Relationships Among Aquatic Macroinvertebrates, Endangered Waterbirds, and Macrophytes in Taro Lo'I At Hanalei National Wildlife Refuge, Kauai, Hawaii

Hanalei National Wildlife Refuge (HNWR) on the island of Kauai provides yearround critical wetland habitat for five endangered waterbirds (EWBs) and supports nearly one-third of the remaining taro loi cultivated in the Hawaiian archipelago. This study focuses on the use patterns of this agricultural crop by two of these EWBs, the Hawaiian duck or koloa (Anas wyvilliana) and the Hawaiian common moorhen (Gallinula chloropus sandvicensis). Furthermore, associations are explored between the habitat conditions across the taro growth cycle, aquatic macroinvertebrate community characteristics, and the feeding ecology of koloa and moorhen during pre-breeding, nesting, brood-rearing, and molting when these waterbirds require increased protein, lipids, and minerals. Taro is grown at HNWR under a sustainable yield regime in a wetland complex where loi in different classes of crop development are adjacent to each other. This patchwork layout provides an interspersion of open water and vegetation, where each taro class has a slightly different vegetation structure and suite of invertebrates. Data collected during scan surveys indicate that koloa and moorhen densities are highest in wet fallow loi (3.2 – 8.4 individuals/ha) and during harvest (3.2 – 4.6 individuals/ha), while slowly decreasing in taro classes between planting and before harvesting (1.3 – 2.7 individuals/ha). Refuge-wide flooding in March 2005 seemed to have a positive effect on the abundance and/or visibility of koloa (161.5 individuals/survey) and moorhen (139.5 individuals/survey), with abundances generally decreasing on HNWR after this time period. Ampullariidae (apple snails), Chironomidae (midges), Glossiphoniidae (leeches), Lymnaeidae (pond snails), Oligochaeta (aquatic worms), Sphaeriidae (fingernail clams), and Thiaridae (thiarid snails) were the most prolific invertebrate taxa among taro loi in sweep net samples in 2005. Freshly flooded loi during and recently after planting are dominated by chironomids and oligochaetes, shifting to snails and then other insects as the taro crop matures. Invertebrate taxa richness in sweep net samples seemed to increase throughout the taro growth cycle, with the lowest taxa richness recorded in wet fallow loi before planting (3.8 taxa) and the highest in wet fallow vegetated loi (8.2 taxa). Taro loi with > 25% wetland vegetation generally had higher taxa richness and higher insect density (181.5 – 333.7 insects/m2) than non-vegetated loi in similar stages of development (44.1 – 306.4 insects/m2). In contrast, loi with more open water had higher total invertebrate density, but were much less diverse, mostly consisting of chironomids and oligochaetes. Within taro loi, hydrology and agricultural practices seem to drive the invertebrate communities. Because both koloa and moorhen are omnivorous and opportunistic foragers, all but 227 of the 93,192 invertebrates identified during this study are considered diet items. This allows them to shift their suite of diet items as hydrologic regimes, taro growth, and agricultural practices affect invertebrate life cycles while meeting their physiological needs as they change during different life events. Koloa and moorhen experience peak demands for breeding and molting between March and August, when the acquisition of high protein and lipid foods like oligochaetes and chironomids are available in less vegetated loi. Calcium essential for egg development is available through lymnaeid snails, which are positively correleated with total submergent vegetation, algae, herb, and sedge macrophyte communities (0.19 < rho < 0.37, p < 0.0008). Thiarid snails, which are negatively correlated with all vegetation (-0.15 ≥ rho ≥ 0.30, p < 0.01) except those categorized as robust stems, can also provide this mineral to egg-laying hens. Management that maximizes the abundance and availability of aquatic macroinvertebrates to koloa and moorhen in wet fallow loi and during taro harvest between March and August should benefit these EWBs while having little effect on the production of the taro crop. Identifying diet items by the nutritional components needed by waterbirds during certain life history events will assist managers in providing the right foods at the right time. This increased understanding of the relationships among aquatic macroinvertebrates, wetland vegetation, taro cultivation, and the life history needs of koloa and moorhen is critical in guiding management for the recovery of these EWBs.

Name thesis:degree_name

Master of Science (MS)

Level thesis:degree_level

Thesis - University Access Only

Discipline thesis:degree_discipline

Wildlife and Fisheries Science

Year

2011

Author dc:creator

• Gutscher-Chutz, Jennifer Leigh

Contributors dc:contributor

• Leigh H. Fredrickson

• waterbirds
• aquatic macroinvertebrates
• macrophytes
• hanalei national wildlife refuge
• hawaii
• Natural Resources and Conservation

Statement dc:rights

• Copyright © 2011 Jennifer Leigh Gutscher-Chutz. All rights reserved.

Language dc:language

en

Repository record dc:identifier

https://openprairie.sdstate.edu/etd/448

OAI identifier oai:identifier

oai:openprairie.sdstate.edu:etd-1448