prof. dr. hanan mitwally, marine biology meiofauna

Prof. Dr. Hanan Mitwally, Marine BiologyMeiofaunaMeiofauna

Prof. Dr. Hanan Mitwally, Marine Biology

ExpectationsExpectations? ??


ObjectivesObjectives• Definition

• Abiotic conditions affecting meiofauna.

• What taxa are meiofauna?

• Adaptations of meiofauna.

• Meiofauna community zonation.

• Meiofauna life history and diversity traits.

• More variation in meiofauna communities.

• Meiofauna food webs.


• Definition• The tiny, but abundant, organisms that live in sand

and mud.

• They are > .062 mm, but < 0.5mm

• Endobenthic organisms plow through interstitial space by displacing particles.

• Mesobenthic live within the interstitial spaces.

• Epibenthic organisms live at the sediment water interface.


Benthic organisms can live on the ocean floor (epifauna/epiflora) or in the ocean floor (infauna). Which type (epi/in) depends on the particle size?. Why are the few large organisms associated with

cobble and shingle? Activity 1Why is there no “inflora”?

Highestmeiofaunanumbers


• Abiotic conditions affecting meiofauna• The following abiotic factors affecting meiofauna• Rearrange them according to their importance to

meiofauna.• Temperature, • wave action, • Water circulation,

• Grain size, Activity 2• Salinity, • Oxygen


• Abiotic conditions affecting meiofauna• Environmental conditions affecting the

meiofauna are somewhat different from those that affect the macro fauna in the same area.

• The most important factor influencing meiofauna is grain size (why?)

• Because this has a strong influence on other abiotic conditions.


• Coarse grain size Vs fine grain size • Coarse grain size means greater interstitial space.

• Fine grain size means less interstitial space.

• Coarse-grained sediments hold less water by

capillary action than fine-grained sediments.


• Salinity and waves• Reductions in salinity due to flooding with

• fresh water usually affect only the uppermost

• layers of sediment (Why?)

• Because the lower layers retain seawater by capillary action.

• Wave action churns up the sediment, constantly rearranging it and increasing the chances of throwing the meiofauna into the open water.


• Abiotic conditions affecting meiofauna• Circulation of water and oxygen is greater in coarse• sediments and reduced in fine-grained sediments.• In very fine grained sediments, such as mud, water• circulation practically ceases, the interstitial habitat• becomes anoxic, and the meiofauna disappears.• Temperature is another factor of importance in

determining presence, absence, and distribution of meiofaunal organisms.

• Temperatures are most variable in the surface layer of• sediment, and the variability decreases with depth.


• What taxa are meiofauna?• The types of organisms constituting the meiofauna

include a broad range of invertebrate phyla dominated by those phyla that normally have small enough sizes to fit between the sediment grains.

• Phyla that consist primarily of large or sedentary or sessile organisms are poorly represented in the meiofauna.


• Phyla or Group• 1- Gastrotricha

• 2- Crustacea/Ostracoda

• 3-Crustacea/Copepoda/Harpacticoidea

• 4- Nematoda

• 5- Turbellaria

• 6-Nemertina

• 7-Archiannelida

• 8-Polychaeta

• 9-Oligochaeta


CRUSTACEA: OSTRACOD

CRUSTACEA: HARPACTICOID COPEPOD

GASTROTRICH:

TARDIGRADE

POLYCHAETENEMATODE


• Adaptations of meiofauna• The most obvious adaptation of meiofaunal

organisms is that they are :

• 1-Very small in size.

• 2- Elongated or vermiform in shape and flattened.

• 3-An adaptation to the dynamics of sediment movement is the presence of skeletons that offer some protection against crushing.

• 4-Most animals in the interstitial are free-moving and have various adaptations to cling to the sediment grains.

• 5- Statocysts, organs that detect gravity.


• Meiofauna community zonation• The composition of the meiofauna varies both

horizontally and vertically in the substrate, and most are concentrated in the upper layers.

• Vertical zonation of meiofauna in the sediment appears to be related to oxygen concentration and/or predation.

• Vertical migration triggered by temperature or salinity changes is especially prominent in temperate zone beaches.


• Meiofauna life history Temporary meiofauna consists of newly settled juveniles of macrofaunal organisms,

• Permanent meiofauna consists of organisms that spend their entire lives in the interstices of the sediment.

• Due to their small size, meiofauna produce very few eggs and ensure their fertilization and survival by various mechanisms that retain the embryos in the interstitial space.

• Sperm transfer is direct, including spermatophore.


• Meiofauna diversity traits• Worldwide, the average number of meiofaunal

organisms per square meter is 106.

• Diversity was measured as 70 spp. per 50 cm2 of sand.

• There is no apparent gradient in richness with change in latitude.


• More Variation in Meiofauna Communities• There are also seasonal changes in abundances of

organisms and species composition.

• Factors affecting seasonal abundances of meiofauna

• 1- Primary productivity 2- Predation.

• Meiofauna are sensitive to natural or human-induced

• perturbations.

• Meiofauna are distributed patchily, even where the sediment grain size is homogeneous.

• There is little information on the long-term variability of meiofaunal communities, and the information that is available is conflicting.


• Meiofauna food webs• Trophic relations among the components of the interstitial• fauna are not well known.• Predators on the meiofauna include certain fishes and

macrofaunal deposit feeders that kill meiofauna when they ingest the sediment. There are also meiofaunal predators.

• The meiofauna also contains herbivores, detritus feeders,• and suspension feeders,• The significance of meiofauna to macrofaunal communities• and food webs appears to depend on the sediment type.• Meiofauna is more significant to macrofauna in finer• sediments, probably partly due to the concentration of the• meiofauna in the top layers, where they are more accessible.


Summary

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Supports It.

prof. dr. hanan mitwally, marine biology meiofauna

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