Gametogenesis, Embryogenesis, and Fertilization Ecology of Platygyra acuta

Understanding the reproductive biology of dominant coral species in subtropical nonreefal coral communities is critical in providing important information on the processes underlying the distribution limits of coral species and communities. This is the first study that investigates the reproduction cycle, gametogenesis, and fertilization ecology of Platygyra acuta. Results indicated that P. acuta is hermaphroditic and exhibits a single annual gametogenic cycle. Oogenic and spermatogenic cycle occurs for 6-7 months and for 2 months, respectively, prior to annual mass spawning event in May to June in Hong Kong. It took 18 hours for P. acuta to complete embryonic development, develop cilia, and start to rotate. High (>70%) fertilization success can be achieved under a broad range of sperm concentrations from 104 to 107 sperms mL−1. Fertilization success remained consistently high 6 h after spawning, indicating a prolonged viability of its gametes that is much longer than that recorded for other coral species. Significantly higher percentage of fertilization success was recorded in the first of the two consecutive nights of spawning, suggesting differences in the quality of the eggs and/or sperms between days of spawning. These results serve as important baseline information for better understanding of corals in marginal communities

Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia

© 2018 The Author(s) Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including “reef compression” (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas

Natural dynamics and matrix models of a fucus distichus (phaeophyceae, fucales) population in Vancouver, British Columbia, Canada

Patterns of reproduction, micro-recruitment, macro-recruitment, age- and size-dependent reproduction, growth and mortality in a population of the brown alga Fucus distichus in Vancouver, British Columbia, Canada, were examined from May 1985 to November 1987. Using log linear and association analyses, age and size are both found to be significant, but size more so than age, as descriptors of the demographic parameters. Reproductive plants were found throughout the sampling period, but peaked in fall and winter of each year. Estimated monthly egg production, calculated by the observed number of eggs in clusters extruded from the receptacle, is independent of plant size. Two types of recruits were monitored. Microrecruits (< 1 month-old of microscopic size) are germlings developed from fertilized eggs. Their numbers were assessed using settling blocks. Macrorecruits are detectable by the unaided eye and are plants appearing in the permanent quadrats for the first time. The recruitment pattern of microrecruits is significantly correlated with reproductive phenology and patterns of potential and estimated monthly egg production. However, peaks in micro-recruitment are not always followed by peaks in macro-recruitment. This apparent discrepancy is probably due to a differential survivorship of microrecruits over time or to the possible existence of a "germling bank". Patterns of survival and emergence of macrorecruits may be independent of those of microrecruits or may be unrelated to the prevailing reproductive phenology. This population of Fucus distichus showed seasonal variations in plant mean length and growth rates. Mean length was greater in winter (4.2-5.3 cm) and lower in summers of 1986 and 1987 (2.7 - 4.3 cm). Absolute growth rates showed a significantly opposite trend, being higher in spring and summer (0.24 - 1.17 cm/month) and lower in fall to winter (-0.5 - 0.4 cm/month). The relationship between reproduction, growth and mortality was also evaluated in terms of the cost of reproduction. There is no clear indication of cost of reproduction with respect to the longevity or mortality of fertile vs. non-fertile plants. Fertile plants, especially those > 17 cm in length, tend to exhibit negative or zero growth much more often than non-fertile plants, suggesting the cost of reproduction may be manifested in the form of reduced growth rather than in greater mortality or shorter longevity of the fertile plants. The failure to detect cost of reproduction may be due to the modular character of the plants, where cost occurs at the level of the modules (branches) rather than at the level of the whole plant. The effect of density on mortality and growth among recruits in this population was also monitored. In the first 2 months of development, germlings growing at high density experienced a lower mortality than those growing at lower densities. At later stages (> 2 months), the effect of density on mortality was reversed. Plant growth rate was generally not related to density but was related to plant length. The dynamics of the population was further evaluated with a 9 x 9 matrix model based on recruit stages and plant size. From the elasticity analysis, the survival and transition of the plants among size classes was found to be the most important parameter and contributed at least 50% to the population growth rate (lambda). Fucus does not grow by vegetative propagation, the population can only experience positive growth in the presence of recruitment. The current population size structure is unstable and is very different from the projected stable distribution. Overall, the population is on the decline. However, it is likely that the population may recover by occasional pulses of a large number of recruits, an example of which was observed in 1986.Science, Faculty ofBotany, Department ofGraduat

High tolerance to temperature and salinity change should enable scleractinian coral Platygyra acuta from marginal environments to persist under future climate change.

With projected changes in the marine environment under global climate change, the effects of single stressors on corals have been relatively well studied. However, more focus should be placed on the interactive effects of multiple stressors if their impacts upon corals are to be assessed more realistically. Elevation of sea surface temperature is projected under global climate change, and future increases in precipitation extremes related to the monsoon are also expected. Thus, the lowering of salinity could become a more common phenomenon and its impact on corals could be significant as extreme precipitation usually occurs during the coral spawning season. Here, we investigated the interactive effects of temperature [24, 27 (ambient), 30, 32°C] and salinity [33 psu (ambient), 30, 26, 22, 18, 14 psu] on larval settlement, post-settlement survival and early growth of the dominant coral Platygyra acuta from Hong Kong, a marginal environment for coral growth. The results indicate that elevated temperatures (+3°C and +5°C above ambient) did not have any significant effects on larval settlement success and post-settlement survival for up to 56 days of prolonged exposure. Such thermal tolerance was markedly higher than that reported in the literature for other coral species. Moreover, there was a positive effect of these elevated temperatures in reducing the negative effects of lowered salinity (26 psu) on settlement success. The enhanced settlement success brought about by elevated temperatures, together with the high post-settlement survival recorded up to 44 and 8 days of exposure under +3°C and +5°C ambient respectively, resulted in the overall positive effects of elevated temperatures on recruitment success. These results suggest that projected elevation in temperature over the next century should not pose any major problem for the recruitment success of P. acuta. The combined effects of higher temperatures and lowered salinity (26 psu) could even be beneficial. Therefore, corals that are currently present in marginal environments like Hong Kong, as exemplified by the dominant P. acuta, are likely to persist in a warmer and intermittently less saline, future ocean

Mean size of <i>Platygyra acuta</i> recruits.

<p>Mean (+SE) size (mm²) of <i>Platygyra acuta</i> recruits in response to different temperature and salinity treatments. Number in () under each set of data represents number of replicates. Data indicated with the same letter showed no significant difference in the recruit sizes (Two-way ANOVA, <i>P</i> > 0.05; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179423#pone.0179423.t001" target="_blank">Table 1C</a>).</p

Results of Two-way (A and C) and Mixed (B) ANOVA showing the effects of different factors and their interaction on (A) cumulative settlement, (B) post-settlement survival of recruits and (C) size changes of the recruits.

<p>Results of Two-way (A and C) and Mixed (B) ANOVA showing the effects of different factors and their interaction on (A) cumulative settlement, (B) post-settlement survival of recruits and (C) size changes of the recruits.</p

Mean percentage of newly settled <i>Platygyra acuta</i> larvae and cumulative surviving settlers.

<p>Mean (+SE) percentage (%) of newly and cumulatively settled <i>Platygyra acuta</i> larvae in response to different temperature and salinity treatments (<i>n</i> = 3 replicates per treatment). Data indicated with the same letter showed no significant difference in settlement success (Two-way ANOVA, <i>P</i> > 0.05; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179423#pone.0179423.t001" target="_blank">Table 1A</a>).</p

Schematic representation of the experimental design to study the interactive effects of temperature and salinity change on <i>Platygyra acuta</i> larvae.

<p>Schematic representation of the experimental design to study the interactive effects of temperature and salinity change on <i>Platygyra acuta</i> larvae.</p

Mean percentage of surviving settlers of <i>Platygyra acuta</i>.

<p>Mean (+SE) percentage (%) of surviving settlers of <i>Platygyra acuta</i> in response to different temperature and salinity treatments (<i>n</i> = 3 replicates per treatment). * denotes those results of pairwise comparisons that showed significant difference (<i>P</i> < 0.05) between ambient salinity and lowered salinity treatments under the fixed factor of temperature. Data indicated with the same letter showed no significant difference in percentage of post-settlement survival (Mixed ANOVA, <i>P</i> > 0.05; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179423#pone.0179423.t001" target="_blank">Table 1B</a>).</p