Sandro Lanfranco, Department of Environmental Science, GF Abela Junior College, University of Malta, Msida

Introduction
Several wetlands characterised by a level of salinity that is intermediate between that of seawater and freshwater are situated along the coast of the Maltese Islands. Such wetlands form through the accumulation of seawater in coast-fringing depressions. To this are added freshwater inputs from atmospheric and terrestrial sources. Input of water is linked to climatic cycles and therefore varies seasonally. Initial flooding of the habitat by rainfall generally occurs at the start of the wet season, in September/October, and proceeds intermittently until the onset of the dry season in March/April. Increased frequency and intensity of wave action during the wet season also enhances saltwater input into these habitats.

The dry season is characterised by high temperatures, low rainfall and decreased wave activity, all of which contribute to desiccation of smaller wetlands. Salinity of poolwater increases as these wetlands dry up and hypersalinity is characteristic of the latter stages of the aquatic phase of the habitats.

The abiotic stresses characteristic of these wetlands therefore set distinct biological limits to which colonising species must conform. The resident biota colonising such habitats are consequently characterised by behavioural strategies and physiological adaptations that promote tolerance of drastic fluctuations in salinity and survival of the dry phase.

Species richness in coastal wetlands is generally lower than that of adjoining freshwater or marine habitats of comparable dimensions, however it is not uncommon for coexistence of marine and freshwater species to occur.

Two broad categories of coastal wetland are generally identified:

• Saline marshlands: these contain brackish water for all or part of the year. The substratum is composed of fine-grained particles and is generally colonised by a flora of halophilic plants.
•  Transitional coastal wetlands: these are generally smaller than the major saline marshes and characteristically harbour a species assemblage that contains elements typical of freshwater coexisting with species typical of more saline waters.

Coastal wetlands only form at the boundary between the terrestrial and marine ecosystems. They are therefore limited in their spatial extent and are consequently ecologically vulnerable. Several such sites throughout the islands have already been degraded or obliterated.

Saline marshlands
These are represented by the larger coastal wetlands that retain water throughout much or all of the year, although with very marked reductions in volume during the dry season. The relatively longer water retention period in saline marshlands promotes the establishment of a biota that is qualitatively different from that of wetlands that are completely desiccated for longer periods.

In a global context, coastal marshes are generally grasslands that are regularly inundated by tidal currents. In the Maltese Islands, where the mean tidal range is very low (c.6cm), tidal effects are insignificant and these habitats are maintained by other processes, mainly wave action, precipitation and contribution by runoff and high-level springs.

Saline marshlands are very scarce in the Maltese Islands. Several have been obliterated by human activity and only a few such sites are still extant, although under constant threat.

• Salina: This is the largest remaining coastal marshland of the Maltese Islands, and harbours the only known local populations of various species of marsh vegetation and saltmarsh invertebrates. Additionally a number of bird species exploit this marsh as a resting ground and feeding ground. Proposals for commercial development of this marsh have recently been put forward.
• Il-Maghluq (Marsascala): A large marsh colonised by several halophytes, some of which are of very restricted distribution in the islands.
• Ghadira Nature Reserve: The present nature reserve at Ghadira has been artificially deepened in order to permit retention of water throughout the year. It is of obvious interest as a resting and feeding ground for several birds. However, this marsh also harbours a diverse biota which contains elements that are restricted to this locality.
• Is-Simar (Pwales Valley, St Paul’s Bay): This wetland has been designated as a nature reserve and is colonised by several halophytic species, some of which are of a restricted local distribution.
• Il-Ballut (Marsaxlokk): This habitat is highly significant as it harbours a number of species with a very restricted local distribution. An assemblage of brackish water snails also occur in this marsh.

Transitional coastal wetlands
Such habitats are characterised by a biota that comprises freshwater species and brackish-water species. The appearance of freshwater forms is probably more related to the ephemeral nature of these habitats rather than to the chemical properties of poolwater. The freshwater species that appear in these transitional coastal wetlands are all typical of temporary waters. This observation associated with the relatively wide salinity tolerance of some of these forms, suggests that ephemerality is the overriding factor in the assembly of communities typical of transitional coastal wetlands.
At least four principal wetlands of this type may be identified in the Maltese Islands, all of which are of considerable ecological significance.
 

• Ghadira s-Safra: An area of 0.8ha. located on the Northeast coast of Malta. This site represents the only locality from where the extremely rare liverwort Riella helicophylla has been recorded. This pool is also one of only two localities in Malta where the fairy shrimp Branchipus visnyai has been noted. Additionally, the tadpole shrimp Triops cancriformis has also been recorded from this pool, the last sighting being in December 1989.
• il-Qaliet: This wetland consists of a number of coastal pools close on the northern coast of Malta. The largest of these is characterised by dense growths of the rush Juncus acutus. This is the only other locality, apart from Ghadira s-Safra, from where Branchipus visnyai has been recorded (September and October 1995). These pools are sited on land that is earmarked fro development.
• Qammieh pools: This wetland forms on the shore platform at Qammieh and is of limited extent. Saltwater input from wave action is diluted by water running off the clay slopes that form a hinterland to this site. These pools harbour a plant community that comprises brackish-water species (e.g. Juncus acutus) and freshwater forms (e.g. the green alga Tolypella nidifica)
• il-Qattara (Gozo): This site is maintained by a permanent seep of freshwater. The biota is generally typical of permanent freshwaters with none of the ephemeral regime species that are typical of temporary saltmarshes. Although the hydrologic regime is essentially non-saline, the pool may become temporarily brackish through flooding of the watercourse that connects it to the sea.

 Saline marshes and transitional coastal wetlands of the Maltese Islands
 

Locality	Remarks
Mouth of Mistra Valley	degraded
Mouth of Wied Musa, Marfa	degraded
Il-Qawra, Dwejra, Gozo	degraded
Mouth of Ramla Valley, Gozo	degraded
Mouth of Wied Santa Marija Comino	degraded
il-Qattara, Dwejra, Gozo	disturbed transitional wetland
Ras ic-Caghaq, Delimara	extinct
il-Menqa	extinct
Mouth of Wied il-Kbir, Spinola	extinct
Ghadira z-Zghira, Mellieha	extinct
Mouth of Xlendi Valley, Gozo	extinct
Qbajjar, Gozo	extinct
Mouth of Wied Mas-Sabtan Birzebbugia	highly degraded
Site of Marsa Sports Club	highly degraded
Ta’Xbiex	highly degraded
Ramla tal-Qortin, Marfa	highly degraded
Mouth of Marsalforn Valley, Gozo	highly degraded
Mouth of Wied il-Faham, Bahar ic-Caghaq	highly degraded
Ramla tal-Bir, Marfa	highly degraded
il-Ballut (Marsaxlokk)	limited area but ecologically important
is-Simar	recently engineered as a nature reserve
Ghadira Nature Reserve	retains water throughout the year due to artificial deepening
il-Maghluq (Marsascala)	several halophilic species
Ta’ Qassisu	small and inaccessible
Salina	threatened by proposed development
il-Qaliet	threatened transitional wetland
Ghadira s-Safra	threatened transitional wetland
Qammieh	transitional wetland