Copepods

Table of Contents:

Introduction Page 3

What is Labidocera Pages 3-4

What makes Copepods Important Pages 4-6

Anatomy of Copepods Pages 6-10

Cephalosome region Pages 7-8

Metasome region Pages 8-9

Urosome region Page 10

Developmental stages Page 11

Current research Pages 11-12

References Pages 13-15

Introduction:

The planet Earth has an incredible level of biodiversity across its surface, amongst the most diverse regions is that of the oceans. One of the many creatures within this vast region is a group of Copepods called Labidocera. Labidocera is genus of living organisms within the phylogenic tree. More specifically it is classified by the following branches of the phylogenic tree: Kingdom-Animalia, Phylum-Arthropoda, Class-Hexanauplia, (Subclass-Copepoda), Order-Calanoida, Family-Pontellidae, and Genus-Labidocera (Walter, 2021). This being just a Genus, there are several species within Labidocera. Labidocera are found in water ways across the planet. One specific type of waterway in which samples can be found for research are estuaries. Estuaries are where rivers or streams reach a large body of water, likely an ocean. This area is a good site for samples, because it is the area in which concentrated nutrients are delivered to the ocean. This is beneficial for the lower-level organisms within the food web of an ecosystem.

What is a Labidocera?

Labidocera can be classified using the taxonomic system as previously stated. This is great for the classification of types of organisms but can still be vague if someone is not familiar with what separated each classification. First it is important to understand what a copepod is before knowing the genus. Copepods are, named from the Copepoda-subclass, are small crustaceans found within fresh and salt water. They can function as “free-living organisms, symbionts, or as parasites” (Anderson, 2021). Copepods can then be further divided into either bethic or planktonic forms (Anderson, 2021). Labidocera are categorized within the planktonic category, meaning it drifts between water columns and can use its’ appendages to swim. Labidocera has nearly a hundred species across the world, (Walter, 2021). These Labidocera also grow in large numbers making them easy to harvest. Within the United States there is not currently a set of regulations dictating what researchers cannot do with regards to copepods. This makes the Genus Labidocera an ideal sample organism for research, especially that of this course which is designed around the techniques and skills of microscopes.

What Makes Copepods Important?

As previously stated, Copepods are a crucial organism within the aquatic ecological community. They are amongst the basal layer, meaning that collectively they contain more energy and are responsible for the distribution of energy from plants into predators. Further illustrating the point that copepods are a good source of energy, researchers state “[t]hey Copepods (Crustacea: Arthropoda) are the most abundant and probably the most ecologically significant zooplanktonic animals of the first consumer level of the marine food-chain. They are considered to be “nutritionally superior live feeds” for commercially important cultivable species, as they are valuable source of proteins, lipids, carbohydrates and enzymes all of which play an important role in digestion…” (P, Rajkumar. M, Santhanam. 2009). This quote by the researchers shows that not only are the copepods a good source of energy, but they are concentrated sources of macronutrients. Labidocera not only are an important transporter of energy within the ecosystem, they also eat the underdeveloped members of their own subclass. This helps maintain the fitness of their population as well as keep it in check. Labidocera help self-regulate the population of fellow copepods, maintaining their populations through feeding on nauplii and other vulnerable stages of copepod developments. This self-regulation allows them to maintain stable populations within their ecosystems (Conley & Turner 1985).

Beyond levels of energy transfer and biodiversity Copepods can also be an important indicator of ocean acidification. This is important for tracking levels of carbon in the water as a result of the air saturation. The ocean uses a similar buffer system to that of the human body which uses the flow of carbon dioxide, oxygen, bicarbonate and carbonic acid to modulate the concentration of free hydrogen atoms. This is relevant to Copepods because they have calcareous shells (Perumal. P, Rajkumar. M, Santhanam. 2009), which means their exoskeletons are at least partially composed of calcium carbonate. Like other hard-shell organisms, such as clams, snails, and mussels, Copepods are vulnerable to low pH levels. This is because under acidic conditions the increased amounts of hydrogen can outcompete the calcium in calcium carbonate needed to create or maintain their’ calcareous shells. Sampling of Copepods and their shells can show not just the direct pH of the environment, but their daily movement patterns alter when exposed to higher concentrations of hydrogen (Smith. J, Richter. C, Fabricius. K, and Cornilis. A, 2017). This also adds to the evidence supporting the claim for the climate change theory.

Copepods and climate change sound like two unrelated subjects. When in fact copepods add further evidence to support that climate change is not only real but is exasperated by the actions of mankind. The first part of this is due to the compositions of their exoskeleton changing as a result of limiting resources, which occurs during periods of excessive carbon in the air being precipitated into the ocean. The second part is due to the behavioral changes observed by the copepods as a result of the growing inhospitable environment that occurs within the physical composition of the ecosystem (A, Vehmaa. H, Hogfors. E, Gorojhova A, Brutemark T. Holmborn. & J, Engstrom-ost. 2013). The final aspect of climate change that is directly affecting the populations of these copepods are the increasing temperatures which are “…decreased egg viability, nauplii development, and oxidative status” (A, Vehmaa. H, Hogfors. E, Gorojhova A, Brutemark T, Holmborn. & J, Engstrom-ost. 2013 p. 1). This study also goes further into detail relating that the increased temperature and pH are not causing a change in the eggs being produced but this means the resources being placed into the attempt of reproduction are being wasted in comparison to copepods in ideal conditions. This does illustrate how the change in climate is already affecting a phylum subclass that is very valuable to the health of an ecosystem.

Anatomy of Copepods:

Copepods being spread across the world and being such a numerous group of organisms has led to the thorough studying of their anatomy. There are several physical differences between the genus’ and species’ that make each one unique. This being said, the generalized anatomy of the phylum subclass Copepod is as follows and will be based upon (J. Mauchline, 1998). Copepods have segments of their body that can be broken down by order from the cephalic to caudal regions, cephalosome, metasoma, and urosome. To be more concise they can also be labeled as head, thorax and abdominal regions. In these categories the cephalosome or head regions are where feeding, and sight are primarily controlled. This region contains several appendages such as, antennule, antenna, mandible, maxilla and maxilliped. These are for sensations and the externals processes of eating. The next segment down includes primarily the swimming appendages as well as some possible mating appendages. These swimming appendages are currently being studied by graduate students at Lincoln Memorial University. They are attempting to shed light upon the biomechanics of the swimming appendages of Copepods, specifically the genus Labidocera. The final region contains segments of genital and anal somites.

The Cephalosome region of Copepods:

The Cephalosome region has the most complex external morphology of the three regions. This is due to the far more numerous appendages that serve several different purposes. As illustrated by (J. Mauchline, 1998) this segment has the following appendages, rostrum, antennule, labrum, antenna, labium, mandible, maxillule, maxilla, and maxilliped. The rostrum functions a beak and may be a form of protection according to (J. Kennedy, 2018). The antennules are highly segmented and are bilaterally symmetrical according to (J. Mauchline, 1998), who also states that the antennules have setae or aesthetascs. The setae are microscopic projects which increase the surface area of the antennules helping the copepod maintain its place within the water column. The aesthetascs work as the sensory appendages, which as (J. Mauchline, 1998) says “…detect food, water disturbance and predators.” The labrum is loosely paired with the labium since they form the area of the mouth. Together these two can help feed, by manipulating food, harming the prey, and the release of secretions to modify the food for better digestion (J. Mauchline, 1998). The paired antenna works as a feeding appendage that has microscopic projections which help bring food into eating orifice. The mandible of copepods is similar to that of people, since in both organisms the mandible is responsible for the mastication of food. Within the mandible of the Copepods, (J. Mauchline, 1998) says they can grow spines which are nearly homologs to teeth in humanoids. These spines have a protective layer of silica which functions similar to enamel. The maxillule and maxilla are sequential appendages which are functionally the names for “first and second maxillae” according to (Lewis, 1969). These two appendages, according to (Lewis, 1969) contain motor neurons but do not contain muscles. Which (Lewis, 1969) claims must mean the motor neurons send signals for the projections at the ends to assist with the movement of food towards the mouth. The maxillipeds are paired appendages which are among the most variable sections within different copepods. According to (F. Ferrari, H. Dahms, 1998) the maxillipeds can differ in number of segments, length, projections and branches. These differences occur across different species as well as between male and females. These appendages are a more complex form of feeding appendage than those previously stated. This is because some are used to funnel food towards the mouth, which is like the other feeding appendages, but some are used as grasping appendages with as (F. Ferrari, H. Dahms, 1998) say “claw like structures.” To summarize these external structures of the cephalosome region are primarily used for the feeding of the copepod, by the detection, movement and grasping of food.

The Metasome Region of Copepods:

The metasoma region is the region most associated with motility. This region is composed of roughly five segments, and five paired appendages. These five appendages are also commonly referred to as pleopods, legs, thoracopods, or swimming legs. These appendages are responsible for the etymology of the name Copepods, originating from the “Greek words “kope”, and oar and “podos”, a foot” again from (J. Mauchline, 1998). These oar-like projections are the primary source of locomotion, which is achieved via a power stroke. This power stroke is partially responsible for the high speeds produced. This is necessary considering as Von Dassow says “to small organism, however, water is sticky, and to them water feels about like it would to us if we had to swim in Karo syrup” during his interview with (J. Barlow 2020). This is a result of the molecular forces which create surface tension, these forces must be felt greater on an organism that is so small. One of the factors that allows the Copepods to produce such a quick movement despite these strong forces, are their projects of setae on the swimming appendages. These setae were observed by (V. Dassow and R. Emlet, 2020) who refer to them as “plumose setae” and compare them to the barbs of a feather. These setae increase the surface area of the pleopods used for swimming, this then works as a fin to better propel the copepods through the water. This was observed under the microscope and camera in the study done by (V. Dassow and R. Emlet, 2020), who further tried to analyze the setae on slide to better focus on the linkages. This was difficult to do considering as (V. Dassow and R. Emlet, 2020) previously stated the copepods are fragile and easily damaged, let alone removing and analyzing specific appendages. These researchers claim to have observed the setae connections unravel in front of them. While also observing some elastic qualities at the base of the setae. This supports the claim that the setae fold like similar species with the recovery stroke. However according to (V. Dassow and R. Emlet, 2020), due to the fragility of the setae, it could not be observed under scanning electron microscopy. On the opposite end of these appendages, graduate students at Lincoln Memorial University are currently processing the Copepods, Labidocera, and sampling their swimming appendages in attempts to better understand the biomechanics of the swimming motion. These students are attempting to examine the articulations of the pleopods and what makes this motion possible, and with such a strong force in relation to their bodies.

As previously stated, copepods tend to have five pairs of appendages in their metasome region. This is yet again another site with variations between copepods. Some genuses have five pairs of swimming pleopods, where as some genuses such as Labidocera have four pairs of swimming pleopods and a pair of mating pleopods. Specifically in the males of Labidocera, the pair of mating pleopods are not the same. One is used for grasping of the female, but the other is used for passing the sac of sperm off to the female.

Urosome Region of Copepods:

This is the most caudal region of the copepods. This region has the fewest number of appendages, if any at all. The segmentation of this area is broken down into the genital, and anal somites with the possibilities of furca or caudal ramus according to (D. Conway, 2006). The genital somite is larger in the females within their respective species and is where the males place the before mentioned sac of sperm for the females to reproduce. The anal somite contains the anus and serves as the connective site for the caudal rami as supported by (G. Boxshall. 1985). Yet another site of variation, some copepods have only one caudal ramus, where some can have two caudal rami. According to (Stachowitsch, 1992) these rami, or caudal furca have a great diversity in their physical structure, which some having claw like projections and others having setae projections coming off. This would lead someone to say it is safe to assume that theses caudal appendages have differing functions. This is further elaborated by (A. Parker, 1997) who describes the caudal furca of a particular genus when they say, “furcal claws often bear teeth (robust spines/setules) on their anterodorsal margins…” this researcher further complicates when discussing the function. This researcher, (A. Parker, 1997) gives the assumption that these appendages would likely be used for scavenging but after further examination states “However, the use of the furca in the feeding mechanism of scavenging cypridinids has not been studied using modern techniques. In fact, little is known about the function of the caudal furca in any crustacean group” which shows that this appendage needs to be further studied to find an accurate function.

Developmental Stages of Copepods:

Copepods go through four developmental stages in their life. First is birth as an egg, larval stage as a nauplii, molt through the copepodite stage, then become an adult copepod. Within each of these stages is a series of developmental changes (NOAA, 2021). As an egg, they are laid in groups called sacs, despite there being “little evidence that the eggs are carried in a bag” as (J. Mauchline, 1998) says. What can be discerned by the eggs that have been released, is the species and the number of membranous layers surrounding the egg. Another thing that can be discerned according to (J. Mauchline, 1998), is whether an egg is fertilized or not, a fluorescent dye can illustrate the nuclei within the egg. If one is present, it must be only female if two pronuclei are found it has been fertilized by both male and female. The next stage of development is the nauplius stage. It is divided into six naupliar stages (J. Mauchline, 1998). The first three stage produce three paired appendages, which are the feeding appendages antennules, antennae, and mandibles (J. Mauchline, 1998). It should be noted that Labidocera which is an exception to this rule, as it undergoes the equivalent first naupliar stage as an egg (J. Mauchline, 1998). The next three stages show signs of abdominal and thoracic growth. Next the copepodite stage will also occur within six stages. These stages are separated by a series of molting which results in sequential development of both thoracic and abdominal segments. As (J. Mauchline, 1998) says, the abdominal segments grow cephalically away from the anal somite. Then the thoracic segments grow caudally towards the abdominal region. The most visual representation of these stages is the presence or absence of the swimming legs. By the sixth and final stage, the copepodite will undergo sexual differentiation, and become a full adult copepod. Where it will halt development, and instead be primarily focused on feeding and reproduction.

Current Research on Copepods:

Research on copepods has been occurring for centuries and is still going on today. Some of the current projects are as follows. The first of these is titled, “Trophic Transfer of Microplastics from Copepods to jellyfish in the Marine Environment” by (E. Costa, V. Piazza, S. Lavorano, M. Faimali, F. Garaventa, and Chiara Gambardella, 2020) which as the title suggests tracks if the microplastics consumed by copepods can be transferred up the food chain. This is incredibly important to people, since humans have continued to flood the oceans with tons of plastics causing a rise in microplastics within the ocean. This study has the potential to show whether this will directly affect people via their diets, or if it will just damage the marine ecosystem. Next another study based upon the feeding of copepods, titled, “How Copepods Can East Toxins Without Getting Sick: Gut Bacteria Help Zooplankton to Feed in Cyanobacteria Blooms” which as the title states focuses on the ability of copepods to consume toxins (E, Gorokhova, E. El-Shehawy, M. Lehtiniemi, and A. Garbaras, 2021). This is similar to the before mentioned study which shows the complexity of dietary effects on the food chain. A current study also associated with toxicity and copepods is titled, “Predicted Near-Future Oceanic Warming Enhances Mercury Toxicity in Marine Copepods” this study attempts to find molecular mechanisms by which copepods can respond to mercury pollution (Y, Chen. & W, Dong. 2021). This is a an especially useful field of research considering both climate and mercury levels are on the rise. Another novel research project is one that has been mentioned already. A study currently being done by graduate students at Lincoln Memorial University, it focusses on the mechanism of motion and how the swimming appendages of Labidocera work. This study is one that is seemingly neglected by many researchers, who focus primarily on the feeding of the copepods. This study shows promise in developing an understanding for the biomechanics of copepods.

References:

1. Walter, T.C.; Boxshall, G. (2021). World of Copepods Database. Labidocera acuta (Dana, 1849). Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=104726 on 2021-10-07

2. Anderson, Hayley, (2021) Copepods: Classification, Characteristics, Adaptations and Culture. https://www.microscopemaster.com/copepods.html

3. Walter, T.C.; Boxshall, G. (2021). World of Copepods Database. Labidocera Lubbock, 1853. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=104208 on 2021-10-08

4. Perumal. P, Rajkumar. M, Santhanam. (2009) Journal of Environmental Biology. Biochemical composition of wild copepods, Acartia spinicauda and Oithona similis, from Parangipettai coastal waters in relation to environmental parameters http://www.jeb.co.in/journal_issues/200911_nov09/paper_13.pdf

5. Conley, W. J., & Turner, J. T. (1985). Omnivory by the coastal marine copepods Centropages hamatus and Labidocera aestiva. Marine Ecology Progress Series, 21(1/2), 113–120. http://www.jstor.org/stable/24816921

6. Smith, J. N., Richter, C., Fabricius, K. E., & Cornils, A. (2017). Pontellid copepods, Labidocera spp., affected by ocean acidification: A field study at natural CO2 seeps. PloS one, 12(5), e0175663. https://doi.org/10.1371/journal.pone.0175663

7. Anu Vehmaa, Hedvig Hogfors, Elena Gorokhova, Andreas Brutemark, Towe Holmborn, Jonna Engström-Öst. (2013) Ecology and Evolution 2013; 3( 13): 4548– 4557 https://onlinelibrary.wiley.com/action/showCitFormats?doi=10.1002%2Fece3.839

8. J. Mauchline (1998). Advances in Marine Biology, The Biology of Calanoid Copepods. Academic Press.

9. Kennedy. J (2018). Rostrum, As Used in Marine Life. https://www.thoughtco.com/rostrum-definition-2291744

17. Parker. A. (1997).Functional Morphology of the Myodocopine (ostracoda) Furca and Sclerotized Body Plate :Journal of Crustacean Biology, 17(4). https://academic.oup.com/jcb/article/17/4/632/2418909