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Assessing the Antarctic lithodidae (King crab) hypothesis: invasion or endurance?

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PCAS 19 (2017/2018)

Critical Literature Review

(ANTA602)

Assessing the Antarctic lithodidae (King crab)

hypothesis: Invasion or endurance?

Simon Stent

Student ID: 36229649

Word count: 2819

Abstract (ca. 200 words):

Rising sea temperature, as a result of anthropogenic climate change, has contributed to dynamic ecological changes across the globe. As a result the previously isolated

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Introduction:

In recent years, the discovery of Lithodidae species on the Antarctic continental shelf has been contributed as an impact of climate change; a metaphor for the adverse impacts of rising sea temperatures. This hypothesis, known as the ‘invasion theory’ follows that Lithodidae crab species, commonly known as king crabs, were driven out of Antarctica 15-40 million years ago (Eocene epoch); and have recently began to migrate back to Antarctica as similar 'warm' temperatures and habitats become available once again (Griffiths, H., 2013).

Lithodid crabs are common in the deep sea across the globe, as well as in shallow depths in sub-polar latitudes. They are well known across deep sea habitats of the southern ocean and are common in shallow Sub-Antarctic waters (Hall, S. 2009).

The common nature of Lithodid species in cold, deep water habitats, has led to an opposing hypothesis known as the ‘endurance theory’, largely put forth by Griffiths et al (2013). This hypothesis associates the invasion hysteria as a result of inadequate sampling and monitoring techniques, at a limited range of sites. Thus positing that Antarctic Lithodidae had the

potential to, and did likely, endure even the coldest extents of the last glacial maximum; in deep water habitats suitable to their biophysical limits. Therefore suggesting Lithodids are in fact native to Antarctica as opposed to being an invasive species.

The following piece of literature will look at the historical record of Lithodid in Antarctica, whilst highlighting some of the discrepancies in sampling and gaps in knowledge associated with both theories; assessing which theory appears more robust in terms of relevant literature.

Antarctic Lithodidae fossil record:

The fossil record of Antarctic Lithodids is relatively poor due to a number of factors. As a large percentage of the Antarctic continent is covered in snow and ice, the exposure area within which fossils can be found is restricted. As a result, fossil records of Antarctic Lithodids mostly come from geological units that span large temporal intervals, causing an intermittent historical record (Griffiths, H., 2013).

Though the ‘invasion theory’ suggests that Antarctic Lithodids migrated off continental Antarctica, as a result of inhospitable temperatures during the Eocene to Oligocene period. Fossil records from the La Meseta Formation on Seymour Island (off the Antarctic

Peninsula), show that decapod diversity was still high at this time, suggesting that decapods didn’t leave continental Antarctica until much later, when cooling was even greater

(Feldmann, R. 2003).

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In summary, the historical fossil record of Lithodidae is virtually non-existent, making it difficult to assess the significance of modern day distribution patterns, and ultimately whether populations have endured or are indeed invading Antarctic waters, though some insights into the global origins of Lithodids have been drawn from molecular methods and recent depth distribution patterns (Hall, S. 2009).

Recent Lithodid sampling/monitoring:

The earliest known living record of Antarctic Lithodidae date back to an individual of the Paralomis birsteini species, discovered in 1967 near Scott Island, North of the Ross Sea. They were not recorded again until 1994, near Peter I Island (Arana, E. 1999). It was not until 1998 that Lithodids were recorded on the continental slope off the West Antarctic Peninsula, since this date there has been a total of nine encounters with Lithodidae from the slope/shelf of Antarctica (Ahyong S. T. 2010).

These nine recorded encounters with Lithodids (either observed or specimen collection) on or near to the Antarctic continental shelf/slope (<50km from the 1000m bathymetric contour), represent four different species (N.yaldwyni, P.birsteni, N.capensis and P.stevensi). These records range from 850 metres to 1947 metres deep and occur from the slope of the Ross Sea, through to the North West end of the Antarctic Peninsula. There are no records of Lithodids on the Antarctic shelf/slope past the Ross, Amundsen and Bellingshausen Sea (Griffiths, H. 2013).

Of these four species, two Lithodid species (Neolithodes capensis and Paralomis birsteini) have been reported from the West Antarctic Peninsulas continental slope itself, in the Palmer Deep region. These recent records of N. capensis and P. birsteini are theorised to indicate a Lithodid invasion up the Antarctic Peninsula slope and onto the continental shelf, achieved by seafloor immigration of adults, or the dispersal of demersal larvae. However, the reproductive status and population densities of N. capensis, P. birsteini and other Lithodids on the West Antarctic Peninsulas slope are unknown (no ovigerous females have been collected from this location), and the ecosystem impacts of these and other Lithodid species remain

undocumented in Antarctic waters (Smith, C. 2012).

Antarctic Lithodid Bio-geography and distribution:

Temperature has long been associated as a key abiotic factor in determining the distributions patterns of organisms (Clarke, A. 2009). Sea water temperature appears to be a key

determining factor in the geographic distribution of Lithodid crabs in Antarctica, placing physiological constraints on distribution extent. When studied, a sharp temperature cut-off point was observed for most Southern Ocean Lithodids at around 0.5oC, though four species

(N.yaldwyni, P.stevensi, P.formosa and P.birsteini) had ranges extending between 0.5oC and

0oC. The known distributions of all recent Lithodidae in the Southern ocean are constrained

by temperature, with no records from areas with a water temperature less than 0oC (Hall, S.

2011).

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The relative high diversity, from a low number of samples, advocates a community that has developed and endured over a few centuries. (Griffiths, H. 2013).

Invasion theory:

The invasion theory, as aforementioned, is the hypothesis that Lithodidae were driven off the Antarctic continental shelf as a result of inhospitable conditions approximately 15-40 million years ago, and have recently returned due to rising sea temperatures.

The first study to hypothesize an Antarctic ‘invasion’ of Lithodidae, as a result of climate change, was Thatje et al. (2005). This report postulated a Lithodid re-colonisation of Antarctica via the deep-sea, facilitated by analogous evolutionary selection pressures; most notably scarcity of food combined with low temperatures (Thatje, S. 2005).

A possible invasion pathway via the shallows of Sub-Antarctic islands, alluded to by the distribution patterns of Lithodid species along the islands of the Scotia Arc, was also put forth. Though this alternative pathway is deemed less likely than that of the deep sea

connection, as a result of the demersal characteristics of lecithotrophic larvae. As well as their low potential for dispersal from the bathyl zone into the euphotic zone of shallow waters, indicating Lithodidaes ability to cope with the high-pressure regime of the deep-sea (Thatje, S. 2005).

Though Thatje et al. (2005), was the first publication to postulate an invasion of Lithodidae onto the Antarctic continental shelf, the first report to provide evidence in support of this theory was Smith et al. (2011). Based on a single ROV (Remotely Operated underwater-Vehicle) dive at Palmers Deep, off the West Antarctic Peninsula. The ROV dive located a large population of adult Lithodids (N. yaldwyni) which were abundant over large areas of the Palmer Deep seafloor at depths of 950-1419 metres, in February 2010 (Smith, C. 2012). Lithodid species were absent from any samples collected from depths shallower than 725 metres on the West Antarctic Peninsula, which coincided with Thatje et al. (2008) sampling at depths of 500-600 metres in Marguerite Bay in 2008, which yielded no Lithodid samples (Thatje, S. 2008). Indicating that Lithodid crabs were absent, or extremely rare, on the West Antarctic Peninsula shelf at depths shallower than 725 metres, prior to 2010. The abundance, bioturbation and depth isolation of dense Lithodid populations in Palmers Deep suggested that the population had been established for years, consolidated by the Lithodid recorded off the West Antarctic Peninsula in 1998 (Sumida, P. 2008).

The apparent absence of Lithodid crabs at depths of less than 725 metres, as well as at temperatures below 1.4oC, has implications for the invasion theory. If the distribution of

Lithodids in Antarctic waters is limited by a lower temperature threshold of 1.4oC, as argued

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thermal barrier restricting this population from migrating into shallow, near-shore habitats, with severe ecological impacts (Aronson, R. 2015).

Endurance theory:

The alternative theory, contrasting that of the 'invasion' hypothesis, is known as the endurance theory, largely proposed by Griffiths et al. (2013). This hypothesis suggests that Lithodid crabs have always inhabited Antarctic waters, and that the ‘invasion’ hysteria is a product of poor fossil records and insufficient sampling efforts.

Recent records of Lithodid crabs inhabiting the slopes of the West Antarctic Peninsula, the Ross Sea and deepened basins on the shelf have encouraged people to believe that these species are both new and expanding within the marine community. Griffiths et al. (2013) argues that virtually no scientific work, using suitable sampling methods, has been conducted below 1000 metres. To date, there has also been no continual investigation targeting decapod distributions over time, in a single geographic region, to assess any density or distribution variations (Griffiths, H. 2013).

The lower temperature tolerance of 1.4oC for N.yaldwyni is argued by Griffiths et al. (2013),

as it strongly contradicts the temperature cut-off observed by Hall et al. (2011) for this species of Lithodid. In fact 1.4oC is at the higher end of the spectrum recorded for this species. Smith

et al. (2012) cite their finding as being an important model for potential invasive species due to the Palmer Deep seafloor warming rising from 1.20°C to 1.47°C since 1982. Stating that this temperature rise allowed N. yaldwyni to colonise the region.

The temperature range observed by Hall et all. (2011) suggests that the temperatures recorded in the Palmer Deep have not been sufficiently cold enough to exclude the observed species, being that the temperature has always been at least 1oC higher than the observed lower

temperature tolerance for this species. Therefore the presence of this species in Palmers Deep is most likely explained, as put forth by Smith et al. (2012), through ‘pulsed larval transport’ across the continental slope (Griffiths, H. 2013).

Griffiths et al. (2013) goes onto explain that the absence of any shallow water Lithodids supports the premise that Antarctic Lithodid communities sought out a deep water refuge. Though the exact nature of the oceanography and seafloor temperature off the West Antarctic slope during the last glacial maximum is unknown, it is believed that both the geographic and depth distribution of circumpolar deep water was similar to that of present. Allowing the current deep water Lithodid communities to have existed, even through the lowest

temperature extents of the last ice age, in suitable deep water habitats (Anderson, R. 2002). Although they are the most cold-tolerant of the reptant decapods, Lithodids are believed to still be physiologically incapable of surviving below 0.4°C. As such, Lithodids are currently excluded from nearshore, shallow-shelf environments along the West Antarctic Peninsula (because there the shallowest waters over the shelf are colder than the slope-waters) (Clarke, A. 2009). If this physiological limitation is general for Lithodids, it would thus confine these crabs almost completely to deeper water in the Southern Ocean, where the Antarctic

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In contrast to this, Aronson et al. (2015) states that even if Antarctic Lithodid species have endured on the continental shelf historically, the summertime sea surface temperatures and Antarctic shelf bottom waters off the West Antarctic Peninsula have risen by nearly 1.5oC

over the past 50 years (approximately double the global average). This excessive warming will likely remove the thermal barriers inhibiting Lithodids expansion onto shallow, near shore habitats, likely having severe impacts on previously isolated shallow benthic

communities, judging by the predation behaviour of Arctic Lithodids (Aronson, R. 2015). This is backed up by Griffiths et al. (2016), stating that Antarctic benthic invertebrates living within present Antarctic shelf temperatures, are typically capable of surviving at higher temperatures. (Griffiths, H. 2016).

Discussion:

Assessing the robustness of the ‘invasion theory’ against the ‘endurance theory’ is difficult for a number of reasons. Namely, the lack of historical context regarding Lithodid species in terms of distribution in the Antarctic environment. The lack of distribution records and Antarctic Lithodid fossils, in combination with scarce sampling and the rising sea

temperature, makes the newly observed distribution of Antarctic Lithodid, appear to be a consequence of anthropogenic climate change. Yet there is little evidence to suggest this is the case (Griffiths, H. 2013).

Though the invasion theory appears to be supported by a larger number of authors as well as being the centre of more research, it unfortunately makes a lot of assumptions due to the lack of data available. Sampling has only occurred in a small number of locations, using

parameters that are not specific to Antarctic Lithodids, potentially skewing the accuracy of results (Smith, C. 2012).

The endurance theory, in contrast, identifies the flaws of the invasion hypothesis. Most notably the inadequate sampling techniques, such as the low temperature tolerance for Lithodids in Palmer Deep. Though the endurance theory doesn't rule out the potential for extended distribution patterns for Lithodids as sea temperature rises, it found no evidence to suggest that the distribution patterns of Lithodid species in the southern ocean has expanded or been altered by the present rise in sea temperature (Griffiths, H. 2013).

In terms of academic contribution, I believe that the Griffith et al. (2013) report has played an important role, as it has highlighted the inadequate methods (E.g. limited depth, and

temperature monitoring ranges) and scarcity of available data to conclude and invasion event. The report also suggests an avenue for more effective data collection, in order to bridge gaps in knowledge, such as a collective database and calling for an integrated research program of repeated sampling of Antarctic Lithodid distribution. Going further to assert that future research must clearly differentiate between describing potential invasive species, as opposed to native species extending their distribution range in relation to environmental change (Griffiths, H. 2013).

Though there is little evidence to suggest that drastic changes in Lithodid distribution patterns are presently occurring, given the rate of sea temperature rise (especially in the West

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Therefore, although the endurance hypothesis is more robust, due to the relative diversity of Antarctic Lithodid, as well as having explainable historical and present distribution patterns. The premise of the invasion theory should be noted, as it is likely that the associated impacts will still occur as Antarctic Lithodid expand their distribution into the shallower reaches of continental Antarctica.

Conclusion:

In summary the limited extent of historical record, sampling accuracy and lack of information specific to Antarctic Lithodid species, results in a large gap in knowledge necessary to determine the origin, and typical distribution patterns, of Antarctic Lithodidae. As such the invasion theory must draw too many assumptions in order to assert an invasion event is occurring.

Given the relative diversity of Antarctic Lithodidae, as well as Antarctic deep water

conditions, historically being a viable habitat for these species, it appears that the endurance theory is more robust, as well as having significant academic contributions through indicating poor monitoring and sampling efforts.

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References:

1. Griffiths HJ, Whittle RJ, Roberts SJ, Belchier M, Linse K (2013) Antarctic Crabs: Invasion or Endurance? PLoS ONE 8(7): e66981. https://doi.org/10.1371/journal.pone.0066981

2. Thatje, S., Anger, K., Calcagno, J. A., Lovrich, G. A., Pörtner, H.-O. and Arntz, W. E. (2005), CHALLENGING THE COLD: CRABS RECONQUER THE ANTARCTIC. Ecology, 86: 619–625. doi:10.1890/04-0620

3. Arana EP, Retamal MA (1999) New distribution of Paralomis birsteini Macpherson, 1988 in Antarctic waters (Anomura, Lithodidae, Lithodinae). Invest Mar (Valparaíso) 27: 101–110.

4. Craig R. Smith, Laura J. Grange, David L. Honig, Lieven Naudts, Bruce Huber, Lionel Guidi, Eugene Domack. A large population of king crabs in Palmer Deep on the west Antarctic Peninsula shelf and potential invasive impacts. Proc. R. Soc. B 2011 -; DOI:

10.1098/rspb.2011.1496. Published 7 September 2012

5. Thatje, S., Hall, S., Hauton, C. et al. Polar Biol (2008) Encounter of lithodid crab Paralomis birsteini on the continental slope off Antarctica, sampled by ROV. 31: 1143.

https://doi.org/10.1007/s00300-008-0457-5

6. Ahyong S. T. 2010. The marine fauna of New Zealand: king crabs of New Zealand, Australia and the Ross Sea (Crustacea: Decapoda: Lithodidae). NIWA Biodiv. Memoir 123, 3–194

7. García Raso, J.E., Manjón-Cabeza, M.E., Ramos, A. et al. New record of Lithodidae (Crustacea Decapoda, Anomura) from the Antarctic (Bellingshausen Sea). Polar Biol (2005) 28: 642. https://doi.org/10.1007/s00300-005-0722-9

8. R.M. Feldmann, C.E. Schweitzer and S.A. Marenssi. Journal of the Geological Society, 160, 151-160, 1 January 2003, https://doi.org/10.1144/0016-764901-136

9. Paulo Y.G. Sumida, Angelo F. Bernardino, Victoria P. Stedall, Adrian G. Glover, Craig R. Smith, Temporal changes in benthic megafaunal abundance and composition across the West Antarctic Peninsula shelf. Volume 55, Issues 22–23, 2008, Pages 2465-2477, ISSN 0967-0645, https://doi.org/10.1016/j.dsr2.2008.06.006.

10. Hall, S. and Thatje, S. (2009), Global bottlenecks in the distribution of marine Crustacea: temperature constraints in the family Lithodidae. Journal of Biogeography, 36: 2125–2135. doi:10.1111/j.1365-2699.2009.02153.x

11. Hall, S. & Thatje, S. Temperature-driven biogeography of the deep-sea family Lithodidae (Crustacea: Decapoda: Anomura) in the Southern Ocean. Polar Biol (2011) 34: 363.

https://doi.org/10.1007/s00300-010-0890-0

12. Clarke, A., H. J. Griffiths, D. K. A. Barnes, M. P. Meredith, and S. M. Grant (2009), Spatial variation in seabed temperatures in the Southern Ocean: Implications for benthic ecology and biogeography, J. Geophys. Res., 114, G03003, doi:10.1029/2008JG000886.

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Studies in Oceanography, Volume 49, Issues 9–10, 2002, Pages 1909-1938, ISSN 0967-0645, https://doi.org/10.1016/S0967-0645(02)00018-8.

14. Richard B. Aronson, Kathryn E. Smith. No barrier to emergence of bathyal king crabs on the Antarctic shelf. PNAS 2015 112 (42) 12997-13002; published ahead of print September 28, 2015, doi:10.1073/pnas.1513962112

References

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