Seagrass sediments reveal the long‐term deterioration of an estuarine ecosystem

Abstract

The study of a Posidonia australis sediment archive has provided a record of ecosystem dynamics and processes over the last 600 years in Oyster Harbour (SW Australia). Ecosystem shifts are a widespread phenomenon in coastal areas, and this study identifies baseline conditions and the time-course of ecological change (cycles, trends, resilience and thresholds of ecosystem change) under environmental stress in seagrass-dominated ecosystem. The shifts in the concentrations of chemical elements, carbonates, sediments <0.125 mm and stable carbon isotope signatures (δ(13) C) of the organic matter were detected between 1850s and 1920s, whereas the shift detected in P concentration occurred several decades later (1960s). The first degradation phase (1850s-1950s) follows the onset of European settlement in Australia and was characterized by a strong increase in sediment accumulation rates and fine-grained particles, driven primarily by enhanced run-off due to land clearance and agriculture in the catchment. About 80% of total seagrass area at Oyster Harbour was lost during the second phase of environmental degradation (1960s until present). The sharp increase in P concentration and the increasing contribution of algae and terrestrial inputs into the sedimentary organic matter pool around 1960s provides compelling evidence of the documented eutrophication of the estuary and the subsequent loss of seagrass meadows. The results presented demonstrate the power of seagrass sedimentary archives to reconstruct the trajectories of anthropogenic pressures on estuarine ecosystem and the associated regime shifts, which can be used to improve the capacity of scientists and environmental managers to understand, predict and better manage ecological change in these ecosystems.

Forty years of seagrass population stability and resilience in an urbanizing estuary

“…Eelgrass populations are stable and resilient in the face of substantial changes to the Puget Sound environment over the past 40 years. However, we strongly suspect the development of Puget Sound pre-1970 led to the widespread loss of eelgrass as has been shown in other systems (Serrano et al 2016).…”

“…However, we strongly suspect the development of Puget Sound pre‐1970 led to the widespread loss of eelgrass as has been shown in other systems (Serrano et al . ).…”

A six thousand‐year record of climate and land‐use change from Mediterranean seagrass mats

“…This type of long‐term ecological research could inform conservation strategies for maintaining seagrasses resilience (Serrano et al . ).…”

“…) and provided information about the trajectories of estuarine ecosystems and associated regime shifts due to anthropogenic pressures since the European settlement in Australia (Serrano et al . ). These studies demonstrate that the palaeoenvironmental information contained in Posidonia mats can be used to understand, predict and manage coastal ecosystems more comprehensively.…”

The application of resilience concepts in palaeoecology

“…This was applied with a linear autoregressive model to test the hypothesis that breakpoints are an inherent feature of the timeseries. Early warning signal metrics were also applied (see below) Serrano et al (2016) Blarquez & Carcaillet (2010) use SEA to examine plant macrofossil influxes before and after fires, interpolated to a constant time-step of 15 years. This required data sorting in time windows relative to fire events to compare responses assess sensitivity between time windows & detect deviations from background.…”