Exploring the State of Heavy Metal Pollution in Hong Kong Mangroves and Its Potential Influence on Mangrove Crabs

Abstract

Mangroves are disappearing at alarming rates in response to a variety of human activities. One of the major threats faced by Hong Kong mangroves is heavy metal pollution, which is introduced by industrial activities. Mangroves have long been suggested as natural ‘sinks’ for contaminants due to their capacity to accumulate pollutants, however little attention has been paid to the influence of heavy metals on mangrove fauna including crabs. Crabs are vital to the health and resilience of mangroves by performing key ecological roles such as nutrient cycling and bioturbation, negative impacts to these communities therefore have the capacity to destabilise whole mangrove ecosystems. This investigation aims to assess the extent of heavy metal contamination in Hong Kong by analysing the metal content (Al, Cu, Cd, Cr, Fe, Mg, Mn, Zn, Ni, Pb and As) of mangrove sediments and representative plant and crab species across four study sites using Induction Coupled Plasma Mass Spectrometry (ICP-MS). This investigation also attempts to explore the influence of heavy metal exposure on the metabolic performance of mangrove crabs, specifically Parasesarma bidens, via respirometric and heart rate experiments. When comparing the thermal performance of P.bidens populations from 2 polluted and 2 pristine sites, we found that populations exposed to high levels of metal pollution displayed suppressed oxygen consumption (μmol min-1 g-1) against an increasing thermal gradient (3°C hour-1 from 22 – 50°C) in comparison to other populations . This research aims to offer insight to investigating human impacts on organisms and ecosystems, promoting inter-disciplinary approaches to investigating such impacts in the hope to inform future conservation and environmental management strategies that reduce human impacts on ecosystems.