Lionfish (Pterois volitans and P. miles) populations have drastically exploded in the western Atlantic and the Caribbean in the past decade, and not without attracting some attention. The trouble is that these gorgeous fish sporting an array of venomous spines are invasive species. They naturally occur in the Indo-Pacific but have been introduced to Florida via aquarium releases and are now potentially causing significant changes to marine ecosystems, the inhabitats of which have not evolved with this fish. They can now be found from Costa Rica and Venezuela up the US eastern seaboard to Rhode Island, a truly impressive extent considering the first individual was found offshore of Florida in 1985. Recently, I was fortunate enough to dive in Roatan, Honduras on my honeymoon and lionfish were a relatively common sight, despite their efforts to hide among the barrel sponges on the benthos. They could potentially spread well into the southern hemisphere, along the the coast of South America, based on the lethal minimum water temperature [pdf] for this fish (10 C). Lionfish feed upon the larvae of reef fishes, undercutting the next generation of fishes. They can spawn year-round and release buoyant egg masses that can float in the currents for weeks, ensuring a wide distribution.
Dr Jason Hall-Spencer has written an excellent essay on the urgency of oceanic action, fueled by the recent findings of the International Programme on the State of the Ocean (IPSO). Make sure to check it out.
The crux of the problem is that the rate of changes in ocean systems is accelerating and outstripping what was expected just a few years ago. Destructive fishing practices, pollution, biodiversity loss, spreading low-oxygen “dead zones” and ocean acidification are having synergistic effects across the board – from coastal areas to the open ocean, from the tropics to the poles.
A theorized cross-section of the ocean, showing some major habitat types. Click to embiggen.
Williams MJ, Ausubel J, Poiner I, Garcia SM, Baker DJ, et al. (2010) Making Marine Life Count: A New Baseline for Policy. PLoS Biol 8(10): e1000531. doi:10.1371/journal.pbio.1000531
The biological pump, a way of moving nutrients and carbon down the water column, in the ocean is fairly straight-forward. Phytoplankton–tiny, photosynthesizing critters bobbing around in the surface ocean–are eaten by larger organisms, like zooplankton and fish. When the zooplankton and their brethren die (or are eaten and excreted by fishes), they sink towards the seafloor. When these organisms produce waste, either the zooplankters themselves or things that ate them, that sinks in the water column as well–something that a former professor of mine lovingly deemed the ‘fecal pellet express’. This entire process exports nutrients, like nitrogen, phosphorous, and iron, as well as carbon, to the deep ocean. However, researchers from the University of Vermont and Harvard recently found another component to this long held oceanographic concept: the whale pump.
Marine mammals breath air. When these creatures dive to feed, they must surface at some point, defecating along the way. Even if they can cross their fins and hold it, the excrement on average would occur higher in the water column than where these animals feed, as their dive depths are related to where the food is. Water samples taken near humpback whale fecal plumes in the Gulf of Maine showed hugely elevated nitrogen levels compared to other locations. Applying these findings to the entire population of marine mammals in the Gulf, 23 thousand metric tons of recycled nitrogen year is released to the surface annually, more than all riverine input for this area. That’s slightly less than adding the mass of the Titanic in nitrogen yearly.
Whale (and other marine mammals’) poop can enhance primary productivity by concentrating nitrogen in surface waters, essentially adding an upward component to the known mechanisms of nutrient recycling in the ocean. This additional nitrogen, which can be the limiting factor in phytoplankton growth, can boost primary productivity, increasing the base of the food web and thus supporting more consumers, like zooplankton, fish, and potentially the whales themselves–a very neat positive feedback.
Marine mammal populations have been drastically reduced by humans; one consequence of this could be that the carrying capacity (the sustainable population size) of coastal ecosystems could be reduced due to the lessening of this nitrogen recycling loop. In the Gulf of Maine, the amount of nitrogen contributed by whales was much higher before commercial hunting. The recovery of whale populations has other ecosystem service benefits as well. As the planets heats up, phytoplankton abundances have been seen to decrease due declining nutrients. Robust whale populations could help counter this negative effect on marine primary producers.
Images 1: Humpback whale breaching, Whit Welles, Wikipedia 2: A simplifed model of the biological and whale pump. Roman and McCarthy 2010.
Roman J, & McCarthy JJ (2010). The whale pump: marine mammals enhance primary productivity in a coastal basin. PloS one, 5 (10) PMID: 20949007
This article is cross-posted at The Urban Times.
One of our climate buffers may be losing steam. A paper just published in Nature (even given treatment by the New York Times) gives evidence that the oceans are becoming less efficient at uptaking atmospheric carbon emissions. This is a big deal. As I mentioned in an earlier article on ocean acidification, the ocean functions as a carbon sink—if the ocean did not have this property, the atmospheric carbon dioxide concentration would be much higher than what it is currently. Most atmospheric carbon emissions end up in the oceans—if they lose efficiency in absorbing emissions (which we now have evidence for), it’s logical to assume that we will see carbon dioxide accumulation in the atmosphere (and its subsequent climatic effects) speed up as we reach a proverbial tipping point in the global climate paradigm.
Khatiwala S et al. 2009. Reconstruction of the history of anthropogenic CO2 concentrations in the ocean. Nature: 462, 346-349. doi:10.1038/nature08526