Historical changes in marine communities uncovered in diverse data sources highlight impacts over half a century

Abstract

Context. Historical records and citizen scientist data are a useful resource for long-term ecological studies, yet their quality and validity have been challenged. Aims. We aimed to investigate how traditional structured surveys and unstructured, opportunistic data sources can be used to understand historical ecological change over half a century. Methods. We studied ~6000 records between 1965 and 2020 from the Shiprock site in the Sydney region, to understand ecological changes and insights that could be derived from these diverse data sources. Key results. We reportthe local disappearance ofsome fish and invertebrate species, declinesin the abundance of many taxa including kelp, potential impacts of the implementation of a marine reserve and range extensions consistent with climate change. Structured surveys provided broadly scientifically useful ecological information, whereas unstructured opportunistic data provided long-term retrospective community information and species presence information. Conclusions. We have described scientifically and managerially relevant insights encompassing foundation, threatened, protected and invasive species, community shifts and the impacts of local and global processes over historical timescales. Implications. Unstructured, opportunistic data sources can document long-term ecological changes arising from local and global processes, but are limited in the ability to provide population and community structure information.