底泥穿刺阻力與沙質潮間帶大型底棲無脊椎動物豐度的關係

Abstract

踩踏與越野車等人類活動都會壓密土壤，也會影響底棲動物的生存與分布。穿刺阻力 (penetration resistance, PR) 是一個方便而有效的壓密程度評估指標，當壓密程度越高，底泥PR就越顯著增加，然而，PR是否同時也是評估底棲動物受影響程度的良好指標則少有研究。為了釐清PR與底棲動物的關聯性，本研究在穿刺阻力有明顯空間差異的沙質潮間帶遊憩區，選擇其他環境條件相近的區域，調查大型底棲無脊椎動物的豐度，包括多毛類、二枚貝、十足類與端腳類 (又細分為大型 (> 4 mm)、中型 (1~4 mm) 和小型 (< 1 mm))，以及PR與其他底泥性質，分析PR和豐度之間的關聯性。各項底泥性質的分析顯示，相對於調查區域中其他底泥性質的均質性，PR呈現出明顯的空間變異，各樣點在0~15 cm深的PR平均值介於0.2~2.2 MPa；對PR平均值和最大豐度之間的迴歸分析則顯示，多毛類、二枚貝與大型、小型端腳類，在PR越高的樣點，其最大豐度有越低的趨勢 (r2 = 0.89, 0.80, 0.54, 0.94, p < 0.05) ，PR最高時最大豐度降低了78~100%；對中型端腳類的最大豐度與PR平均值依深度進一步做分層的迴歸分析時，在中層 (5~10 cm) 與深層 (10~15 cm) 底泥中也同樣具有上述趨勢 (r2 = 0.48, 0.62, p < 0.05) 。這個趨勢顯示，PR的增加形成多毛類、二枚貝與端腳類等底棲無脊椎動物生存上的壓力。由於PR的增加會提高動物在底泥中活動的阻力、降低底泥的孔隙含量，前者可能提高多毛類、二枚貝與端腳類的鑽掘阻力，後者則可能減少小型端腳類的生存空間並降低溶氧在底泥中的通透性。本研究顯示，PR可以評估底棲動物在沙質潮間帶遊憩區的生存壓力，PR有助於底棲生態變化的監測，並可提供人為活動管理之參考。

Human activities, such as trampling and off-road vehicle, compact soil and affect the distribution of benthic macrofauna. As an effective indicator for the degree of compaction, soil penetration resistance (PR) increases as the degree of compaction increases. PR had applied extensively to measure compaction in many fields. However, it’s still poorly understood whether PR is also a good indicator for the effect of human activities on benthic macrofauna. This study investigated the relationships between PR and macrofauna on an intertidal sandy beach of recreational area. The abundance of macrofauna and sediments properties including PR were measured where sediment properties were uniform except for PR. Macrofauna were grouped into Polychaeta, Bivalvia, Decapoda and Amphipoda. Amphipoda was further classified into large (> 4 mm in body length), middle (1~4 mm) and small (< 1 mm) size. Abundance of each macrofauna group was analyzed with different degree of PR. The results showed that PR exhibited higher variance than other sediment properties, ranging from 0.2 to 2.2 MPa of PR average on 0~15 cm depth. Regression analysis between PR average and max abundance of Polychaeta, Bivalvia, large Amphipoda and small Amphipoda showed similar trend (r2 = 0.89, 0.80, 0.54, 0.94, p < 0.05), the higher the PR average, the lower the max abundance, which can decreased 78 to 100% as PR increased from lowest to highest. Further regression analysis between PR average and max abundance of middle Amphipoda on 5~10 cm and 10~15 cm depth layers also showed the same trend (r2 = 0.48, 0.62, p < 0.05) as described above. This trend implies the increase of PR is a stress for benthic macrofauna such as Polychaeta, Bivalvia and Amphipoda. The increase of PR represents an increase of resistance to activities in sediments and decrease of porosity in sediments, the former may increase resistance of burrowing by Polychaeta, Bivalve and Amphipoda, and the latter may decrease pore space accessible for small Amphipoda and lower permeability to oxygen in sediments. This study suggests that PR is a good indicator to evaluate the stress to benthic macrofauna, and this would apply to monitor benthic ecology and manage human activities on an intertidal sandy beach.