Freshwater biomonitoring with macroinvertebrates in the Philippines: Towards the development of the Philippine biotic index

Abstract

Streams and rivers are the most threatened and exploited freshwater ecosystems worldwide. Land-use changes, particularly the conversion of forests to agricultural, residential, and industrial areas, have greatly impacted them, leading to declining water body quality and biodiversity loss. Thus, evaluating rivers and identifying threats is crucial to protect and rehabilitate them adequately. A combination of physical, chemical, and biological indicators in assessing the ecological conditions of aquatic ecosystems is now a prerequisite. Most river biomonitoring studies focus on benthic macroinvertebrates. However, river biomonitoring is not commonly practiced in the Philippines as it is not implemented regularly and officially. This review aims to determine macroinvertebrate families that could serve as sensitive bioindicators of river ecosystem health, determine the overall status of streams and rivers based on benthic macroinvertebrate assemblages, and identify research gaps to guide the development of a macroinvertebrate-based biomonitoring tool. Using Google Scholar, we conducted a quantitative search of studies that assessed water body quality and condition of streams and rivers in the Philippines using benthic macroinvertebrates published from January 2000 to December 2021. Of the 945 search results, 23 studies satisfied the criteria for inclusion in this review. These studies covered 35 Philippine rivers distributed in Luzon (18), Visayas (10), and Mindanao (7). Of the 166 benthic macroinvertebrate families, one family (Hebridae; velvet water bugs) was found solely in the Class AA water body (waters in uninhabited watersheds or declared protected areas based on the Philippine water quality guidelines), 18 in A (intended as a source of drinking water), 17 in C (boating, fishing, aquaculture, agriculture, irrigation and livestock watering), and only one (Amnicolidae; freshwater snail) was found in D (navigable waters). However, none of the studies assessed streams or rivers solely under Class B (intended for primary contact recreation). In addition, several single-metric biotic indicators commonly used in the Philippines varied in their evaluation of the stream condition. Thus, we propose developing a macroinvertebrate-based, multimetric biotic index to assess stream and river health in the Philippines.