National Centre for Biological Sciences, Rajiv Gandhi Nagar, Kodigehalli, Bengaluru, Karnataka, 560065, India; Nature Conservation Foundation, 1311 Amritha, 12th Cross, Vijayanagar 1st Stage, Mysore, 570017, India.
Nature Conservation Foundation, 1311 Amritha, 12th Cross, Vijayanagar 1st Stage, Mysore, 570017, India; Centre D'Estudis Avançats de Blanes (CEAB, CSIC), Carrer D'Accés a La Cala Sant Francesc 14, 17300, Blanes, Spain.
Mar Environ Res. 2023 Oct;191:106146. doi: 10.1016/j.marenvres.2023.106146. Epub 2023 Aug 19.
Multi-specific seagrass meadow assemblages dominate most tropical intertidal regions but the relative role of environmental stress in determining distribution patterns is still uncertain. Here we combine observational and experimental approaches to examine aerial exposure as a factor driving species occurrence patterns in intertidal meadows of the Andaman archipelago, where up to 6 seagrass species co-occur. In the studied meadow, patterns of exposure did not map onto distance from the coast, instead creating a patchy matrix of exposure, based on fine-scale bathymetric differences. Distributional surveys showed that seagrass species were similarly patchy, often tracking the degree of aerial exposure during low tide. While some species (Halophila ovalis, Halophila minor, and Thalassia hemprichii) frequently occurred in submerged or subtidal areas and were rarely found in completely exposed areas, other species (Cymodocea rotundata, Halophila beccarii, and Halodule uninervis) also occupied areas that were subject to partial or complete aerial exposure during low tide. To confirm this pattern, we used field-based transplant experiments, employing a natural gradient of tidal exposure to subject six seagrass species to different desiccation exposure times. After a month, H. beccarii and H. uninervis transplants survived in areas that sustained more than 3 h of aerial tidal exposure without significant mortality, compared with other species (H. ovalis, H. minor, T. hemprichii, C. rotundata) that showed dramatic shoot mortality at the same exposure regimes. For all species, 4 h represented the upper limit of exposure, in both experimental and distributional studies. However, despite their wider tolerance of exposure to air, H. beccarii and H. uninervis did not dominate the entire meadow. This could be a result either of their poor tolerance to other environmental factors or their lower competitive abilities among other mechanisms. This suggests that in tropical multi-specific meadows, strong environmental filters could override clear intertidal zonation to create patchy matrices based on species tolerances.
多特异性海草草地组合在大多数热带潮间带地区占主导地位，但环境压力在确定分布模式方面的相对作用仍不确定。在这里，我们结合观察和实验方法，研究安达曼群岛潮间带海草草地中空气暴露作为驱动物种出现模式的因素，在该地区多达 6 种海草共存。在所研究的草地中，暴露模式与离海岸的距离无关，而是根据精细的水深差异，形成了一个暴露的斑块基质。分布调查表明，海草物种同样是斑片状的，通常在低潮时跟踪空气暴露的程度。虽然有些物种（Halophila ovalis、Halophila minor 和 Thalassia hemprichii）经常出现在淹没或亚潮带区域，很少出现在完全暴露的区域，而其他物种（Cymodocea rotundata、Halophila beccarii 和 Halodule uninervis）也占据了在低潮时部分或完全暴露于空气的区域。为了证实这一模式，我们使用了基于现场的移植实验，利用潮汐暴露的自然梯度，使六种海草物种经受不同的干燥暴露时间。一个月后，H. beccarii 和 H. uninervis 移植体在超过 3 小时的空气潮汐暴露下没有显著死亡率，而其他物种（H. ovalis、H. minor、T. hemprichii、C. rotundata）在相同的暴露条件下显示出明显的茎死亡率。对于所有物种，4 小时是暴露的上限，无论是在实验还是分布研究中。然而，尽管它们对空气暴露的耐受性更强，但 H. beccarii 和 H. uninervis 并没有主导整个草地。这可能是由于它们对其他环境因素的耐受性较差，或者是由于其他机制导致它们在其他物种中的竞争力较低。这表明，在热带多特异性草地中，强烈的环境过滤器可能会覆盖明显的潮间带分带，形成基于物种耐受性的斑块基质。
