# Understanding trends in Zostera research, stressors, and response variables: a global systematic review of the seagrass genus

## TL;DR

This paper reviews global research on Zostera seagrass, identifying key stressors, species, and geographic trends to highlight knowledge gaps and support conservation efforts.

## Contribution

The study provides the most comprehensive review of Zostera seagrass research to date, using a standardized team approach to minimize bias and create a centralized knowledge base.

## Key findings

- Nutrients, temperature, and light were the most studied stressors affecting Zostera seagrass.
- Zostera marina was the most researched species, while five other Zostera species had no stressor studies.
- The United States and Australia produced the most research on Zostera seagrass.

## Abstract

Seagrass meadows are ecologically significant habitats that are globally threatened. Thus, there is increased interest in conservation of seagrasses as they face widespread decline. Biotic and abiotic factors that influence seagrass can be classified as stressors, such as rising temperature and eutrophication. Our study met an imminent need to consolidate data from previous studies to discern knowledge gaps and identify trends in studies, stressors, species, and geographic origination of research for the genus Zostera. For our systematic review, the objectives were to (A) qualitatively assess and summarize the current state of literature focused on seagrass species within the Zostera genus and their stressors; (B) utilize data extracted from full-text articles to identify trends and knowledge gaps for the study of stressors, response variable measurements, species, geography, and study designs; and (C) map the distribution, type, and number of these studies globally.

We included articles that focused on stressors associated with Zostera seagrass species, and excluded studies of other seagrasses and non-stressor related articles. We conducted a Web of Science search of all databases, concluding in January of 2021, followed by a standardized review and data extraction protocol using Colandr (colandrapp.com) as our article screening tool. All 15 review participants were trained on the same set of practice articles and decision trees to minimize variation between individuals. After full text extraction, we analyzed our data by frequency and association between species, stressors, and geographic locations studied.

We screened 7,331 titles and abstracts and extracted data from 1,098 full-text articles. We found nutrients, temperature, and light were the most studied stressors. The United States of America produced the most articles in our review, followed by Australia. Zostera marina was most frequently studied, and our review found no stressor studies for five species in the genus. Studies most frequently measured response variables across multiple levels of ecological organization, including the individual plant, biotic community, and environmental conditions. As a part of our review, we made all extracted data publicly available as an interactive map.

Undertaking a review of global studies allowed us to assess more seagrass articles for a single genus than any prior systematic review, summarizing a breadth of stressor studies related to the Zostera genus. A team effort and standardized training minimized bias during screening and data extraction. Evidence limitations may exist due to the single database used in our search protocol, as well as species, geographic, and stressor biases in included studies. Our review creates a centralized knowledge base that serves as a foundational information source for Zostera research, while highlighting existing knowledge gaps in the literature.