Editor’s Selection IconWell I haven’t done a Research Blogging post in a very long time. But I was inspired by this news release I read today about crabs spilling onto the Antarctic peninsula with warming waters. On a recent voyage to Antarctica, marine biologists collected digital images of these deep water predators moving closer to shallow coastal waters which have been excluded from for potentially millions of years, because the shallow coastal waters, until recently, have been too cold to support these predators. This can be devastating to the coastal shelf community in Antarctica, which has adapted no defenses in the absence of these predators – many organisms here have thin shells or don’t burrow into sediments.
My friend and fellow Southampton College alum, Molly, recently blogged about this issue. She is currently doing graduate work at the University of Alaska Fairbanks on snow crabs, so she loves crabs (as her blog title suggests). The idea is that, as the above article states, these crabs are moving closer to the Antarctic shelf, and this can have devastating impacts on the local fauna there. It was highlighted in a National Geographic article in 2008.
According to research, the Antarctic coastal shelf experienced a cooling trend starting around 40 mya, and the waters, due to the cooler temperatures, essentially became devoid of many types of predators. The subsequent community had evolved over those millions of years in the absence of major durophagous predators – known for their shell crushing abilities. The major predators in these bottom waters are slow moving invertebrates, and the community developed over time accordingly. Now as surface waters are warming, crabs are able to enter these new areas from the depths, and can have potentially harmful impacts.
At first, this might seem counter-intuitive – typically bottom waters, and the deep ocean, are very cold, and the water warms as you get shallower. This is not the case on the Antarctic shelf, where the shallow waters are actually colder than the surrounding deep waters. This is due to the cold Antarctic circumpolar current, which runs clockwise around Antarctica, isolating its cold water and continental shelf from crabs and fish with bony jaws.
However, the absence of crushing predators was not due to geograhic isolation of the Antarctic continental shelf (although Antarctica is oceanographically isolated, the barriers of biological invasion in this case are physiological, according to Richard Aronson, professor of biology at the Florida Institute of Technology, and others in 2007). Physiologically, the crabs are unable to process magnesium in their blood at the normal shelf water temperatures, resulting in narcotic effects. So the crabs, for millions of years, had stayed away. The resulting shelf community, consisting of epifaunal suspension feeders, lacked the typical defense mechanisms seen in other benthic environments where soft bottom bethos have been evolving with predators in an evolutionary arms race. As already mentioned, the archaic communities of the Antarctic shelf, consist of animals with thin shells which don’t burrow. So one could imagine that if these crab predators were allowed to move into these coastal waters, it could have devastating consequences on the community there.
This is not a crab you would encounter in the Antarctic, however, it is as close a figure to the "arms race" - crab claws, thick clam shell - as I could find on the interwebs.
Recent research suggests that the physiological barrier separating these durophagous predators are being lifted by a rapidly warming Southern Ocean and Antarctic shelf. This warming is allowing predators to move closer to the shelf communities, as demonstrated by Sven Thatje, evolutionary biologist at the University of Southampton in England. Thatje and colleagues found the shallowest lithodid crab every recorded on the Antarctic shelf (photo above) and suggested they were “reconquering” the Antarctic back in 2005. This led to Aronson and colleagues (2009) to predict rapid changes over the coming decades in the benthic community on the Antarctic shelf. The crab populations could reduce or eliminate suspension feeding echinoderms (starfish, sea cucumbers), and the overall impact will likely render the formerly unique Antarctic shelf benthic community to resemble other benthic communities in low latitudes.
Range expansions are something that are particularly interesting to me. The lifting of physiological barriers due to temperature will allow biological invasions of numerous species. How these species interact with native species is of great concern. In particular, predator-prey relationships between novel predators and naive prey can restructure communities in warming oceans. Despite its perceived isolation, this research suggests that Antarctica will not be immune to these impacts (and it fact, polar regions are likely to experience a greater magnitude of temperature change).
And the real news here, is not only is there evidence the crabs are moving closer to these shallow shelf communities, but that it is occurring at a much more rapid rate than anticipated.
A quote by Dr. Aronson from the new article: “If you look at the warming trends on the peninsula, you would expect that the crabs would come back in 40 or 50 years,” Aronson said from his office in Melbourne, Fla. ”But boom, they’re already here. This is the last pristine marine system on Earth and it could get destroyed”.
This is big and bad news for the Antarctic bottom communities. Clearly, this is something that should be monitored closely. But it is not in any means an Antarctic phenomenon. In many regions where warming is taking place, range expansion of novel predators can occur. This is something all benthic communities could experience in the near future.
Aronson, R., Thatje, S., Clarke, A., Peck, L., Blake, D., Wilga, C., & Seibel, B. (2007). Climate Change and Invasibility of the Antarctic Benthos Annual Review of Ecology, Evolution, and Systematics, 38 (1), 129-154 DOI: 10.1146/annurev.ecolsys.38.091206.095525
Aronson RB, Moody RM, Ivany LC, Blake DB, Werner JE, & Glass A (2009). Climate change and trophic response of the Antarctic bottom fauna. PloS one, 4 (2) PMID: 19194490
Thatje, S., Anger, K., Calcagno, J., Lovrich, G., Pörtner, H., & Arntz, W. (2005). CHALLENGING THE COLD: CRABS RECONQUER THE ANTARCTIC Ecology, 86 (3), 619-625 DOI: 10.1890/04-0620
Thatje, S., Hall, S., Hauton, C., Held, C., & Tyler, P. (2008). Encounter of lithodid crab Paralomis birsteini on the continental slope off Antarctica, sampled by ROV Polar Biology, 31 (9), 1143-1148 DOI: 10.1007/s00300-008-0457-5
Because I couldn't have a climate related article without citing the Church of the Flying Spaghetti Monster
As marine scientists, sometimes we forget or don’t even realize how much local baymen and fishermen actually know. Or maybe we don’t trust them because they are “lay” persons. But they work the bay, they try to catch many of the species we study (as money is a big driver of research), and they know things. Local baymen who have worked the bay for years suggest that bay scallop recruitment is higher in years after cold/wet winters. Sometimes, we take what they say with a grain of salt. However, they know. They have often been working with these species for as long or longer than we have, and it is often also a generation thing. Generations of baymen can’t be wrong in their assessment, can they?
A 2001 study in the Dutch Wadden Sea supports these claims, however, their conclusions are not what you think. Matthius Strasser and Carmen-Pia Gunther observed patterns in larval supply of predators and prey after a series of consecutive winters in which temperatures were severe, moderate or mild. Originally, the prevailing thought was that egg production increased after severe winters of many benthos, and this is why recruitment was higher in the following spring. However, their research indicates that the numbers and peaks in recruitment were actually highest in the mild winter. So why isn’t recruitment highest during these years? Their theory, a mismatch in the predator and prey larval supply. After severe winters there is a delay in the peak larval supply of the major predators, green crabs, of almost 6-8 weeks. This delay is not as apparent as their bivalve prey, and with the average larval time of the bivalves also being shorter, they settle much earlier than the green crabs and have a potential head start in growth. According to the researchers, this mismatch is what fuels observations of higher recruitment after severe winters.
An alternative scenario is one which was observed in Chesapeake Bay. Using local climate response variables Kimmel et al were able to demonstrate noticeable and significant differences in phytoplankton, copepod, gelatinous zooplankton and finfish abundances and composition between years with “wet” winters and years with “dry” winters. Essentially, wet winters led to an increase of freshwater flow and nutrients into the system, which resulted in higher phytoplankton, more copepods, more ctenophores and higher numbers of striped bass. In years of dry winters, there was less phytoplankton, more scyphomedusae and more menhaden. The basic premise is that the local climate had a significant impact on the community composition of Chesapeake Bay by controlling the amount of fresh water flux into the system.
Both are interesting reads, and the idea of the interplay between climate and marine ecology is one that is becoming even more important to understand with the current climate change scenarios. It is quite clear that atmospheric conditions and local climate can have a fairly significant impact on subsequent year classes – something baymen have been familiar with for decades, if not centuries, but something marine scientists have only been exploring for the past decade, give or take.
Strasser, M. (2001). Larval supply of predator and prey: temporal mismatch between crabs and bivalves after a severe winter in the Wadden Sea Journal of Sea Research, 46 (1), 57-67 DOI: 10.1016/S1385-1101(01)00063-6
Kimmel, D., Miller, W., Harding, L., Houde, E., & Roman, M. (2009). Estuarine Ecosystem Response Captured Using a Synoptic Climatology Estuaries and Coasts, 32 (3), 403-409 DOI: 10.1007/s12237-009-9147-y
Apparently, climate change might not be such a bad thing. Especially not if you are an exploited species of bivalve. Now I am not trying to be a climate change apologist, but too often we get caught up in this debate and science is 99% of the time on the side saying “It’s bad.” However, as I have learned in my own research with invasive species, there are always two sides to every coin. A warming ocean could be a benefit to numerous species, probably as many species as it might be of detriment. Obviously, there are a whole suite of ecosystem processes that are also affected, but in certain cases, it might not be so bad. At least not according to a paper in Marine Biology entitled “Strengthening recruitment of exploited scallops Pecten maximus with ocean warming.” Its an interesting read. The essential idea is that over a long(ish) time period, the researchers were able to demonstrate a highly significant correlation between increasing temperature and increasing settlement and recruitment of juvenile scallops to a local scallop population. Shifts in recruitment can be attributed to temperature related shifts in feeding, gonad development and larval survival – and this impacts are more apparent in species who use environmental cues to induce development and spawning. Such is the case for many species of bivalves, including scallops, and so a warming ocean could potentially enhance scallop recruitment. There are some stats involved in their methods, but the basic results are pretty simple, over the past decade, scallop landings around the Isle of Man have been increasing. IN addition, mean springtime temperatures have been increasing (which cues development). I know what you all might be thinking, correlation does not equal causation (you know the one, mean global temperature has increased as the number of global pirates has decreased, meaning that the number of pirates somehow influences the climate), but that goes into their methods of using residuals and proxy values and all sorts of things. Basically, recruitment increase isn’t significantly related to other things (spawning stock, dissolved oxygen, chlorophyll a), and is strongly related to temperature. They even examined a number of scallops during the three month conditioning period and the GSI – which indicates relative gonad development – was significantly higher in years when temperature was higher. So when temperature goes up, the scallops develop larger gonads and subsequently release more larvae which show up as strong recruitment classes.
So what does this mean for bay scallops? Well, there are plenty of issues with ocean warming and bay scallops – and one of particular concern is predator range expansion and new predators coming into the bay scallops range. In terms of recruitment, we haven’t seen any patterns that would suggest this is the case in New York. However, there hasn’t been many scallops here to spawn over the past 20 years until recently – due to the restoration efforts – and there needs to be a local spawning population in order to observe any of the patterns described from the paper. That said, bay scallop recruitment is not likely to be effected by ocean warming in terms of larger populations – although timing of first spawn might change, the number of times they spawn might change, etc, but it is my opinion that there are numerous variables that influence the size of recruitment classes in local scallop populations, particularly in the bay, which is already a dynamic environment.
Shephard, S., Beukers-Stewart, B., Hiddink, J., Brand, A., & Kaiser, M. (2009). Strengthening recruitment of exploited scallops Pecten maximus with ocean warming Marine Biology, 157 (1), 91-97 DOI: 10.1007/s00227-009-1298-7