Number of grid cells (and percentage of total) designated as benthic fish biodiversity hotspots (temporal consistency ranging from 0 years hot to 8 years hot) for Coast-wide and the North biogeographic regions and for the minimum, mean, and maximum universal thresholds and annual threshold calculated for 2003–2010.

<p>Number of grid cells (and percentage of total) designated as benthic fish biodiversity hotspots (temporal consistency ranging from 0 years hot to 8 years hot) for Coast-wide and the North biogeographic regions and for the minimum, mean, and maximum universal thresholds and annual threshold calculated for 2003–2010.</p

Evaluating Temporal Consistency in Marine Biodiversity Hotspots

<div><p>With the ongoing crisis of biodiversity loss and limited resources for conservation, the concept of biodiversity hotspots has been useful in determining conservation priority areas. However, there has been limited research into how temporal variability in biodiversity may influence conservation area prioritization. To address this information gap, we present an approach to evaluate the temporal consistency of biodiversity hotspots in large marine ecosystems. Using a large scale, public monitoring dataset collected over an eight year period off the US Pacific Coast, we developed a methodological approach for avoiding biases associated with hotspot delineation. We aggregated benthic fish species data from research trawls and calculated mean hotspot thresholds for fish species richness and Shannon’s diversity indices over the eight year dataset. We used a spatial frequency distribution method to assign hotspot designations to the grid cells annually. We found no areas containing consistently high biodiversity through the entire study period based on the mean thresholds, and no grid cell was designated as a hotspot for greater than 50% of the time-series. To test if our approach was sensitive to sampling effort and the geographic extent of the survey, we followed a similar routine for the northern region of the survey area. Our finding of low consistency in benthic fish biodiversity hotspots over time was upheld, regardless of biodiversity metric used, whether thresholds were calculated per year or across all years, or the spatial extent for which we calculated thresholds and identified hotspots. Our results suggest that static measures of benthic fish biodiversity off the US West Coast are insufficient for identification of hotspots and that long-term data are required to appropriately identify patterns of high temporal variability in biodiversity for these highly mobile taxa. Given that ecological communities are responding to a changing climate and other environmental perturbations, our work highlights the need for scientists and conservation managers to consider both spatial and temporal dynamics when designating biodiversity hotspots.</p></div

North Biogeographic region—location of 1600 km² grid cells with ≥ 3 scientific trawls/year and hotspots for A) benthic fish species richness, and B) benthic fish Shannon diversity, H′.

<p>Each grid cell contains an identification number and shading indicates the number of years (out of 8, 2003–2010) that the cell exceeded the universal threshold value to be classified as a hotspot (31.1 for species richness, 2.37 for Shannon diversity H′).</p

Expanding window approach used to identify cells that contained at least three trawls for each year (2003–2010).

<p>1600 km² (40 x 40 km) cells offered both the highest number of cells that qualified, as well as a high degree of spatial connectivity between the cells.</p

Location of 1600 km² grid cells with ≥ 3 scientific trawls/year and hotspots for A) benthic fish species richness, and B) benthic fish Shannon diversity, H′.

<p>Each grid cell contains an identification number and shading indicates the number of years (out of 8, 2003–2010) that the cell exceeded the universal threshold value to be classified as a hotspot (34.4 for species richness, 2.42 for Shannon diversity H′).</p

Thin-plate spline interpolation of fish species richness (A), fish Shannon diversity (B), fish functional diversity (C), invertebrate species richness (D) and invertebrate Shannon diversity (E) from the West Coast Groundfish Bottom Trawl Survey, 2003–2010 (fish) and 2004–2010 (invertebrates).

<p>Warmer (red) areas indicate regions of higher biodiversity, while cooler (blue) regions indicate lower biodiversity. The maps were drawn using the <i>maps</i> package for R.</p

The effect of latitude on model importance for fish and invertebrate richness (S), Shannon diversity (H′) and Rao’s quadratic entropy (Q).

<p>This was determined using the evidence ratio (ρ), which is calculated by first determining the best model using Akaike’s Information Criterion correction (AICc), and then dividing the AICc weight of the model when the term is in the model (w_i) by the AICc weight of the model when the term is removed (w_j). The greater the ρ, the more important latitude is as a predictor in the model.</p><p>The effect of latitude on model importance for fish and invertebrate richness (S), Shannon diversity (H′) and Rao’s quadratic entropy (Q).</p

Mean fish and invertebrate species richness by degree latitude (A and C) and depth (B and D) for 2003–2010 (fish) and 2004–2010 (invertebrates) from the West Coast Groundfish Bottom Trawl Survey.

<p>Species richness by latitude was calculated by averaging trawl results over 1 degree bins, while richness by depth was calculated by averaging richness values within a 100-meter depth bin. Error bars have been left off for visualization of temporal variability in the averages.</p

Patterns and Variation in Benthic Biodiversity in a Large Marine Ecosystem

<div><p>While there is a persistent inverse relationship between latitude and species diversity across many taxa and ecosystems, deviations from this norm offer an opportunity to understand the conditions that contribute to large-scale diversity patterns. Marine systems, in particular, provide such an opportunity, as marine diversity does not always follow a strict latitudinal gradient, perhaps because several hypothesized drivers of the latitudinal diversity gradient are uncorrelated in marine systems. We used a large scale public monitoring dataset collected over an eight year period to examine benthic marine faunal biodiversity patterns for the continental shelf (55–183 m depth) and slope habitats (184–1280 m depth) off the US West Coast (47°20′N—32°40′N). We specifically asked whether marine biodiversity followed a strict latitudinal gradient, and if these latitudinal patterns varied across depth, in different benthic substrates, and over ecological time scales. Further, we subdivided our study area into three smaller regions to test whether coast-wide patterns of biodiversity held at regional scales, where local oceanographic processes tend to influence community structure and function. Overall, we found complex patterns of biodiversity on both the coast-wide and regional scales that differed by taxonomic group. Importantly, marine biodiversity was not always highest at low latitudes. We found that latitude, depth, substrate, and year were all important descriptors of fish and invertebrate diversity. Invertebrate richness and taxonomic diversity were highest at high latitudes and in deeper waters. Fish richness also increased with latitude, but exhibited a hump-shaped relationship with depth, increasing with depth up to the continental shelf break, ~200 m depth, and then decreasing in deeper waters. We found relationships between fish taxonomic and functional diversity and latitude, depth, substrate, and time at the regional scale, but not at the coast-wide scale, suggesting that coast-wide patterns can obscure important correlates at smaller scales. Our study provides insight into complex diversity patterns of the deep water soft substrate benthic ecosystems off the US West Coast.</p></div

Relationships among depth and latitude and (A) fish species richness, (B) fish Shannon diversity, (C) invertebrate species richness, and (D) invertebrate Shannon diversity.

<p>Data were visualized using a smoothing function to examine the interactive effect of depth and latitude on species diversity. Across latitude, fish diversity generally decreases after about 200 m depth, while invertebrate diversity increases with depth. However for both taxa, abundance-weighted diversity (Shannon’s, B, D) shows greater heterogeneity across latitude and depth.</p