Collaborative Research: Does larval transport or physiological tolerance set the southern range boundary of a northern blue mussel?

本项目将测试北贻贝（Mytilus trossulus）的南部活动范围边界，是否取决于幼虫的扩散限制，或幼虫及/或幼体的生理耐受能力。鹦鹉螺和它的姊妹种，鹦鹉螺，在加拿大沿海各省和缅因湾北部都有。当M. trossulus的数量在加拿大边境以南突然减少时，M. edulis分布在北卡罗莱纳以南。迄今为止的研究表明：1)缅因州东北部的成年M. trossulus栖息在缅因州东部沿海流（EMCC）较冷的水域内的沿海地点、岛屿和人工结构中。2)在EMCC释放的漂浮物很少进入南部近岸水域，表明跨大陆架的移动极为有限。3)两种幼虫的热耐受性可能略有差异，有证据表明，热耐受性也可能受营养状况的影响。4)移植到缅因州东北部地区，但在EMCC之外的贻贝幼体存活率高，而移植到西南地区的贻贝幼体死亡率高。综上所述，这些结果表明，幼虫运输设定了缅因州东北部（10公里范围内）的近似范围边界，但热耐寒将最终限制其在更大的空间尺度（200公里）上的分布。本研究项目旨在通过实地和实验室实验的结合来验证这对假设。配有温度记录仪的卫星漂船将在柔轮鼠幼虫扩散季节（6月中旬至8月中旬）部署在EMCC内外，用于量化幼虫扩散期间的物理流场和温度状况。试验将使我们能够评估不同深度的幼虫是否会经历不同的流场。来自水文调查的数据，结合对贻贝幼虫和新定居者的定期空间和时间取样，将用于评估幼虫和定居后阶段与不同水体之间的可能联系。新定居者的生理耐受性将通过移植到EMCC内外的地点来测定。最后，实验室生长和生存实验将测定不同温度和饲养制度下的幼虫性能。研究人员将使用分子标记来识别这些兄弟物种在形态上难以区分的幼虫和定居者。更广泛的影响该项目将为一名硕士和一名博士研究生以及几名本科生提供培训。pi是在强调本科和研究生研究的机构，我们的项目将提供许多学生在海洋学和底栖生态学领域和实验室研究的机会。这样的研究机会可能会吸引一些本来会从事生物医学研究的学生。缅因湾是一个蓬勃发展的褐藻养殖业的家园，而M. trossulus是一个商业上的劣势物种-种植者担心它可能蔓延。因此，更好地了解决定该物种范围边界的因素将有助于种植者避免M. trossulus口蹄疫。将传播结果，以加强与缅因州水产养殖界的沟通。所有的实地考察将在缅因州面临巨大教育挑战的地区进行；将从当地学校招募教师协助暑期实地和实验室工作。

Intellectual MeritThis project will test whether the southern range boundary of a northern blue mussel, Mytilus trossulus, is determined by limitations on the dispersal of larvae, or the physiological tolerance of larvae and/or juveniles. Mytilus trossulus and its sister species, M. edulis, co-occur throughout the Canadian maritime provinces and the northern Gulf of Maine. While the abundance of M. trossulus decreases abruptly south of the Canadian border, M. edulis ranges south to North Carolina. Work to date has demonstrated that: 1) Adult M. trossulus in northeastern Maine inhabit coastal sites, islands, and man-made structures that are within the colder water of the Eastern Maine Coastal Current (EMCC). 2) Drifters released in the EMCC rarely enter nearshore waters to the south, suggesting that across-shelf transport is extremely limited. 3) Larvae of the two species may differ slightly in thermal tolerance, and some evidence suggests that tolerance may also be affected by nutritional status. 4) Mytilus trossulus juveniles transplanted within the northeastern Maine region, but outside of the EMCC, have high survivorship, while transplants further to the southwest suffer high mortality. In combination, these results suggest that larval transport sets the proximate range boundary within northeastern Maine (on a scale of 10 km), but thermal tolerance would ultimately limit the distribution on a larger spatial scale (200 km).This research project is designed to test this pair of hypotheses via a combination of field and lab experiments. Satellite drifters equipped with temperature loggers deployed in and out of the EMCC during the season of M. trossulus larval dispersal (mid-June to mid-August) will be used to quantify the physical flow fields and temperature regimes during larval dispersal. Drogues will allow us to assess whether larvae at different depths may experience different flow fields. Data from hydrographic surveys, combined with regular spatial and temporal sampling of mussel larvae and new settlers, will be used to assess possible associations between larval and post-settlement stages and different water masses. The physiological tolerance of new settlers will be assayed via transplants to sites in and out of the EMCC. Finally, laboratory growth and survival experiments will assay larval performance in different thermal and feeding regimes. The investigators will use molecular markers to identify the morphologically indistinguishable larvae and settlers of these sibling species.Broader ImpactsThis project will provide training for one MS and one PhD student, and several undergraduates. The PIs are at institutions that emphasize undergraduate and graduate research, and our project will provide numerous student opportunities for field and laboratory research in oceanography and benthic ecology. Such research opportunities are likely to attract a number of students who would otherwise pursue careers in biomedical research. The Gulf of Maine is home to a thriving Mytilis edulis aquaculture industry, and M. trossulus is a commercially inferior species - growers are concerned about its possible spread. Hence a better understanding of the factors determining the range boundary of this species will help growers avoid M. trossulus spat. Results will be disseminated to enhance communication with the Maine aquaculture community. All of the fieldwork will be conducted in a region of Maine facing great educational challenges; teachers from area schools will be recruited to assist with summer field and laboratory work.