Lavender in the Salt

Sea Lavender, Limonium humile

With its sprigs of purple flowers on stalked shoots, Sea Lavender (Limonium humile) does indeed resemble its namesake Lavender (Lavandula spp.). Its there though that the similarity ends, as the resemblance is superficial with no relationship existing. L. humile can be found growing, sometimes with local abundance, in salt marshes where its flower bearing stems can rise to 20 cm above a basal rosette of rounded leaves. Salt marshes pose the dual problem of high salinity and low oxygen levels. Both of these pose there own particular problems for L. humile, but the lack of oxygen to the root systems is possibly the greater of the two evils. It, along with other Limonium spp., overcome this problem by switching root respiration to a very high level of lactate fermentation, a protracted level much greater than the transient lactate glycolysis seen in most plants at the transition from normoxic to anoxic conditions (1). The lactate subsequently produced in the Limonium spp. root cells is of a degree that would lethally acidify them and is transported out of the cells into the environment, thus maintaining cell homeostasis.

Sea Lavender, Limonium humile

References:

1. Rivoal and Hanson, 1993. Plant Physiology 101 pp. 553–560

Two Sun Planet

As recently mentioned on this blog, its been a miserable summer sun-wise. Not so for a planet recently discovered by the Kepler spacecraft. Launched in March 2009, Kepler's aim is to find and analyse terrestrial and larger planets in or near the habitable zone of a wide variety of stars (1). And its come up with quite the find: a planet in orbit around two suns (2). Known as Kepler-16b, the Saturn sized planet describes a 229-day orbit around its two stars, which in turn eclipse each other. The stars are 20% and 69% the size of our own star, the sun, and have a 41 day orbit.

Kepler-16b (in blue) orbiting its two stars (orange and yellow).
Note that distances are not to scale

References:

1. http://kepler.nasa.gov/
2. Doyle et al., 2011. Science 333 pp. 1602-1606

Sun Bathing Butterfly

Silver-washed Fritillary, Argynnis paphia

The sun has been in short supply in Ireland this year, and with September in full swing it looks (and feels) like we've had our, some may say inadequate, share for the year. These some would not include the Silver-washed Fritillary, Argynnis paphia. A large and attractive species native to Ireland that is common in woodlands, it has a yellow-orange upperwing marked with black that are similar to other Fritillary species, but is distinguished by the silvery sheen of the underwings (1). The adults are often found on their favourite food of brambles, basking in the sun. Here, they use their wings to absorb solar radiation and maintain their temperature above the ambient. By adjusting the angle of its wings at rest, it can absorb as much or as little sun as possible. Under artificial conditions, A. paphia was seen to adjust its wing position to maintain a thoracic temperature of 34±1.5 °C (3).

References:

1. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 106
2. Kammer and Brachi, 1973. Comparative Biochemistry and Physiology 45 pp. 1057-1063
3. Vielmetter, 1958. Journal of Insect Physiology 2 pp. 13-16

Cormorant Washing Line

Cormorant, Phalacrocorax carbo

The Cormorant (Phalacrocorax carbo) is one of the largest seabirds in Ireland, and also one of the most familiar. It can often be seen feeding in estuaries and perched in trees, where they sometimes breed (1). With its dark body and long, hooked bill it could be mistaken for its relative the Shag (P. aristotelis). However, the Shag is a smaller bird by about 20 cm and is rarely seen inland. Adult Cormorants have an attractive blue-green sheen to their plumage, a yellow and white bare patch of skin on its face and a white thigh patch that disappears after the breeding season (1).

Cormorant, Phalacrocorax carbo

Recently, I observed a Cormorant perched on an old mooring post in a river estuary. It held its wings out from its body in a drooping fashion that is known as a spread-wing posture. Many birds engage in this type of behaviour. Cormorant feathers retain moisture when diving for food, which decreases buoyancy and aids underwater pursuit of prey. Only the outer layer of feathers are wettable however, and a a layer of insulating air is maintained next the skin when diving (2). Yet the outer feathers remain wet upon emergence and therefore need to be dried. Hence the spread-wing posture (as seen in the photographs) of the Cormorant, a living washing line.

References:

1. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 34.
2. Elowson, 1984. The Auk 101 pp. 371-383

Spooky Dragonflies

Male Common Darter, Sympetrum striolatum

The Common Darter (Sympetrum striolatum) is, as its name suggests, a common and widespread dragonfly in Ireland, indeed in Europe as a whole. Flying between June and October, it can often seen resting on paths or stones in sunny, open areas. S. striolatum is a very aggressive, territorial species and will “dart” at other, often larger dragonfly species. Males and females differ in their colouring, with mature males having orange-red, unwaisted abdomens in contrast to the the dull, yellow-brown females.

Female Common Darter, Sympetrum striolatum

Individuals are most often seen near favoured breeding sites of shallow ponds and small lakes, so it was therefore a surprise when in Hungry S. striolatum (along with five other species of Sympetrum)  individuals were observed in large numbers in a cemetery that was nowhere near any water source (1). Were they just being spooky or was there a more rational answer?

Common Darter, Sympetrum striolatum

The dragonflies were seemingly attracted to polished black gravestones, where their behaviour was the same as if by water. This involved perching near the gravestones and defending their perch, flying individuals repeatedly touching the gravestone surfaces with their ventral sides and pairs in tandem position frequently circling over the gravestones. It was found that the gravestones reflect highly and horizontally polarised light in a manner almost identical to smooth water. S. striolatum, along with many other dragonfly species, find their aquatic habitats by means of polarotaxis, the use of reflected polarised light to discriminate between surfaces (2). This explains the attraction to the gravestones, an attraction that is so strong that females are sometimes lead to oviposit on the gravestones.

References:

1. Horváth et al., 2007. Freshwater Biology 52 pp. 1700–1709
2. Bernáth et al., 2002. Freshwater Biology 47 pp. 1707–1719

The World's Largest Bony Fish

Reaching a weight of 1500 kg, the pelagic Ocean Sunfish (Mola mola) is a spectacular animal. Its distinctive laterally compressed shape and “chopped off” appearance make it one of the most distinctive of fish (1). Its truncated shape lends it its common name, as well as its tendency to bask on its side, close to the surface. One of only five members of the Molidae family, it has some unique features including the largest number of eggs produced by a vertebrate (300,000,000 eggs at one time) and larval metamorphosis that passes through two distinct stages (1). M. mola is distributed throughout the worlds oceans, with reports from the North and South Atlantic, the Pacific, the Mediterranean and the Gulf of Mexico (2). It feeds mainly on jellyfish and comb jellies, making it one of the few animals to do so. The increase in jellyfish numbers worldwide as commented on in this blog (here and here) means that there has been a marked increase in research into M. mola and the other sunfish species world wide. Satellite tracking of individuals has shown that they move up and down in the water column during the day and night, most probably in synchrony with their prey (2). They are also shown to migrate north in spring/summer and south in winter, again in response to prey movements but possibly also due to its preferred temperature range of 10-19°C (2). M. mola is preyed upon by relatively few other animals with reports of sharks, orcas and sea lions reported as feeding on them (3). They are, however, prone to high levels of parasitism, possibly due to their large surface area.

Ocean Sunfish, Mola mola

Unfortunately the picture used to illustrate this post is of a dead M. mola, caught off the south coast of Ireland and photographed in a fishmongers*. And while a live example would have been much more preferable, this picture does point to the fact that sunfish are being caught in huge numbers as a result of commercial fishing of swordfish and tuna species. These bycatch numbers are alarming: in South African swordfish and tuna fishing, 170 sunfish are caught for every 1000 hooks deployed (2). In Californian drift gillnet fishing for swordfish M. mola comprised 29% of total catch – much more than the target species (4). The enigmatic nature of this sunfish means that the effect of fishing practices on populations remains unknown.

*Note: The sale of all Molidae species is banned in the EU as they are classed as poisonous under Chapter II part G of Regulation (EC) no 854/2004 of the European Parliament and of the Council. I can only assume that the fish was for display purposes only.

References:

1. Bass et al., 2005. Marine Biology 148 pp. 405–414
2. Sims et al., 2009. Journal of Experimental Marine Biology and Ecology 307 pp. 127-133
3. Pope et al., 2010. Reviews in Fish Biology and Fisheries 20 pp. 471-487
4. Cartamil and Lowe, 2004. Marine Ecology Progress Series 266 pp. 245-253

The Caring Leech

Glossiphonia complanata

Mention leeches and immediately images of large, swamp dwelling beasts, stuck to the bodies of fever racked unfortunates, to be removed with a lighted cigarette, are conjured up. Yet Ireland has its fair share of the animals, some thirty two species from two orders and five families (1). Eighteen of these are marine. And they are not all out for your blood either. Many feed exclusively on other invertebrates. Take the fresh water Glossiphonia complanata, a snail leech. As its common name implies, it feeds on aquatic gastropods that it encounters in fast flowing, rock streams, although it will also feed on Oligochaeta, Chironomidae, and Amphipoda in decreasing magnitude (2). It achieves this by inserting its probiscus into the soft parts of its prey and sucking out their body fluids. G. complanata is a relatively short leech, with a broad body that is flattened dorso-ventrally. It is often encountered attached to the underside of stones, waiting for prey (3).

G. complanata shows a degree of parental care that is surprising for an invertebrate. As hermaphrodites, each individual produces a cocoon with a soft transparent covering containing the developing embryos. This is attached a stone and brooded over by the parent for about 20 days. Upon hatching, the young cling to the ventral surface of the parent (4).

References:

1. Ferriss et al., 2009. Irish Biodiversity: a Taxonomic Inventory of Fauna pp. 74-75
2. Wrona et al., 1979. Canadian Journal of Zoology 57 pp. 2136-2142
3. Mann, 1956. Journal of Animal Ecology 26
4. Kutschera, 1986. Animal Behaviour 34 pp. 941-942