Algae (kingdom Protoctistia; subkingdom Algae)
Algae are complicated primitive organisms that mostly obtain their nutrients from photosynthesis. They are related to the Protozoans and less so to Plants, which they resemble in appearance. Phytoplanktonic Algae are the basic food source of virtually all life thriving in the oceans; Kelp forests act as shelters for many young fish, mollusks and crustaceans.
eg 1 Japanese Kelp
Phylum: Heterokontophyt (Brown Algae)
Scientific name: Undaria pinnatifida
This kelp is native to the seas of the Far East between China, Korea and Japan. It is olive-brown in colour, growing to 2m tall and 1m broad; robust rhizoid holds the kelp to the sea bottom in shallow intertidal zones along rocky shorelines. Blades are lobate in shape, flat, broad, lubricous and mid-ribbed. Though cultivated in the native Japan for food for ages, the weed has proved to be an opportunistic organism capable of quick growth in areas, which it has been introduced, for example in Australia, New Zealand and the Mediterranean, even to Argentina, where it has clogged up shorelines in many places. The thick canopy of the kelp forms dense oceanic forests, displacing native species and obscuring the underwater environment, reducing the amount of light and space available for other photosynthesizing plants and algae living along the coast. Ship hulls are also biofouled. They reproduce both by producing spores and gametes, and spores can be turned out in the order of millions in hours. Reproductive fragments of floating kelp can be carried along with the current for kilometres, and they have the ability of hitchhiking on the hulls of ships, dispersing equally well through this method. It is tolerant of temperature changes from the range of 2 to 29°C, and salinity changes are also of little concern to the kelp.
The microscopic phase of the kelp makes it incredibly difficult to eradicate, and manual removal is still relied upon. It is thought highly unlikely that this species will be removed from the infested area as a result.
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eg 2 Caulerpa Seaweed
Phylum: Chlorophyta (Green Algae)
Scientific name: Caulerpa taxifolia
The Latin name of this Alga describes the similarities of its photosynthetic surfaces to the leaves of Yew trees, which are flattened and dark-green in colour. The fronds have a thick central axis and many pinnules grow from it, and are longer in the tropical strains than the temperate ones. Frond density can reach over 10000 per square metre and dense mats can be formed to places where the water is 30m deep. A network of filamentous rhizoid covers the seabed and absorbs nutrients for the consumption and growth of the Alga. It reproduces mainly by fragmentation, a type of asexual reproduction that enables the weed to proliferate whenever auspicious conditions arrive.
Caulerpa is widely distributed throughout the tropical seas along the coasts of Brazil, Venezuela, Colombia, Costa Rica, the Antilles, Gulf of Guinea, Red Sea, Somalia, Kenya, Tanzania, Madagascar, Maldives, Seychelles, Pakistan, India, Sri Lanka, Bangladesh, Malaysia, Indonesia, Philippines, Vietnam, China, Japan, Hawaii, Fiji, New Caledonia, and North Australia, where it grows in isolated patches and does not present ecological problems. Accidentally released from the wastes of Monaco Aquarium in the Mediterranean in the 1980s, now the noxious seaweed is covering over 5000 hectare of the sea in the infested area, and many Mediterranean countries are adversely affected. In 2000 the Mediterranean strain has been found around California and Southern Florida, and it is feared that similar effects will ensue as seen in the invasion of the Mediterranean.
Capable of both sexual and vegetative reproduction and does so vigorously, with maximum growth during August and September, Caulerpa is dispersed with ships navigating widely across the oceans as vectors, as the seaweed adheres to anchors and drops off in the destinations --- where the boats anchor in harbours and marinas are likely to be newly colonized areas. This tropical seaweed has adapted well to colder waters in exotic ranges, showing different morphological and physiological characteristics from their tropical counterparts. The introduced forms have managed to adapt by showing a huge range of temperature tolerance from 7 to 32°C, impressive for an Alga of tropical origin. Its compensation point is very low, and it can photosynthesize even in extremely low light conditions; it is also grow under low nutrient levels, especially the Mediterranean strain, which is worse news for the native floral community of the area, as this competitive weed is outnumbering even the dominant seaweed in the Mediterranean community, Posidonia oceanica, in fact killing up to a half of the seagrass in some invaded areas. Drastic drop in the populations of other native Algae is observed and this has led to local extinctions of many native species. The intractability of this exotic Alga largely lies in the toxic metabolites (caulerpenyne andmono- and sesqui-terpenes) produced in large concentrations in the Mediterranean, which are toxic to many herbivores such as Sea Urchins that otherwise would have kept the populations of the seaweed down to acceptable levels, and phytoplankton, which are the primary producers of the sea along with other macro Algae. The invertebrate fauna is reduced in diversity also as the basic food source, which are the seaweeds displaced by Caulerpa. Eventually the food webs are collapsing from the very base.
Manual control is applicable to isolated patches but large mats of Algae in many affected areas must be dealt with chemically. Chlorine is by far the most effective method, but as it also harms the native fauna and flora, it cannot be used extensively. Meanwhile, Caulerpa wins and is still proliferating.
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