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

Abstract

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.

Mangrove Leaf Herbivory along a Hydrocarbon Pollution Gradient in a Mangrove Forest (Rhizophora racemosa) in the Niger River Delta, Nigeria

“…Palatability of leave influenced consumption [41,42]. Other studies had shown that the presence of chemicals in leaves can deter herbivore feeding [8]. This is in line with the hypothesis that hydrocarbon pollution will deter herbivory of mangrove leaves.…”

“…An image impression of the leaf samples were made with a digital camera (Nikon) at focal length of 30 cm. To confirm the validity of the images a portable handy scan model TSN410 was used to acquire images in line with [8]. The leaf area in pixel was converted to millimeter in image measurement software called Image J for the "pre" and "post" consumption values [37] at a scale of 7.983 pixel mm-1.…”

“…Younger leaves have higher herbivory because they have higher photosynthetic ability than older leaves. Insect incision on premature leaves cause the loss of apical buds, lowers productivity and changes plant architecture [7,8]. Insect herbivory causes defoliation, which reduces the survival potential of mangroves [9].…”

Seasonal changes of nutrient levels and nutrient resorption inAvicennia marinaleaves in Yingluo Bay, China

“…In A. marina, a mangrove species of tropical and subtropical coastlines with a continuous growing season, the active growing foliage probably serves as a sink for nutrients resorbed from senescing leaves (Lambers et al 1998). The intertidal habitat is a stressful environment and mangroves expend large amounts of their energy on adaptations to those stresses (Tong et al 2006). This is a further reason why a high RE for essential nutrients is needed.…”

Hong Kong’s mangrove biodiversity and its conservation within the context of a southern Chinese megalopolis. A review and a proposal for Lai Chi Wo to be designated as a World Heritage Site

“…Similarly, Tong et al (2006) studied the species associated with leaf herbivory in K. candel at two contrasting mangroves in Hong Kong. showing how these can be divided into three longitudinal zones (---): estuarine in the west, transitional in the centre and oceanic in the east as described above (After Morton and Morton 1993).…”