Species-area relationship and potential role as a biomonitor of mangrove communities of Malayan mudskippers

The rapid and extensive destruction of mangrove forests and adjacent peritidal ecosystems in the Indo-Pacific region requires the development of efficient management and conservation actions. Mudskippers (Gobiidae: Oxudercinae) are amphibious gobies that are strictly linked to mangrove forests and tropical mudflats. I recorded the presence and habitat distribution of mudskipper species in four mangrove ecosystems along the west coast of Peninsular Malaysia. Different localities host different mudskipper communities, while in each locality species are differentially distributed along the intertidal gradient. At the ecosystem level, I found a significant exponential correlation between sampled area and the species richness of these communities, consistent with the SAR hypothesis. At the habitat level, the presence of a vertical zonation along the intertidal gradient suggests the possibility of using the species living exclusively in higher or lower levels as bioindicators for habitat anthropogenic impact, respectively from the land and from the sea.     

Bacterial productivity and microbial biomass in tropical mangrove sediments

Bacterial productivity (³H-thymidine incorporation into DNA) and intertidal microbenthic communities were examined within five mangrove estuaries along the tropical northeastern coast of Australia. Bacteria in mangrove surface sediments (0–2 cm depth) were enumerated by epifluorescence microscopy and were more abundant (mean and range: 1.1(0.02–3.6)×10¹¹ cells·g DW^–1) and productive (mean: 1.6 gC·m^–2· d^–1) compared to bacterial populations in most other benthic environments. Specific growth rates (¯x=1.1) ranged from 0.2–5.5 d^–1, with highest rates of growth in austral spring and summer. Highest bacterial numbers occurred in winter (June–August) in estuaries along the Cape York peninsula north of Hinchinbrook Island and were significantly different among intertidal zones and estuaries. Protozoa (10⁵–10⁶·m^–2, pheopigments (0.0–24.1g·gDW^–1) and bacterial productivity (0.2–5.1 gC·m^–2·d^–1) exhibited significant seasonality with maximum densities and production in austral spring and summer. Algal biomass (chlorophylla) was low (mean: 1.6g·gDW^–1) compared to other intertidal sediments because of low light intensity under the dense forest canopy, especially in the mid-intertidal zone. Partial correlation analysis and a study of possible tidal effects suggest that microbial biomass and bacterial growth in tropical intertidal sediments are regulated primarily by physicochemical factors and by tidal flushing and exposure. High microbial biomass and very high rates of bacterial productivity coupled with low densities of meiofaunal and macroinfaunal consumers observed in earlier studies suggest that microbes may be a sink for carbon in intertidal sediments of tropical mangrove estuaries.     

真红树和半红树植物叶片性状的比较研究

红树植物是一类生长在热带、亚热带海岸潮间带的乔木、灌木或草本植物,根据其分布特征可分为真红树植物植物和半红树植物。为了探究两者对海岸潮间带高盐、高光和缺氧等环境的生态适应策略的异同,该文选取5种真红树植物植物[卤蕨(Acrostichum aureum)、木榄(Bruguiera gymnorrhiza)、老鼠簕(Acanthus ilicifolius)、桐花树(Aegiceras corniculatum)、秋茄(Kandelia candel)]和4种半红树植物[银叶树(Heritiera littoralis)、水黄皮(Pongamia pinnata)、黄槿(Hibiscus tiliaceus)、杨叶肖槿(Thespesia populnea)]为研究对象,对叶片解剖和功能性状进行了对比研究。结果表明:(1)9种红树植物叶片的共同特征表现为均具有角质层、叶肉具有栅栏组织和海绵组织分化、气孔下陷等。(2)不同之处在于真红树植物植物叶片有蜡质层和内皮层、无表皮毛、气孔仅分布在下表皮,而半红树植物的叶片则较少有蜡质层,部分有表皮毛,无内皮层,气孔在上下表皮分布不完全一致。(3)真红树植物植物的气孔密度和比叶面积显著小于半红树植物(P<0.05),而叶片厚度、含水量、比叶重和鲜干重比则显著大于半红树植物(P<0.05)。以上结果说明真红树植物植物的叶片性状使其在维持盐度平衡及贮水保水能力方面强于半红树植物,从而能更好地适应海岸潮间带高盐环境。     

Lanceispora amphibia gen. et sp. nov., a new amphisphaeriaceous ascomycete inhabiting senescent and fallen leaves of mangrove

Lanceispora amphibia gen. et sp. nov. in the Amphisphaeriaceae is described from senescent and fallen leaves ofBruguiera gymnorrhiza in mangrove forests in the Southwest Islands, Japan. The fungus produces immersed ascomata in leaf tissue, cylindrical asci with an apical ring staining blue with iodine, and oblanceolate ascospores with a septum above the middle. Studies on the fungal succession on the mangrove leaves revealed thatL. amphibia infects senescent leaves on the tree and inhabits intertidal fallen leaves, showing the highest frequency of occurrence at the late stage of decomposition. In culture the optimal conditions for hyphal growth were 20 ppt salinity and 30°C, and those for sexual reproduction were 10 ppt salinity and 25°C. Growth at 0 ppt (fresh water) was depressed. The fungus has amphibious habits, growing on the tree and in intertidal water; and it is adapted to the high osmotic conditions in leaf tissues of the mangrove tree and to the subtropical, brackish water environment of mangrove forests.     

Soil-plant interactions in a neotropical mangrove forest: iron, phosphorus and sulfur dynamics

We examined soil porewater concentrations of sulfate, alkalinity, phosphorus, nitrogen, and dissolved organic carbon and solid phase concentrations of pyrite in relation to mangrove species distributions along a 3.1-km-long transect that traversed a 47.1-km² mangrove forest in the Dominican Republic. Iron, phosphorus, and sulfur dynamics are closely coupled to the activity of sulfate-reducing bacteria, the primary decomposers in anoxic soils of mangrove ecosystems. Patterns in the chemistry data suggested that sulfate reduction rates and storage of reduced sulfur were greater in the inland basin forest dominated by Laguncularia racemosa than the Rhizophora mangle dominated forest of the lower tidal region. The distribution of Laguncularia was significantly correlated with concentrations of total phosphorus (r= 0.99) and dissolved organic carbon (r= 0.86), alkalinity (r= 0.60), and the extent of sulfate depletion (r= 0.77) in the soil porewater and soil pyrite concentrations (r= 0.72) across the tidal gradient. Leaf tissue chemistry of Laguncularia was characterized by lower C:N and C:P ratios that could fuel the higher rates of decomposition in the Laguncularia-dominated forest. We suggest that a plant-soil-microbial feedback contributes to the spatial patterning of vegetation and soil variables across the intertidal zone of many mangrove forest communities. Received: 28 May 1997 / Accepted: 23 January 1998     

Zonation and seasonality of benthic primary production and community respiration in tropical mangrove forests

Benthic oxygen consumption and primary production were measured using the bell jar technique in deltaic and fringing mangrove forests of tropical northeastern Australia. In a deltaic forest, rates of sediment respiration ranged from 197 to 1645 mol O₂ m^–2 h^–1 (mean=836), but did not vary significantly with season or intertidal zone. Gross primary production varied among intertidal zones and seasons, ranging from –281 to 1413 mol O₂ m^–2 h^–1 (mean=258). Upon tidal exposure, rates of gross primary production increased, but respiration rates did not change significantly. In a fringing mangrove forest, benthic respiration and gross primary production exhibited strong seasonality. In both forests, rates of oxygen consumption and production were low compared to salt marshes, but equivalent to rates in other mangrove forests. The production:respiration (P/R) ratio varied greatly over space and time (range:–0.61 to 1.76), but most values were «1 with a mean of 0.15, indicating net heterotrophy. On a bare creek bank and a sandflat, rates of gross primary production and P/R ratios were generally higher than in the adjacent mangroves. Low microalgal standing stocks, low light intensity under the canopy, and differences in gross primary production between mangroves and tidal flats, and with tidal status, indicate that benthic microalgae are light-limited and a minor contributor to primary productivity in these tropical mangrove forests.     

Are mangroves in the tropical Atlantic ripe for invasion? Exotic mangrove trees in the forests of South Florida

Two species of mangrove trees of Indo-Pacific origin have naturalized in tropical Atlantic mangrove forests in South Florida after they were planted and nurtured in botanic gardens. Two Bruguiera gymnorrhiza trees that were planted in the intertidal zone in 1940 have given rise to a population of at least 86 trees growing interspersed with native mangrove species Rhizophora mangle, Avicennia germinans and Laguncularia racemosa along 100 m of shoreline; the population is expanding at a rate of 5.6% year⁻¹. Molecular genetic analyses confirm very low genetic diversity, as expected from a population founded by two individuals. The maximum number of alleles at any locus was three, and we measured reduced heterozygosity compared to native-range populations. Lumnitzera racemosa was introduced multiple times during the 1960s and 1970s, it has spread rapidly into a forest composed of native R. mangle, A. germinans, Laguncularia racemosa and Conocarpus erectus and now occupies 60,500 m² of mangrove forest with stem densities of 24,735 ha⁻¹. We estimate the population growth rate of Lumnitzera racemosa to be between 17 and 23% year⁻¹. Populations of both species of naturalized mangroves are dominated by young individuals. Given the long life and water-dispersed nature of propagules of the two exotic species, it is likely that they have spread beyond our survey area. We argue that the species-depauperate nature of tropical Atlantic mangrove forests and close taxonomic relatives in the more species-rich Indo-Pacific region result in the susceptibility of tropical Atlantic mangrove forests to invasion by Indo-Pacific mangrove species.     

Plant-animal interactions and the structure and function of mangrove forest ecosystems*

Trophic interactions involving plants and animals in tropical mangrove forests have important controlling influences on several population, community and ecosystem-level processes. Insect herbivores remove up to 35% of leaf area from some mangrove tree species and can cause the death of seedlings. Leaf chemistry and toughness and soil nutrient status all appear to be important in explaining the between- and among-species variance in leaf damage. Insects also attack and damage, mainly by boring, a large proportion of mangrove seeds. Shadehouse experiments have shown that such post-dispersal predation can have a significant effect on seedling survival, growth and biomass allocation to leaves, stems and roots. Sesarmid crabs are also responsible for severe post-dispersal seed predation. In field trials, crabs consumed more than 70% of the seeds of five tree species. For four of these five species there was an inverse relationship between seed predation rate and the dominance of conspecific adult trees, while the within-site distribution pattern of one tree species appears to be partially controlled by crabs. The same crab species also consume 30–80% (depending on forest type and intertidal elevation), of the annual litter fall in mangrove forests and, thus, have an important role in controlling the rate of remineralization of detritus within forests and the export of particulate matter from the forests to other nearshore habitats. The other major component of litter in the forests is wood, which is broken down relatively rapidly by teredinid molluscs (shipworms). More than 90% of the weight loss from decomposing trunks of Rhizophora species during the first four years of decay is through ingestion by teredinids. The annual turnover of dead wood mass in Rhizophora forests is equivalent to that of the processing of leaf detritus by crabs. Because of the relatively low species richness of trees and consumers in tropical mangrove forests, they are likely to serve as productive sites for further investigations of the influence of plant-animal interactions on the dynamics of tropical forests.     

Resistance of red mangrove (Rhizophora mangle L.) seedlings to deflection and extraction

Red mangrove (Rhizhophora mangle L.) is the dominant tree species in the intertidal zone of ecosystems on the Atlantic shores of the Caribbean and tropical western Atlantic. The propagules of this species are initially buoyant, becoming negatively buoyant before rooting in a variety of substrates. After establishment, these seedlings form aerial roots, leading to communities of plants with complex networks of stems and aerial roots. While established mangrove communities assist in stabilizing coastlines, seedlings are susceptible to wave, current and wind energy and this limits the habitats that they can successfully colonize. In this experiment, the mechanical resistance of seedlings growing at five locations with different substrate and canopy conditions was tested. The 78 seedlings tested ranged in height from 27 to 47 cm, had between one and ten pairs of leaves but had not yet formed aerial roots. Seedlings were pulled horizontally. The reaction force at 20° deflection in four cardinal directions and then force to failure in the landward direction was measured. Seventy-five percent of the seedlings failed in the root system. The remainder failed near the base of the stem. Larger seedlings were more likely to fail at the roots. Seedlings growing outside of mangrove overstory on coral rubble were 3.5 times more strongly anchored than those growing within the mangrove overstory on sand. In spite of directional loading by waves and on-shore breezes, the deflection resistance did not vary systematically with pulling direction. Seedling anchorage varies among locations with different overstory and substrate conditions, likely due to differences in competition and acclimation to wind and wave energy along with differences in rooting among substrates.     

Structure of a unique inland mangrove forest assemblage in fossil lagoons on the Caribbean Coast of Mexico

Scrub mangrove wetlands colonize the intertidal zone of fossil lagoons located in carbonate continental margins along the Yucatan Peninsula of Mexico. These unique ecological types were investigated in October, 1994, by locating transects in several mangrove forests along the Caribbean coast of the peninsula. Four species of mangrove occurred at these sites including Rhizophora mangle, Avicennia germinans, Laguncularia racemosa, Conocarpus erecta. This is one of the first examples of a species rich scrub forest. The mangroves fell into three height categories: short scrub less than 1.5 m, tall scrub to 3.0 m, and basin forests between 4.5 and 6 m. Average height, diameter (dbh), basal area, and complexity index generally increased from short scrub to basin forests. Basal area, ranged from 0.16 m² ha^–1 in a short scrub forest intermixed with Cladium jamaicense to 12.9 m² ha^–1 in a basin forest. Density ranged from 1520 trees ha^–1 to over 25,000 trees ha^–1 in a short scrub forest dominated by R. mangle. The complexity index ranged from 0.01 to 8.3. Height, dbh, basal area, and complexity index were positively related. A number of trees were growing as sprouts from larger downed trunks, suggesting that hurricanes, such as Gilbert that occurred in 1988, are important in controlling the structure of these forests. These forests appear isolated from the sea, but are influenced by groundwater exchange occurring at the land-margin zone.     

不同生长光强下8种红树植物幼苗叶片的光响应特征

为探讨红树植物光适应的生理生态策略,对6种真红树植物[无瓣海桑(Sonneratia apetala)、秋茄(Kandelia candel)、木榄(Bruguiera gymnorrhiza)、桐花树(Aegiceras corniculatum)、老鼠簕(Acanthus ilicifolius)、卤蕨(Acrostichum aureum)]和2种半红树植物[银叶树(Heritiera littoralis)、黄槿(Hibiscus tiliaceus)]的1 a生幼苗在不同生长光强(自然光强的100%、45%、30%、10%)下的光合光响应特征进行了研究。结果表明,不同生长光强对红树植物光响应特征的影响因物种而异,遮荫显著提高了秋茄和木榄的最大净光合速率(Pmax),而对其他红树植物的Pmax没有显著影响;秋茄在45%光强下具有较高的Pmax,木榄的Pmax则在45%和30%光强下显著高于其他2个处理。随着生长光强的下降,秋茄幼苗叶片的光饱和点显著上升,木榄、老鼠簕和卤蕨的光补偿点呈下降趋势,木榄和卤蕨的表观量子效率升高的同时暗呼吸速率下降。木榄、老鼠簕和卤蕨具有较强的耐荫性,...     

Mangrove expansion and salt marsh decline at mangrove poleward limits

Mangroves are species of halophytic intertidal trees and shrubs derived from tropical genera and are likely delimited in latitudinal range by varying sensitivity to cold. There is now sufficient evidence that mangrove species have proliferated at or near their poleward limits on at least five continents over the past half century, at the expense of salt marsh. Avicennia is the most cold‐tolerant genus worldwide, and is the subject of most of the observed changes. Avicennia germinans has extended in range along the USA Atlantic coast and expanded into salt marsh as a consequence of lower frost frequency and intensity in the southern USA. The genus has also expanded into salt marsh at its southern limit in Peru, and on the Pacific coast of Mexico. Mangroves of several species have expanded in extent and replaced salt marsh where protected within mangrove reserves in Guangdong Province, China. In south‐eastern Australia, the expansion of Avicennia marina into salt marshes is now well documented, and Rhizophora stylosa has extended its range southward, while showing strong population growth within estuaries along its southern limits in northern New South Wales. Avicennia marina has extended its range southwards in South Africa. The changes are consistent with the poleward extension of temperature thresholds coincident with sea‐level rise, although the specific mechanism of range extension might be complicated by limitations on dispersal or other factors. The shift from salt marsh to mangrove dominance on subtropical and temperate shorelines has important implications for ecological structure, function, and global change adaptation.     

Ecosystem carbon stocks of mangrove forests along the Pacific and Caribbean coasts of Honduras

Among the many ecosystem services provided by mangrove ecosystems, their role in carbon (C) sequestration and storage is quite high compared to other tropical forests. Mangrove forests occupy less than 1 % of tropical forested areas but account for approximately 3 % of global carbon sequestration by tropical forests. Yet there remain many areas where little data on the size and variation of mangrove C stocks exist. To address this gap and examine the range of C stocks in mangroves at landscape scales, we quantified C stocks of Honduran mangroves along the Pacific and Caribbean coasts and the Bay Islands. We also examined differences in ecosystem C stocks due to size and structure of mangrove vegetation found in Honduras. Ecosystem C stocks ranged from 570 Mg C ha^?1 in the Pacific coast to ~1000 Mg C ha^?1 in Caribbean coast and the Bay Islands. Ecosystem C stocks on the basis of mangrove structure were 1200, 800 and 900 Mg C ha^?1, in low, medium and tall mangroves, respectively. We did not find significant differences in ecosystem C stocks on the basis of location (Pacific coast, Caribbean coast and Bay Islands) or mangrove type (low, medium and tall). Mangrove soils represented the single largest pool of total C in these ecosystems, with 87, 81 and 94 % at the Pacific coast, Caribbean coast and the Bay Islands, respectively. While there were no significant differences in total ecosystem stocks among mangrove types, there were differences in where carbon is stored. Mangrove soils among low, medium and tall mangroves contained 99, 93 and 80 % of the total ecosystem C stocks. In addition, we found a small yet significant negative correlation between vegetation C pools and pore water salinity and pH at the sampled sites. Conversion of mangroves into other land use types such as aquaculture or agriculture could result in loses of these soil C reserves due to mineralization and oxidation. Coupled with their other ecosystem services, an understanding of the size of mangrove ecosystem C stocks underscores their values in the formulation of conservation and climate change mitigation strategies in Central America.     

The Southeast Saline Everglades revisited: 50 years of coastal vegetation change

Abstract. We examined the vegetation of the Southeast Saline Everglades (SESE), where water management and sea level rise have been important ecological forces during the last 50 years. Marshes within the SESE were arranged in well‐defined compositional zones parallel to the coast, with mangrove‐dominated shrub communities near the coast giving way to graminoid‐mangrove mixtures, and then Cladium marsh. The compositional gradient was accompanied by an interiorward decrease in total aboveground biomass, and increases in leaf area index and periphyton biomass. Since the mid‐1940s, the boundary of the mixed graminoid‐mangrove and Cladium communities shifted inland by 3.3 km. The interior boundary of a low‐productivity zone appearing white on both black‐and‐white and CIR photos moved inland by 1.5 km on average. A smaller shift in this ‘white zone’ was observed in an area receiving fresh water overflow through gaps in one of the SESE canals, while greater change occurred in areas cut off from upstream water sources by roads or levees. These large‐scale vegetation dynamics are apparently the combined result of sea level rise ‐ ca. 10 cm since 1940 ‐ and water management practices in the SESE.     

Mangrove sesarmid crab feeding experiments in Peninsular Malaysia

The feeding ecology of mangrove sesarmid crabs in Peninsular Malaysia was investigated by field and laboratory experiments using four mangrove leaf species (Avicennia officinalis, Bruguiera gymnorrhiza, B. parviflora and Rhizophora apiculata) and leaves of different condition (fresh and senescent). Leaves tethered on strings at high (Bruguiera zone) and low (Rhizophora zone) intertidal positions, both upstream (Sungai Pasir) and downstream (Lower Merbok) showed significant amounts of leaf litter removal in 24 h (mean 79±3% initial dry mass). Significantly more B. gymnorrhiza was consumed in Bruguiera zones and significantly less senescent A. officinalis in the upstream Rhizophora zone. In Bruguiera zones, significant numbers of leaves were taken down burrows but there were no preferences for leaf species or condition of leaf taken down burrows at all sites. In 24 h, under laboratory conditions, the sesarmid crabs Sesarma (Perisesarma) eumolpe and S. (Perisesarma) onychophorum were offered with a mangrove species choice of either fresh or senescent leaves. There was no difference in mangrove species taken when the leaves were senescent for both crab species, but when the leaves were fresh, significantly more A. officinalis leaves were consumed by both sesarmid crab species. S. onychophorum ate significantly more B. parviflora than did S. eumolpe. The crab distribution in the field was related to the preferred tree species dominance, indicating that tree species may be important for crab species distribution, or vice versa. The mean rate of leaf consumption was not significantly different between the crab species; S. eumolpe was 29.9±5.9 and S. onychophorum was 35.3±7.2 mg dry mass per wet mass gram of crab in 24 h. Rhizophora spp. were the least preferred species in all feeding experiments, a finding which may have implications for ecosystem functioning in monoculture rehabilitation projects.     

基于多源遥感的红树林监测

红树林是生长在热带以及亚热带海岸潮间带上的生态群落, 其生产力高, 固碳能力强, 对保持海岸带生物多样性具有十分重要的价值。本文介绍了利用多源遥感数据监测红树林的一些主要研究内容, 分为3个方面: (1)在时空模式研究方面, 利用高空间分辨率影像像素和对象结合的方法对红树林树种进行分类以及利用Landsat影像对红树林进行动态变化监测并分析其驱动因素; (2)在结构参数研究方面, 利用无人机多光谱数据及地面激光雷达数据对红树林叶面积指数进行反演; (3)在生理生化参数研究方面, 探讨了红树林叶绿素含量对淹没状况的响应、互花米草(Spartina alterniflora)入侵是否影响红树林光能利用率, 以及光化学反射指数(photochemical reflectance index, PRI)与光能利用率(light use efficiency, LUE)的关系。上述系列研究为提取红树林相关信息要素时如何选择合适的分析方法提供了有力的参考, 强调了遥感在研究红树林时空模式, 提取结构参数和生物生化参数监测的有效性, 从而更好地促进红树林生态系统的生物多样性保育工作。     

The influence of crabs on litter processing in high intertidal mangrove forests in tropical Australia

Summary Measurements of litter fall and litter removal by crabs, in conjunction with estimates of litter decay by microbes and tidal export of litter from three high-intertidal mangrove forests were made during a year-long study in tropical northeastern Australia. In forests dominated by Ceriops tagal and Bruguiera exaristata, litter standing stocks remained low on the forest floor (mean 6 g·m^-2), although litter fall was high; 822 and 1022 g·m^-2·y^-1, respectively. Sesarmid crabs removed 580 (Ceriops) and 803 (Bruguiera) g·m^-2·y^-1, or 71 and 79%, of the total annual litter fall from the forest floor. Relative to the rate of litter removal by crabs, microbial turnover of whole, unshredded litter was insignificant, accounting for <1% of annual litter fall. Export of litter by tides was estimated to remove 194 (Ceriops) and 252 (Bruguiera) g·m^-2·y^-1 or 24 and 25% of annual litter fall. In a forest dominated by Avicenniamarina, in which an ocypodid crab was more abundant than sesarmids, litter standing stocks were higher (mean 84 g·m^-2) and crabs removed less litter; 173 g·m^-2·y^-1 or 33% of the annual litter fall of 519 g·m^-2·y^-1. Microbial turnover of intact litter was more important in the Avicennia forest (168 g·m^-2·y^-1 or 32% of annual litter fall), and tides exported 107 g·m^-2·y^-1 or 21% of litter production. In areas where sesarmid crabs were absent or rare in Ceriops forests, there were significantly higher standing stocks of litter and slower rates of leaf removal. Taking into account the probable assimilation efficiencies of sesarmid crabs feeding on mangrove leaves, we estimate that in Ceriops and Bruguiera forests leaf processing by crabs turns litter over at >75 times the rate of microbial decay alone, thus facilitating the high sediment bacterial productivity in these forests. The importance of litter processing by crabs increases with height in the intertidal in tropical Australia, in contrast to New World mangrove forests, where the reverse is true.Contribution No. 445 from the Australian Institute of Marine Science     

红树植物多样性及其研究进展

红树植物是分布于热带、亚热带海岸潮间的木本植物群落。因因适应海岸带和作的生长环境形成了独特的形态结构和生理生态特性。红树林是海岸有重要价值的湿地。论述了红树植物的物 多样性、适应多样性、物侯多样性以及分子水平的多样性及其研究进展。     

Aerial exposure and body temperature of the intertidal sea anemone Anthopleura elegantissima

The sea anemone Anthopleura elegantissima is a common member of intertidal communities along the west coast of North America, and can experience extended periods of increased temperature during summertime low tides. Internal body temperatures of emersed individuals of A. elegantissima were monitored in a laboratory wind tunnel and in the field, and factors influencing the anemones’ thermal experience were examined. Larger body size and aggregation with conspecifics slowed body temperature increases in controlled wind tunnel conditions. In the field, anemones in the interior of an aggregation stayed cooler than those on the edges, and microhabitat features related to light exposure and surface orientation overshadowed any direct effects of body size. In the warmest month only (July), aggregations of A. elegantissima were significantly larger at the upper limit of their distribution than they were at the mid and lower limits, suggesting aggregation in high intertidal zones may be a behavioral response to desiccation and temperature stress. As this sea anemone can host multiple species of symbiotic algae with different thermal tolerances, the ability to slow body heating may affect the type of algae hosted and thus the potential contribution of this abundant anemone to primary production in the intertidal zone.     

The Herbivore Assemblage, Herbivory and Leaf Chemistry of the Mangrove Kandelia obovata in Two Contrasting Forests in Hong Kong

The herbivore assemblage, intensity of herbivory and factors determining herbivory levels on the mangrove Kandelia obovata (previously K. candel, Rhizophoraceae) were studied over a 13-month period at two forests with contrasting growing conditions in Hong Kong. Mai Po was part of an eutrophic embayment in the Pearl River estuary and generally offered more favourable conditions for mangrove growth, whereas Ting Kok had a rocky substratum and oceanic salinity. Twenty-four insect herbivore species were recorded on K. obovata, with lepidopteran larvae that consume leaf lamina being the dominant species. While leaf litter production was similar at the two forests, herbivory level at Mai Po (mean = 3.9% in terms of leaf area loss) was more severe than that at Ting Kok (mean = 2.3%). Peak herbivory levels were found in summer at both locations (6.5% for Mai Po and 3.8% for Ting Kok). Young leaves of K. obovata at both locations were generally preferred by the herbivores from the period of late spring to summer. Concentrations of most feeding deterrents (ash, crude fibre, and total soluble tannins) were significantly higher in both young and mature leaves at Ting Kok, whereas leaf nutrients (total nitrogen and water) were the same at the two sites. Young leaves at Ting Kok contained about 30% more tannins than their counterparts at Mai Po. Significant differences in leaf chemistry also existed between young and mature leaves at either site. The differences were concomitant with the observed patterns of leaf herbivory on K. obovata, and suggest a potential relationship between environmental quality and plant defence against herbivory.