ABSTRACT
Abstract Crustaceans classed as Thalassinidea are shrimp-like marine organisms that burrow predominantly in sediments. They have generated particular interest over the last decade because of their roles as ecosystem engineers that exert major in¬uences over ecosystem processes and community structure. Their sphere of in¬uence is wide as their burrowing activities substantially affect sedimentary and biochemical properties and processes, translating into both positive and negative impacts on co-occurring organisms spanning bacteria, microalgae, meiofauna, macrofauna and seagrasses, and possibly up the food chain to ™sh and birds. The speci™c microclimates they create within their burrows are particularly important for microbes and meiofauna, which in turn play important roles in organic and inorganic nutrient cycling. The physical turnover of sediments from burrows to the sediment surface signi™cantly in¬uences macro-invertebrate community structure, generally by negatively affecting surface fauna or organisms such as ™lter-feeders and epibenthic grazers that are dependent on the interface of sediment and water for feeding. Their burrowing activities increase sediment penetrability and porosity, which can favour burrowing macrofaunal species. Sediment turnover can also reduce recruitment of macro-invertebrates, either indirectly by diminishing microbial bio™lms that act as food, sediment stabilizers and biochemical cues for larval settlers or directly by burying recruits. Thalassinidean bioturbation also in¬uences marine vegetation, in some instances excluding seagrasses; together with the ecosystem services these plants provide for co-occurring species. Thalassinideans also affect commercial aquaculture operations for oysters and penaeid shrimps. Sediment turnover by thalassinideans buries adult and juvenile oysters, and their propensity to increase ¬uxes of toxic nutrients and sulphides, allied with their high oxygen consumption, reduces yields of cultured shrimps, leading to ™nancial losses. Harvesting of thalassinideans for bait has important consequences for soft-sediment ecosystems as the physical disturbance induced by bait-collectors, associated with the removal of the ecosystem services provided by thalassinideans, leads to changes in oxygenation, sediment granulometry and the structure of invertebrate communities. Lastly, ecosystem engineering by thalassinideans acts as a selective agent leading to the evolution of novel morphology, behaviour and social interactions in co-occurring organisms. Most of the effects of thalassinidean shrimps are manifested via their in¬uence on environmental conditions, including the stability, granulometry, turnover and geochemical properties of sediments, all re¬ecting their powerful ecosystem engineering.
