Browsing by Author "Katharoyan, Chaitanya"

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    Caught in transition: changes in brachyuran diversity following mangrove encroachment into saltmarshes at a southern distribution limit
    (Frontiers Media SA, 2024) Katharoyan, Chaitanya; Rajkaran, Anusha; Peer, Nasreen
    Mangroves are expanding polewards due to global change, often encroaching into adjacent temperate saltmarshes. In both vegetated ecosystems, brachyurans are responsible for ecological processes and functions such as nutrient cycling and sediment bioturbation. South African mangroves occur at a latitudinal limit and are establishing further south due to past planting events and global change, making these ideal study systems for the effects of mangrove expansion and encroachment. Here, we investigated the effect of mangrove encroachment on brachyuran community composition at two saltmarsh sites with planted mangrove stands of different ages. Transects were laid perpendicular to each estuary where three habitat types were demarcated (mangrove, ecotone, saltmarsh). Sediment samples were collected for analyses and quadrats were used to measure pneumatophore density, saltmarsh cover, and brachyuran abundance and diversity. We found that brachyuran community structure at each site has significantly changed over seven years, with two mangrove-associated fiddler crab species, Tubuca urvillei and Paraleptuca chlorophthalmus, now recorded at the younger planted site, indicating a new southern distributional limit.
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    Kelp holdfasts in the Great African Seaforest provide habitat for diverse assemblages of macroinvertebrates
    (Inter-Research, 2024) Samaai, Toufiek; Katharoyan, Chaitanya; Peer, Nasreen
    Kelp forests along the southwestern and west coasts of South Africa, dominated by the species Ecklonia maxima and Laminaria pallida, are locally termed ‘the Great African Seaforest’. They form 3-dimensional biogenic habitats that provide 4 distinct microhabitats—canopy, fronds, stipe and holdfast—with the latter typically supporting the highest abundance and diversity of associated macroinvertebrates. The macrofauna inhabiting kelp holdfasts in South Africa have rarely been studied, resulting in a near complete lack of baseline data. In this study, macrobenthic assemblages from 40 E. maxima holdfasts were examined over 2 marine ecoregions and 4 locations. Macroinvertebrates were identified and counted for univariate and multivariate analyses using family-level data. A total of 120 families from 9 phyla were identified and were generally dominated by Arthropoda (48 families), Annelida (24 families) and Mollusca (23 families). Marine ecoregion had no significant effect on composition of macroinvertebrate assemblages, whereas location had a significant effect. There was no significant relationship between holdfast volume and macroinvertebrate diversity or abundance, suggesting that other environmental and physicochemical factors are important in determining community structure. This study serves as a baseline for future research aimed at understudied holdfast macroinvertebrate communities in the Great African Seaforest.
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    Temporal shifts in key mangrove crab species linked to biotic and abiotic factors at a latitudinal range limit
    (Academic Press, 2025) Rajkaran, Anusha; Katharoyan, Chaitanya; Peer, Nasreen
    Mangroves in South Africa occur at a southern latitudinal limit (33°12′51″ S, 27°34′54″ E) where distribution is influenced by global climate change. Mangroves are experiencing poleward expansion, affecting the distribution of associated macrofauna. Monitoring surveys have been conducted for South African mangrove macrofauna, with research focusing on drivers of ocypodid crabs rather than grapsoid crabs, despite the key role of grapsoids in this ecosystem. Using uni- and multivariate models, we investigated (i) changes in brachyuran community over time (2016 vs 2023), (ii) the potential biotic (food availability, brachyuran diversity and abundance) and abiotic (sediment, water and geographic parameters) factors influencing occurrence and abundance of three co-occurring mangrove crabs (Austruca occidentalis, Neosarmatium africanum and Cristarma eulimene) along the east coast of South Africa, and (iii) the potential distribution of these three species under climate change scenarios. Brachyuran community structure changed significantly over time (2016–2023) at all mangrove sites sampled (df = 1, pseudo-f = 13.95, p < 0.05). Overall, the presence and abundance of all three species were influenced by total brachyuran abundance and diversity, with latitude also influencing the occurrence of these crabs. Specifically, A. occidentalis occurrence was correlated with sediment organic matter and importance values of mangrove tree species to forest structure, while temperature, salinity and sediment moisture influenced their abundance. The presence and abundance of both sesarmids were driven by microphytobenthos and salinity, while temperature influenced abundance. Both climate change scenarios (SSP245 and SSP585) projected future shifts in distribution of all three crab species, with warmer temperatures and increased rainfall patterns expanding habitat suitability of sesarmids in a poleward direction while contracting fiddler crab ranges. This study highlights the ongoing and future impacts of climate change in South African mangroves and their associated macrofauna, suggesting a projected poleward expansion in response to climate change. Additionally, this study highlights future distributional shifts of mangrove associated crabs that can likely alter coastal ecosystem dynamics.