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VARIABLE DESCRIPTIONS
The selection of variables (as shown in the tables) to represent the ecological settings in which coastlines occur was a subjective exercise supported by expert elicitation. The decision to include variables representing the land-side, the water-side, and the coastline itself follows earlier integrative classification work7,20 and acknowledges that coastal variation is multidimensional, with strong geomorphological and oceanographic drivers. This section describes each of the variables, their source data and how their values were attributed to the segments (segment midpoints):
Ocean variables
1. Marine physical environment—an integrated measure of sea surface temperature, oxygen, and salinity.
Temperature, primary productivity, and oxygen level vary spatially throughout the ocean and are recognized as key drivers of
marine ecology.25,26,27 Organisms have
varying tolerances to salinity levels,
and changing salinity is therefore another important driver of marine species distributions,28 but salini- ty in the open ocean has long been recognized as relatively uniform and stable.29 In the coastal zone, however, salinity levels are more variable due to the influences of tidal action, fluvial discharge, and evaporation; salinity is therefore recognized as a key driver of coastal zone ecology.28
raster format. We averaged the long-term (1997–2019) monthly mean chlorophyll values to identify a long-term annual average. The derived long-term annual average will likely have smoothed seasonally high and low values of chlorophyll, precluding straightfor- ward classification into CMECS trophic productivity levels (oligotrophic, mesotrophic, and eutrophic). We therefore simply identified three chlorophyll classes (low, moderate, and high) according to natural breaks32 in the chlorophyll data and did not assign a CMECS trophic productivity class label. The chlorophyll value attributed to each seg- ment was the value from the raster cell whose center was closest to the segment mid- point. The three chlorophyll classes are presented in Table 2.
3. Tidal range
In 2017, our team developed a com-
prehensive set of 3D global ecolog-
ical marine units (EMUs)21 from an
analysis of NOAA World Ocean At-
las data on the marine physical and
chemical environment. Data on the
sea surface physical environment from
the set of EMUs distributed along the
coastlines were used to attribute the
coastal segments. For every coastline
segment, an integrated measure of
temperature, salinity, and dissolved oxygen was obtained from the closest EMU point to the segment midpoint. The integrated measure is a categorical variable that expresses the combination of the three inputs: salinity, oxygen, and temperature. There were 23 classes of the integrated measurement, as presented in Table 1.
2. Chlorophyll a concentration
Primary production is another key driver of marine ecology, and chlorophyll concen- tration as a measure of plankton abundance,
the base of the ocean food web, is used as
a proxy variable for representing primary
production.27,30 The data on chlorophyll a
concentration were obtained from the Euro-
pean Space Agency Ocean Colour Climate
Change Initiative (linked at GISforScience.
com). This dataset contains merged chlorophyll measurements from 1997 to 2020 pro- vided from SeaWiFS, MODIS, MERIS, and VIIRS sensors.31 The chlorophyll variable is continuous and was used as such in our analyses. The chlorophyll data are in a 4-km
Tidal activity is an important hydrodynamic
driver of coastal zone ecology, mediating sa-
linity levels,33 nutrient availability,34 tempera-
ture,35 root zone aeration,36 carbon flux,37
species distributions,38 and other environ-
mental features of importance to organisms.
The tidal range, the difference between low
and high tide, establishes the vertical limits
within which waves and tidal currents inter-
act. Tides create a gradient of environmental
conditions wherein species have adapted to
various tidal regimes (e.g. see the paper on
pulsing ecosystems39 written by William Odum, his father Eugene Odum, and Eugene’s brother Harold Odum. The two Odum brothers were seminal in establishing ecosystem ecology as a discipline and wrote the pioneering textbook Fundamentals of Ecology.40) Of course, tidal variation is also an extremely important and regular environmental phe- nomenon impacting human livelihoods and behavior. As Davis and Fitzgerald8 noted, “the rise and fall of the tides is one of the major rhythms of planet Earth.”
Tidal range data were obtained from the French Space Agency (CNES) through the AVISO+ data dissemination program (website linked at GISforScience.com). The dataset used is the FES2014 finite elements solution. The data are derived from a compendium of global satellite altimetry measurements and are available in a 1/16th° (~6 km) raster grid. The tidal range data are continuous data and were used as such in the analysis. For subsequent classification grouping and labeling purposes, our team used six CMECS classes to describe tidal ranges (Table 3). Each coastline segment midpoint was attribut- ed with a tidal range value from the raster cell whose center was closest to the segment midpoint.
4. Wave height
In the coastal zone, wave energy is a key determinant of marine physical environmental structure through its influence on erosional and
depositional processes.17 Similarly, wave height
and exposure influence the composition and
Tidal Range Category
Tidal Range (m)
Atidal
Less than 0.1
Microtidal
0.1–0.3
Minimally Tidal
0.3–1.0
Moderately Tidal
1.0–4.0
Macrotidal
4.0–8.0
Megatidal
More than 8.0
Salinity Dissolved Oxygen Temperature Class Class Class
Euhaline Highly Oxic Superchilled
Euhaline Oxic Warm to Very Warm
Euhaline Oxic Moderate
Euhaline Oxic Moderate to Cool
Euhaline Oxic Cold
Euhaline Oxic Very Cold
Euhaline Oxic Superchilled
Euhaline Hypoxic Moderate to Cool
Euhaline Severely Hypoxic Cold
Euhaline Severely Hypoxic Very Cold
Polyhaline Highly Oxic Superchilled
Polyhaline Oxic Cold
Polyhaline Oxic Very Cold
Polyhaline Severely Hypoxic Cold
Polyhaline Severely Hypoxic Very Cold
Polyhaline Anoxic Cold
Polyhaline Anoxic Very Cold
Mesohaline Highly Oxic Very Cold
Mesohaline Oxic Moderate to Cool
Mesohaline Oxic Cold
Mesohaline Oxic Very Cold
Mesohaline Hypoxic Cold
Mesohaline Severely Hypoxic Very Cold
Table 3
Table 1
Wave Height Category
Wave Height Range (m)
Quiescent
Less than 0.1
Very Low Wave Energy
0.1–0.25
Low Wave Energy
0.25–1.0
Moderate Wave Energy
1.0–2.0
Moderately High Wave Energy
2.0–4.0
High Wave Energy
4.0–8.0
Very High Wave Energy
More than 8.0
Chlorophyll Level
Concentration (μg/l)
Low
Less than 2.0
Moderate
2.0–5.0
High
More than 5.0
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GIS for Science
Table 2
distribution of biological assemblages.41 Mean significant wave height data were obtained from the NOAA WaveWatch III® 30-year Hindcast Phase 2 resource. The data are available as a 30-minute (~55 km) global grid. The wave height data are continuous data and were used as such in the analysis. For the subsequent classification grouping and labeling purposes, the team used seven CMECS classes to describe wave height ranges (Table 4). Each coastline segment midpoint was attributed with a wave height value from the raster cell whose center was closest to the segment midpoint.
Table 4