Effects and control of barnacle infestation on mangrove seedlings in a mangrove rehabilitation site / Tan Yee Siang

Tan, Yee Siang (2013) Effects and control of barnacle infestation on mangrove seedlings in a mangrove rehabilitation site / Tan Yee Siang. Masters thesis, University of Malaya.

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Abstract

A study on the development, effects and control of biofouling on replanted mangrove seedlings (40-50cm height) was carried out, from April 2008 to July 2010, at Kampung Sungai Haji Dorani and Kampung Sungai Limau, Selangor, Malaysia. The dominant biofoulers were barnacles (Amphibalanus amphitrite), which were the main causal organism of mangrove seedling damage or death. The high density (>100 no./ 10 cm section of plant stem) and cover (>30 %) of barnacles appeared to obstruct development of new leaves, shoots and roots, as well as imposing weight loads as high as six times the weight of the seedlings. The 10-20cm section of the stem above ground had the highest number of barnacles (mean = 125±106; p<0.05). However, growth and survival of seedlings with low percentage cover (<30%) of barnacles and other fouling organisms were not affected over the 20 weeks of study; these were seedlings planted on higher ground (2.0-2.5m above chart datum). Histological study showed that the percentage thickness of the palisade layer of fouled leaves was significantly (p<0.05) lower compared to non-fouled leaves, but there was no significant difference (p>0.05) in the number of abaxial hairs. The mean abundance of barnacles attached on the seedlings planted using the ‘conventional’ stake method (wooden stake tied to the seedling) (3710 no./plant) was significantly higher compared to seedlings planted inside PVC piping or encasements (25.6 no./plant) after 10 weeks. Another study conducted using three planting methods showed that barnacle abundance in the elevated planting method (seedlings raised up by 15cm above ground by planting them inside a cylindrical ‘net pot’) (1.5 no./plant) was significantly (p<0.05) lower compared to that of seedlings planted using the short stake method (a short wooden stake of 10 cm tied to the base of the plant) (5.5 no./plant) and conventional method (21.3 no./plant). Results support the contention that reducing the inundation time of mangrove seedlings by the flood tide, either by raising their height above ground, planting them on higher ground, iii or using taller seedlings will reduce or ameliorate the effects of barnacle infestation. In the chemical control study, weekly topical applications of Clorox, Ivermectin, Neguvon and tea seed extract significantly (p<0.001) reduced the abundance of barnacle infestation as compared to the control (distilled water). Ivermectin and Clorox however caused negative side effects to crabs, but not to gastropods and fishes. Other factors controlling barnacle infestations and recommendations on their control are discussed.

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