Friday, January 27, 2012

Dolphins, more intelligent than people

- From the Hitchhiker's Guide to the Galaxy, by Douglas Adams 

As a card carrying marine biologist who doesn't study dolphins or whales, I am obliged to say that they are some of the most uninteresting animals in the sea. But, over at Why Evolution is True, there is a post about dolphins playing with whales that other people might like.

Thursday, January 26, 2012

Flowering plants in the sea, part 1 - photosynthesis

Just as whales are mammals that have gone back to the sea, so seagrasses are flowering plants that have gone back to the sea. Interestingly, seagrasses appear to have gone back to sea several times, but have evolved many strikingly similar features for survival in the marine environment.

Seagrass in the genus Zostera
The feature that gives seagrasses their name, is the strap-like leaves which look similar to the leaves of the true grasses. Although the leaf shape is similar among the different groups of seagrass there are enough differences to indicate that it's a trait that has evolved separately in each of the seagrass lineages. Something that is supported by genetic analyses.

Seagrass growing at depth appears blue because water absorbs more light at the red end of the spectrum
One of the important selection pressures on seagrasses is access to light for photosynthesis. Water absorbs light and absorbs some wavelengths of light better than others, which is what makes it appear blue. Suspended particles in the water column and organisms growing on the leaf surface (epiphytes) attenuate light available to seagrass for photosythesis further. The light environment of seagrasses is, therefore, very different from that experienced by terrestrial plants.

Seagrass from the genus Halodule with epiphytic organisms growing on its leaves
Seagrasses have several adaptations that allow them to survive in low-light conditions. Their chloroplasts occur in shallower tissues than terrestrial plants. The leaves also contain very little structural material, so a larger proportion of the plant is capable of photosynthesis than most terrestrial plants.

Another property of the marine environment that differs from terrestrial plant habitats is wave action. Wave action moves the seagrass backwards and forwards exposing different sides of the leaf to alternating high and low light levels. As a adaptation to these conditions both sides of the seagrass leaf are equally capable of photosynthesis. This is unlike many terrestrial plants where photosynthesis occurs mostly in the upper surface of the leaf.

Light levels can vary strongly in the marine environment on short and long time scales. For instance, light levels can vary on short time scales with changing tide heights and increased turbidity due to wind and wave action or can vary on long time scales with changes in day length and the number of organisms growing on the seagrass. To cope with periods of low light, seagrasses make use of rhizomes. Rhizomes are modified stems that grow horizontally and are used to store the products of photosynthesis when times are good for times when little or no photosynthesis can be achieved.

The seagrass Zostera marina showing the rhizome in the bottom of the image
It's the energy-rich rhizomes that make seagrass an important source of food for many marine animals and water birds, such as dugongs, manatees, turtles and swans.

Thursday, January 19, 2012

Phytoplankton from space

The plankton consists largely of small organisms such as bacteria, plants and animals that drift at the mercy of ocean currents. The phytoplankton is the component of the plankton that is able to photosynthesize and it therefore very important in marine food-webs as primary producers. Indeed, phytoplankton are important for almost all life on Earth as they carry out about half of all photosynthetic activity, and therefore produce much of the oxygen in the atmosphere.

Diatoms, one of the most numerically dominant types of phytoplankton. Other important groups include dinoflagellates, cyanobacteria and algae.
Phytoplankton are restricted to the surface water where sunlight can reach them. Their numbers there are limited by the availability of certain nutrients. When these nutrients become abundant, such as during the upwelling of water from the deep ocean, the phytoplankton numbers increase rapidly. Such events are called 'blooms' and can be large enough to be detected from space.

A false-colour image of a phytoplankton bloom in the South Atlantic Ocean taken by the Earth-observing satellite Envisat. The colours represent the density (shade) and types (colour) of phytoplankton present.
Different types of phytoplankton use different combinations of pigment for photosynthesis. Different pigments absorb different wavelengths of light and this allows satellites to make a coarse identification of the species of phytoplankton present in a bloom by detecting the reflected light. Using this information false-colour pictures of a bloom, such as the one above, can be constructed to identify when, where and what types of phytoplankton are blooming. This is important information that assists with our understanding of the effects of human impacts on the marine environment, such as pollution and climate change.

Like life on the deep seafloor, the diversity of species in the plankton presents a paradox. Phytoplankton exist in a seemingly uncomplicated environment and compete for a small number of limiting resources, a situation that should favour a limited set of species, yet there is a huge diversity. Perhaps small variations in the spatial and temporal availability of the resources and variations in temperature create the complex set of niches required to support high diversity, as they do in the deep.

This post was inspired by a post on Sandwalk. The image of the phytoplankton bloom can be found (and downloaded) on the European Space Agency website here.

Tuesday, January 17, 2012

Good news from England

The Department of Education will now be able to withdraw funding from schools that seek to teach nonsense in science classrooms. Views that are presented as evidence-based but run contrary to well established scientific evidence and explanations, such as intelligent design creationism, will no longer be able to be taught as fact. For more here is an article from the Guardian.

Friday, January 13, 2012

Japanese incursion

Two days ago a Japanese vessel, the Yushin Maru No. 3, associated with the whaling fleet in the Southern Ocean sailed 8 nautical miles into Australia's Territorial Waters in pursuit of a Sea Shepherd vessel. The Yushin Maru No. 3 is a harpoon ship used for whale catching and is unwelcome in Australian Territorial Waters where whaling is illegal. Despite Australian Government protests to Japan the vessel stayed within Australian waters for more than 24 hours. Moreover, it stayed within Australian waters for several hours after it was said to be leaving. It continues the pugnacious approach that Japan has adopted in its dispute with Australia over its whaling activities in the Southern Ocean. 

The Yushin Maru No. 2, a harpoon vessel similar to the Yushin Maru No. 3

Although the vessel is now within Australian's Exclusive Economic Zone there is apparently little legal recourse for Australia as long as the vessel does not hunt whales. Australia has  claimed its Exclusive Economic Zone as a whale sanctuary. Under international law Australia should have the legal right to regulate fishing, including whaling, within this zone. But, Japan continues to hunt whales within the sanctuary under the guise of scientific research*. Finally, after much dithering by both major political parties, Australia launched legal proceedings against Japan over the whaling in the International Court of Justice. Australia submitted its case in May 2011 and Japan is due to make its submission in March this year.

Map of Antarctic territorial claims. Australia claims two territories (orange) which sandwich the French claim (dark blue). Norway claims the next largest territory (purple). New Zealand (green) also claims territory. The UK (red), Chile (yellow) and Argentina (light blue) have overlapping claims.
Any reduction in the area that Japanese can catch whales in as a result of Australia's action in the International Court for Justice is, unfortunately, unlikely to have a great effect on the supply of whale meat in Japan. Australia claims and exclusive economic zone in the waters off its Antarctic territory, but Japan and most of the rest of the world does not recognise this claim. Indeed, only four countries who also claim large exclusive economic zones in the Antarctic recognise Australia's claim. Japan is therefore likely to be able to continue whaling in these areas. Moreover, Iceland now exports whale meat to Japan, reportedly earning the country $US 17 million in the last four years. Like Japan, Iceland's whale hunt is conducted under the guise of scientific research. I guess they have a lot of collaborators in Japan...

The Japanese and Icelandic whale research programmes produce few, if any, valuable data on whales. Moreover, non-lethal research can be used to produce much of the same information. Scientific reviews of the research programmes conducted by the International Whaling Commission have found that experimental designs are shoddy, and that the information is either not required for management or obtainable by non-lethal means. That has not stopped either of the countries from whaling. Indeed, Japan has tried to use their data to argue that whale numbers are growing and need to be culled to preserve commercially important fish species. Of greater threat to Japan's commercially important fish stocks is certainly Japan's fishing fleets. I'll write more on that sometime.

*As Terry Pratchett and Neil Gaiman joke in Good Omens, the research is primarily concerned with determining how many whales can be caught during the whaling season.

Coral Sea Marine Park

The Australian Government is considering submissions to its Coral Sea Commonwealth Marine Reserve proposal. The proposal is seen by many leading scientists as insufficient to properly protect the area from fishing and other impacts (e.g. here and here).

Should the park go ahead as it is currently proposed it will be the largest marine park ever established. But, less than half of it will be given full protection and this area is the part furthest from shore and already the least impacted by commercial and recreational fishing.

Overfishing is a significant threat to coral reefs and is likely to decrease the resilience of coral reefs to climate change1. It would be good to get greater protection of this area from fishing activities. If you would like to contribute go here for a guide to writing a submission, or go here to view the proposal. The consultation process ends on February 24, 2012.

1 Pandolfi, J. M., Connolly, S. R., Marshall, D. J., Cohen, A. L. Projecting Coral Reef Futures Under Global Warming and Ocean Acidification. Science 333 no. 6041, 418-422, doi:10.1126/science.1204794 (2011).

Tuesday, January 10, 2012

Beware the Jabberwock

My favorite poem is the Jabberwocky by Lewis Carroll, which can be found in Through the Looking-Glass and What Alice Found There.

The Jabberwock, by John Tenniel
`Twas brillig, and the slithy toves
  Did gyre and gimble in the wabe:
All mimsy were the borogoves,
  And the mome raths outgrabe.

"Beware the Jabberwock, my son!
  The jaws that bite, the claws that catch!
Beware the Jubjub bird, and shun
  The frumious Bandersnatch!"

He took his vorpal sword in hand:
  Long time the manxome foe he sought --
So rested he by the Tumtum tree,
  And stood awhile in thought.

And, as in uffish thought he stood,
  The Jabberwock, with eyes of flame,
Came whiffling through the tulgey wood,
  And burbled as it came!

One, two! One, two! And through and through
  The vorpal blade went snicker-snack!
He left it dead, and with its head
  He went galumphing back.

"And, has thou slain the Jabberwock?
  Come to my arms, my beamish boy!
O frabjous day! Callooh! Callay!'
  He chortled in his joy.

`Twas brillig, and the slithy toves
  Did gyre and gimble in the wabe;
All mimsy were the borogoves,
  And the mome raths outgrabe. 

Monday, January 9, 2012

Hybrid sharks

Australian scientists have found the first evidence that shark species can hybridise. The Australian black-tip shark (Carcharhinus tilstoni) and the common black-tip shark (C. limbatus) are found along much of the northern Australian coastline and have extensively overlapping distributions. The larger common black-tip can tolerate cooler waters and it is therefore found in more southerly locations.

The find is also interesting because the hybrid sharks are morphologically indistinguishable from the Australian black-tip shark, but they are found further south like the common black tip. The scientists involved in the study believe that the hybridisation could allow the ability to tolerate cold water to spread into the Australian black-tip, which would facilitate a southerly range expansion. 

Common black-tip shark Carcharhinus limbatus

If the hybrid sharks mate with the pure-bred Australian black-tips and the genes for cold-tolerance spread in the population it would be an example of 'evolution in action'. Most people familiar with the theory of evolution by natural selection would know that the stuff that natural selection works on is variation in heritable traits. The best known way in which heritable variation can arise is through genetic mutation, but there are other ways it can occur, which include hybridisation.

Hybrids are rarely found in the wild. Partly this is because often they or their offspring are less fit and therefore do not persist for long when hybridisation occurs. The scientists involved in finding the hybrid sharks are now attempting to measure the fitness of the hybrids. I wish them luck because measurements of fitness in the wild are more rare than in the laboratory, but more informative about the process of natural selection. What's more, measuring fitness in wild populations is difficult, especially for a large animals that can move long distances.

Monday, January 2, 2012

Deep-sea diversity

Many people, if they were asked "in which ecosystem would you find the highest diversity of species in the ocean?", would answer "coral reefs". And they'd probably be right. But there is another ecosystem in the ocean that is comparably diverse. Surprisingly, it's the deep seafloor.

Ecosystems that support high diversity are generally those that are spatially complex and have a high productivity allowing for a large number of niches that various organisms can occupy. In contrast to the high diversity habitats that most people are familiar with, the deep sea consists of energy poor, spatially uncomplicated mud flats. It was therefore expected that there would not be a high diversity of life in the deep ocean. However, in the 60's and 70's surveys of species richness in deep-sea sediments found that hundreds of species could exist in just a few square meters.

The deep seafloor is energy poor because no light reaches it and consequently there are no primary producers, except in rare locations like hydrothermal vents and methane seeps. The energy reaching the deep seafloor, therefore, comes almost entirely from the shallow oceans above where photosynthesis is possible. The detritus of the life above that trickles down to the deep is called marine snow. Very little of of the productivity of the shallow seas reaches the deep seafloor because most of the detritus is consumed before it gets to the bottom.

The source and fate of marine snow in the oceans.

One reason that has been proposed to explain the high diversity is that the marine snow does not fall evenly across the seafloor, but is variable in both space and time. This means that the amount of energy available to deep seafloor organisms is patchy and some species may be better adapted to different levels of energy availability. The reasons that marine snow is variable at large scales are depth (shallower parts of the seafloor receive more marine snow because there is less time for things in the water column to eat it before it gets to the bottom) and the productivity of the sea surface. Large and small scale water currents also play a role in the distribution of marine snow reaching the bottom.

Some studies published last year find support for the 'marine snow' hypothesis of deep seafloor diversity. Looking at small scales (1 - 350 meters), one  study1 found that samples taken close together were only slightly more likely to contain similar species that samples taken 350 meters apart. However, samples were more likely to contain similar species when they contained similar amounts of energy. 

A second study2 looked how the diversity of two particular groups changed with depth, temperature and energy availability. They found that energy availability was the most important factor for determining the distribution of species, but depth and temperature also played a role.

A third study3 also looked at the effect of depth, temperature and energy availability on deep seafloor diversity. This study, though, added a whole host of other environmental variables and looked at how dispersal ability affected diversity. This study again found that energy availability was the most influential factor influencing species distributions, but temperature was also important. Depth had an influence, but it was less important. None of the other environmental variables were very important, but dispersal ability was.

Maps showing the distribution of ocean depths (top left; lighter blues are shallower), marine snow (top right; yellows are higher), and temperature (bottom; redder is greater) in the study regions. The red points show the sampling sites from the third study, while the white are the sampling sites in the second.

These studies are interesting because they show that even in energy poor, physically simple environments there can be great spatial complexity. Indeed, small variations in just a few factors can explain a good deal of the amazing diversity of organisms living in the deep sea. And it's the small differences in the amount of marine snow reaching the seafloor in particular that seems to be most important in determining this diversity.

Cited references:
1 McClain, C., Nekola, J., Kuhnz, L. & Barry, J. Local-scale faunal turnover on the deep Pacific seafloor. Marine Ecology Progress Series 422, 193-200, doi:10.3354/meps08924 (2011).

2 Tittensor, D. P., Rex, M. A., Stuart, C. T., McClain, C. R. & Smith, C. R. Species-energy relationships in deep-sea molluscs. Biology Letters 7, 718-722, doi:10.1098/rsbl.2010.1174 (2011).

3 McClain, C. R., Stegen, J. C. & Hurlbert, A. H. Dispersal, environmental niches and oceanic-scale turnover in deep-sea bivalves. Proceedings of the Royal Society B: Biological Sciences, doi:10.1098/rspb.2011.2166 (2011).