Guidelines for early warning indicators of regime shifts

The tool consists of implementing a simple protocol to obtain early warning indicators of a regime shift or collapse of marine forests, including macroalgal canopies and seagrass meadows. This requires monitoring the spread of algal turfs, low-lying (usually filamentous) algae at the edge of marine forests. A healthy forest provides a barrier against the invasion of algal turfs, which provide a less productive and usually species-depauperate alternative state. The more algal turfs spread into the forest, the greater the risk of collapse.

Aim of the tool

This tool aims to provide guidelines for monitoring early warning indicators of regime shifts or collapsing marine forests.

Main objectives

The objective of the tool is to provide a protocol to obtain early warning indicators of a regime shift or collapse of marine forests, including macroalgal canopies and seagrass meadows.

Technological infrastructure

Spreadsheet software

Training

A minimum of training is required for MPA staff in charge of establishing the permanent transects and for those involved in experimental validation. Personnel need to be trained in field measurements and sample algal turfs with visual methods (e.g., photographic) and data entering into spreadsheets.

Investment

Costs will vary according to the site. Investments are needed for: a training workshop directed to MPA staff, which could be planned within AMARE plus; a field-based demonstration to ensure the efficient and correct implementation of the methodology; and personnel and field equipment costs.

Concept

The early warning system consists of establishing permanent transects at the edge between a forested patch and an area colonised by algal turfs. The abundance (percent cover) of algal turfs will be monitored just outside the canopy and 1-1.5 m within the forested patch. The indicator, called the recovery length, is quantified as the distance at which the cover of algal turfs will be reduced to 50% of that observed in a plot just outside the canopy. Large values of the indicator correspond to a larger penetration of algal turf inside the macroalgal forest or the seagrass meadow. When implementing the recovery length in a new area, it is recommended to perform a preliminary small-scale thinning experiment to ensure that the system behaves as expected and that algal turfs expand upon canopy removal. Probing the recovery length allows establishing the early warning system on the basis of observations alone, without any additional manipulation. Several transects can be established in an area and sampling can be done yearly or more frequently if necessary.

Pilot areas

Secche Della Meloria MPA (SIC/ZSC), Tuscany, Italy

Implementation Dates

Establish at least five replicate 1.5 m transects at the border of each focal macroalgal forest or seagrass meadow and sample the transect once a year at the peak of vegetative cover of algal turfs, usually in summer.

Implementing the tool is simple after a minimum of training. Data analysis to quantify the recovery length is more complicated, but personnel involved in AMARE Plus will help.

Quantitative results

The ability to quantify and clearly communicate the health status of key marine coastal ecosystems, such as macroalgal forests and seagrass meadows.

Key deliverables

Demonstration activity, reports, web-based communication tools.

Transfer potential

The proposed tool can be immediately implemented in MPAs, but we recommend having additional experimental tests assess the generality of its assumptions in a sample of locations.

The proposed tool originates from a robust theory on the dynamical behaviour of complex systems.

There are a number of key papers defining the proposed indicator and its implementation under controlled laboratory conditions and in more complex real-world systems:

• Dai, L., Korolev, K. S. & Gore, J. Slower recovery in space before collapse of connected populations. Nature 496, 355-358, doi:10.1038/nature12071 (2013).
• Rindi, L., Dal Bello, M., Dai, L., Gore, F., Benedetti-Cecchi, L. 2017. Direct observation of increasing recovery length before collapse of a marine benthic ecosystem. Nature Ecology and Evolution. doi:10.1038/s41559-017-0153.
• Rindi, L., M. Dal Bello, and L. Benedetti-Cecchi. 2018. Experimental evidence of spatial signatures of approaching regime shifts in macroalgal canopies. Ecology 99:1709-1715.

The recovery length in the figure above, quantifies the propagation of a perturbation in space. In the figure, algal turfs propagate from a low-quality patch into a macroalgal forest. The larger the propagation, the closer the proximity of the forest to a point of collapse. The indicator is the distance at which the algal turfs decline to 50% of their abundance in the low-quality patch. This is called the half-point recovery length. An experimental test of the indicator is recommended before establishing the monitoring tool in a new area.