Spatial scaling properties of coral reef benthic communities

The spatial structure of ecological communities on tropical coral reefs
across seascapes and geographies have historically been poorly understood.
Here we addressed this for the first time using spatially expansive and
thematically resolved benthic community data collected around five
uninhabited central Pacific oceanic islands, spanning 6° latitude and 17°
longitude. Using towed-diver digital image surveys over ~140 linear km of
shallow (8 – 20 m depth) tropical reef, we highlight the autocorrelated
nature of coral reef seascapes. Benthic functional groups and hard coral
morphologies displayed significant spatial clustering (positive
autocorrelation) up to kilometre-scales around all islands, in some
instances dominating entire sections of coastline. The scale and strength
of these autocorrelation patterns showed differences across geographies,
but patterns were more similar between islands in closer proximity and of
a similar size. For example, crustose coralline algae (CCA) were clustered
up to scales of 0.3 km at neighbouring Howland and Baker Islands and
macroalgae were spatially clustered at scales up to ~3 km at both
neighbouring Kingman Reef and Palmyra Atoll. Of all the functional groups,
macroalgae had the highest levels of spatial clustering across geographies
at the finest resolution of our data (100 m). There were several cases
where the upper scale at which benthic community members showed evidence
of spatial clustering correlated highly with the upper scales at which
concurrent gradients in physical environmental drivers were spatially
clustered. These correlations were stronger for surface wave energy than
subsurface temperature (regardless of benthic group) and turf algae and
CCA had the closest alignments in scale with wave energy across functional
groups and geographies. Our findings suggest such physical drivers not
only limit or promote the abundance of various benthic competitors on
coral reefs, but also play a key role in governing their spatial scaling
properties across seascapes.