Response by Jason Helyer, Coral Reef Specialist
This is a great question, but a difficult one to provide a straight forward answer for. Some researchers believe that the cold, nutrient-rich waters that bathe the west side of Jarvis (see blog post “Questions pertaining to the Oceanography of Jarvis Island” regarding upwelling at Jarvis) may provide biological communities at Jarvis protection from climate change associated impacts. In other words, if adjacent ocean temperatures rise, the waters around Jarvis may remain cooler thanks to upwelling associated with the EUC. This cooler water could provide protection to corals at Jarvis from bleaching from rising sea surface temperatures associated with global warming. But this is just a thought shared by some scientists and we really do not know how the oceanographic conditions around Jarvis might change with a changing climate. For example, if the EUC changed as a result of a changing climate, either weakening or deepening, the effects at Jarvis could be substantial as the impact of the current on the oceanographic conditions at Jarvis is a dominant feature structuring the reef community. This uncertainty makes it difficult to answer large questions about how systems might change from global warming and is one of the main reasons why it is important to monitor both biological and physical processes at these remote reefs.
Question 2: In reference to your post that "Jarvis has about 300 times more predatory fish biomass than the entire island of Oahu." What are the factors that reduce the predatory fish volumes in Oahu?
Response to this question as well as the following are by Brian Zgliczynski, Fish Biologist
There are multiple factors that negatively impact populations of predatory fishes. They include fisheries extraction, pollution, and habitat loss. However, fisheries extraction has been shown to have the most deleterious effect on the abundance and biomass of predatory fishes globally. Artisanal, commercial, and recreational fisheries typically target large-bodied commercially-valuable fishes that play an important role in structuring marine ecosystems. As large-bodied species are removed from the system the abundance and biomass of large-bodied predatory species available in the system is reduced.
Question 3: Does illegal fishing occur in the waters around Jarvis and what impact does it have on the trophic pyramid?
Jarvis is one of the most remote and isolated islands under U.S. jurisdiction. This geographic isolation affords Jarvis some protection from anthropogenic disturbances including fisheries. However, this same geographic isolation makes Jarvis potentially vulnerable to illegal fishing activities. As fish populations near inhabited coastal areas are reduced, the threat of commercial fisheries moving offshore to exploit resources at remote and uninhabited islands like Jarvis can become a reality. Fortunately, Jarvis has been designated as a National Marine Monument and is managed and protected under U.S. law out to the 50 nautical mile boundary. This designation provides the necessary legal protection and technologies are being developed to monitor and enforce the Monument boundaries. To date, we have not observed any signs of illegal fishing activities during our biennial reef assessment and monitoring efforts.
Question 4: How does the percentage of predatory biomass at Jarvis compare to Cocos Islands and other areas with high levels of predatory biomass?
Having conducted similar surveys throughout the tropical Pacific including Cocos Island (Costa Rica), the predatory biomass densities observed at Jarvis are among the highest. Additionally, all of the sites where predatory species are abundant display similar inverted trophic pyramids with predatory species accounting for the largest proportion of total fish biomass.