Variation in responses of fishes across multiple reserves within a network of marine protected areas in temperate waters

Meta-analyses of field studies have shown that biomass, density, species richness, and size of organisms protected by no-take marine reserves generally increase over time. The magnitude and timing of changes in these response variables, however, vary greatly and depend upon the taxonomic groups protected, size and type of reserve, oceanographic regime, and time since the reserve was implemented. We conducted collaborative, fishery-independent surveys of fishes for seven years in and near newly created marine protected areas (MPAs) in central California, USA. Results showed that initially most MPAs contained more and larger fishes than associated reference sites, likely due to differences in habitat quality. The differences between MPAs and reference sites did not greatly change over the seven years of our study, indicating that reserve benefits will be slow to accumulate in California’s temperate eastern boundary current. Fishes in an older reserve that has been closed to fishing since 1973, however, were significantly more abundant and larger than those in associated reference sites. This indicates that reserve benefits are likely to accrue in the California Current ecosystem, but that 20 years or more may be needed to detect significant changes in response variables that are due to MPA implementation. Because of the high spatial and temporal variability of fish recruitment patterns, long-term monitoring is needed to identify positive responses of fishes to protection in the diverse set of habitats in a dynamic eastern boundary current. Qualitative estimates of response variables, such as would be obtained from an expert opinion process, are unlikely to provide an accurate description of MPA performance. Similarly, using one species or one MPA as an indicator is unlikely to provide sufficient resolution to accurately describe the performance of multiple MPAs.

野外研究的荟萃分析表明，受禁捕海洋保护区（no-take marine reserves）保护的生物量、种群密度、物种丰富度以及个体体型通常随时间推移而增长。然而，这些响应变量（response variables）的变化幅度与发生时机差异显著，其影响因素涵盖所保护的生物分类类群、保护区的规模与类型、海洋水文状况以及保护区设立后的时长。我们在美国加利福尼亚州中部的新建海洋保护区（marine protected areas, MPAs）及其周边海域开展了为期7年的非渔业依赖型鱼类调查（fishery-independent surveys）。调查结果显示，研究初期多数海洋保护区内的鱼类种群密度更高、个体体型更大，该现象大概率源于栖息地质量差异。在为期7年的研究周期内，海洋保护区与对照样点（reference sites）间的差异未出现显著变化，这表明加利福尼亚温带东边界流（eastern boundary current）海域的保护区效益积累速度较为缓慢。然而，1973年起全面禁捕的老旧海洋保护区内，鱼类种群丰度与个体体型均显著高于对应的对照样点。这表明保护区效益确实可在加利福尼亚洋流（California Current）生态系统中逐步显现，但需历经20年乃至更久，才能检测到由海洋保护区实施所引发的响应变量显著变化。由于鱼类补充模式（fish recruitment patterns）存在显著的时空异质性，在动态变化的东边界流海域的多样生境中，需开展长期监测才能识别鱼类对保护措施的正向响应。仅通过专家咨询等方式获取的响应变量定性评估，难以准确反映海洋保护区的实际效能。同理，仅以单一物种或单一海洋保护区作为评估指标，也不足以精准刻画多个海洋保护区的整体效能。