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

Abstract

This study was done to test the palatability of leaves of mangroves growing in a highly and lowly polluted environment. We hypothesized that bottom-up transfer of pollutants from soil to leaves would influence herbivory due to the toxic effect of pollution. Exclusion experiment was done to test for leave herbivory in lowly and highly polluted plots while cafeteria experiment was done to determine the feeding preference of 20 West African red mangrove crabs (Goniopsis pelii). In the first experiment a total of 453 mangrove leaves were sampled for six months, one year and two years. Results indicate that there was significant difference in herbivory between highly and lowly polluted treatment in the six months (F2, 160=3.33, P=0.04), one year (F2, 184=1.90, P=0.02) and two years (F1, 169=7.58, P=0.01) samples. There was more leave herbivory in highly than in lowly polluted plot. The pattern of incisions indicates that crab herbivory was the highest (53%) followed by insects (25%) and undetermined (22%). In the laboratorybased experiment, there was significant difference in leave incisions from both plots (P=0.01) with more leaves from highly polluted plot consumed (4, 521.69 cm2) than leaves from lowly polluted plot (2, 769.83 cm2). This implies that hydrocarbon pollution influenced leaf herbivory.

Rhizophora racemosa and Nypa fruticans leaf litter decomposition at different soil levels under mangrove forest stands in the Niger River Delta, Nigeria

“…Leaves of R. racemosa decomposed faster (Figures 1 and 2) likely because they are nutritious and less fibrous and attract more soil microbes (Simpson et al, 2020) as compared to leaves of N. fruticans that have high fibre content and take longer time to decompose. Herbivores feed on R. racemosa leaves because of their palatability (Banerjee et al, 2020) and nutrients (Numbere & Camilo, 2019), which influence decomposition. Differences in decomposition rate are influenced by species diversity, leaf chemistry and soil condition.…”

“…Herbivores feed on R. racemosa leaves because of their palatability (Banerjee et al, 2020) and nutrients (Numbere & Camilo, 2019), which influence decomposition. Differences in decomposition rate are influenced by species diversity, leaf chemistry and soil condition.…”

Mangroves of the Niger Delta

“…For this reason, it is not easy to differentiate the various Rhizophora species. Rhizophora racemosa is dominant among the three species, according to [2,3]; in some instances, a different Rhizophora species is dominant in a different mangrove forest in the Niger Delta. Rhizophora mangroves have been known to grow as tall as 25-30 m in a pristine mangrove forest.…”

“…Rhizophora sp. Langucularia racemosa and Aviecina germinans are also known as red, white, and black mangroves, respectively, while C. erectus is known as buttonwood in the Niger Delta [2,3]. Red mangroves are easily identified in the Niger Delta by their prop roots, leaves, and propagules; white mangroves are easily identified by their oval leaves, fruits, and seeds; and black mangroves can easily be distinguished from other mangroves by their elongated leaves, fruits, and seeds, including the presence of pneumatophores.…”

Evaluation of Total Hydrocarbon Contents in the Leaves of Selected Crops Grown on Crude Oil Polluted Agricultural Soil

“…This was determined using UV-Vis spectrophotometric method as described by Numbere [12]. The polluted test plants' fresh leaves were dried in an oven at 60°C for 24 hours to remove the moisture.…”