Michel R. Claereboudt

Fertilization success in spatially distributed populations of benthic free-spawners: A simulation model

Fertilization is the first major determinant in reproductive success in free-spawning invertebrates. A spatially-explicit, 3D, diffusion and fertilization model was used to explore the effects of spatial distribution, rate of gamete release and population structure (density and sex ratio) on the larval production of benthic free-spawners. The results of the simulations indicate that high population density, spatial aggregation and high rate of gamete release significantly increase the overall larval production in large populations. Moreover, in a population undergoing even mild fishing pressure, the model predicts a very strong decrease (90%) in larval production. This evidence of sperm limitation suggests that recruitment in some heavily exploited populations of free spawners rely on either natural or human induced refuge populations that act as reservoir for larval production.

Long-Distance Dispersal via Ocean Currents Connects Omani Clownfish Populations throughout Entire Species Range

Dispersal is a crucial ecological process, driving population dynamics and defining the structure and persistence of populations. Measuring demographic connectivity between discreet populations remains a long-standing challenge for most marine organisms because it involves tracking the movement of pelagic larvae. Recent studies demonstrate local connectivity of reef fish populations via the dispersal of planktonic larvae, while biogeography indicates some larvae must disperse 100–1000 s kilometres. To date, empirical measures of long-distance dispersal are lacking and the full scale of dispersal is unknown. Here we provide the first measure of long-distance dispersal in a coral reef fish, the Omani clownfish Amphiprion omanensis, throughout its entire species range. Using genetic assignment tests we demonstrate bidirectional exchange of first generation migrants, with subsequent social and reproductive integration, between two populations separated by over 400 km. Immigration was 5.4% and 0.7% in each region, suggesting a biased southward exchange, and matched predictions from a physically-coupled dispersal model. This rare opportunity to measure long-distance dispersal demonstrates connectivity of isolated marine populations over distances of 100 s of kilometres and provides a unique insight into the processes of biogeography, speciation and adaptation.

Interannual changes of the Arabian Sea productivity

Abstract Inter-annual changes in temperature and chlorophyll a across the Arabian Sea (subdivided into 61 2-degree regions) were analysed. For each 2-degree region, from appropriate databases, remotely sensed chlorophyll a, sea surface temperature, and wind speed time series were retrieved. Spatial and temporal trend analysis showed physical–biological oscillations with dominant periods of 12 and 6 months (reflecting the seasonality of monsoonal winds) with a globally warming trend, but no overall increase in chlorophyll during the period 1997–2009. Variation coefficients of the inter-annual time series of chlorophyll a implied high variability in western regions of the sea in comparison to eastern regions. The basin-wide maps of chlorophyll distribution did not show the enlargement of the productive area over time and overall, not only did the Arabian Sea not get more productive, but several regions in its eastern basin showed a decline in chlorophyll a concentration.

Past summer upwelling events in the Gulf of Oman derived from a coral geochemical record

We used a high-resolution oxygen isotope (δ18Ocoral), carbon isotope (δ13Ccoral) and Sr/Ca ratios measured in the skeleton of a reef-building coral, Porites sp., to reveal seasonal-scale upwelling events and their interannual variability in the Gulf of Oman. Our δ13Ccoral record shows sharp negative excursions in the summer, which correlate with known upwelling events. Using δ13Ccoral anomalies as a proxy for upwelling, we found 17 summer upwelling events occurred in the last 26 years. These anomalous negative excursions of δ13Ccoral result from upwelled water depleted in 13C (dissolved inorganic carbon) and decreased water-column transparency. We reconstructed biweekly SSTs from coral Sr/Ca ratios and the oxygen isotopic composition of seawater (δ18OSW) by subtracting the reconstructed Sr/Ca-SST from δ18Ocoral. Significant δ18OSW anomalies occur during major upwelling events. Our results suggest δ13Ccoral anomalies can be used as a proxy for seasonal upwelling intensity in the Gulf of Oman, which, driven by the Indian/Arabian Summer Monsoon, is subject to interannual variability.

Extraocular vision in the sea urchin Diadema setosum

Abstract In most organisms, specific structures are responsible for detecting light patterns and vision. Several species of sea urchins appear to have a diffuse photoreceptor system that enables them to detect light and in some cases objects. The presence of extraocular vision was investigated on a sea urchin common in northern Oman, Diadema setosum. Urchins from 8- to 10-m deep coral communities were used in controlled experiments that quantified the orientation response of the urchins to various visual cues: size, contrast and colour of circular targets simulating urchins’ outlines. Urchins responded to black discs down to 11° initial visual angle but not to smaller discs. The minimum grey-scale value triggering a response was between 50 and 37% black. Urchins responded to red targets but not to green or blue ones. An average angular distance between spines of 5.3° suggested a visual acuity of about 10.6°. D. setosum thus showed extraocular vision allowing them to detect objects of different sizes, contrasts and to some extent colour, supporting the hypothesis that the whole sea urchin’s body acts as a single large compound eye.

A New Species of the Genus Electra (Bryozoa, Cheilostomata) from Southern Oman, Arabian Sea

A new cheilostome bryozoan Electra omanensis n. sp. is described in Southern Oman (Dhofar Region, Arabian Sea) and is also the first description of any bryozoan from this area. The new species morphologically most resembles Electra indica (Menon and Nair (Mar Biol Ass India 17:553–579, 1975), but differs in (1) colony shape – colonies consist of long narrow branching strips, and (2) in the shape of the gymnocystal spines. The combination of these features is sufficiently distinctive and allows discriminating the new species from all other known species in this genus. Genetic analyses of nuclear and mitochondrial ribosomal genes also support separate species status for this species of Electra.

Gene expression plasticity and frontloading promote thermotolerance in Pocilloporid corals

Ecosystems worldwide are suffering from climate change. Coral reef ecosystems are globally threatened by increasing sea surface temperatures. However, gene expression plasticity provides the potential for organisms to respond rapidly and effectively to environmental changes, and would be favored in variable environments. In this study, we investigated the thermal stress response in Pocillopora coral colonies from two contrasting environments by exposing them to heat stress. We compared the physiological state, bacterial and Symbionaceae communities (using 16S and ITS2 metabarcoding), and gene expression levels (using RNA-Seq) between control conditions and heat stress (the temperature just below the first signs of compromised health). Colonies from both thermal regimes remained apparently normal and presented open and colored polyps during heat stress, with no change in bacterial and Symbionaceae community composition. In contrast, they differed in their transcriptomic responses. The colonies from Oman displayed a more plastic transcriptome, but some genes had a higher basal expression level (frontloading) compared to the less thermotolerant colonies from New Caledonia. In terms of biological functions, we observed an increase in the expression of stress response genes (including induction of tumor necrosis factor receptors, heat shock proteins, and detoxification of reactive oxygen species), together with a decrease in the expression of genes involved in morpho-anatomical functions. Gene regulation (transcription factors, mobile elements, histone modifications and DNA methylation) appeared to be overrepresented in the Oman colonies, indicating possible epigenetic regulation. These results show that transcriptomic plasticity and frontloading can be co-occurring processes in corals confronted to highly variable thermal regimes.

Sea turtles tourism in Oman: Current status and future prospects:

This paper provides an overview of the current status and future potentials of nature-based tourism in the Sultanate of Oman with particular focus on sea turtles at Ras Al Hadd. The paper uses objective yardsticks such as inbound tourist arrivals, nationality and spending patterns, seasonality, employment, as well as gross domestic product contribution derived from secondary data from national and international sources to appraise the current situation. Additionally, based on the review of relevant literature, a strengths, weaknesses, opportunities, and threats analysis is used to summarize relevant socioeconomic, political, environmental, and regulatory issues. While there is strong evidence of government commitment to develop nature-based tourism in the country, a number of key issues related to tourist facilities, human activities, environmental conditions, economic research, and capacity development are highlighted for further attention. Most importantly, the analysis suggests a potential to increase the contribution of sustainable sea turtle tourism to Oman’s gross domestic product. To realize this potential the sector needs to (1) consider the seasonal variation of tourists, (2) develop its accommodation capabilities especially at sites with ecological uniqueness while ensuring minimum negative impacts on biodiversity, (3) increase the number of Omani nationals employed in the tourism industry and improve their skills through training, (4) develop marketing tools to attract the dominant inbound ecotourism groups to the country, (5) enhance sustainable planning implementation in the Omani tourism sector, and (6) most importantly ensure an effective implementation of legislation protecting sea turtles and their habitats. It is hoped that policymakers can use these findings to set a direction on sustainable sea turtle tourism in Oman, while promoting the effective conservation of these species.

Consumers' Preference Mapping and Their Behavior with Regard to Traditional Halwa Using a Structured Survey Questionnaire

In this study, a structured survey questionnaire was used to determine consumers’ preferences and their behavior with regard to halwa. Five types of consumer groups were identified thorough hierarchical cluster analysis based on ranked attributes. Color was ranked within the top three attributes for all the groups. In general, color, sweetness, appearance, and solubility were found to be the most important attributes for selecting the halwa. Five types of groups were identified based on their preference levels (i.e., intensity) of attributes. These could be recognized in terms of preferences for halwa with (1) black with high sweetness, (2) dark-brown with high-medium sweetness, (3) dark with low-medium sweetness, (4) brown with medium sweetness, and (5) dark with high-medium sweetness preferred consumers. The consumer segmentations identified could be used to develop retail marketing strategies and to develop store brands of diversified Arabian sweets and intermediate moisture fruit snacks, such as dates.