesting that individual alga can endure several months of phosphorus depletion.

Growth and cell cycle of Ulva compressa (Ulvophyceae) under LED illumination.

The cell-cycle progression of Ulva compressa is diurnally gated at the G1 phase in accordance with light-dark cycles. The present study was designed to examine the spectral sensitivity of the G1 gating system. When blue, red, and green light-emitting diodes (LEDs) were used for illumination either alone or in combination, the cells divided under all illumination conditions, suggesting that all colors of light were able to open the G1 gate. Although blue light was most effective to open the G1 gate, red light alone or green light alone was also able to open the G1 gate even at irradiance levels lower than the light compensation point of each color. Occurrence of a period of no cell division in the course of a day suggested that the G1 gating system normally functioned as under ordinary illumination by cool-white fluorescent lamps. The rise of the proportion of blue light to green light resulted in increased growth rate. On the other hand, the growth rates did not vary regardless of the proportion of blue light to red light. These results indicate that the difference in growth rate due to light color resulted from the difference in photosynthetic efficiency of the colors of light. However, the growth rates significantly decreased under conditions without blue light. This result suggests that blue light mediates cell elongation and because the spectral sensitivity of the cell elongation regulating system was different from that of the G1 gating system, distinct photoreceptors are likely to mediate the two systems.

Change in the transfer profile of orally administered tetrodotoxin to non-toxic cultured pufferfish Takifugu rubripes depending of its development stage.

To investigate the effects of growth (organ development) on tetrodotoxin (TTX) dynamics in the pufferfish body, TTX-containing feed homogenate was administered to 6- and 15-month old non-toxic cultured specimens of the pufferfish Takifugu rubripes at a dose of 40 mouse units (MU) (8.8 µg)/20 g body weight by oral gavage. After 24 h, the specimens were killed and the skin tissues (dorsal and ventral), muscle, liver, digestive tract, and gonads were separated. TTX content (µg/g) in each tissue, determined by liquid chromatography/mass spectrometry, revealed that the TTX distribution profile, particularly the TTX content of the liver, greatly differed between the two ages; the TTX score of 15-month old fish (3.3 µg/g) was nearly 5-fold that of 6-month old fish (0.68 µg/g). The total remaining TTX amount per individual (relative amount to the given dose) was 31% in 6-month old fish, of which 71% was in the skin, and 84% in 15-month old fish, of which 83% was in the liver. The gonadosomatic index (GSI) and hepatosomatic index (HSI) scores, and histologic observations of the gonads and liver suggest that although there is little difference in maturation stage between these two ages, there are clear distinctions in the developmental stage of the liver. The results suggest that the TTX dynamics in T. rubripes are linked to the development of the liver, i.e., the TTX taken up into the pufferfish body via food organisms is eliminated or transferred mainly to the skin in young fish with an undeveloped liver, but as the fish grow and the liver continues to develop, most of the TTX is transferred to and accumulated in the liver.

DURATIONS OF GAMETE MOTILITY AND CONJUGATION ABILITY OF ULVA COMPRESSA (ULVOPHYCEAE)(1).

The present study was designed to develop a technique for crossing and to gain insight into how sexual reproduction contributes to the maintenance of local populations of Ulva compressa L. To examine the durations of gamete motility and conjugation ability, freshly released gametes were incubated for various periods of time prior to mixing both mating types. The conjugation ability of the gametes gradually declined after being released from the thalli when the gametes were incubated without mixing with the opposite mating type. The ability to conjugate decreased by half after 6 h, although most of the gametes remained motile. The gametes released 4 h later had the same level of conjugation ability when mixed immediately after releasing. When the mature thalli were wrapped in a moist paper towel to prevent gametes from being released, the gametes were preservable for 7 h without a significant decrease in their conjugation ability. Conjugation occurred soon after mixing gametes of both mating types and reached a plateau after 30 s. However, conjugation rates did not exceed a rate of ∼70%, even though freshly released gametes were used. Interestingly, a portion of the gametes newly conjugated 30 min after mixing both mating types, and conjugation rates reached a second plateau at ∼90%. Gametes with delayed conjugation are provided some period of time that allows them to be transported away and increases their chances of mating with more distant populations, thus contributing to the maintenance of genetic variation.

The interaction of CO2 concentration and spatial location on O2 flux and mass transport in the freshwater macrophytes Vallisneria spiralis and V. americana.

The biology of aquatic organisms determines the maximum rates of physiological processes, but the mass transport of nutrients determines the nominal rates at which these processes occur. Maximum O(2) flux (P(max)) at 17.1 mmol m(-3) CO(2) was higher for the leaves of the freshwater macrophyte Vallisneria spiralis [P(max)=0.013+/-0.001 mmol m(-2) s(-1) (g(chla+b) m(-2))(-1) (mean +/- s.e.m.)] than for the closely related species, Vallisneria americana [P(max)=0.008+/-0.001 mmol m(-2) s(-1) (g(chla+b) m(-2))(-1)]. The O(2) flux saturated at freestream velocities >4.5+/-1.2 cm s(-1) and was spatially invariant for both species. However, a tenfold decrease in CO concentration to 1.71 mmol m(-3) changed the nature of the relationship between O(2) flux and spatial location along the leaf surface, and reduced the O(2) flux of V. spiralis to values similar to V. americana. The O(2) flux [P(max)=0.007+/-0.001 mmol m(-2) s(-1) (g(chla+b) m(-2))(-1)] saturated at the upstream location (i.e. 1 cm from the leading edge of the leaf) but was found to increase linearly with freestream velocity [slope=0.057+/-0.011 mmol m(-2) s(-1) (g(chla+b) m(-2))(-1) (m s(-1))(-1)] at the downstream location (i.e. 7 cm from the leading edge) at freestream velocities >1.8+/-0.9 cm s(-1). Conversely, mass transfer rates did not vary with CO(2) concentration, and were characteristic of a laminar concentration boundary layer at the upstream location and a turbulent concentration boundary layer at the downstream location. Rates of mass transfer measured directly from O(2) profiles were not predicted by theoretical values based on hydrodynamic measurements. Moreover, the concentration boundary layer thickness (delta(CBL)) values measured directly from O(2) profiles were 48+/-2% and 21+/-1% of the predicted theoretical delta(CBL) values at the upstream and downstream locations, respectively. It is evident that physiological processes involving mass transport are coupled and vary in space. Mass transport investigations of biological systems based solely on hydrodynamic measurements need to be interpreted with caution.