Characterizing the second wave of fish and invertebrate colonization of an offshore petroleum platform

Offshore Oil and Gas (O&G) infrastructure affords structurally complex hard substrata in otherwise featurless areas of the seafloor. Opportunistically collected industrial ROV imagery was used to investigate the colonization of a petroleum platform in the North Sea 1-2 years following installation. Compared to pre-construction communities and pioneering colonizers, we documented 48 additional taxa, including a rare sighting of a pompano (Trachinotus ovatus). The second wave of motile colonizers presented greater diversity than the pioneering community. Occurrence of species became more even over the 2 years following installation, with species occurring in more comparable abundances. No on-jacket sessile taxa were recorded during first-wave investigations; however, 17 sessile species were detected after 1 year (decreasing to 16 after 2). Motile species were found to favour structurally complex sections of the jacket (e.g. mudmat), while sessile organisms favoured exposed elements. Evidence of on-jacket reproduction was found for two commercially important invertebrate species - common whelk (Buccinum undatum) and European squid (Loligo vulgaris). Moreover, abundance of larvae-producing species experience an 8.5-fold increase over a 2-year period compared to baseline communities. These findings may have implications for decommissioning and resource-management strategies, suggesting that a case-by-case reviewing approach should be favoured over the most common "one size fits all".