Compromised Refugia: Latitudinal Gradients Mimic Depth and Constrain Subtropical Reef Habitats in the Nilotic Basin
- 1Kadas Nexus, Leon H. Charney School of Marine Sciences University of Haifa Haifa Israel
- 2Faculty of Marine Sciences Ruppin Academic Center Michmoret Israel
- 3Department of Evolutionary and Environmental Biology University of Haifa Haifa Israel
Abstract
Upper‐mesophotic rocky reefs (25–30 m depth) have been proposed as climate refugia in the ultra‐oligotrophic Eastern Mediterranean for fish communities in warming shallow waters. A pronounced environmental gradient runs from north to south along the southeastern Levant, driven by sediment and nutrient discharge downstream of the receding Nile Delta. We hypothesized that higher surface productivity near the Nile Delta would support an algae‐dominated epibenthic food web and richer fish assemblages at the southern sites. We surveyed epibenthic cover, habitat structure, and fish assemblages at five sites spanning ~160 km of coastline within a shared 25–30 m depth band between 2017 and 2022. Contrary to this hypothesis, our findings reveal a distinct coastal ecocline, a benthic shift from algae‐ to bryozoan‐dominated epibenthos that closely mirrored the depth‐related shift observed at the northern sites (between 10 m and 45 m). This benthic shift was coupled with reduced abundance of herbivorous and micro‐invertivorous fish and with significantly lower fish species richness and diversity at the southern sites, despite their higher structural complexity. Redundancy analysis showed that depth, latitude, visibility, and season together explained 55.5% of the variance in epibenthic community composition, while an analogous spatial model explained 20% of the variance in fish abundance. This benthic shift, associated with gradients in depth, latitude, sedimentation, and light attenuation, appears to be a major architect of fish community structure in this region, rather than structural complexity. This implies that the southern Levant may act not as a corridor but as a restrictive filter, trapping species between warming surface waters and a deep‐sea‐like habitat that lacks the conditions required to support higher trophic levels; the capacity of upper‐mesophotic reefs to serve as thermal refugia is not uniform across space.
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BibTeX
@article{tsemel2026compromised,
title = {{Compromised Refugia: Latitudinal Gradients Mimic Depth and Constrain Subtropical Reef Habitats in the Nilotic Basin}},
author = {Anat Tsemel and Hagai Nativ and Stephane Martinez and Shai Einbinder and Ole Johannes Ringnander Sørensen and Yair Suari and Ido Izhaki and Dan Tchernov},
journal = {Ecology and evolution},
year = {2026},
month = oct,
doi = {10.1002/ece3.74367},
url = {https://europepmc.org/article/PMC/PMC13654655},
note = {CC BY},
}
RIS
TY - JOUR
TI - Compromised Refugia: Latitudinal Gradients Mimic Depth and Constrain Subtropical Reef Habitats in the Nilotic Basin
AU - Anat Tsemel
AU - Hagai Nativ
AU - Stephane Martinez
AU - Shai Einbinder
AU - Ole Johannes Ringnander Sørensen
AU - Yair Suari
AU - Ido Izhaki
AU - Dan Tchernov
PY - 2026
DA - 2026/10/01
JO - Ecology and evolution
DO - 10.1002/ece3.74367
UR - https://europepmc.org/article/PMC/PMC13654655
AB - Upper‐mesophotic rocky reefs (25–30 m depth) have been proposed as climate refugia in the ultra‐oligotrophic Eastern Mediterranean for fish communities in warming shallow waters. A pronounced environmental gradient runs from north to south along the southeastern Levant, driven by sediment and nutrient discharge downstream of the receding Nile Delta. We hypothesized that higher surface productivity near the Nile Delta would support an algae‐dominated epibenthic food web and richer fish assemblages at the southern sites. We surveyed epibenthic cover, habitat structure, and fish assemblages at five sites spanning ~160 km of coastline within a shared 25–30 m depth band between 2017 and 2022. Contrary to this hypothesis, our findings reveal a distinct coastal ecocline, a benthic shift from algae‐ to bryozoan‐dominated epibenthos that closely mirrored the depth‐related shift observed at the northern sites (between 10 m and 45 m). This benthic shift was coupled with reduced abundance of herbivorous and micro‐invertivorous fish and with significantly lower fish species richness and diversity at the southern sites, despite their higher structural complexity. Redundancy analysis showed that depth, latitude, visibility, and season together explained 55.5% of the variance in epibenthic community composition, while an analogous spatial model explained 20% of the variance in fish abundance. This benthic shift, associated with gradients in depth, latitude, sedimentation, and light attenuation, appears to be a major architect of fish community structure in this region, rather than structural complexity. This implies that the southern Levant may act not as a corridor but as a restrictive filter, trapping species between warming surface waters and a deep‐sea‐like habitat that lacks the conditions required to support higher trophic levels; the capacity of upper‐mesophotic reefs to serve as thermal refugia is not uniform across space.
SN - 2045-7758
ER -