Title: Crabs, heavy metals and near future ocean acidification – what do we know?

Durban Harbour, Richards Bay Harbour and Mlalazi estuary are part of KwaZulu-Natal estuarine

systems. Durban and Richards Bay, like most estuarine harbours, are persistently subjected to

anthropogenic activities (intense urbanization and industrialization) as well as expansion of

commercial shipping resulting in bioaccumulation of pollutants i.e. heavy metals, chemical and

organic pollutants. The uMlalazi estuary on the other hand is situated in a coastal nature reserve

and the watershed is in a lower population density area and as a consequence is less prone to

anthropogenic effects. Crabs, as both predator and prey, form an important component of marine

food webs. They are mostly benthic with restricted mobility and are especially sensitive to

pollution because they reside on the substrate where chemical contaminants accumulate. Crabs

accumulate pollutants including metals, resulting in biological alterations from molecular to

tissue level depending on pollutant concentrations and duration of exposure. Pollutants may

therefore be bioaccumulated in crabs resulting in several orders of magnitude higher than those

of the surrounding water, with further biomagnification in the food chain to higher trophic levels,

including human consumers.

The background levels of heavy metals (Pb, Cd, Zn and Cu) in tissues (hepatopancreas, gills,

muscle and exoskeleton) of sand bubbler crabs (Dotilla fenestrata), sediments and water were

investigated through nitric acid digestion and metal analysis was done using Inductive Coupled

Plasma Mass Spectrometry (ICP-MS). Crabs were also exposed to varying concentrations of Cd

and Pb under near-future pH for 96 hours to replicate heavy metal uptake under predicted 2030

levels of ocean acidification. Acute toxicity test (lethal concentration) was determined after 96

hours of exposure using a range finder test to determine the concentration of metals in

combination with varying pH. Crabs were dissected after 96 hours exposure to determine heavy

metal bioaccumulation in tissues as a result of interactive reaction of metal solutions and pH.

Results obtained from this study will contribute to our understanding of how crabs respond to

heavy metal uptake in the context of global climate change, more specifically with respect to

near-future ocean acidification.