Chapter 23
Decline and Recovery of Seagrass Ecosystems—
The Dynamics of Change
Diana I. Walker
∗ and Gary A. Kendrick
School of Plant Biology (Botany M90), The University of Western Australia, 35 Stirling Highway,
Crawley 6007, Australia
Arthur J. McComb
School of Environmental Science, Murdoch University, Murdoch 6152, Australia
I. Introduction
The distribution of seagrass beds has often been described in the literature as if these communities were
naturally static components of coastal ecosystems
(Larkum, 1977; McRoy and McMillan, 1977; Orth
and Moore, 1983; Kirkman and Kuo, 1990), disturbed only by human influences. A paradigm of seagrass bed stability, developed for large bed-forming
seagrasses such as Posidonia as in the Mediterranean
Sea (Boudouresque et al., 1980), and the western and
southern coasts of Australia (Larkum, 1976; Larkum
and West, 1983; Kirkman, 1978), suggested that sea
level had been stable for the last 5–8,000 years and
assumed that these large monospecific seagrass beds
were static for that period.
Immense variations have been shown in detailed
studies of such beds, on a seasonal and spatial basis (e.g. Duarte et al., 1994; Alcoverro et al., 1995;
Duarte et al., 2003). Change is a naturally-occurring
process, which takes place in the absence of human influence (Patriquin, 1975; Hottinger and Vischer, 1983; Clarke and Kirkman, 1989; Marba and
Duarte, 1995; Marba and Duarte, 1998). There have
also been massive declines in seagrass due to anthropogenic effects (Orth and Moore, 1983; Walker
and McComb, 1992; Short and Wyllie-Echeverria,
1996), raising the possibility that such losses may be
irreversible. Recent research findings suggest this is
not the case (Kendrick et al., 1999, 2002).
∗ Author for correspondence, email: diwalker@cyllene.uwa.
edu.au
This chapter will detail aspects of more recent
research demonstrating changes, both negative and
positive, in seagrass distributions, as revealed by
mapping and other detailed investigations. The extent of decline dominates the literature, but an increasing number of studies record the dynamic nature of seagrass meadows (Williams, 1988; Kendrick
et al., 1999, 2000, 2002; Cambridge et al., 2000,
2002; Durako et al., 2002). The rates of decline and
recovery will be compared. The evidence for largescale recovery of seagrass beds, based on mapping
projects, will then be described. A case study will
be presented that compares and contrasts two regions on the Western Australian coast: Cockburn
Sound, where seagrass loss has been dramatic and is
continuing; and Success and Parmelia Banks where
loss and recovery are in dynamic equilibrium or seagrasses are expanding into unvegetated sand habitats. Comparisons and contrasts in findings in Florida
Bay (USA) will be explored. We will conclude by
suggesting a way in which management of seagrass
landscapes can be made proactive to match their
dynamic nature.
II. Changes in Seagrass Distributions
Many seagrass studies have been made at scales
less than a 1 m
2 quadrat or a 10-m transect, over
time scales of 1–2 years (e.g. Hillman et al., 1989;
McMahon and Walker, 1997). On the other hand,
seagrass losses have been documented over tens
of square kilometres (Orth and Moore, 1983;
551–565.
A. W. D. Larkum et al. (eds.), Seagrasses: Biology, Ecology and Conservation, pp.
c
2006 Springer. Printed in the Netherlands.
Decline and Recovery of Seagrass Ecosystems—
The Dynamics of Change
Diana I. Walker
∗ and Gary A. Kendrick
School of Plant Biology (Botany M90), The University of Western Australia, 35 Stirling Highway,
Crawley 6007, Australia
Arthur J. McComb
School of Environmental Science, Murdoch University, Murdoch 6152, Australia
I. Introduction
The distribution of seagrass beds has often been described in the literature as if these communities were
naturally static components of coastal ecosystems
(Larkum, 1977; McRoy and McMillan, 1977; Orth
and Moore, 1983; Kirkman and Kuo, 1990), disturbed only by human influences. A paradigm of seagrass bed stability, developed for large bed-forming
seagrasses such as Posidonia as in the Mediterranean
Sea (Boudouresque et al., 1980), and the western and
southern coasts of Australia (Larkum, 1976; Larkum
and West, 1983; Kirkman, 1978), suggested that sea
level had been stable for the last 5–8,000 years and
assumed that these large monospecific seagrass beds
were static for that period.
Immense variations have been shown in detailed
studies of such beds, on a seasonal and spatial basis (e.g. Duarte et al., 1994; Alcoverro et al., 1995;
Duarte et al., 2003). Change is a naturally-occurring
process, which takes place in the absence of human influence (Patriquin, 1975; Hottinger and Vischer, 1983; Clarke and Kirkman, 1989; Marba and
Duarte, 1995; Marba and Duarte, 1998). There have
also been massive declines in seagrass due to anthropogenic effects (Orth and Moore, 1983; Walker
and McComb, 1992; Short and Wyllie-Echeverria,
1996), raising the possibility that such losses may be
irreversible. Recent research findings suggest this is
not the case (Kendrick et al., 1999, 2002).
∗ Author for correspondence, email: diwalker@cyllene.uwa.
edu.au
This chapter will detail aspects of more recent
research demonstrating changes, both negative and
positive, in seagrass distributions, as revealed by
mapping and other detailed investigations. The extent of decline dominates the literature, but an increasing number of studies record the dynamic nature of seagrass meadows (Williams, 1988; Kendrick
et al., 1999, 2000, 2002; Cambridge et al., 2000,
2002; Durako et al., 2002). The rates of decline and
recovery will be compared. The evidence for largescale recovery of seagrass beds, based on mapping
projects, will then be described. A case study will
be presented that compares and contrasts two regions on the Western Australian coast: Cockburn
Sound, where seagrass loss has been dramatic and is
continuing; and Success and Parmelia Banks where
loss and recovery are in dynamic equilibrium or seagrasses are expanding into unvegetated sand habitats. Comparisons and contrasts in findings in Florida
Bay (USA) will be explored. We will conclude by
suggesting a way in which management of seagrass
landscapes can be made proactive to match their
dynamic nature.
II. Changes in Seagrass Distributions
Many seagrass studies have been made at scales
less than a 1 m
2 quadrat or a 10-m transect, over
time scales of 1–2 years (e.g. Hillman et al., 1989;
McMahon and Walker, 1997). On the other hand,
seagrass losses have been documented over tens
of square kilometres (Orth and Moore, 1983;
551–565.
A. W. D. Larkum et al. (eds.), Seagrasses: Biology, Ecology and Conservation, pp.
c
2006 Springer. Printed in the Netherlands.