Monthon Ganmanee

The importance of thermal history: costs and benefits of heat exposure in a tropical, rocky shore oyster

ABSTRACT Although thermal performance is widely recognised to be pivotal in determining species’ distributions, assessment of this performance is often based on laboratory-acclimated individuals, neglecting their proximate thermal history. The thermal history of a species sums the evolutionary history and, importantly, the thermal events recently experienced by individuals, including short-term acclimation to environmental variations. Thermal history is perhaps of greatest importance for species inhabiting thermally challenging environments and therefore assumed to be living close to their thermal limits, such as in the tropics. To test the importance of thermal history, the responses of the tropical oyster Isognomon nucleus to short-term differences in thermal environments were investigated. Critical and lethal temperatures and oxygen consumption were improved in oysters that previously experienced elevated air temperatures, and were associated with an enhanced heat shock response, indicating that recent thermal history affects physiological performance as well as inducing short-term acclimation to acute conditions. These responses were, however, associated with trade-offs in feeding activity, with oysters that experienced elevated temperatures showing reduced energy gain. Recent thermal history, therefore, seems to rapidly invoke physiological mechanisms that enhance survival of short-term thermal challenge but also longer term climatic changes and consequently needs to be incorporated into assessments of species’ thermal performances. Summary: Thermal responses and organismal vulnerability to climate largely depend on the proximate thermal history of individuals as exposure to acute heat events can enhance survival and thermal performance.

Ecological and Morphological Profile of Floating Spherical Cladophora socialis Aggregations in Central Thailand

The unique beauty of spherical aggregation forming algae has attracted much attention from both the scientific and lay communities. Several aegagropilous seaweeds have been identified to date, including the plants of genus Cladophora and Chaetomorpha. However, this phenomenon remains poorly understood. In July 2013, a mass occurrence of spherical Cladophora aggregations was observed in a salt field reservoir in Central Thailand. The aims of the present study were to describe the habitat of the spherical aggregations and confirm the species. We performed a field survey, internal and external morphological observations, pyrenoid ultrastructure observations, and molecular sequence analysis. Floating spherical Cladophora aggregations (1–8 cm in diameter) were observed in an area ~560 m2, on the downwind side of the reservoir where there was water movement. Individual filaments in the aggregations were entangled in each other; consequently, branches growing in different directions were observed within a clump. We suggest that water movement and morphological characteristics promote the formation of spherical aggregations in this species. The molecular sequencing results revealed that the study species was highly homologous to both C. socialis and C. coelothrix. However, the diameter of the apical cells in the study species was less than that of C. coelothrix. The pyrenoid ultrastructure was more consistent with that of C. socialis. We conclude that the study species is C. socialis. This first record of spherical aggregations in this species advances our understanding of these formations. However, further detailed physical measurements are required to fully elucidate the mechanism behind these spherical formations.

Spatial and temporal variability of intertidal rocky shore bivalves and gastropods in Sichang Island, East coast of Thailand

Spatial and temporal variability of intertidal rocky shore bivalves and gastropods in Sichang Island, east coast of Thailand were studied over 12 months (March 2008 to February 2009). The study area experiences mixed tides with the largest tidal range of 3.6 m above MTL during spring tides. Shores are exposed to the prevailing northeast monsoon in the winter (November to February), resulting in stronger wave action during this season than in summer (March to May) and rainy season (June to October). Transects were positioned at five different heights from mid shore to high shore (2.5 to 3.5m above MTL) dominated by rock oysters in the mid shore. At each height, abundance of bivalves and gastropods were recorded within fifteen replicate quadrats (25 x 25 cm) on a monthly basis. A total of 2 bivalves and 10 species of gastropods were identified. In the high shore, the littorinid Echinolittorina malaccana dominated. Dense beds of the bivalve Isognomon nucleus were abundant in crevices at 2.5 and 2.75 m above MTL, whilst a large number of snails (Planaxis sulcatus) were found near the midshore. Below this, the rock oyster Saccostrea cucculata was dominant, with a variety of mobile gastropods (Cellana grata, C. toreuma, Patelloidea saccharina and Siphonaria japonica). The general sequence of zonation patterns were clear over time, but the vertical extent of some mobile species varied in accordance with the monsoon effect and increasing tidal range in winter, especially on the more exposed of the two sites. The high shore littorinids, E. malaccana moved up shore and were more abundant near the supralittoral line in winter suggesting that the seasonal monsoon effect and tidal range were important factors determining the distribution of some species of mobile gastropods, allowing them to exploit higher tidal levels.

Polymorphic microsatellite markers in the long-spined sea urchin Diadema setosum

We developed twenty polymorphic microsatellite markers for the long-spined sea urchin Diadema setosum by screening microsatellite enriched library, and characterized their polymorphism using two populations of 45 individuals. The number of alleles per locus ranged from 4 to 17, and the observed and expected heterozygosity varied from 0.0714 to 1.000 and 0.6655 to 0.9321, respectively. Twelve loci conformed to the Hardy–Weinberg equilibrium after Bonferroni correction. These polymorphic microsatellite markers will facilitate studies of population genetics and connectivity in D. setosum.