Baseline Ecological Survey of Te Matuku Marine Reserve, Waiheke Island, New Zealand

Abstract

Te Matuku Marine Reserve, located on Waiheke Island New Zealand, was established in 2005. This study focuses on the Te Matuku estuary, which makes up approximately 75% of the marine reserve. It aims to (1) assess diversity and relative abundance of fish and hyperbenthic invertebrates in different habitats in the Te Matuku estuary; (2) identify important trophic linkages between these species assemblages; (3) compare the marine reserve’s diversity to other marine reserves in New Zealand; and (4) make recommendations for future monitoring. Existing data was reviewed to understand knowledge gaps and to learn about methods that were used successfully. A pilot study was first conducted to test logistics and the catch efficiency of four different types of gear including a small plastic fish trap with glow stick, barrel light trap, square fish trap and fyke net. The fyke net proved to be the least selective and most efficient type of gear. In total, 7 different fish species were caught. Most of the fish (98% of the catch) were juvenile fish. Fish diversity was the highest in the subtidal channels (7 species) followed by the mangroves (5 species) and then the tidal flats (2 species). Yellow eyed mullet (Aldrichetta forsteri) was the dominant species in the subtidal channels and estuarine triplefin (Forsterygion nigripenne) were dominant in the mangroves. On the tidal flats, only yellow eyed mullets were caught. Comparison of fyke net surveys at identical sites from different seasons in two consecutive years indicated temporal changes in abundance. Diets of the estuarine triplefin (Forsterygion nigripenne) and the exquisite goby (Favonigobius exquisitus) were dominated by hyperbenthic invertebrates. Consequently, they play an important role linking the invertebrate and fish assemblages. The estuarine triplefin diet specialized on small shrimps and midges. The diet of the exquisite goby was dominated by amphipods, isopods and copepods. The yellow-eyed mullet had a generalist omnivorous diet consisting of insects, detritus, copepods and algae. The grey mullet were feeding mostly on microalgae. Twenty four different species of hyperbenthic macro invertebrates were recorded from 8 different taxa. The hyperbenthic invertebrate survey found that overall diversity and abundance decreased towards the upper reaches of the estuary. Only the fauna of the shell rubble substrate was significantly different from that of rock, mud, muddy sand and sand habitats. Rocky habitat had the most unique species. Mysids and amphipods were the two most common and abundant taxonomic groups. The Te Matuku Marine Reserve shared 20% of its species with Long Bay-Okura Marine Reserve. This was the most similar marine reserve to Te Matuku out of the 22 New Zealand marine reserves used in this analysis. This emphasized the importance of the reserve in protecting biodiversity in New Zealand. This study recommends that modified lift nets to sample fish and light traps to sample hyperbenthic macro invertebrates should be used in future surveys of this type. These should be applied in a stratified random sampling design, using habitat and depth as strata. Sampling for hyperbenthic invertebrate and fish should be undertaken simultaneously in late summer and winter, every two to three years.