Index scoring tool developed to enable Bight ’23 assessment of eelgrass health

SCCWRP and its partners have developed an initial version of a condition index scoring tool for evaluating the health of Southern California eelgrass beds based on their ecological functioning – a prototype tool that has paved the way for the Southern California Bight 2023 Regional Monitoring Program to complete its first regional assessment of eelgrass health and for researchers to explore extending this assessment approach to coastal estuary environments.

The Zostera Ecosystem Function Reporter (ZEFR, pronounced “zephyr”) prototype tool – described in a SCCWRP technical report published in April – integrates estimates of seven key measures of ecosystem functioning and services to produce a single combined score.

ZEFR evaluates an individual eelgrass bed’s ability to provide refugia to fish and other animals, as well as provide other ecosystem services, including attenuating ocean waves, promoting sediment stabilization, and sequestering carbon.

Eelgrass beds, which are scattered across shallow, soft-bottom coastal areas of Southern California, are the dominant type of seagrass found in California’s coastal embayments. In recent years, California has invested significant resources into restoring and protecting eelgrass and other seagrass beds, which have been decimated by a range of human activities.

Traditionally, eelgrass assessments in Southern California have focused primarily on documenting the location and size of eelgrass beds. Furthermore, this monitoring has historically been uneven, with some sites not getting monitored at all and other sites being monitored using less rigorous, non-standardized assessment methods.

As part of ZEFR’s development, researchers evaluated 31 randomly selected Southern California eelgrass beds, finding that 12% of the region was in Good condition, 65% was in Moderate condition, 20% was in Poor condition, and 3% was in Bad condition.

Researchers also broke down the assessment into three different habitat types – large embayments, small embayments, and estuaries – finding that eelgrass from large embayments was in the best condition, with 80% in Good or Moderate condition and 0% in Bad condition. Conversely, small embayment eelgrass was in the worst condition, with only 60% in the Good or Moderate condition and 20% in Bad condition.

The Bight ’23 Submerged Aquatic Vegetation (SAV) study element is applying ZEFR to conduct a similar but independent assessment of eelgrass condition across the Southern California Bight. The Bight ’23 SAV final assessment report is expected to be published this summer.

Regional assessments of eelgrass beds will enable coastal managers to place site-specific assessments into regional context, as well as enable managers to quantitatively assess the success of eelgrass restoration and mitigation projects, including for determining compliance with the California Eelgrass Mitigation Policy, which calls for no net loss of eelgrass habitat function.

More broadly, the assessment approach will help managers determine if coastal estuaries – of which eelgrass beds are a part – have achieved beneficial-use designations that are required under state and federal regulatory programs.

Eventually, ZEFR is expected to serve as a proof-of-concept for how to develop condition index scoring tools for coastal estuaries – a much larger, more ecologically diverse habitat type than eelgrass beds.

ZEFR is based on seven functional measures of eelgrass health: carbon sequestration, sediment stabilization, primary production, secondary production, nekton habitat, waterfowl habitat, and improvement of water quality. SCCWRP convened an expert advisory panel to reach consensus on which measures to include in the condition index tool.

The technical underpinnings for ZEFR were originally co-developed by SCCWRP in 2020 and piloted at smaller scales.

While ZEFR was developed for use in Southern California, the index could be readily adapted for use outside Southern California. Already, some pilot testing is underway in Morro Bay in Central California.

For more information, contact Dr. David Gillett and Dr. Jill Tupitza.