Growth rate of the kelp Saccharina sessilis​ under different wave conditions

Growth rate of the kelp <i>Saccharina sessilis</i> (C. Agardh Kuntze; previously <i>Hedophyllum sessile</i>) among different wave exposures. During June and July 2013, the growth rate of S. sessilis was measured using the hole punch method (Mann 1973 <i>Science</i>) at the rocky intertidal site at Fogarty Creek, Oregon USA (44.838N, -124.058W). Three locations within that site were measured as having low, intermediate, and highly wave exposed conditions (Barner et al. 2016 <i>Journal of Ecology</i>). Growth rate was measured by making a small hole punch in multiple kelps in the different wave-exposed areas, then returning within two weeks to measure growth. Each row in the data is an independent sample - a different individual kelp plant.<br>Original Question: does growth rate of <i>S. sessilis</i> differ among wave exposures?<br><br>Variables in data (column headers)Date: year_month_dayExposure: L=low wave exposure, M=intermediate wave exposure, H = highly wave exposedLength.to.hole: the length between the holdfast and the point at which the hole was initially punched (cm)Growth: difference (in cm) between the original hole punch and the location of the punch after N daysWhen.punched?: date (year_month_day) that the growth measurement was takenN.days: the number of days of growthGrowth.per.day: growth rateWithin tide-series?: was the growth measurement taken during a period of negative low tides or not (1 or 0)

不同波浪暴露条件下囊状海带（*Saccharina sessilis*）的生长速率研究（该物种曾被归为*Hedophyllum sessile*，学名由C. Agardh与Kuntze定名）。
2013年6月至7月，研究团队于美国俄勒冈州福格蒂溪（Fogarty Creek）的岩质潮间带生境（坐标：44.838°N，-124.058°W），采用打孔法（hole punch method；Mann，1973，《Science》）测定囊状海带的生长速率。该生境内选取3个区域，分别对应低、中、高波浪暴露环境（Barner等，2016，《Journal of Ecology》）。
实验流程为：在不同波浪暴露区域的多株海带植株上打出小孔，于两周后回访测量其生长情况。数据集中每一行代表一个独立样本，即一株不同的海带个体。

原始研究问题：囊状海带的生长速率是否随波浪暴露程度存在差异？

数据集变量（列名）：
Date：日期，格式为年_月_日
Exposure：波浪暴露等级，L=低波浪暴露，M=中等波浪暴露，H=高波浪暴露
Length.to.hole：固着器至初始打孔位置的长度（单位：厘米）
Growth：初始打孔位置经过N天生长后的位移差值（单位：厘米）
When.punched?：打孔日期（即生长测量的起始日期，格式为年_月_日）
N.days：生长观测的持续天数
Growth.per.day：日生长速率
Within tide-series?：是否在低潮退潮时段开展生长测量（1代表是，0代表否）