From ‘clean and green’ to ‘brown and down’: A synthesis of historical changes to biodiversity and marine ecosystems in the Marlborough Sounds, New Zealand

Abstract

Ecosystem-based management (EBM) is a potential antidote to the alleviation of multiple stressors in highly-valued and contested marine environments. An understanding of the magnitude and drivers of past ecosystem changes can inform the development of realistic ecological and social outcomes for different places. These goals should aim to increase the ecological health and resilience of coastal ecosystems and their connected land- and sea-scapes by minimising anthropogenic disturbances. To address knowledge gaps, we present a marine historical synthesis of the Marlborough Sounds in New Zealand's South Island. These rias are strongly coupled to the surrounding land and inland river catchments. We took an integrated approach by examining effects of land use change on coastal ecosystems, along with case studies of the effects of exploitation on foundational marine species. We found that ecosystems have gone through a series of transformations since Māori settlement ca. 700 years ago, with localised extirpations of marine megafauna, overharvesting of exploited species, and disruption to ecological functioning through ongoing clearfelling of terrestrial and marine biogenic communities since European settlement in the 1800s. There has been a decline from great abundance of marine life to relative scarcity, which is currently evident to local people in increased effort and reduced allowable catches of fish and shellfish. Recovery of biodiversity in the short-term within the Marlborough Sounds is uncertain, given ongoing multiple and interacting stressors from unsustainable land-use and over-exploitation of marine life. Lifting baselines are possible but will require significant changes to land and marine management to restore ecological health and enhance resilience in the face of climate change. Increased marine protection, regeneration of biodiverse biogenic habitats, spatial fishing measures to increase predators of sea urchins, stricter regulation of plantation forestry and a replanting prohibition in critical erosion source areas, are all needed within an EBM framework. Large experimental areas are proposed to develop, test and integrate different management techniques, and to facilitate community understanding, participation, and support for the transition to EBM.