Meroplankton are a wide variety of aquatic organisms which have both a

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic stage and at least one other component, such as

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

or nektonic, in their life cycles. Much of the meroplankton consists of

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

l stages of larger organisms. Meroplankton can be contrasted with holoplankton, which are planktonic organisms that stay in the pelagic zone as plankton throughout their entire life cycle. After a period of time in the plankton, many meroplankton graduate to the nekton or adopt a

(often sessile) lifestyle on the seafloor. The larval stages of benthic

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s make up a significant proportion of planktonic communities. The planktonic larval stage is particularly crucial to many benthic invertebrate in order to disperse their young. Depending on the particular species and the environmental conditions, larval or juvenile-stage meroplankton may remain in the pelagic zone for durations ranging from hour to months. Not all meroplankton are larvae or juvenile stages of larger organisms. Many

dinoflagellate The Dinoflagellates (), also called Dinophytes, are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered protists. Dinoflagellates are mostly marine plankton, but they are also commo ...

s are meroplanktonic, undergoing a seasonal cycle of encystment and dormancy in the benthic zone followed by excystment and reproduction in the pelagic zone before returning to the benthic zone once more. There also exist meroplanktonic

diatom A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...

s; these have a seasonal resting phase below the

photic zone The photic zone (or euphotic zone, epipelagic zone, or sunlight zone) is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological ...

and can be found commonly amongst the benthos of

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

s and coastal zones.

Spatial distribution

Meroplankton species composition depends on spatial distribution and reproductive habits of adults in a given area. Biotic and abiotic factors such as tidal and lunar cycles and availability of food determine adult spawning schedules, in turn, determining subsequent meroplankton populations. Behavioural factors, such as predator avoidance are also important. Freshwater inputs play a key role in meroplankton species composition in estuarine environments. Effects of tides contribute greatly to meroplankton species distribution. One study conducted in a Patagonian

Fjord In physical geography, a fjord (also spelled fiord in New Zealand English; ) is a long, narrow sea inlet with steep sides or cliffs, created by a glacier. Fjords exist on the coasts of Antarctica, the Arctic, and surrounding landmasses of the n ...

found that species composition of the meroplankton community depended on the seasonally varying input levels from the Baker river as well as vertical and horizontal stratification of the water column.7. Castrob L., R., Meerhoffa E., Tapiab F. J. 2014. Spatial structure of the meroplankton community along a Patagonian Fjord – The Role of Changing Freshwater Inputs. Vo. 129A, pp.125-135 Events such as wind driven

upwelling Upwelling is an physical oceanography, oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted sur ...

and downwelling also affect meroplankton species distribution. Most species are swept in the direction of the flow of water, either off shore during an upwelling or near shore during a downwelling. Some species, such as

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

larvae, have the ability to maintain their nearshore position during these events.10. Brubaker J., Largier J., Shanks A.L., 2003. Observations on the Distribution of Meroplankton During an Upwelling Event. Journal of Plankton Research. Vo. 25, No 6, pp: 645-667 The distribution of meroplankton is also highly seasonal. Many meroplankton have short residence times in the pelagic zone which follow seasonal reproduction patterns. The timing of meroplankton population rises can be used as a proxy to estimate the timing of seasonal reproduction of the species in question.

Dispersal

Survival rate of Meroplankton is critical to successful development of adult organisms. One factor which often determines meroplankton survival is larval dispersal. Most species within the meroplankton community rely on ocean currents for dispersal. Currents play a key role in delivering larval organisms to specific settlement locations, where they are able to transition and mature into adult forms. Organisms which do not make it to the right settlement site are unlikely to complete their lifecycle.5. Brink L., Brubaker J., Hooff R., Largier J., Shanks A.L, 2002. Observations on the distribution of meroplankton during a downwelling event and associated intrusion of the Chesapeake Bay estuarine plume. Journal of Plankton Research. Vo. 24, No. 4, pp. 391-416

Food availability

A major factor affecting meroplankton survival is food availability. While some larval or juvenile stage organisms are lecitotrophic, many members of the meroplankton community are

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

ic. In order to ensure that larvae have sufficient sources of nutrition, many species coordinate larval release with times of algal blooms. This synchronicity between release of larvae and algal blooms often leads to meroplankton making up the largest percentage of the planktonic community during such reproductive periods.3. Attrill M.J., Conway D.V.P., Eloire D., Highfeild J.M., Lindeque P.K., SomerfeildP.J., 2010. Seasonal dynamics of meroplankton assemblages at station L4. Journal of Plankton Research. Vol. 00, No. 0, pp.1-11 It has been demonstrated that certain species are able to commence spawning as they come into contact with phytoplankton cells. These species store embryos in the mantle cavity until they detect algal blooms. This adaptation allows for better larval survival.2. Arntz W.E., Schnack-Schiel S., Thatje S., 2003. Developmental trade-offs in Subantarctic meroplankton communities and the enigma of low decapod diversity in high southern latitudes. Marine Ecology Progress Series. Vo. 260, pp. 195-207

Diversity and abundance

Meroplankton diversity and abundance are affected by many factors. Seasonal and spatial variations are among some of the main causes of such variability. A study which was conducted in Dunkellin Estuary, determined that spawning times of many species are timed to maximise food availability at a particular time of year, while minimising presence of other species which exploit the same food source 8. Byrne, P., 1995. Seasonal Composition of Meroplankton in the Dunkellin Estuary, Galway Bay. Biology and Environment: Proceedings of the Royal Irish Academy, Vo. 95B, No. 1, pp. 35–48 Diversity and abundance are depth dependent qualities. Generally, shallow coastal waters contain far greater numbers of meroplankton than deep, open ocean waters. Most abundant regions occur at depths between 0 and 200 meters of the water column, where light penetration is highest. Availability of sunlight allows for proliferation of phytoplankton, which serves as one of the major food sources for meroplankton. Deep oceanic waters show significantly lower abundance than shelf regions, due to poor light penetration.9. Gallego R., Lavery S., Sewell M.A., 2014. Meroplankton Community of the Oceanic Ross Sea During Late Summer. Antarctic Science Antarctic Science, Vo. 26, No. 4, pp. 345–360

Effects of pollution

Water and benthos pollution from industrial sources has been demonstrated to have varying effects on biological diversity and survival potential of meroplankton. One study conducted in the Vostok Bay region in

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

, demonstrated that even in the presence of industrial pollutants, most species of meroplankton were able to proliferate almost unaffected. The authors of this study attribute these findings to the fact that meroplankton are transported by ocean currents generally from cleaner open waters inshore. Furthermore, the same study also concluded that even in heavily polluted areas, meroplankton populations were able to reestablish if pollution was brought under control and sufficient time was allowed to pass. However, the rate of recolonization was demonstrated to be notably slow, on average taking about 10 years before the abundance and diversity of meroplankton returned to its original levels. This is in part due to the slow nature of detoxification of benthic

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s, which retain much of the heavy metal

pollution Pollution is the introduction of contaminants into the natural environment that cause harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...

.6. Kulikova V. A., Omelyanenko V. A., Tarasov V. G. 2004. Effect of Pollution on the Meroplankton of Gaidamak Bight (Vostok Bay, Sea of Japan), Russian Journal of Ecology, Vo. 35, No. 2, pp. 91-97

Meroplankton and climate change

A study conducted in the

North Sea The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Se ...

between 1958-2005, collected samples of meroplankton using a CPR survey. These samples consisted of larval

echinoderms An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as larv ...

, decapods, bivalves, cirripedes, and ectoprocts. Meroplankton abundance as well as PCI levels (amount of chlorophyll in each sample in relation to sea surface temperature) were examined. Researchers concluded that echinoderm larvae increased in abundance throughout the study, with the largest increase occurring in the Northern and Central regions. Decapod larvae were found to increase in abundance as well, and were found to appear earlier in the year. Bivalve larvae showed an overall decline in abundance. It was also concluded that PCI levels increased throughout the study, particularly during the summer months. It was determined that climate, particularly sea surface temperature, drives meroplankton abundance. Warmer sea surface temperature shortens developmental time of the larvae, increasing their survival rate.4. Beaugrand G., Kirby R. R., Lindley J. A., 2008. Climate-induced effects on the meroplankton and the benthic-pelagic ecology of the North Sea. American Society of Limnology and Oceanography, pp. 1805–1815

References

Sources

Meroplankton
(Australian Museum) {{plankton Aquatic ecology Planktology Oceanographical terminology