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In-Depth Information
Algae swept into the mangroves from adjacent rocky shore and estuarine
habitats can become entangled in pneumatophores, persist, and at times reproduce
to establish persistent free living colonies. It is suspected that these drift algae
increase the likelihood of colonization by mollusks in mangroves by increasing
substrate complexity and possibly serve as an additional food source (Bishop et al .
2009 ). The complex surface of fucalean macroalgae also represents an additional
surface area for the growth of microfilms. Bishop et al . ( 2009 ) determined that algae
originating from estuaries were capable of attracting more mollusks than algae
coming from rocky shores. This is likely due to the typically higher nutrient content
of estuarine systems which is capable of enriching algae and increasing its palat-
ability for mollusks.
Some herbivorous fishes living within and adjacent to mangroves depend upon
macroalgae growing as epiphytes on mangrove prop roots as a primary food source.
For example, in Cura¸ao, the doctorfish, Acanthurus chirurgus , acquires approxi-
mately 55% of its macroalgal diet directly from mangrove surfaces (Nagelkerken
and van der Velde 2004 ). The largest herbivorous reef fish in the Atlantic Ocean,
Scarus guacamaia , is exclusively dependent on the mangrove habitat during its
development and has suffered local extinctions where mangroves have been
removed (Mumby et al . 2004 ). Of particular concern is the recent appearance of
the invasive predatory lionfish, Pterois volitans , in Caribbean mangrove systems
and the impacts that it will have on the recruitment of vital herbivorous fish species
to adjacent coral reef habitats (Barbour et al . 2010 ; Albins and Hixon 2008 ).
16.5 Conclusion
Tropical macroalgae are essential elements of the complex coastal ecosystems they
inhabit. They provide a wide range of vital ecological functions, like the stabiliza-
tion of reefs, retention of nutrients, and provision of habitat and food. Macroalgae
are able to provide all of these different functions due to their enormous diversity
and habitat-specific adaptations. Over the last few decades, macroalgae have
become more abundant across the globe, in coral reef, seagrass, and mangrove
habitats, often as a response to human activities. At times, the proliferation of algae
has led to regime shifts in these already threatened habitats. These ecosystem shifts
have had profound consequences on tropical systems worldwide. In most cases a
combination of coral mortality, eutrophication, reductions in grazing pressure due
to disease, and overfishing form the basis for these shifts. In the near future, these
shifts are likely to be exacerbated and prolonged, resulting in reduced overall
habitat complexity and biodiversity.
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