Table_1_Global Patterns of Species Richness in Coastal Cephalopods.DOCX

Within the context of global climate change and overfishing of fish stocks, there is some evidence that cephalopod populations are benefiting from this changing setting. These invertebrates show enhanced phenotypic flexibility and are found from polar regions to the tropics. Yet, the global patterns of species richness in coastal cephalopods are not known. Here, among the 370 identified-species, 164 are octopuses, 96 are cuttlefishes, 54 are bobtails and bottletails, 48 are inshore squids and 8 are pygmy squids. The most diverse ocean is the Pacific (with 213 cephalopod species), followed by the Indian (146 species) and Atlantic (95 species). The least diverse are the Southern (15 species) and the Arctic (12 species) Oceans. Endemism is higher in the Southern Ocean (87%) and lower in the Arctic (25%), which reflects the younger age and the “Atlantification” of the latter. The former is associated with an old lineage of octopuses that diverged around 33 Mya. Within the 232 ecoregions considered, the highest values of octopus and cuttlefish richness are observed in the Central Kuroshio Current ecoregion (with a total of 64 species), followed by the East China Sea (59 species). This pattern suggests dispersal in the Central Indo-Pacific (CIP) associated with the highly productive Oyashio/Kuroshio current system. In contrast, inshore squid hotspots are found within the CIP, namely in the Sunda Shelf Province, which may be linked to the occurrence of an ancient intermittent biogeographic barrier: a land bridge formed during the Pleistocene which severely restricted water flow between the Pacific and Indian Oceans, thereby facilitating squid fauna differentiation. Another marked pattern is a longitudinal richness cline from the Central (CIP) toward the Eastern Indo-Pacific (EIP) realm, with central Pacific archipelagos as evolutionary dead ends. In the Atlantic Ocean, closure of the Atrato Seaway (at the Isthmus of Panama) and Straits of Gibraltar (Mediterranean Sea) are historical processes that may explain the contemporary Caribbean octopus richness and Mediterranean sepiolid endemism, respectively. Last, we discuss how the life cycles and strategies of cephalopods may allow them to adapt quickly to future climate change and extend the borealization of their distribution.

在全球气候变化与鱼类种群过度捕捞的背景下，已有证据表明头足类（cephalopod）种群正从这一环境变化中获益。这类无脊椎动物展现出更强的表型可塑性，其分布范围覆盖从极地到热带的所有海域。然而，近岸头足类的全球物种丰富度（species richness）格局至今仍未明确。本研究共确认370个物种，其中164种为章鱼（octopus）、96种为乌贼（cuttlefish）、54种为耳乌贼与瓶乌贼、48种为近岸枪乌贼，另有8种为矮枪乌贼。物种丰富度最高的大洋为太平洋（共计213种头足类），其次为印度洋（146种）与大西洋（95种）；物种丰富度最低的则为南大洋（15种）与北冰洋（12种）。南大洋的特有性（endemism）比例高达87%，北冰洋仅为25%，这一差异反映出北冰洋形成年代较晚且经历了“大西洋化”过程。南大洋的特有分布格局与约3300万年前分化的古老章鱼支系密切相关。在本次研究涵盖的232个生态区（ecoregion）中，章鱼与乌贼的物种丰富度峰值出现在黑潮主流域生态区（共计64种），其次为东海海域（59种）。该格局暗示，头足类的扩散路径集中于中印度-太平洋（Central Indo-Pacific, CIP）域，且与生产力极高的亲潮/黑潮洋流系统密切相关。与之形成鲜明对比的是，近岸枪乌贼的物种热点同样位于CIP域，具体为巽他陆架海域，这一现象或与一处古老的间歇性生物地理屏障有关：更新世时期形成的陆桥曾严重阻隔太平洋与印度洋间的海水交换，进而推动枪乌贼类群的区系分化。另一显著的分布格局为，物种丰富度从中印度-太平洋域向东印度-太平洋（Eastern Indo-Pacific, EIP）域呈现经度梯度递减的趋势，中太平洋群岛则属于进化死胡同（evolutionary dead ends）。在大西洋海域，巴拿马地峡（Isthmus of Panama）处阿特拉托海道（Atrato Seaway）的闭锁，以及直布罗陀海峡（Straits of Gibraltar，地中海区域）的历史封闭过程，分别解释了当前加勒比海章鱼物种丰富度与地中海耳乌贼特有性的形成机制。文末我们还探讨了头足类的生活史与生存策略如何使其能够快速适应未来气候变化，并拓展其分布的北界范围。