Mapping habitats in a marine reserve showed how a 30-year trophic cascade altered ecosystem structure

Time-series studies have reported trophic cascades in land, freshwater and marine environments in many geographic areas. However, the spatial extent of habitats, a key metric of ecosystem structure, has not been mapped in these studies. Marine reserves can provide experimental, before-after and inside-outside (control-impacted), situations for assessing the impact of fishing on ecosystems. We mapped seabed habitats and their associated communities (biotopes) in New Zealand’s oldest marine reserve for comparison with pre-reserve maps created about 30 years previously. Areas grazed bare by sea urchins were entirely replaced in the centre of the reserve by kelp, or alga turf, an intermediate biotope between heavily grazed encrusting algae and lightly grazed kelp. Urchins declined following increased abundance and body size of spiny (rock) lobsters and fish (especially snapper) in the reserve but maintained bare rock outside. While this gradient in habitat change matched the gradient of pre...多项时间序列研究已在全球众多地理区域的陆地、淡水与海洋生境中报道过营养级联（trophic cascade）效应。然而，此类研究尚未对作为生态系统结构关键指标的生境空间范围进行测绘。海洋保护区可为评估捕捞对生态系统的影响提供实验性的前后对照（干预前-干预后）与内外对照（对照区-受影响区）研究场景。我们对新西兰最古老海洋保护区内的海底生境及其关联群落（生物群落生境，biotopes）开展了测绘，并与约30年前绘制的该保护区设立前的生境地图进行对比分析。在保护区中心，原本被海胆啃食殆尽的区域完全被海带（kelp）或藻垫取代——藻垫是介于重度啃食的结壳藻类与轻度啃食的海带之间的过渡型生物群落生境。随着保护区内多刺龙虾（岩龙虾，spiny (rock) lobster）与鱼类（尤其是笛鲷（snapper））的丰度及个体体型提升，海胆种群数量随之下降；而保护区外的海胆仍维持着裸岩生境。尽管此次生境变化的梯度与前期[原文未完整呈现]的梯度相匹配。