Sargassum

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Sargassum

sargassum.jpg

Introduction

Sargassum is a type of brown algae[1] which often serves as a Macroalgal Bed in oceans. Sargassum algae serves several benefits to marine life, providing food, refuge, and breeding grounds to much fishlife. Due to impacts of climate change, in recent years sargassum has grown at an uncontrollable rate and beginning to threaten reefs.

Habitats and Location of Sargassum

bermuda_sargasso.jpg Sargassum are generally found in “tidal splash zones, rocky marine pools, the intertidal zone, coral reefs and moderately deep coastal zone waters”[1]. Sargassum is found in throughout the Gulf of Mexico and North Atlantic[2]. Sargassum typically circulates in those regions and towards the Sargasso Sea in the North Atlantic Ocean, which is 1000 km wide and 3200 km long[3]. Scientists estimate that the Sargasso sea contains up to 10 million metric tons of Sargassum[3]. In the spring and summer, the seaweed typically arrives on shores in the Gulf of Mexico, the southern U.S. Atlantic coast and the northern Caribbean, crowding beaches[2]. As the seaweed has become more dense and widespread it washes up on these beaches more frequently, and has even been found on the Western Coast of Europe[4] where it is invasive and non-native to these coastal areas.

Biology

Appearance and Composition

Sargassum is a type of brown algae, genetically similar to yellow-green algae[1] which can appear anywhere from green to red in color. There are over 2800 estimated species, a number which has grown in recent years[1]. Brown algae are slender, and often branch with multiple thin tubes and large leaves[1]. Additionally, it often branches oxygen filled “berries”[5]. Sargassum may be macroscopic or microscopic[1]. Sargassum typically grows to about 2-3 meters, but there have been documented cases of Sargassum growing up to 16 meters[4]. A sargassum plant lives for approximately 3-4 years[4].

Reproduction

Sargassum has the ability to reproduce both sexually and asexually via floating fragments[4]. Sargassum’s flagellate spores alternate between releasing haploid and diploid gametes[1] during external fertilization. Sargassum’s ability to reproduce sexually has caused its spike in species variety. It is this variety which has allowed sargassum to survive in diverse environments throughout the Atlantic. If sexual reproduction continues at its current rate, it is expected that Sargassum will become more abundant in non-native regions. Sargassum lacks much scientific research due to its inability to sample [5], however scientists believe that “a decline in pH, increase in summer temperatures, and changes in the abundance” and distribution of Sargassum in an area lead to this instability in reproduction [6].

Ecology

367px-Fish4283_-_Flickr_-_NOAA_Photo_Library.jpg Floating Sargassum beds serve critical ecosystem functions to a variety of marine species. These habitats contain a diverse assemblage of creatures including fish, sea turtles, and over 145 species of invertebrate, including sponges, fungi, bacteria, and protists. [7]


Ecological Roles


Sargassum beds can form floating rafts that extend for miles across the ocean. The majority of sargassum is found in the Sargasso Sea, known as the "golden floating rainforest" because of its rich biodiversity. [3] These rafts provide habitats, food, and breeding grounds for a variety of marine organisms, and some creatures, like the Sargassum fish, live their entire lives in sargassum. [5]

Nurseries


Sargassum beds provide a nursery area for many commercially important fish species such as mahi mahi, jacks, and amberjacks.[5] Additionally, juvenile sea turtles often hide from predators among the sargassum.[3]

Food


Sargassum rafts serve as feeding grounds for fish, seabirds, and other organisms in the open ocean. When the algae dies, it sinks and provides organic carbon to the water column and seafloor. It may act as a supplementary food source for bottom-dwelling organisms in the deep sea.[5]

Shelter


Floating sargassum rafts provide shelter in the otherwise completely open ocean. Juveniles from many species can mature to adulthood in the safety of the algae, and larger creatures such as dolphins and even whales use it as a shelter. Within the water column the sargassum creates layers in which different species occur. Smaller filefishes and triggerfishes are found within the algae network, while juveniles of larger fish species swim just below the raft and larger predators, like dolphins, are further down. [8]

Environmental Impacts

As sea-surface temperatures have been rising, winds in the subtropics have been growing weaker. These factors affect ocean currents, especially the North Atlantic Gyre that creates the Sargasso Sea. As a result of these changing currents, among other factors, the Caribbean has experienced an influx of Sargassum in recent years. This overabundance of algae on beaches and among coral reefs has implications for the health of local environments. [3]


Coral Reefs


Climate Change Effects


Human Influence

Notes

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