Sandy beaches: verschil tussen versies

Uit Kust Wiki
Ga naar: navigatie, zoeken
(Redirected page to Sandy shores)
Regel 1: Regel 1:
Shorelines worldwide comprise of extensive '''sandy beaches''', dominating both temperate and tropical coastlines.  The [[biodiversity]] of these sandy beaches is made up of [[macrofauna]], [[meiofauna]] and insects.  Diversity patterns help illustrate the effect that human pressures can have on coastal environments and the need for an integrated management approach in order to maintain these levels of coastal diversity.
#REDIRECT[[Sandy shores]]
==Sandy beaches==
The coastal area ([[coastal zone]]) is an extremely dynamic environment where interface between sand, water and air are always observed. This interface is composed of specific gradients or boundaries whose dimensions range from a few nanometres to a kilometre or more.
Coastal areas contain:
*maritime zone
*"sea" zone
*[[littoral]] or intertidal zone, where specialized fauna and flora at the sea-land interface is found
Beach types based on '''morphodynamic scale''' of Short & Wright (1983)<ref>Short & Wright (1983)</ref>:
*intermediate (a few types)
Beach types based on the '''degree of exposure''' Brown & McLachlan (1990)<ref name="Brown and McLachlan"/>:
*very sheltered
*very exposed
Sandy shorelines are some of the most extensive intertidal systems worldwide<ref>Short, A.D. 1999. Beach and shoreface morphodynamics. John Wiley and Sons Inc., Chichester. 215 p</ref>, dominating most of the temperate and tropical coastlines, where they represent both excellent recreational assets and buffer zones against the sea <ref>Davies, J.L. 1972. Geographical variation in coastal development. Longmans, London.</ref>. Despite their initial barren and sterile appearance, many sandy beaches sandy littoral localities might even be considered as highly productive <ref>McLachlan, A. 1983. Sandy beach ecology – A review. In: McLachlan, A. and T. Erasmus (eds). Sandy beaches as Ecosystems. W. Junk, The Hague. pp. 321-380</ref>. Shallow marine sands that appear to consist of clean mineral grains only harbour a microscopic community of microorganisms (bacteria, fungi, protozoa), meio- and macrofauna organisms that in its diversity rivals that of terrestrial [[ecosystems]]. Every single individual of this sedimentary community affects the processing of organic matter within the sediment and thereby enhances the [ biocatalytical filtration] capacity of the permeable sand beds<ref>COSA - [ COastal SAnds as biocatalytical filters ]</ref>.
==[[Biodiversity]] of sandy beaches==
Most invertebrate phyla are represented on sandy beaches, either as interstitial forms or as members of the [[macrofauna]] <ref name="Brown and McLachlan"/>. The [[Macrofauna|macrofaunal]] forms are by far the better known. Some of them are typical of intertidal sands and their surf zone, while others are more characteristic of sheltered sandbanks, sandy muds or estuaries and are less common on open beaches of pure sand <ref name="Brown and McLachlan"/>.
[[Macrofauna]] of the sandy beaches are often abundant and, in some cases, attain exceptionally high densities. Their main  feature is the high degree of mobility displayed by all species. These animals may vary from a few mm to 20 cm in length.  The [[macrofauna]] community consists of those organisms too large to move between the sand grains. The [[macrofauna]] of  sandy beaches includes most major invertebrate taxa although it has been recognised that molluscs, [[crustacea|crustaceans]] and  polychaetes are the most important. There is a tendency for [[crustacea|crustaceans]] to be more abundant on tropical sandy beaches or  more exposed beaches and molluscs to be more abundant on less exposed and on temperate beaches although there are  many exceptions of this and polychaetes are sometimes more abundant than either of these taxa. Generally [[crustacea|crustaceans]] dominate the sands towards the upper tidal level and molluscs the lower down level <ref name="Brown and McLachlan">Brown & McLachlan 1990</ref>. Physical factors,  primary wave action and particle size of the sand largely determine distribution and diversity of the invertebrate [[macrofauna]] of sandy beaches. Food input and surf-zone productivity may determinate the abundance population. Water  movement is important parameter controlling [[Macrofauna|macrofaunal]] distribution on beaches.
In contrast to the wave-swept surface sand inhabited by most of the [[macrofauna]], the interstitial system is truly three-dimensional, often having great vertical extent in the sand. The porous system averages about 40% of the total sediment volume. Its inhabitants include small metazoans forming the [[meiofauna]], protozoans, bacteria and diatoms<ref name="Brown and McLachlan"/>. The [[meiofauna]] is defined as those metazoan animals passing undamaged though 0.5 to 1.0 mm sieves and trapped on 30 mm screens. On most beaches the interstitial fauna is rich and diverse, even exceeding the [[macrofauna]] in [[biomass]] in some cases<ref name="Brown and McLachlan"/>. The dominant taxa of sandy beach [[meiofauna]] are nematodes and harpacticoid copepod with other important groups including turbellarians, oligochaetes, gastrotrichs, ostracods and tardigdades.
Terrestrial insects and vertebrates are frequently ignored in accounts of sandy beaches. These animals are usually a conspicuous component of the [[ecosystems|ecosystem]], often rivalling the aquatic [[macrofauna]] in terms of [[biomass]] and having a significant impact on the system with regard to predation and scavenging.
==Latitudinal [[biodiversity]] patterns of [[meiofauna]] from sandy [[littoral]] beaches==
Recently, large-scale patterns of marine [[biodiversity]] were the subject of many discussions (e.g.<ref>Rex et al. 1993</ref><ref>Rex et al. 1997</ref><ref name="Angel 1994">Angel 1994</ref><ref>Krause and Angel 1994</ref><ref>Gray 1995</ref><ref name="Gray 1997">Gray 1997</ref><ref>Gee and Warwick 1996</ref><ref>Heip et al. 1998</ref><ref>Lambshead et al. 2000</ref><ref name="Allen et al. 2002">Allen et al. 2002</ref>). These attempts to develop a general picture of diversity in the sea are hampered by the small number of key studies, the varied sampling protocols applied, the different diversity indices and the varying levels of taxonomic resolution<ref name="Clarke and Crame 1997">Clarke and Crame 1997</ref>. A general trend of species impoverishment towards the poles was reported for some taxa (e.g., corals, gastropods), but this does not hold for others (e.g., amphipods and decapods crustaceans)<ref>Dworschak 2000</ref><ref>Bellwood and Hughes 2001</ref><ref>Rodriguez et al. 2001</ref>. In addition, it seems probable that there is a cline in increasing diversity from the arctic to the tropics, but the cline from the Antarctic to the tropics is far less well-established<ref name="Gray 1997"/> since the Antarctic has high diversity for many taxa<ref>Clarke 1992</ref><ref>Starmans and Gutt 2002</ref>. Broad latitudinal gradients in species richness are illustrated for open-ocean pelagic and deep-sea taxa, but some debate continues to surround evidence for shallow-water systems, particularly for non-calcareous taxa<ref name="Clarke and Crame 1997"/>. Gray (1997)<ref name="Gray 1997"/> stated that marine [[biodiversity]] is higher in [[benthic]] (bottom-related) rather than in [[pelagic]] (in the water column) systems, and on coasts rather than in the open ocean, since there is a greater range of habitats near the coasts. A good comparison of multispecies [[macrofauna|macrofaunal]] assemblages inhabiting the same type of habitat (sublittoral, fine sediment bottom) showed little if any difference among tropical, temperate and arctic sites in terms of diversity<ref>Kendall and Aschan 1993</ref>. There was some dispute on how far the observed latitudinal patterns are size-dependant and small bodied taxa (Protoza and meiofauna) tend to be more ubiquitous and their richness is less latitude dependant compared to large organisms<ref>Finlay 1998</ref><ref>Hillebrand and Azovsky 2001</ref><ref name="Allen et al. 2002"/>.
In coastal environments the interactions between coastal morphology, land-ocean exchanges, meteorological and tidal conditions, create a highly complex and finely scaled network of environmental boundaries. These boundary conditions explain why coastal waters have both higher species richness and a richer [[ecosystems|ecosystem]] than their oceanic counterparts <ref name="Angel 1994"/>. [[Coastal zone characteristics|Sandy beaches]] are among the most ‘simple’ systems in terms of habitat complexity in comparison to other coastal ecosystems as, for example, rocky shores, algae and seagrass beds. [[Biodiversity]] and [[biomass]] of interstitial organisms are rather low. However, recent findings have shown that marine sands transfer energy very effectively, and that chemical and biological reactions take place faster there than in fine-grained sediments<ref>Boudreau et al. 2001</ref>.
The maximum [[meiofauna]] densities reported in the study of Kotwicki et. al (2005)<ref name="Kotwicki et. al (2005)">Kotwicki et. al (2005)</ref> ranged between 15 and 4312 individuals 10 cm sq. The reported densities rank among the meiofauna densities in sandy beaches reported in available literature. In general, high [[meiofauna]] density can be found in intertidal muddy estuarine habitats, while much lower values are recorded in the deep sea<ref>Coull 1988</ref>. In fine sediments such as organic rich muds, [[meiofauna]] densities of 104 individuals 10 cm sq and more are common<ref>Ellison 1984</ref>.
The available [[meiofauna]] data showed a large within-site (within-region) variation in the temperate zone while there was very little variation within the [[meiofauna]] densities of the antarctic and arctic zones<ref name="Kotwicki et. al (2005)"/>. These patterns demonstrate that attempts to project global [[biodiversity]] from the results of regionally based studies must include the significant variation in diversity among sampling sites. The low salinity effect on [[meiofauna]] occurrence was not clear – two brackish water locations have the same range of [[meiofauna]] density as full marine sites (Kotwicki et. al 2005). As was reported in cited literature, the lower salinity was not associated with decrease of [[meiofauna]]<ref name="Brown and McLachlan"/>.
In terms of taxonomical composition, the [[meiofauna]] taxa that were encountered during study of Kotwicki et. al (2005)<ref name="Kotwicki et. al (2005)"/> are similar to those of muddy sediments. There were no [[meiofauna]] taxa found that were restricted to shallow permeable sediments only. The percentage composition, on the other hand, differed significantly between the different study sites along the latitudinal gradient. In general, nematodes dominate [[benthic]] [[meiofauna]] communities comprising more than half of the total [[meiofauna]] abundance. This was indeed the case for most sampling sites except for both polar regions (arctic and antarctic), where turbellarians were the dominant [[meiofauna]] group.
Some small [[macrofauna|macrofaunal]] [[crustacea|crustacean]] species (Cumacea, Amphipoda, Mysidacea) that can occasionally be found in [[meiofauna]] samples, were absent in the [[littoral]] zone of polar waters<ref name="Kotwicki et. al (2005)"/>. Small size in [[macrofauna]] is often associated with a fast development, r-strategy and warm environmental conditions that permit fast egg incubation and growth<ref>Steele and Steele 1986</ref>. That strategy is unlikely to be fruitful in cold regions. These results support the hypothesis that warm regions support fast growing, smaller and more abundant organisms, and cold regions are dominated by larger and less abundant [[meiofauna]]. [[Macrofauna]] taxa may contribute to the [[meiofauna]] size class only in the tropics. A lower number of taxa was collected in both polar sites and, this in combination with slightly higher diversity in the temperate and tropic zones, supported the general pattern of diversity increase towards lower latitude. When only ‘[[meiofauna]] sensu stricto’ (i.e., without the small [[macrofauna|macrofaunal]] organisms) were taken into account, no clear latitudinal change could be found.
However, data at species level can give a more detailed and perhaps different outcome. Average number of nematode species from sandy [[littoral]] sites ranges between 50 and 60 species in warm temperate localities (Italy), cold temperate (Baltic) and slightly less are reported from arctic Svalbard (Gheskiere, Ghent University, personal communication). The results of the classification illustrated the clear difference between the polar sampling sites on the one hand and the more temperate beaches on the other hand. Archambault and Bourget (1996)<ref>Archambault and Bourget (1996)</ref> showed that large-scale heterogeneity explains a larger proportion of the variance in [[macrofauna]] species richness than substratum heterogeneity on a more local scale. In this context, it is fairly reasonable to refer to the important human pressure on temperate beaches. Recent studies (e.g.<ref name="Weslawski et al. 2000">Weslawski et al. 2000</ref><ref>Gheskiere, unpublished data</ref>) focused on the effects of recreational pressure (trampling, beach cleaning and nourishment). Weslawski et al. (2000)<ref name="Weslawski et al. 2000"/> suggested that a highly diverse [[meiofauna]] and diatom assemblage in undisturbed beaches may act as an effective biological filter for some types of pollutant, while less diverse, but more abundant biota in disturbed areas are more effective in processing organic matter (self-cleaning of the beach). Largely as a result of conflicting uses of coastal habitats, losses of marine diversity are highest in coastal areas. The best way to conserve marine diversity is to conserve habitat and landscape diversity in the coastal area. Marine protected areas are only a part of the conservation strategy needed. A framework for coastal conservation should include integrated coastal area management, where one of the primary goals is sustainable use of coastal [[biodiversity]]<ref name="Gray 1997"/>.
|AuthorName= Lechu
|AuthorFullName= Kotwicki, Lech}}
[[Category:Theme 6]]
[[Category:Estuaries and tidal rivers]]
[[Category:Geomorphological processes and natural coastal features]]
[[Category:Integrated coastal zone management]]
[[Category:Sea ice ecosystems]]
[[Category:Sediment shorelines]]

Huidige versie van 21 apr 2018 om 17:41

Doorverwijzen naar: