Temporal variability of a protected multispecific tropical seagrass meadow in response to environmental change

E Alonso Aller,M Gullström,J S Eklöf,H W Linderholm,L M Nordlund,U Kloiber

doi:10.1007/s10661-019-7977-z

E Alonso Aller, M Gullström + Show 4 more

Open Access

https://doi.org/10.1007/s10661-019-7977-z

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Abstract

In a changing environment, there is an increasing interest to monitor ecosystems to understand their responses to environmental change. Seagrass meadows are highly important ecosystems that are under constant pressure from human activities and climate impacts, with marked declines observed worldwide. Despite increasing efforts, monitoring of multispecific tropical seagrass meadows is scarce, particularly in low-income regions. Based on data from a monitoring programme in a marine protected area in Zanzibar (Tanzania), we assessed temporal changes in seagrass cover and species composition during a 10-year period in relation to local variability in environmental variables. We observed a strong, gradual decline in seagrass cover and changes in species composition, followed by a period of recovery. However, the timing and length of these temporal patterns varied in space (between transects). Multiple environmental variables—cloud cover, temperature, storm occurrence, sunspot activity, and tidal amplitude and height—influenced seagrass cover, although only to a minor extent, suggesting that the monitored seagrass meadow may be influenced by other unmeasured factors (e.g. water currents and sediment movement). Our results show that seagrass meadows can be highly dynamic at small (10–50 m) spatial scales, even in the absence of major local anthropogenic impacts. Our findings suggest that high-resolution monitoring programmes can be highly valuable for the detection of temporal changes in multispecific seagrass meadows; however, to understand the causes of change, there is a need of long-term (> 10 years) data series that include direct measurements of environmental variables and extreme events.

Highlights

In a time of rapid environmental changes, there has been an increasing interest to monitor ecosystems and understand the causes of gradual as well as sudden ecosystem changes (Callahan 1984)
Our results show that seagrass meadows can be highly dynamic at small (10–50 m) spatial scales, even in the absence of major local anthropogenic impacts
Our findings suggest that high-resolution monitoring programmes can be highly valuable for the detection of temporal changes in multispecific seagrass meadows; to understand the causes of change, there is a need of long-term (> 10 years) data series that include direct measurements of environmental variables and extreme events

Summary

Introduction

In a time of rapid environmental changes, there has been an increasing interest to monitor ecosystems and understand the causes of gradual as well as sudden ecosystem changes (Callahan 1984). Terrestrial environmental monitoring dates back several centuries, but for long lagged in the marine environment. Over the last few decades, there has been a dramatic increase in efforts to assess how marine ecosystems change over time and respond to environmental changes, in the coastal zone. Seagrass meadows are one of the most important coastal habitats occupying inter- and subtidal nearshore environments and are frequently emphasized in coastal ecosystem health assessments (Borum et al 2004; Romero et al 2015; Roca et al 2016). Most seagrass meadows are monospecific (with a single seagrass species) but multispecific meadows are common in certain regions, in the tropics, where overall seagrass diversity is the highest

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