Turra Alexander, Pombo Maíra, Petracco Marcelo, Siegle Eduardo, Fonseca Mariana, Denadai Márcia R
Instituto Oceanográfico, Universidade de São Paulo, São Paulo, São Paulo, Brazil.
Faculdade de Oceanografia, Instituto de Geociências, Pós-Graduação em Ecologia, Universidade Federal do Pará, Belém, Pará, Brazil.
PLoS One. 2016 Jan 8;11(1):e0146323. doi: 10.1371/journal.pone.0146323. eCollection 2016.
Stranding combined with mass-mortality events of sandy-beach organisms is a frequent but little-understood phenomenon, which is generally studied based on discrete episodes. The frequency, magnitude, and possible causes of stranding and mass-mortality events of the trigonal clam Tivela mactroides were assessed based on censuses of stranded individuals, every four days from September 2007 through December 2008, in Caraguatatuba Bay, southeastern Brazil. Stranded clams were classified as dying (closed valves did not open when forced) or dead (closed valves were easily opened). Information on wave parameters and the living intertidal clam population was used to assess possible causes of stranding. This fine-scale monitoring showed that stranding occurred widely along the shore and year-round, with peaks interspersed with periods of low or no mortality. Dead clams showed higher mean density than dying individuals, but a lower mean shell length, attributed to a higher tolerance to desiccation of larger individuals. Wave height had a significant negative relationship to the density of dying individuals, presumed to be due to the accretive nature of low-energy waves: when digging out, clams would be more prone to be carried upward and unable to return; while larger waves, breaking farther from the beach and with a stronger backwash, would prevent stranding in the uppermost areas. This ecological finding highlights the need for refined temporal studies on mortality events, in order to understand them more clearly. Last, the similar size structure of stranded clams and the living population indicated that the stranded individuals are from the intertidal or shallow subtidal zone, and reinforces the ecological and behavioral components of this process, which have important ecological and socioeconomic implications for the management of this population.
沙滩生物搁浅并伴有大规模死亡事件是一种常见但却鲜为人知的现象，通常是基于离散事件进行研究。2007年9月至2008年12月期间，每四天对巴西东南部卡拉瓜塔图巴湾搁浅的三角蛤（Tivela mactroides）个体进行一次普查，据此评估了三角蛤搁浅及大规模死亡事件的频率、规模和可能原因。搁浅的蛤被分类为濒死（强制时闭合的瓣膜无法打开）或死亡（闭合的瓣膜很容易打开）。利用波浪参数和潮间带活体蛤种群的信息来评估搁浅的可能原因。这种精细尺度的监测表明，搁浅现象全年都在海岸广泛发生，高峰期间夹杂着低死亡率或无死亡的时期。死亡蛤的平均密度高于濒死个体，但平均壳长较短，这归因于较大个体对干燥的耐受性更高。波高与濒死个体的密度呈显著负相关，推测这是由于低能量波浪的堆积性质所致：挖掘时，蛤更容易被向上冲走而无法返回；而较大的波浪在离海滩更远的地方破碎且回流更强，会阻止在最上部区域搁浅。这一生态学发现凸显了对死亡事件进行更精细时间研究的必要性，以便更清楚地了解它们。最后，搁浅蛤和活体种群相似的大小结构表明，搁浅个体来自潮间带或浅亚潮带，并强化了这一过程的生态和行为组成部分，这对该种群的管理具有重要的生态和社会经济意义。
