Effects of Invasive Algae Removal Group

Abstract

A sudden shift in stable states, from a native seagrass (Halophila hawaiiana) and native algae dominated habitat to one overrun by invasive algae, has taken place in Maunalua Bay. In addition to channelization of water bodies, and the resulting sedimentation due to runoff, mudweed and gorilla ogo invasions have been correlated with alterations to regional sediment catch and therefore, the ecology of the bay. The presence of mudweed results in increased sediment levels that smother native seagrass beds allowing mudweed to outcompete native seagrass and algae. The Huki Project in Maunalua Bay is a large-scale invasive algae removal operation targeting Mudweed (Avrainvillea amadelpha) that aims to clear the dominating algae from Maunalua Bay’s ecosystem. The presence of mudweed in Maunalua Bay undoubtedly influences the composition of local invertebrate assemblages. Invasive algae provides habitat for amphipods, molluscs, and polychaete worms, all of which are prey species for dominant macrofauna and forage-feeding, predatory fishes. Benthic-dwelling invertebrates provide a crucial prey base for predatory fishes, fulfilling a key role in marine food webs through the provision of nutrients to native and non-native fish species. Therefore, invertebrate assemblages are helpful indicators of the fish populations due to dependence of fish on a variety of factors provided by invasive algae such as prey availability and shelter during larval stages. As primary users of the resource, fishers’ perspectives and direct observations within Maunalua Bay include valuable knowledge of changes happening within the area. Incorporating human dimensions is an important factor within the scope of this project, not only with citizen science volunteers to yield scientific outcomes, but local community who regularly benefit from the resource. Ensuring the needs of the individuals directly connected to areas being restored is a major concern and fishermen were targeted in this project as citizens directly affected by the Huki Project. In order to understand changes to Maunalua Bay, measurements of fish population diversity, abundance, and biomass were taken across the Paiko area, literature of seagrass and invertebrate communities at Maunalua Bay were examined, fishermen were surveyed for perspectives, and historical data about the area was examined. Invertebrate communities have been found to shift post-removal of mudweed to communities commonly found among native algae. Fish biomass was very low, with average biomass at 0.57 g/m2 during daytime observations and 0.64 g/m2 during a single night observation. Uouoa (Neomyxus leuciscus) and kaku (Sphyraena barracuda) were observed nearshore outside of study plots. Fishermen were mostly targeting ‘o‘io and papio and 11% of fishermen caught fish while surveyed and 11% usually caught something regularly. Most fishermen (89%) thought that fish populations are decreasing.