Intertidal in the context of Tidal flats

A rocky shore is an intertidal area of seacoasts where solid rock predominates. Rocky shores are biologically rich environments, and are a useful "natural laboratory" for studying intertidal ecology and other biological processes. Due to their high accessibility, they have been well studied for a long time and their species are well known.

Coralline algae are red algae in the order Corallinales, characterized by a thallus containing calcareous deposits within its cell walls, giving it hardness. The colors of these algae are typically some hue of pink, or another shade of red, but some species can be purple, yellow, blue, white, or gray-green. Typically, these algae grow in a crustose manner (encrusting rocks and other hardscape); in the intertidal zone of rocky shorelines, and within coral reefs, these algae appear as an abundance of colorful patches on rock surfaces. Unattached specimens (maerl, rhodoliths) may form relatively smooth compact balls, or forming warty to fruticose thalli.

The red algae belong to the division Rhodophyta, within which the coralline algae form the order Corallinales. There are over 1600 described species of nongeniculate coralline algae. The corallines are presently grouped into two families on the basis of their reproductive structures. Most are marine, though one species lives in freshwater; Pneophyllum cetinaensis.

A tide pool or rock pool is a shallow pool of seawater that forms on the rocky intertidal shore. These pools typically range from a few inches to a few feet deep and a few feet across. Many of these pools exist as separate bodies of water only at low tide, as seawater gets trapped when the tide recedes. Tides are caused by the gravitational pull of the sun and moon. A tidal cycle is usually about 25 hours and consists of two high tides and two low tides.

Tide pool habitats are home to especially adaptable animals, like snails, barnacles, mussels, anemones, urchins, sea stars, crustaceans, octopus, and small fish, as well as seaweed. Inhabitants must be able to cope with constantly changing water levels, water temperatures, salinity, and oxygen content. At low tide, there is the risk of predators like seabirds. These pools have engaged the attention of naturalists and marine biologists, as well as philosophical essayists: John Steinbeck wrote in The Log from the Sea of Cortez, "It is advisable to look from the tide pool to the stars and then back to the tide pool."

Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal flat ecosystems are as extensive globally as mangroves, covering at least 127,921 km (49,391 sq mi) of the Earth's surface. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries; they are also seen in freshwater lakes and salty lakes (or inland seas) alike, wherein many rivers and creeks end. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of estuarine silts, clays and aquatic animal detritus. Most of the sediment within a mudflat is within the intertidal zone, and thus the flat is submerged and exposed approximately twice daily.

A recent global remote sensing analysis estimated that approximately 50% of the global extent of tidal flats occurs within eight countries (Indonesia, China, Australia, United States, Canada, India, Brazil, and Myanmar) and that 44% of the world's tidal flats occur within Asia (56,051 km or 21,641 sq mi). A 2022 analysis of tidal wetland losses and gains estimates that global tidal flats experienced losses of 7,000 km (2,700 sq mi) between 1999 and 2019, which were largely offset by global gains of 6,700 km (2,600 sq mi) over the same time period.

Jamaica Bay Wildlife Refuge is a wildlife refuge in New York City managed by the National Park Service as part of Gateway National Recreation Area. It is composed of the open water and intertidal salt marshes and wetlands of Jamaica Bay. It lies entirely within the boundaries of New York City, divided between the boroughs of Brooklyn to the west and Queens to the east.

Macrobenthos consists of the organisms that live at the bottom of a water column and are visible to the naked eye. In some classification schemes, these organisms are larger than 1 mm; in another, the smallest dimension must be at least 0.5 mm. They include polychaete worms, pelecypods, anthozoans, echinoderms, sponges, ascidians, crustaceans.

The marine macrobenthos community is a critical component and reliable indicator of the biotic integrity of marine ecosystems, especially the intertidal ecosystems. On the one hand, macrobenthos plays a vital role in maintaining ecosystem functions, such as material cycling in sediments and energy flow in food webs. On the other hand, macrobenthos is relatively sedentary and therefore reflects the ambient conditions of sediments, in which many pollutants (e.g., heavy metals and organic enrichment) are ultimately partitioned.

Phoronids (taxonomic name Phoronida, sometimes called horseshoe worms) are a small phylum of marine animals that filter-feed with a lophophore (a "crown" of tentacles), and build upright tubes of chitin to support and protect their soft bodies. They live in most of the oceans and seas, including the Arctic Ocean but excluding the Antarctic Ocean, and between the intertidal zone and about 400 meters down. Most adult phoronids are 2 cm long and about 1.5 mm wide, although the largest are 50 cm long.

The name of the group comes from its type genus: Phoronis.

The common periwinkle or winkle (Littorina littorea) is a species of small edible whelk or sea snail, a marine gastropod mollusc that has gills and an operculum, and is classified within the family Littorinidae, the periwinkles.

This is a robust intertidal species with a dark and sometimes banded shell. It is native to the rocky shores of the northeastern, and introduced to the northwestern, Atlantic Ocean.

Scaphopoda (/skəˈfɒpədə/; from Ancient Greek σκᾰ́φης (skáphēs) 'boat' and πούς (poús) 'foot') is a class of shelled marine molluscs (invertebrates within the phylum Mollusca), whose members are known as scaphopods (/ˈskæfəˌpɒdz/) and commonly called tusk shells or tooth shells. They have a worldwide distribution and are the only class of exclusively infaunal marine molluscs. Shells of species within this class range in length 0.5–18 cm (0.20–7.09 in), with Fissidentalium metivieri being the longest. Members of the order Dentaliida tend to be larger than those of the order Gadilida.

These molluscs live in soft substrates offshore (usually not intertidally). Because of this subtidal habitat and the small size of most species, many beachcombers are unfamiliar with them; their shells are not as common or as easily visible in the beach drift as the shells of sea snails and clams.

Sea pens are marine cnidarians belonging to the superfamily Pennatuloidea, which are colony-forming benthic filter feeders within the order Scleralcyonacea. The order comprises 16 families and 44 extant genera, with around 235 accepted species.

Sea pens have a cosmopolitan distribution, being found in tropical and temperate waters worldwide, from intertidal shallow waters to deep seas of more than 6,100 m (20,000 ft).

Between Pacific Tides is a 1939 book by Edward F. Ricketts and Jack Calvin that describes the intertidal ecology of the Pacific coast of the United States, Canada, and Mexico. The book was originally titled "Between Pacific Tides: An Account of the Habits and Habitats of Some Five Hundred of the Common, Conspicuous Seashore Invertebrates of the Pacific Coast Between Sitka, Alaska, and Northern Mexico".

Prior to Ricketts' work, the standard descriptive text of intertidal species of the Pacific was Seashore Animals of the Pacific Coast jointly coauthored by Myrtle E. Johnson and Harry James Snook, published in 1927 (reprinted 1935, 1952, 1967, 1980).