Aquatic ecology and Biodiversity

Unit 11- Intertidal zone

11.3.2. Biological diversity
Plants
Due to the mobility of the substrate, plant life is very limited in both diversity and abundance. Seaweeds are mostly absent, but diatoms and bluegreen algae may be common in sheltered, sandy, mud conditions. Ulva and Enteromorpha develop in summer on many sandy-mud flats.

Animals
The absence of hard substrate results in the predominance of infaunal species. Distribution and abundance are controlled largely by the tide level and mobility of the sand. At low-tide levels, the sand seldom dries out, but is mobile due to currents and wave action. Animals have to burrow to maintain their position on the beach. On exposed beaches, polychaete worms (Nephtys) and molluscs (Tellina, Spisula, Ensis) occur at low-tide level. Isopod and amphipod crustaceans also occur at the mid- and low-tide levels. At the high-tide mark, amphipods are common, feeding on organic matter in the drift line, and overlap in their occurrence with insects, including the larvae of flies and beetles. Where the sand grades into sandy mud in sheltered conditions, the fauna increases in both diversity and abundance. Ribbon worms (Cerebratulus spp.), polychaetes (Nereis spp. and Nephtys spp.), bivalves (Mya arenaria, Macoma balthica) and mud snails (Nassarius,) are typical. Where patches of gravel occur on the lower shore, clumps of blue mussels are found with associated barnacles and other epifauna. Sandy shores provide important feeding grounds for a variety of shore birds, including sandpipers and plovers.

Biota
The distribution and abundance of the sediment infauna is mostly controlled by complex interactions between the physicochemical and biological properties of the sediment.
Macrofauna
Macrofauna of the sandy beaches are often abundant and, in some cases, attain exceptionally high densities. The macrofauna of sandy beaches includes most major invertebrate taxa although it has been recognised that molluscs, crustaceans and polychaetes are the most important. Low diversity compared to rocky shore.
• Polycheates, bivalves and crustaceans are dominant forms
• Amphipods and isopods burrow during day and feed at night on detritus
• Ghost crab (Ocypoda) – dominant scavenger in sandy beats
• High species diversity of macro fame at mid and lower tidal zones.
• Fast burrowing Donax – Tellina – clams present in large numbers
• Larger razon clams (Ensis, Siliqua) are common
• Cockles (Cardium) Arca sp. – thick shelled bivalves also common in sandy
• Snails – Olivella, Natica, Polinices – predator and abundant in sandy shores
• Sand dwelling polychaetes (Napthys, Glycera) are predators /scavengers are deposit feeder at Mid / Low tide level
• Crustaceans - Mole crab (Emerita) present at mid tidal level
• Prawns (Crangon) – Sandy shore crustacean
• Echimodesms – Heart urchins, sand dollers star fish sea cucumber – deposit feeds present at lower tidal levels.
• Sand eels, flatfish are also burrow into good.
Meiofauna
The dominant taxa of sandy beach meiofauna are nematodes and harpacticoid copepod with other important groups including turbellarians, oligochaetes, gastrotrichs, ostracods and tardigdades. Meiofauna interstitial fauna present both sand grass, Biomass of meiofauna varied between 10 and 2g/m². Average numbers to be 106/m².