The formation, alteration, and maintenance of habitats by organisms through the production of physical structures or the transformation of existing ones is known as ecosystem engineering. In one of these cases, the role of Alitta virens (Sars) as an ecosystem engineer in pristine sediments was assessed. Nereidid polychaetes are able to exploit vacant niches and pristine sediments owing to their ability to swim, crawl, and burrow as well as to be carried passively by currents. They engineer their own environment by burrowing, feeding and respiring, and produce a diverse array of potential sedimentary and endobenthic habitats for other organisms. Changes in the burrowing behavior and modifications of the event beds by the burrowing nereidid were examined using laboratory microcosms with either abiotic sediments or organic-rich mud and pristine sand. In all the microcosms, modification of the environment by the nereidids to permit long-term residence was observed. Moreover, the nereidids demonstrate different behavioural strategies and burrow morphologies based on sediment characteristic and nutrient availability. Alitta virens used a variety of feeding strategy viz. scavenging, surface deposit feeding, suspension feeding, microbial gardening, deposit feeding at depth, and cannibalism. Many nereidids are known to employ suspension feeding using mucus but has never been documented before for A. virens. The extended use of suspension feeding may indicate low availability of biotic sediments for deposit feeding. Though A. virens characteristically produced burrows similar to Arenicolites and Skolithos, burrow morphologies similar to Polykladichnus, Planolites, Palaeophycus, and Thalassinoides were formed under differing sedimentary conditions and over different time scales. According to the rock record, such ichnological diversity might be interpreted as indicating paleoeco- logical diversity, rather than the response of one taxon to changing conditions. On the whole, Alitta virens is an allogenic ecosystem engineer, changing the physical and geochemical characters of its environment by its behaviour. These changes, combined with the widespread occurrence and population longevity of A. virens, demonstrate that burrowing polychaetes are important ecosystem engineers in shallow marine environments, and are likely to have been so over geological time scales.

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