Dr Emily Howells

Increasing trends of coral mortality is a challenge to coral reef management worldwide, and a need exists to identify the causes and pathways involved. Pathology is useful to help decipher potential causes of mortality in animals, because it illuminates agents associated with lesions and gives insights on the nature of how a host responds to said agents. To better understand the nature of threats facing corals in the Arabian Peninsula, we performed gross and microscopic pathology on corals from Saudi Arabia, Qatar, and United Arab Emirates. Among 321 coral fragments examined from 21 genera, tissue loss was the most common lesion seen in 31% of samples, reflecting its widespread presence on reefs from the Arabian Peninsula. Histologically, 68% of lesions exhibited necrosis, predominantly in the basal body wall and surface body wall. Endolithic filamentous microalgae and sponges, originating from the skeleton, were associated with 57% and 39% of lesions respectively, and were often linked to necrosis and hyaline membrane formation. Cell-associated microbial aggregates and coccidia were detected mainly in Acropora, Pocillopora, and Porites but were not associated with adverse host response. Notably, 69-100% of fragments showing lesions were female likely reflecting temporal reproductive life history of corals in the region. Our findings highlight endolithic organisms as major contributors to coral tissue degradation in the Arabian Peninsula.

With constant improvements in the accuracy and availability of open-source digital elevation models (DEMs) comes a need to properly understand the relevance of their derived topographic variables in ecological research, particularly in marine environments. Here, we provide data and scripts used to investigate the ecological relevance of two open-source bathymetric models for deriving topographic variables to perform species distribution modelling of coral across the Great Barrier Reef (GBR), Australia. We illustrate our methods with a case study based on three common Acropora coral species (A. hyacinthus, A. spathulata, A. kenti) across 23 reefs of the GBR, where we produce high performing distribution maps using purely topographic variables derived from three open-access bathymetry models.

A script is provided to first download and process bathymetry DEMs from the Allen Coral Atlas and the DeepReef projects, before performing a multiscale generalisation to acquire these DEMs at 15m, 30m, 60m, 100m, 120m resolutions. From these DEMs, we provide code for deriving 14 topographic variables used in analyses. We provide the csv files containing values of the DEM and topographic variables at random assessment points across the 23 reefs, as well as at the coral colony sample sites. The script contains all analyses, including DEM vertical depth assessment, variable correlations, and MaxEnt species distribution models.