LTREB, Community Ecology on Rocky Shores: Long-Term Research in the Subtidal Zone (Massachusetts, 1978 - 2003)

马萨诸塞州北部三个地点的落基潮下群落现在已经被持续研究了长达20年。方法包括标记样方的摄影，掠食者丰度的横断面，以及对物理环境的选定方面的测量。自1978年以来，海胆的种群密度急剧增加，而大多数鱼类的种群数量减少。Sebens博士和合作者还记录了几个非本土物种的外观和影响；捕食性裸目动物Tritonia plebeia和殖民地海鞘Botrylloids sp.是最成功的，并对土著群体产生了可衡量的影响。其他非土著海鞘(Botryllus schlosseri，Styela clava，Diplosoma sp.)很少出现在这些地点，而且还没有发展出稳定的当地种群。Tritonia对八珊瑚Alcyonium siderium的种群造成了严重影响，这些种群仍未恢复。在1984-1986年间，海胆种群密度翻了一番，Tritonia对Alcyonium的去除导致垂直岩石表面上大多数其他无脊椎动物的数量大幅下降，而以结壳珊瑚藻类为主的表面范围增加。1978-1988年间，当海胆扩展到的新区域时，以海带和叶状红藻为主的水平表面被退化为海胆荒地(以珊瑚为主)。Botrylloides sp.在岩壁和水平面上建立的群落，即使在海胆觅食强烈的地方也是如此，因此可能具有阻止海胆的防御措施。海胆种群数量增加的协同效应，以及十年内几个非本土物种的出现，导致了这些地点无脊椎动物和藻类组合的重大转变。持续较高的海胆密度可能有利于抗海胆的空间优势种，包括珊瑚藻类、海葵(老年海葵)、海绵(Isodicya spp.)和非本土物种，如Botrylloides sp.。这些对马萨诸塞州北部潮下岩面(1978-1997)的研究提出并验证了关于岩石底质上群落结构的长期稳定性和短期调节的假说。以前的研究集中在岩壁上物种之间的相互作用，几个最常见物种的种群生物学，以及水分运动对个体、种群和群落过程的影响。本项目是长期研究的延伸：将使用实验和相关方法来研究捕食、物理效应、幼虫扩散、补充以及由此对群落结构的影响之间的相互作用。这项研究的目标是：1)确定构建群落的重要的长期和短暂的过程(物理、生物)，2)确定哪些过程对群落结构有强烈的直接和间接影响(如海胆捕食)，3)对补充及其对群落的影响进行定量研究，4)利用多种扩散尺度，将这些发现纳入一个孤立的景观亚单元上的物种共存和群落结构模型。一旦完成，将对长期数据集进行统计分析(自相关、交叉相关、其他时间序列分析)，以确定哪些物理过程和哪些捕食者种群与公共空间占有者覆盖率的变化最相关。该项目在马萨诸塞州海岸沿线8公里的五个现场站点，每年4-6次旅行期间继续进行长期研究，使用摄影、视频和直接(潜水)采样(样机、样带)。

9811576SebensRocky subtidal communities at three sites in Northern Massachusetts have now been under continuous study for up to 20 years. Methods include photography of marked quadrats, transects of predator abundance, and measurement of selected aspects of the physical environment. Since 1978, there has been a dramatic increase in sea urchin (Strongylocentrotus droebachiensis) population density and a decrease in most fish populations. Dr. Sebens and collaboartors have also recorded the appearance and effects of several non-indigenous species; the predatory nudibranch Tritonia plebeia and the colonial ascidian Botrylloides sp. have been the most successful, and have had measurable effects on indigenous assemblages. Other non-indigenous ascidians (Botryllus schlosseri, Styela clava, Diplosoma sp.) appeared only rarely at these sites, and have not yet developed stable local populations. Tritonia had a severe impact on populations of the octocoral Alcyonium siderium, which still have not recovered. The removal of Alcyonium by Tritonia and the doubling of sea urchin population density (both during 1984-1986) caused a major decline in most other invertebrates on vertical rock surfaces, and an increase in the extent of surfaces dominated by crustose coralline algae. Horizontal surfaces dominated by kelp and foliose red algae during 1978--1988 were reduced to urchin barrens (coralline-dominated) when urchins expanded into new areas in 1989. Botrylloides sp. established colonies on rock walls and horizontal surfaces, even where urchin grazing is intense, and thus may have defenses that deter urchins. The synergistic effects of urchin population increase, and the appearance of several nonindigenous species within one decade, has caused a major shift in invertebrate and algal assemblages at these sites. Continued high urchin densities could favor urchin-resistant spatial dominants, which include coralline algae, sea anemones (Metridium senile), sponges (Isodictya spp.), and nonindigenous species such as Botrylloides sp. These studies of subtidal rock surfaces (1978-1997) in northern Massachusetts have produced and tested hypotheses concerning the long-term stability and short term regulation of community structure on rocky substrata. The previous research focused on the interactions among species on rock walls, on population biology of several of the most common species, and on the effects of water movement on individual, population, and community processes. The present project is an extension of the long-term research: an experimental and correlative approach will be used to address the interactions among predation, physical effects, larval dispersal, recruitment, and the resulting impact on community structure. The goals of the study are to: 1) identify important chronic and transient processes structuring the community (physical, biological), 2) determine which processes have strong direct and indirect effects (e.g. sea urchin predation) on community structure, 3) conduct quantitative studies of recruitment and its effects on the community, and 4) incorporate these findings into a model of species coexistence and community structure on isolated sub-units of a landscape, using multiple dispersal scales. Once complete, the long-term data set will be examined statistically (autocorrelation, cross-correlation, other time-series analyses) to determine which physical processes and which predator populations are most strongly correlated with changes in percent cover of the common space occupiers. This project continue long-term studies during 4-6 trips annually, using photographic, video, and direct (SCUBA) sampling (quadrat, transect) at five field sites along 8 km of the Massachusetts coast.