Introduction

Understanding matter circulation in the biosphere constitutes one of the fundamental research objectives for ecologists. Stocks of materials, their distribution, and their fluxes between different compartments are basic parameters that need to be characterized to explain the functioning of any ecosystem. Their study is usually arduous owing to the variety of routes that materials can follow, and to the complexity of the processes that are involved. Leopold (1949) described matter flux in ecosystems in a brief but elegant way in what he named 'The odyssey of the atom X': "An atom at large in the biota is too free to know freedom; an atom back to the sea has forgotten it. For every atom lost to the sea, the prairie pulls another one out of the decaying rocks. The only certain truth is that its creatures must suck hard, live fast, and die often, lest its losses exceed its gains" When an atom abandons its long rest in the lithosphere and joins the organic com

* Author for correspondence, email: [email protected]

partment of the biosphere, it enters in that fast cyclic dynamic that characterizes life. Autotrophic organisms bring an atom to life, while the organism's death leaves it at the mercy of decomposers that return it to the inorganic compartment where it waits to join a new cycle. The persistence of an ecosystem relies on both the optimization of carbon and nutrient acquisition and on the minimization of carbon and nutrient losses (Hemminga et al., 1991). In other words, persistence requires a continuous effort to prevent the atoms essential for life from escaping the fast cycles that enable the high production we observe on our planet. Therefore, a fine tuned balance between production and remineralization (and the fluxes between sources and sinks) govern the rhythm of the ecosystems.

This chapter, far from pretending to be an exhaustive examination or reassessment of what is known about carbon fluxes in seagrass ecosystems, is an attempt to put a picture of carbon flux in focus by combining equal parts of literature review, personal achievements (including some recent unpublished and submitted results), a critical appraisal, and

A. WD. Larkum et al. (eds.), Seagrasses: Biology, Ecology and Conservation, pp. 159-192. © 2006 Springer. Printed in the Netherlands.

Table 1. Comparison between average seagrass and other marine and terrestrial ecosystems. NPP (net primary production). Simplified and modified from Margalef, 1986 and Duarte and Cebrian, 1996.

Area covered NPP Total NPP

Marine phytoplankton

Table 1. Comparison between average seagrass and other marine and terrestrial ecosystems. NPP (net primary production). Simplified and modified from Margalef, 1986 and Duarte and Cebrian, 1996.

Area covered NPP Total NPP

Marine phytoplankton

Oceanic waters

332

130

43

Coastal waters

27

167

4.5

Coastal macrophytes

Mangroves

1.1

1000

1.1

Seagrasses

0.6

817

0.49

Macroalgae

6.8

375

2.55

Microphytobenthos

6.8

50

0.34

Terrestrial ecosystems

Forests

41

400

16.4

Crops

15

350

5.25

Deserts

40

50

2

Terrestrial ecosystems

148

200

29.6

Continental waters

1.9

100

0.19

Oceans

359

132

47.5

thought-provoking estimates. Our goal is to provide a critical summary of the current knowledge of the topic and identify relevant areas of seagrass research for the coming decade.

Was this article helpful?

0 0

Post a comment