Macroalgae blooms and their effects on seagrass ecosystems

Abstract

Seagrass decline caused by the macroalgae blooms is becoming a common phenomenon throughout temperate and tropical regions. We summarized the incidence of macroalgae blooms throughout the world and their impact on seagrass beds by direct and indirect ways. The competition for living space and using resources is the most direct effect on seagrass beds when macroalgae are blooming in an aquatic ecosystem. The consequence of macroalgae blooms (e.g., light reduction, hypoxia, and decomposition) can produce significant indirect effects on seagrass beds. Light reduction by the macroalgae can decrease the growth and recruitment of seagrasses, and decomposition of macroalgae mats can increase the anoxic and eutrophic conditions, which can further constrict the seagrass growth. Meanwhile, the presence of seagrass shoots can provide substrate for the macroalgae blooms. Controlling nutrient sources from the land to coastal waters is a general efficient way for coastal management. Researching into the synergistical effect of climate change and anthropognic nutrient loads on the interaction between searsasses and macroalgae can provide valuable information to decrease the negative effects of macroalgae blooms on seagrasses in eutrophic areas.

Combined nutrient and macroalgae loads lead to response in seagrass indicator properties

“…Phase shifts from seagrass-dominated to macroalgae-dominated ecosystems have been well documented in different areas worldwide, such as in Tomales Bay, California, USA (Huntington and Boyer, 2008) and the Mondego estuary, Portugal (Cardoso et al, 2004; for a review see Han and Liu, 2014). The present study showed a rapid (i.e.…”

Blooms of Ephemeral Green Algae in San Andres Island, International Biosphere Reserve Seaflower, Southwestern Caribbean

“…The algae were not floating on the surface, but they were always found tumbling along the substrate, sometimes attaching to seagrass leaves and shoots; this behavior has already been reported, for the species, in other locations (Flindt et al, 2007). These mats, beside the scouring effect, reduce light availability for seagrass shoots (Krause-Jensen et al, 1996;McGlathery, 2001), increase the sediment organic matter load, inducing the risk of anoxia and sulfide intrusion into meristematic areas of segrasses, therefore restricting seagrass growth (Nelson and Lee, 2001;Thomsen and Wernberg, 2009;Han and Liu, 2014). On the adjacent coral reefs, the presence of the mats was not observed.…”

Evidence for ‘critical slowing down’ in seagrass: a stress gradient experiment at the southern limit of its range

“…We suggest that this represents an under-studied topic. While opportunistic macroalgae are known to outcompete seagrass beds in eutrophic systems 4 , 59 , 60 , less attention has been dedicated to the microphytobenthos (MPB) communities which often dominate soft-sediments and could represent a later stage of the succession from vegetated to bare 61 . Even though all the die-off plots showed gradual recovery, our findings nevertheless suggest that biofilm layers can have a significant negative effect on seagrass recovery and may be responsible for an alternative stable state characterised by bare sediment.…”