Some inherently poorly dispersive marine species have surprisingly large or patchy distributions that might be explained by rafting or ‘hitchhiking’. The genus Durvillaea (southern bull kelp) includes both highly buoyant and entirely non-buoyant species. Several of the non-buoyant, poorly dispersive species have puzzling distributions that are hard to explain without invoking long-distance dispersal hypotheses. We propose that these non-dispersive species of Durvillaea may be able to hitchhike with buoyant, dispersive congenerics by interspecific holdfast coalescence. Although many cases of intraspecific holdfast coalescence have been recorded, interspecific coalescence is less well documented. To determine whether interspecific holdfast coalescence occurs in Durvillaea, a rock platform on the south-east coast of New Zealand was surveyed, revealing multiple examples of naturally occurring interspecific holdfast coalescence. Samples were taken from coalesced holdfasts and genetic sequencing was performed to attempt to gauge whether tissue from both species was mixed throughout the holdfast or remained discrete. The discovery of interspecific coalescence between non-buoyant and buoyant Durvillaea raises the possibility that non-buoyant seaweeds may disperse with buoyant congenerics by rafting, and could help explain the distributions of various other non-buoyant macroalgae.

一些固有的分散性差的海洋物种具有惊人的大或零散分布，这可能可以通过漂流或“搭便车”来解释。属丛梗藻（南部公牛海带）包括高度浮力和完全没有浮力的物种。一些非漂浮的、分散性差的物种具有令人费解的分布，如果不援引长距离分散假设就很难解释。我们提出，这些非分散的Durvillaea物种可能能够通过种间固定合并与漂浮的、分散的同系物搭便车。尽管已记录了许多种内保持合并的案例，但种间合并的记录较少。确定是否在Durvillaea 中发生种间保持合并，对新西兰东南海岸的一个岩石平台进行了调查，揭示了自然发生的种间固结聚结的多个例子。从合并的holdfasts 中取样并进行基因测序，以试图衡量来自两个物种的组织是在整个holdfast 中混合还是保持离散。不能漂浮和浮力种间聚结的发现丛梗藻引发非漂浮海藻可以通过漂流有漂浮congenerics分散，并可能有助于解释其他各种非漂浮海藻的分布的可能性。