Shanahan et al. 2023. Guidance on council seagrass monitoring

Shanahan, B., J. Crawshaw, K. Squires, T. McElroy, R. Griffiths, O. Wade. 2023. Guidance on council seagrass monitoring. Coastal Special Interest Group (CSIG) internal document.

Executive summary
Seagrass (Zostera muelleri) is a critical component of coastal ecosystems, providing several
ecosystem services. Z. muelleri is an at risk-declining species in New Zealand, and loss of seagrass
in New Zealand and internationally has been attributed to stressors such as sedimentation,
nutrient enrichment, and physical disturbances. The extent of seagrass has been monitored by
authorities around New Zealand over the past few decades. In many regions, significant changes
in extent have been identified since the early 1940s. Due to a lack of national guidance on how
to monitor seagrass habitats, there is a wide variation in monitoring methodologies and effort
across different regions of New Zealand.

Since there is not a “once size fits all” approach to monitoring seagrass, background information,
guidance, and considerations are suggested for possible monitoring methods, along with several
recommendations. Monitoring seagrass covers both mapping its overall extent and tracking its
health, utilising seagrass-specific and environmental indicators. To allow for differences in
council priorities and resources, we’ve suggested a “bronze”, “silver”, and “gold” approach to
monitoring (Figure 1).

For councils that are just starting to explore seagrass monitoring, this report should guide them
in selecting methods that work best for their circumstance, while being consistent across

Figure 1. A three-tiered approach to mapping seagrass extent, percent cover, health indicators and stressors. + symbols indicate that lower levels are in addition to variables in higher levels (e.g., gold seagrass indicators include both silver and bronze seagrass indicators). PAR is photosynthetically active radiation and LUX is illuminance. TN is total nitrogen, TC is total carbon, and TP is total phosphorus. Complexity, information gathered, and cost decreases from gold to bronze. *It is preferable to measure light in PAR, however if relationships can be established between PAR and LUX, Hobo LUX loggers can be utilised to decrease costs.