Global gradients in intertidal species richness and functional groups

Abstract

Whether global latitudinal diversity gradients exist in rocky intertidal α-diversity and across functional groups remains unknown. Using literature data from 433 intertidal sites, we investigated α-diversity patterns across 155° of latitude, and whether local-scale or global-scale structuring processes control α-diversity. We, furthermore, investigated how the relative composition of functional groups (algae, grazers, predators and suspension-feeders) changes with latitude. α-diversity differed among hemispheres with a mid-latitudinal peak in the north, and a non-significant unimodal pattern in the south, but there was no support for a latitudinal diversity gradient. Although global-scale drivers had no discernible effect, the local-scale drivers significantly affected α-diversity, and our results reveal that latitudinal diversity gradients are outweighed by local-processes. In three functional groups: predators, grazers and suspension-feeders diversity declined with latitude, coinciding with an inverse gradient in algae. Overall, we propose more studies are needed on the magnitude and influence of physical and biotic drivers across multiple scales.

Marine latitudinal diversity gradients are generally absent in intertidal ecosystems

“…Intertidal systems have unfortunately remained largely overlooked despite the fact that they represent ecosystems with unique stress gradients at a variety of spatial scales compared to other marine habitats. We revisited a previously compiled LDG dataset (Menegotto et al, 2019a), and updated it with intertidal records from datasets, monitoring programs and the scientific literature; the full updated dataset is available online (Thyrring & Harley, 2023). From this, we demonstrate that the intertidal zone across hemispheres, oceans, and coastlines, generally does not conform to the latitudinal decrease in species richness from the equator to the poles.…”

“…We then searched the published literature using Scopus, Google Scholar and Web of Science to update the dataset with intertidal LDG studies not included in the original dataset. Our updated dataset including all references used is freely available at the Zenodo Repository (Thyrring & Harley, 2023), and a summary of the metadata is available in the supplemental materials (Appendix S1: Table S1). Additional data were also extracted from the Multi‐Agency Rocky Intertidal Network (Marine.ucsc.edu., 2019), and intertidal datasets collected by the South American Research Group on Coastal Ecosystems (SARCE) were downloaded from the Ocean Biogeographic Information System website (http://www.obis.org; http://ipt.iobis.org/caribbeanobis/resource?r=sarce_rockyshores).…”

“…This research has utilized the following two data sets published at the Zenodo repository at https://doi.org/10.5281/zenodo.3245484 (Menegotto et al, 2019a) and https://doi.org/10.5281/zenodo.8026395 (Thyrring & Harley, 2023). Intertidal latitudinal diversity gradient studies were found using Scopus (http://www.scopus.com) by searching for “intertidal latitudinal diversity gradient,” “intertidal LDG,” “intertidal biodiversity,” “latitudinal diversity gradient,” and “intertidal richness.” We also used Google Scholar (https://scholar.google.com), with searches for “intertidal latitudinal diversity gradient,” “intertidal LDG,” “intertidal biodiversity,” “latitudinal diversity gradient,” and “intertidal richness,” and Web of Science (https://www.webofscience.com) with searches for “intertidal latitudinal diversity gradient,” “intertidal LDG,” “intertidal biodiversity,” “latitudinal diversity gradient,” and “intertidal richness.” Furthermore, intertidal biodiversity data from South America was downloaded from the Ocean Biogeographic Information System (OBIS) by searching for “sarce_rockyshores” (http://ipt.iobis.org/caribbeanobis/resource?r=sarce_rockyshores).…”

“…Intertidal data from Southeast Alaska to Mexico was downloaded from the Multi‐Agency Rocky Intertidal Network website (Marine.ucsc.edu., 2019), by requesting access to the Long‐Term Monitoring Surveys dataset (https://marine.ucsc.edu/explore-the-data/contact/index.html). The complete list of literature used for our final analysis is available in the Thyrring and Harley (2023) Zenodo release.…”