Marine Science Institute, University of California, Santa Barbara, California, United States of America.
ExxonMobil Upstream Research Company, Spring, Texas, United States, United States of America.
PLoS One. 2020 Nov 10;15(11):e0242017. doi: 10.1371/journal.pone.0242017. eCollection 2020.
Offshore oil and gas platforms have a finite life of production operations. Once production ceases, decommissioning options for the platform are assessed. The role that a platform's jacket plays as fish habitat can inform the decommissioning decision. In this study, conducted along the crossbeams of a California platform jacket and using an ROV, we compared estimates of fish diversity and densities determined from a targeted "biological" survey with those from a replicated "structural" survey. We found that the water column fish species assemblages characterized by the two methods were similar. By contrast, the two survey methods yielded different species assemblages inhabiting the crossbeam at the platform jacket base. This difference occurred because, at least off California, the platform jacket base species diversity tends to be highest where the bottom crossbeam is undercut, creating sheltering sites for many species. Because the structural method inadequately imaged the seafloor-crossbeam interface, particularly where a gap occurred between crossbeam and seafloor, substantial numbers of fishes were not visible. While we cannot extrapolate from this study to all platforms' worldwide, it is clear that routine platform structural integrity surveys may be a valuable source for opportunistic marine community surveys. Intentional planning of the structural survey to incorporate relatively minor variations (e.g., maintaining fixed ROV distance from the infrastructure and consistent 90° camera angle) coupled with a deliberate consideration of the platform ecology (e.g., positioning the ROV to capture the seafloor-crossbeam interface) can substantially improve the effects on fish assemblage assessments from routine structural surveys without compromising the integrity assessment. We suggest that these biases should be both acknowledged and, understood when using routine structural surveys to inform platform ecology assessment. Additional consideration may be given to structural surveys that incorporate incremental adjustments to provide better data applicability to biological assessments.
海上油气平台的生产作业寿命有限。一旦停止生产，就需要评估平台的退役方案。平台导管架作为鱼类栖息地的作用可以为退役决策提供信息。在本研究中，我们沿着加利福尼亚平台导管架的横梁，使用遥控潜水器（ROV），比较了目标“生物”调查和重复“结构”调查确定的鱼类多样性和密度估计值。我们发现，这两种方法所描述的水柱鱼类物种组合相似。相比之下，这两种调查方法在平台导管架底部横梁上栖息的物种组合不同。这种差异的出现是因为，至少在加利福尼亚，平台导管架底部的物种多样性往往在底部横梁被切割的地方最高，为许多物种创造了庇护场所。由于结构方法不能充分地对海底横梁界面成像，特别是在横梁和海底之间存在间隙的地方，大量鱼类无法被看到。虽然我们不能将本研究外推到全球所有平台，但很明显，常规平台结构完整性调查可能是一种有价值的机会性海洋群落调查来源。有计划地规划结构调查，纳入相对较小的变化（例如，保持 ROV 与基础设施的固定距离和一致的 90°相机角度），并认真考虑平台生态学（例如，将 ROV 定位以捕获海底横梁界面），可以在不影响完整性评估的情况下，大大提高常规结构调查对鱼类群落评估的效果。我们建议，在使用常规结构调查来告知平台生态学评估时，应承认并理解这些偏差。可能会考虑进行结构调查，以纳入增量调整，以更好地适用于生物评估的数据。
