Observations and Remote Sensing. http://dx.doi.org/10.1109/
JSTARS.2013.2265255.
Pack, R. T., Brooks, V., Young, J., Vilaca, N., Vatslid, S., Rindle, P.,
Kurz, S., Parrish, C. E., Craig, R., and Smith, P. W., 2012. An
overview of ALS technology. In Renslow, M. S. (ed.), Manual
of Airborne Topographic Lidar. Bethesda: ASPRS Press.
Sithole, G., and Vosselman, G., 2004. Experimental comparison of
filter algorithms for bare-Earth extraction from airborne laser
scanning point clouds. ISPRS Journal of Photogrammetry and
Remote Sensing, 59, 85–101.
Shan, J., and Toth, C., 2009. Topographic Laser Ranging and
Scanning: Principles and Processes. Boca Raton: CRC Press.
Slatton, K. C., Carter, W. E., Shrestha, R. L., and Dietrich, W., 2007.
Airborne laser swath mapping: achieving the resolution and
accuracy required for geosurficial research. Geophysical
Research Letters, 34, 1–5.
Wehr, A., and Lohr, U., 1999. Airborne laser scanning—an introduction and overview. Journal of Photogrammetry and Remote
Sensing, 54, 68–82.
Cross-references
Light Detection and Ranging (LIDAR)
ALGAL BLOOMS
Patricia M. Glibert
Horn Point Laboratory, University of Maryland Center for
Environmental Science, Cambridge, MD, USA
Synonyms
Harmful algal blooms; Nuisance algal blooms; Phytoplankton blooms; Red tides; Spring blooms
Definition
Algal blooms refer to the increase in biomass of algae due
to increased growth or due to physical aggregation,
leading to an above-normal accumulation and generally
adverse ecosystem effects.
Introduction
Algae are a normal part of the aquatic ecosystem; they
form the base of the aquatic food web. Of this large and
diverse group of organisms, most are microscopic in size,
but some are macroscopic. The microscopic algae are
most often single cells, but some can form chains or colonies. Most microalgae live in the water column, while
others live in or near to the sediment or attached to
surfaces for some or all of their life cycle. Macroalgae
can be multicellular and complex, the largest of which
are the seaweeds.
Algal blooms are an important and natural component
of the production of all aquatic systems, but especially
those of temperate, subpolar, and coastal waters.
Spring blooms are triggered by seasonal warming,
increased light availability, water column stratification,
and increased nutrient availability from riverine runoff or
other sources. These blooms are important for
energy and material transport through the food web, and
they also play an important role in the vertical flux of
material out of the surface waters. These blooms are
distinguished from those that are deemed “harmful.”
Algae form harmful algal blooms, or HABs, when either
they accumulate in massive amounts that alone cause
harm to the ecosystem or the composition of the algal
community shifts to species that make compounds
(including toxins) that disrupt the normal food web or to
species that can harm human consumers (Glibert and
Pitcher, 2001). HABs are a broad and pervasive problem,
affecting estuaries, coasts, and freshwaters throughout the
world, with effects on ecosystems and human health, and
on economies, when these events occur. This entry
focuses on those algal blooms that are HABs. After an
introduction to types of HABs and their effects, an emphasis is placed on the ecology and dynamics of the planktonic HABs, their global expansion, and approaches to
their prediction and control.
Types of HABs (representative species groups
and their effects)
Terminology
The term HAB is an operational one, not a technical one
due the diversity of HAB types and effects. Due to
the complexity of toxic or ecosystem effects, with the
exception of a few species, there are no formal definitions
of the concentrations of cells that determine a “bloom.”
Many HAB events were formerly referred to as “red tides”
because of their pigmentation, but this terminology has
been supplanted because not all HABs are red; some
may be green, yellow, or brown depending on their specific pigmentation.
While colors are used less frequently to distinguish
different types of HABs, toxic properties are gaining favor
as a way of distinguishing different types of HABs. By
definition, all HABs cause harm, either to ecological, economic, or human health. Toxic HABs are those that
involve toxins or harmful metabolites, such as toxins
linked to wildlife death or human seafood poisonings, as
described in more detail below. Of the tens of thousands
of algal species, only a few percent have been documented
to be toxic, although new toxins are being identified
regularly (Landsberg, 2002). Some algal toxins are
extremely potent, and thus toxic HABs can occur at cell
densities that would not normally be taken to be in
“bloom” proportion; they can, for example, sometimes
cause poisonings at concentrations as low as a few
hundred cells per liter.
Nuisance algal blooms, or NABs, do not produce toxins
(or such toxins have not yet been identified), but are able
to cause harm through the development of high biomass,
leading to foams or scums, the depletion of oxygen as
blooms decay, or the destruction of habitat for fish or
shellfish such as by shading of submersed vegetation.
Another distinction that some investigators have found
useful is the group of HAB species that are not necessarily
ALGAL BLOOMS
7
JSTARS.2013.2265255.
Pack, R. T., Brooks, V., Young, J., Vilaca, N., Vatslid, S., Rindle, P.,
Kurz, S., Parrish, C. E., Craig, R., and Smith, P. W., 2012. An
overview of ALS technology. In Renslow, M. S. (ed.), Manual
of Airborne Topographic Lidar. Bethesda: ASPRS Press.
Sithole, G., and Vosselman, G., 2004. Experimental comparison of
filter algorithms for bare-Earth extraction from airborne laser
scanning point clouds. ISPRS Journal of Photogrammetry and
Remote Sensing, 59, 85–101.
Shan, J., and Toth, C., 2009. Topographic Laser Ranging and
Scanning: Principles and Processes. Boca Raton: CRC Press.
Slatton, K. C., Carter, W. E., Shrestha, R. L., and Dietrich, W., 2007.
Airborne laser swath mapping: achieving the resolution and
accuracy required for geosurficial research. Geophysical
Research Letters, 34, 1–5.
Wehr, A., and Lohr, U., 1999. Airborne laser scanning—an introduction and overview. Journal of Photogrammetry and Remote
Sensing, 54, 68–82.
Cross-references
Light Detection and Ranging (LIDAR)
ALGAL BLOOMS
Patricia M. Glibert
Horn Point Laboratory, University of Maryland Center for
Environmental Science, Cambridge, MD, USA
Synonyms
Harmful algal blooms; Nuisance algal blooms; Phytoplankton blooms; Red tides; Spring blooms
Definition
Algal blooms refer to the increase in biomass of algae due
to increased growth or due to physical aggregation,
leading to an above-normal accumulation and generally
adverse ecosystem effects.
Introduction
Algae are a normal part of the aquatic ecosystem; they
form the base of the aquatic food web. Of this large and
diverse group of organisms, most are microscopic in size,
but some are macroscopic. The microscopic algae are
most often single cells, but some can form chains or colonies. Most microalgae live in the water column, while
others live in or near to the sediment or attached to
surfaces for some or all of their life cycle. Macroalgae
can be multicellular and complex, the largest of which
are the seaweeds.
Algal blooms are an important and natural component
of the production of all aquatic systems, but especially
those of temperate, subpolar, and coastal waters.
Spring blooms are triggered by seasonal warming,
increased light availability, water column stratification,
and increased nutrient availability from riverine runoff or
other sources. These blooms are important for
energy and material transport through the food web, and
they also play an important role in the vertical flux of
material out of the surface waters. These blooms are
distinguished from those that are deemed “harmful.”
Algae form harmful algal blooms, or HABs, when either
they accumulate in massive amounts that alone cause
harm to the ecosystem or the composition of the algal
community shifts to species that make compounds
(including toxins) that disrupt the normal food web or to
species that can harm human consumers (Glibert and
Pitcher, 2001). HABs are a broad and pervasive problem,
affecting estuaries, coasts, and freshwaters throughout the
world, with effects on ecosystems and human health, and
on economies, when these events occur. This entry
focuses on those algal blooms that are HABs. After an
introduction to types of HABs and their effects, an emphasis is placed on the ecology and dynamics of the planktonic HABs, their global expansion, and approaches to
their prediction and control.
Types of HABs (representative species groups
and their effects)
Terminology
The term HAB is an operational one, not a technical one
due the diversity of HAB types and effects. Due to
the complexity of toxic or ecosystem effects, with the
exception of a few species, there are no formal definitions
of the concentrations of cells that determine a “bloom.”
Many HAB events were formerly referred to as “red tides”
because of their pigmentation, but this terminology has
been supplanted because not all HABs are red; some
may be green, yellow, or brown depending on their specific pigmentation.
While colors are used less frequently to distinguish
different types of HABs, toxic properties are gaining favor
as a way of distinguishing different types of HABs. By
definition, all HABs cause harm, either to ecological, economic, or human health. Toxic HABs are those that
involve toxins or harmful metabolites, such as toxins
linked to wildlife death or human seafood poisonings, as
described in more detail below. Of the tens of thousands
of algal species, only a few percent have been documented
to be toxic, although new toxins are being identified
regularly (Landsberg, 2002). Some algal toxins are
extremely potent, and thus toxic HABs can occur at cell
densities that would not normally be taken to be in
“bloom” proportion; they can, for example, sometimes
cause poisonings at concentrations as low as a few
hundred cells per liter.
Nuisance algal blooms, or NABs, do not produce toxins
(or such toxins have not yet been identified), but are able
to cause harm through the development of high biomass,
leading to foams or scums, the depletion of oxygen as
blooms decay, or the destruction of habitat for fish or
shellfish such as by shading of submersed vegetation.
Another distinction that some investigators have found
useful is the group of HAB species that are not necessarily
ALGAL BLOOMS
7