Global Seagrass Research Methods

F.T. Short,R.G. Coles

• Éditeur: Elsevier Science
• Année: 2001
• ISBN:
  9780080525617
• Sujet: Biological Sciences
• Sous-sujet: Botany

This thorough and informative volume presents a set of detailed, globally applicable techniques for seagrass research.The book provides methods for all aspects of seagrass science from basic plant collection to statistical approaches and investigations of plant-animal interaction. The emphasis is on methods that are applicable in both developing and developed countries.

The importance of seagrasses in coastal and near shore environments, and ultimately their contribution to the productivity of the world's oceans, has become increasingly recognised over the last 40 years.Seagrasses provide food for sea turtles, nearly 100 fish species, waterfowl and for the marine mammals the manatee and dugong. Seagrasses also support complex food webs by virtue of their physical structure and primary production and are well known for their role as breeding grounds and nurseries for important crustacean, finfish and shell fish populations. Seagrasses are the basis of an important detrital food chain. The plants filter nutrients and contaminants from the water, stabilise sediments and act as dampeners to wave action. Seagrasses rank with coral reefs and mangroves as some of the world's most productive coastal habitat and strong linkages among these habitats make the loss of seagrasses a contributing factor in the degradation of the world's oceans.

Contributors from around the world provide up-to-date methods for comparable collection of ecological information from both temperate and tropical seagrass ecosystems.

Part I

Status of Seagrass

Chapter 1

Global seagrass distribution

Frederick T. Short, Department of Natural Resources, Jackson Estuarine Laboratory, University of New Hampshire, 85 Adams Point Rd, Durham, NH 03824, USA. E-mail address: [email protected]

Robert G. Coles, Department of Primary Industries Queensland, Northern Fisheries Centre, P.O. Box 5396, Cairns, Qld 4870, AUSTRALIA. E-mail address: [email protected]

Christine Pergent-Martini, University of Corsica, Faculty of Sciences, B.P. 52, 20250 Corte, FRANCE. E-mail address: [email protected]

1.1 Chapter Objective:

To present the most up-to-date information on global seagrass distribution relative to ecology in a form that provides the reader with a list of what seagrass species may be expected in different regions or, to some extent, in specific areas.

1.2 Introduction

Seagrasses are specialized marine flowering plants that have adapted to the nearshore environment of most of the world’s continents. Most are entirely marine although some species cannot reproduce unless emergent at low tide or subject to fresh water inflow. Some seagrasses can survive in a range of conditions encompassing fresh water, estuarine, marine, or hypersaline. There are relatively few species globally (about 60) and these are grouped into just 13 Genera and 5 Families.

Seagrass distribution has been described for most species (den Hartog 1970, Phillips and Menez 1988, Mukai 1993). There is now a broad understanding of the range of species and seagrass habitats. Areas less well known include the southeast Pacific reefs and islands, South America, the southern Atlantic, the Indian Ocean islands, the west African coast, and Antarctica (Figure 1-1). Shallow sub-tidal and intertidal species distributions are better recorded than seagrasses in water greater than 10 m below MSL. Surveying deeper water seagrass is time consuming and expensive, and it is likely that areas of deepwater seagrass are still to be located (Lee Long et al. 1996).

Figure 1-1 Global regions for identifying seagrass distributions (Table 1-1)

The distribution of a seagrass species can be defined as the range over which a species occurs or the area within a location where a particular species is located. In this chapter we consider the former. Detailed mapping protocols for the finer scale distribution questions are in Chapter 5.

With well-recorded events of seagrass loss from many coastal environments (Short and Wyllie Echeverria 1996), it is important to map and record the distribution of not only the location of existing seagrass but also areas of potential seagrass habitat. Such areas are generally shallow, sheltered coastal waters with suitable bottom type and other environmental conditions for seagrass growth Potential habitat may include areas where seagrass was known to grow at some time in the past but from which it has recently been eliminated

Destruction or loss of seagrasses have been reported from most parts of the world (Short and Wyllie Echeverria 1996), often from natural causes, e g, “wasting disease” (den Hartog 1987) or high energy storms (Patriquin 1975, Poiner et al 1989) However, destruction commonly has resulted from human activities, e g, as a consequence of eutrophication (Bulthuis 1983, Orth and Moore 1983, Cambridge and McComb 1984, Short and Burdick 1996) or land reclamation and changes in land use (Kemp et al 1983) Increases in dredge and fill, construction on the shoreline, damage associated with commercial overexploitation of coastal resources, and recreational boating activities along with anthropogenic nutrient and sediment loading have dramatically reduced seagrass distribution (Short and Wyllie Echeverria 1996) Anthropogenic impacts on seagrass meadows continue to destroy or degrade coastal ecosystems and decrease seagrass functions and values, including their contribution to fisheries (Walker 1989) Efforts are being made toward rehabilitation of seagrass habitat in some parts of the world: transplantation, improvement of water quality, restrictions on boating activity, fishing and aquaculture, and protection of existing habitat through law and environmental policy (Chapter 23)

A number of general parameters are critical to whether seagrass will occur along any stretch of coastline (see color plates) These include physical parameters that regulate the physiological activity of seagrasses (temperature, salinity, waves, currents, depth, substrate and day length), natural phenomena that limit the photosynthetic activity of the plants (light, nutrients, epiphytes and diseases), and anthropogenic inputs that inhibit the access to available plant resources (nutrient and sediment loading). Various combinations of these parameters will permit, encourage or eliminate seagrass from a specific location.

The depth range of seagrass is most likely to be controlled at its deepest edge by the availability of light for photosynthesis. Exposure at low tide, wave action and associated turbidity and low salinity from fresh water inflow determine seagrass species survival at the shallow edge. Seagrasses survive in the intertidal zone especially in sites sheltered from wave action or where there is entrapment of water at low tide, (e.g., reef platforms and tide pools), protecting the seagrasses from exposure (to heat, drying or freezing) at low tide.

It is important to document seagrass species diversity and distribution and identify areas requiring conservation measures before significant areas and species are lost. Determining the extent of seagrass areas and the ecosystem values of seagrasses is now possible on a local scale for use by coastal zone managers to aid planning and development decisions. Knowledge of regional and global seagrass distributions are still too limited and general for broad scale protection and management. Such infor...

Table des matières

• Cover image
• Title page
• Table of Contents
• Copyright
• Acknowledgments
• Introduction
• Part I: Status of Seagrass
• Part II: Seagrass Research Methods
• Part III: Seagrass Habitat Conservation
• List of Reviewers
• Author Index
• Subject Index