http://www.faculty.umb.edu/anamarija.frankic/eeos476/Class%20Materials/Habitats/GLOBAL%20Seagrass%20distribution.pdf

Global seagrass distribution and diversity: A bioregional model

http://faculty.umb.edu/anamarija.frankic/eeos476/Class%20Materials/Habitats/burkholder2007.pdf

Seagrasses and eutrophication

Seagrasses are important marine foundation species that are reported to be declining worldwide, with almost 15% of species considered threatened. Seagrasses are highly productive plants that reconfigure water flow and influence nutrient cycling, as well as provide critical habitat for a wide array of fish and invertebrate species. Yet, many of these seagrass-dependent species, including economically important fishes and invertebrates, are themselves in danger of overexploitation or extinction. In fact, there is on average more than one threatened associated species for every seagrass species across the globe. Links between threatened seagrasses and their dependent communities illustrate the importance of an ecosystem-based management approach that incorporates interdependencies and facilitation among species.

https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1890/080041

Associations of concern: Declining seagrasses and threatened dependent species

Sustained observations of marine biodiversity and ecosystems focused on specific conservation and management problems are needed around the world to effectively mitigate or manage changes resulting from anthropogenic pressures. These observations, while complex and expensive, are required by the international scientific, governance and policy communities to provide baselines against which the effects of human pressures and climate change may be measured and reported, and resources allocated to implement solutions. To identify biological and ecological essential ocean variables (EOVs) for implementation within a global ocean observing system that is relevant for science, informs society, and technologically feasible, we used a driver-pressure-state-impact-response (DPSIR) model. We (1) examined relevant international agreements to identify societal drivers and pressures on marine resources and ecosystems, (2) evaluated the temporal and spatial scales of variables measured by 100+ observing programs, and (3) analysed the impact and scalability of these variables and how they contribute to address societal and scientific issues. EOVs were related to the status of ecosystem components (phytoplankton and zooplankton biomass and diversity, and abundance and distribution of fish, marine turtles, birds and mammals), and to the extent and health of ecosystems (cover and composition of hard coral, seagrass, mangrove and macroalgal canopy). Benthic invertebrate abundance and distribution and microbe diversity and biomass were identified as emerging EOVs to be developed based on emerging requirements and new technologies. The temporal scale at which any shifts in biological systems will be detected will vary across the EOVs, the properties being monitored and the length of the existing time-series. Global implementation to deliver useful products will require collaboration of the scientific and policy sectors and a significant commitment to improve human and infrastructure capacity across the globe, including the development of new, more automated observing technologies, and encouraging the application of international standards and best practices.

/pdf/essential-ocean-variables-for-global-sustained-observations-39yodg9o0e.pdf

Essential ocean variables for global sustained observations of biodiversity and ecosystem changes

Direct growth measurements require fewer assumptions than those based on reconstructive techniques. When direct measurements, which require repeated visits and considerable effort, are not possible, for instance, in remote populations or in year-round assessments, reconstructive techniques are recommended. Indirect growth measurement methods involve collecting lengths of rhizome with attached stems and leaves, and reconstructing the growth interval and pattern of the plants by counting the number of leaf scars laid down on the stem or rhizome. Reconstructive analyses can also be used to derive estimates of shoot mortality and recruitment in the population. Direct assessments of seagrass growth are recommended using marking methods and the determination of the plastochrone interval, while indirect reconstructive methods are recommended for evaluation of annual growth or long-term cycles from the rhizome record. The marking technique is the choice of approach whenever repetitive visits to the meadow investigated are possible and whenever the different structures to be marked are accessible for marking purposes with tolerable disturbance. However, this is not the case for species with deep-growing rhizomes, where reconstructive techniques are useful. The reconstruction approach is of limited use for species with short life spans or annuals, for which structures older than one year are scarce or non-existent. Application of reconstruction techniques to these populations would likely render biased estimates. In these instances, leaf or rhizome marking must be repeated over time to determine annual growth.

Chapter 8 – Methods for the measurement of seagrass growth and production

Seagrasses are an important coastal habitat worldwide and are indicative of environmental health at the critical land–sea interface In many parts of the world, seagrasses are not well known, although they provide crucial functions and values to the world’s oceans and to human populations dwelling along the coast Established in 2001, SeagrassNet, a monitoring program for seagrasses worldwide, uses a standardized protocol for detecting change in seagrass habitat to capture both seagrass parameters and environmental variables SeagrassNet is designed to statistically detect change over a relatively short time frame (1–2 years) through quarterly monitoring of permanent plots Currently, SeagrassNet operates in 18 countries at 48 sites; at each site, a permanent transect is established and a team of people from the area collects data which is sent to the SeagrassNet database for analysis We present five case studies based on SeagrassNet data from across the Americas (two sites in the USA, one in Belize, and two in Brazil) which have a common theme of seagrass decline; the study represents a first latitudinal comparison across a hemisphere using a common methodology In two cases, rapid loss of seagrass was related to eutrophication, in two cases losses related to climate change, and in one case, the loss is attributed to a complex trophic interaction resulting from the presence of a marine protected area SeagrassNet results provide documentation of seagrass change over time and allow us to make scientifically supported statements about the status of seagrass habitat and the extent of need for management action

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1439-0485.2006.00095.x

SeagrassNet monitoring across the Americas: case studies of seagrass decline

Eelgrass, Zostera marina L., leaf growth measurement methods were investigated and compared in New Hampshire and Maine, USA. The commonly used leaf marking method, developed by Zieman (1974) and embraced by Dennison (1990), was found to underestimate leaf growth, particularly when measured over small time intervals, compared to a method developed by Short (1987) based on the weight of mature leaf tissue. Short's method (1987) was then compared to a modification of the plastochrone interval method of Jacobs (1979), giving very similar results. In our plastochrone method, leaf growth is calculated as the weight of a mature leaf divided by the time interval between initiation of two successive leaves on one shoot, the plastochrone interval. Our investigations demonstrate that the leaf plastochrone interval in eelgrass varies seasonally; to use the plastochrone method, the plastochrone interval must be measured for each growth determination. Based on our comparisons, we recommend what we call the 'plastochrone method' as a more efficient and accurate way to measure eelgrass leaf growth.

Jeffrey L. Gaeckle

Papers

SeagrassNet monitoring across the Americas: case studies of seagrass decline

A plastochrone method for measuring leaf growth in eelgrass, Zostera marina L

Occurrence of Halophila baillonii meadows in Belize, Central America

Sheath length as a monitoring tool for calculating leaf growth in eelgrass (Zostera marina L.)

SeagrassNet monitoring of habitat change across the Americas