Is the Future to be Jellyfish?

Compass Jellyfish, Chrysaora hysoscella

Reduction in the numbers of fish due to commercial fishing activities combined with changes in climate mean that blooms of the Cnidarian subphylum Medusozoa (jellyfish) are becoming more frequent and more numerous (Mills, 2001 Hydrobiologia 451pp. 55–68). While Ctenophores are also on the increase (see here), the physical size of the larger Medusozoa pose a variety of problems for various industries, both direct marine and non. 

Common Jellyfish, Aurelia aurita

Lynam et al. (2006, Current Biology 16 pp. R493-R494) report on blooms of large jellyfish (>13 cm in diameter, such as Chrysaora hysoscella) in the heavily fished area of northern Benguela off the coast of Namibia, where jellyfish biomass (12 million tonnes) now exceeds that of fish (3.6 million tons). This increase has manifested itself in burst fishing nets, blockage of power station coolant intakes and blockage of alluvial sediment suction used in diamond suction. Similar nuisances are reported by Nagata et al. (2009, Pan-American Journal of Aquatic Sciences 4 pp. 312-325) in Southern Brazil where artisanal prawn fishermen noted shortening the duration of trawl hauls, displacement of hauls to areas further away from the landing ports and the necessity of changing to other fishing gear types.

Lion’s Mane Jellyfish, Cyanea capillata

Chessie Season

Flowers of the Horse Chestnut, Aesculus hippocastanum, in May

The Horse Chestnut, Aesculus hippocastanum, is an introduced deciduous tree originally used for decoration in avenues and gardens but now naturalised in woods throughout Ireland (Phillips, 1977 Wild Flowers of Britain pp. 38, 174) where it makes an attractive component of the country's hedge banks (O'Mahony, 2009 Wildflowers of Cork City and County p. 54). It is indigenous to the Balkan Penninsula and was brought to Vienna in 1576, via Constantinople, and onwards to Central and Western Europe (Avtzis et al., Sofia 2007 Phytologia Balcanica 13 pp. 183–187). It has a spreading habit and produces spikes of white to red flowers in April and May (Sterry, 2004 Collins Complete Guide to Irish Wildlife p. 182). The leaves are bright green and divided into 5-7 oval leaflets. A. hippocastanum is among the first trees to turn brown in the autumn.

Leaf of The Horse Chestnut, Aesculus hippocastanum

It is, however, because of its fruit that A. hipposcastanum is best known. These consist of a fleshy outer part that is usually covered in spikes and a glossy brown nut, commonly called conkers, chestnuts or 'chessies'. These were very mush sought after when I was a child and are used to play the game of Chessies (more commonly called Conkers). This involves drilling a hole in the chessie and threading a piece of string or shoe lace through it. One then challenges an opponent and both players take turns to crack the other's dangling chessie with one's own. The winner is that who cracks the others chessie. All sorts of underhand schemes were employed to become the victor, such as yanking the opponent's chessie from their grasp, throwing it to the floor and stamping on it and treating the nuts to make them stronger. Some of these preserving methods are outline by O'Hare and Gerrel (2000, New Scientist: The Last Word 2 pp. 7-11), including baking in the oven, pickling in vinegar, varnishing and even soaking in hand lotion.

Fruit of the Horse Chestnut, Aesculus hippocastanum, in September

Unfortunately A. hippocastanum in Europe is now under threat from a bleeding canker disease which causes bleeding cankers on the stem and branches, foliar discoloration, and crown dieback often leading to tree death (Green et al., 2010 PLoS ONE 5: e10224). This disease was first reported in 2002/3 and has since infected hundreds of thousands of European A. hippocastanum trees across several countries in northwest Europe (Forestry Commission, 2008 Report on the National Survey to Assess the Presence of Bleeding Canker of Horse Chestnut Trees in Great Britain). The causative agent is the bacterium Pseudomonas syringae pathovar aesculi. This pathogen is identical to a P. syringae pathovar that infects Indian horse chestnut (Aesculus indica), indicating that it has found a new host in A. hippocastanum - one in which it is aggressively spreading.

Fruit of the Horse Chestnut, Aesculus hippocastanum

As Old as a Daisy

Daisy, Bellis perennis

The family Asteraceae (Compositae) is one of the most successful and largest group of flowering plants on the planet. Their members are most commonly known as weeds of agriculture and gardens, such as daisy (Bellis perennis), creeping thistle (Cirsium arvense) and dandelion (Taraxacum officinale). They are distinguished as having tiny flowers (referred to as florets) that are bunched together into a composite head surrounded by sepal-like bracts. The petals form two types of florets: ray florets which have a tube ending in a petal like strap and disc florets with the tube ending in five short teeth. The flowerheads may have all ray florets (dandelion), all disc florets (thistle) or a combination of both (daisy). the fruit is tiny and often carried on the wind by a pappus, a tiny parachute (Phillips, 1977 Wild Flowers of Britain p. 177).

Dandelion, Taraxacum officinale

Due to lack of fossil evidence, the origin of the Asteraceae is not well understood (Stuessy, 2010 Science  329 pp. 1605-1606). However Barreda et al. (2010, Science 329 p. 1621) describe capitula and pollen grains of Asteraceae from the Eocene of Patagonia in southern Argentina. These fossils are similar in structure to modern day Asteraceae, such as the thistle family, the Carduoideae. Barreda concludes that the ancestral Asteraceae arose in South America.

Alien Rabbits

European Rabbit, Oryctolagus cuniculus

In the 14 years from 1996 to 2010, Ireland has seen an increase in its number of animal species from 14,616 to 19,122, an increase of over 4,500 (Ferriss et al., 2009 Irish Biodiversity: a Taxonomic Inventory of Fauna). These new discoveries consist of animals that may have been overlooked before, animals that have have expanded their range and some that have been introduced, accidentally or on purpose. This last group, the deliberately introduced, have a long history on the island. One of the most recognisable is the European Rabbit, Oryctolagus cuniculus, was introduced to Ireland around the time of the Norman conquest of 1169 (Sterry, 2004 Collins Complete Guide to Irish Wildlife p. 22).  

O. cuniculus originated in the Iberian peninsula (Branco et al., 2002 Evolution 56 pp. 792-803) and unfortunately are now considered near threatened there due to a combination of disease, habitat loss, hunting and eradication as a pest (Ward, 2005 Reversing Rabbit Decline: One of the Biggest Challenges for Nature Conservation in Spain and Portugal). This decline has a knock on effect on predators such as the critically endangered Iberian Lynx and Iberian Imperial Eagle.

The Remarkable Life Cycle of the Eel

European Eel Elver, Anguilla anguilla

The European Eel, Anguilla anguilla, is a truly remarkable animal. It is an amphihaline fish, spending part of its life in the ocean and part in the fresh water of the streams of continental Europe and western Africa. A. anguilla has been seriously under threat since the 1980's. The reasons for this decline are seen to be manifold according to Feunteun (2002, Ecological Engineering 18 pp. 575-591), namely changes in the Gulf Stream current, obstructions to migration, the effect of fisheries, loss of habitat, parasite infection and poisoning due to pollution. The length of this list is explained by the complex life cycle of A. anguilla.

It begins with the spawning of the leptocephali. It is assumed (Schmidt, 1922 Philosophical Transactions of the Royal Society 211 pp. 179–208) that this is adjacent to the Sargasso Sea in the middle of the North Atlantic. Here the smallest leptocephali have been found, however no mature adults, adults mating or eggs have been found.

The currents carry the leptocephali to European and African coasts where they metamorphose into the glass eel stage. The glass eel is so named as it is translucent and is fished is certain parts of Europe where they are eaten, fried with garlic.

European Eel Elver, Anguilla anguilla

As the silver eels travel from marine to brackish and fresh water, they metamorphose into elvers. As these grow larger, they become a yellow-brown colour and are referred to as yellow eels (Arai et al., 2006 Estuarine, Coastal and Shelf Science 67 pp. 569-578).

These in turn metamorphose into silver eels, which emigrate back to the Atlantic to mate. However nothing is known about this stage of the eels life as it travels deep in the ocean and thus far tracking the eels has proved in the past to be too difficult/expensive (Feunteun, 2002). Yet in 2009 Aarestrup et al. (2009, Science 325 p. 1660) succeeded in tracking A. anguilla for the first 1300 km of its journey from the western coast of Europe using a miniaturized pop-up satellite archival transmitter indicating that the eel's migratory mystery is close to being revealed.