Australia to work on the Great Barrier Reef, I truly felt that I had arrived at a tropical paradise. And the Great Barrier Reef is paradisiacal, being one of the greatest natural wonders on earth. Thousands of people the world over come to immerse themselves in its clear azure waters to observe the beauty and grandeur of many of its coral reefs. Also, if you think tropical rainforests are beautiful, then like me you can also enjoy the remarkable geometry and asymmetry of tropical mangrove forests.
But like all preconceived notions, dreams, and thoughts, the tropics also has a dark side, often subtle, but lurking in the shadows. Tropical waters give rise to cyclones, hurricanes, and typhoons, and the summer months can be unbearably hot and humid; closer to the equator, it is sticky, hot, and humid year‐round. This reality can best be understood in the first instance by reading any of the classic tales of early explorers of the tropics, such as James Cook or the part‐time pirate but intrepid explorer William Dampier or the great German scientist Alexander von Humboldt.
But as I will show in this book, the tropical marine realm is special in myriad ways and for many reasons from seas of higher latitude, in housing iconic habitats such as coral reefs, snow white beaches, crystal clear waters, mangrove forests, extensive and rich seagrass meadows and expansive river deltas, such as the exemplar, the Amazon. The reader will learn that from a global perspective it is in fact the great tropical rivers that have the most significant role to play in the cycles of nutrient and materials that help to foster life in tropical seas. These great conduits of mud, freshwater, and nutrients are the pumps that fuel the primary producers sustaining complex and beautifully intricate food webs. It is an irony that if it wasn't for these least photogenic of habitats, no (or exceedingly little) tropical marine life would exist. Even coral reefs have a tenuous, if important, functional connection to tropical rivers and estuaries; reefs are not quite as self‐sufficient as we once thought, and many rely on connectivity with life in adjacent coastal muddy waters. In a nutshell, coral reefs are not divorced from the waters that bathe them. Nowadays this connection is unfortunately becoming more of a curse than a blessing; destructive human activities on land such as land clearing and overuse of chemical fertilizers, pesticides, and herbicides are on the rise with concomitant increases in human population growth along tropical coastlines.
The purpose of this book is to document the structure and function of tropical marine populations, communities, and ecosystems in relation to environmental factors including climate patterns and climate change and patterns of oceanographic phenomena such as tides and currents and major oceanographic features, as well as chemical and geological drivers. The book focuses on estuarine, coastal, shelf, and open ocean ecosystems. No such book on the tropical marine realm exists for the advanced undergraduate and postgraduate student, researcher, or manager. Another reason for writing this book is to reorient and expand the knowledge base of marine ecology. Several excellent textbooks exist on marine biology and ecology, but they are inadequate in describing life in the tropics; iconic habitats such as coral reefs and mangroves are usually covered only briefly. Until recently, this perfunctory treatment was understandable considering that the study of marine ecology has focused on boreal and temperate seas near where the major oceanographic institutes and universities reside. Since the 1980s, however, there has been a drastic rise in the number of journal articles published on aspects in tropical marine ecology to the extent that a textbook focusing on the tropics is now warranted.
Such an authoritative work is timely given the increasing concern of the problems associated with rapid population growth in developing nations – nearly all of which reside in the tropics – and a growing awareness of the role of the tropical ocean as the heat engine for global climate and in regulating earth's biogeochemical cycles. Many students are still being taught basic principles of marine ecology based on research conducted primarily in high latitudes. This is unfortunate because the tropical ocean is in many ways different from colder seas both structurally and functionally. The tropical ocean contains the centre for marine biodiversity, is a major driver of earth's climate, and is where most freshwater and sediment from land are discharged into the sea, greatly impacting ocean chemistry, geology, and the structure and function of biota. Many major environmental characteristics and adaptive flora and fauna are endemic to or dominant in tropical seas.
A basic understanding of marine biology and ecology is assumed so the reader may be tempted to skip the first part of the book dealing with the climate, physics, geology, and chemistry of the tropical marine environment. I urge the reader not to do so as one cannot properly understand what drives tropical organisms without understanding the uniqueness of the physical milieu in which they live.
The second section focuses on the origins, diversity, biogeography, and the structure and distribution of tropical biota. The tropical marine realm started in the Tethys Sea where most phyla first evolved and radiated through time to produce the major latitudinal patterns we see today. Populations of organisms from the size of microbes to whales will be examined in terms of their population regulation, growth dynamics, fluctuations, and cycles over time, as well as life history traits and strategies, including aggregation and refugia, territoriality, and behaviour. Pelagic and benthic community structure and their drivers, such as adaptations to stress, competition, predation, symbiosis, and other trophic factors, will be dealt with to underscore the fact that ecosystems are not simply ‘black boxes’ but consist of a wide array of complex trophic groups and communities. The ecosystem chapter will deal with not only classification of types (sandy beaches, mangroves, coral reefs, continental shelf, open ocean) but also how they developed over time and how they connect to one another.
The third part explores the rates and patterns of primary and secondary productivity, their drivers, and the characteristics of food webs. All organisms play important roles in the cycling of carbon and macro‐ and micronutrients, and these biogeochemical cycles are considered from the intertidal zone out to the open ocean.
The fourth part examines how humans are altering tropical ecosystems via unsustainable fisheries and the decline and loss of habitat and fragmentation; pollution is altering an earth already in the throes of climate change. This book ends with a hopefully not‐too‐long list of dot points highlighting how tropical biota and their ecosystems are different to those of higher latitude and how their future is in our hands.
I would like to acknowledge the staff of Wiley for doing such a wonderful, professional job in stitching this book together. I thank colleagues Bob Aller, Josie Aller, Michelle Burford, Erik Kristensen, Janice Lough, Matsui Mazda, Dave McKinnon, John (Charlie) Veron, Gullaya Wattayakorn, and Bob Wasson for critically commenting on various chapters. I am grateful to Morgan Pratchett and Ciemon Caballes for the photos of crown‐of‐thorns and coral bleaching. Finally, I thank my loving wife Fiona for her beautiful illustrations that have made this book much better than I had hoped and both my daughters for reminding me that there is indeed life after science. Of course, any errors are mine and I would be grateful for students, faculty, and other readers to bring any errors to my attention.
Daniel M. Alongi, PhD
Email: [email protected]
CHAPTER 1 Introduction
1.1 Definition of the Tropics
There is no standard definition of the tropics. It has been defined in so many ways, as a reflection of its complexity, that only an operational definition can suffice; there have been notable climatological and oceanographic exceptions to all definitions. No one definition meets with universal approval, and there have been many attempts to define it, first most simply, by the patterns of the trade winds of the “torrid zone” (Dampier 1699) to a rigid definition of the region between the Tropic of Capricorn and the Tropic of Cancer (Townsend 2012), that is, the most northerly and southerly position at which the sun may appear directly overhead at its zenith. In fact, the word ‘tropical’ comes from the Greek tropikos, meaning ‘turn’ referring to the fact that these latitudes mark where the sun appears to turn annually in its
