Between Tides - Marine Biology - Lecture Slides, Slides of Biology

Download Between Tides - Marine Biology - Lecture Slides and more Slides Biology in PDF only on Docsity! Chapter 11 Between the Tides Docsity.com What is the intertidal zone? • The intertidal zone is the area between the mean low tide and mean high tide. • By contrast, the subtidal zone is the area that is always submerged. • The intertidal zone, therefore, borders the subtidal zone. • The intertidal zone will be exposed during low tide. Docsity.com Problems Associated with the Intertidal Zone • Due to the exposure seen in the intertidal zone, organisms face a variety of challenges, including: – Desiccation (water loss) – Temperature changes (can be extreme) – Salinity changes (can be extreme) – Interrupted feeding – Wave action and tides – Oxygen availability and build-up of CO2 – Limited space Docsity.com Dessication • When exposed, organisms must deal with potential water loss. • Water loss is more pronounced on hot, dry days or windy days. • Organisms can deal with the potential water loss by hiding or “clamming up.” Docsity.com Desiccation • Hiding may involve moving to a tide pool or an area with more moisture (motile organisms) • Hiding may also mean that some organisms only live in areas where moisture will remain when the tide is out (such as crevices in rocks or low spots in soft bottoms) Docsity.com Changing Salinity • Salinity can change dramatically due to temperatures or weather. • Normal ocean salinity is around 33-35 ppt. • Estuarine salinity normally varies between 5 ppt and 30 ppt. • Organisms in the intertidal are normally euryhaline (can tolerate a wide variety of salinities); subtidal organisms by contrast are normally stenohaline (tolerate a very low range of salinities) Docsity.com Changing Salinity • Salinity may begin at 20-25 ppt and climb dramatically during the day due to water loss when the intertidal is exposed. • Salinity may also drop during the day due to a sudden influx of freshwater provided by a passing thunderstorm. • Mollusks “clam up” to avoid fresh water and those without shells “run and hide” in pockets of seawater Docsity.com Interrupted Feeding • If an organisms “clams up,” feeding will cease. • Feeding will also cease for filter feeders when exposed to air. • A few organisms such as snails can still feed during low tide by scraping algae off surfaces. • organisms may spend nearly half of their day un- submerged and not feeding. Docsity.com Limited Space • In some intertidal communities, proper space may be limited. • This is particularly true in rocky intertidal environments where the amount of surface area is limited. • However, space can be limited in soft bottomed communities as well. Organisms in these areas prefer hard substrate such as living on an “oyster reef” because they do not wash away due to water action. Docsity.com Zonation in the Intertidal • Zonation in the intertidal consists of upper intertidal (most exposed) to middle and lower intertidal (least exposed). Docsity.com Zonation in the Intertidal • Competition will be greater in the lower intertidal because it is the least “severe” of the zones since it is exposed to a lesser degree than the upper intertidal. • The lower intertidal is always more species rich for the same reason (although species will vary greatly by location). Docsity.com Substrate in the Soft Bottomed Intertidal • The grain size is so small in most soft bottomed intertidal communities that all except the top few inches will be anoxic (without oxygen). • Therefore, _____ (microscopic animals that live on bottom) is usually restricted to the oxygenated zone. • _____ (animals that burrow in the substrate) must maintain a connection with the oxygenated zones via tubes, siphons or extended burrows if they are located in the anoxic zone. • In the anoxic zone, many anaerobic bacteria exist that break down organics. Docsity.com Soft Bottom Intertidal Organisms • Diversity of infauna and epifauna that may be found in this community. Sandy Atlantic Coast Community Docsity.com Soft Bottom Food Webs • Detritus (broken down organic particles) and producers such as phytoplankton and benthic diatoms form the basis for the food web in this community. Docsity.com