Marine Biology Terms Starting With L

Lagoon is a shallow coastal or atoll water body partially or fully separated from the open ocean by a barrier such as a coral reef, sandbar, or barrier island.

Lagoons form through several processes: coral atoll growth encircles a central basin, barrier islands accrete parallel to the shore, or sandbars build up across embayments. Salinity within a lagoon varies widely depending on the balance between freshwater input from rainfall and rivers, evaporation, and the degree of tidal exchange with the open sea. Shallow depths and restricted circulation allow water temperatures to rise well above adjacent ocean values, creating warm, calm conditions that support seagrass beds, mangroves, and nursery habitat for juvenile fish and crustaceans.

The Laguna Madre along the Texas and Mexican Gulf Coast is one of the few hypersaline lagoons in the world, where evaporation so far exceeds freshwater input that salinity regularly exceeds 70 parts per thousand, roughly twice that of normal seawater.

Littoral Zone is the shallow nearshore region of a body of water where sunlight penetrates to the bottom, tidal and wave action directly influence conditions, and a high diversity of algae, invertebrates, and fish occupy habitats ranging from rocky intertidal shores to shallow subtidal flats.

In marine systems, the littoral zone spans from the uppermost splash zone, wetted only by wave spray, down through the intertidal and into the shallow subtidal where rooted aquatic plants and macroalgae can grow. Conditions shift dramatically across this gradient: temperature, salinity, and desiccation stress peak in the high intertidal, while wave energy and sediment disturbance shape community structure throughout. Organisms living here show pronounced zonation, with barnacles, limpets, and periwinkles dominating the high intertidal and sea stars, mussels, and kelp becoming more abundant lower on the shore.

Rocky intertidal communities on the Pacific coast of North America have been studied intensively since the 1960s, when ecologist Robert Paine demonstrated through sea star removal experiments at Mukkaw Bay, Washington, that a single predator can control the entire structure of a littoral community.

Longshore Drift is the process by which waves striking a shoreline at an angle transport sediment, including sand and gravel, progressively along the coast in the direction of the dominant wave approach.

When waves break at an angle to the shore, the swash carries sediment diagonally up the beach face while the backwash pulls it straight back down the slope under gravity, producing a zigzag net transport that can move material hundreds of meters per day along an active coast. Over years to decades, this process builds elongated depositional landforms including spits, baymouth bars, and tombolos where sediment accumulates faster than waves can remove it. At Sandy Hook, New Jersey, longshore drift from the south has extended the spit northward by roughly 5 kilometers over the past 200 years, a well-documented example of drift-driven coastal accretion.

Human structures such as groynes are built perpendicular to the shoreline to interrupt longshore drift and retain sand on one beach, though this consistently starves the beach immediately downdrift of sediment.