Overview of Pod Diversity
Copepods provide a near universal benefit to the reef aquarium. They feast on detritus, uneaten feed and pest algae, then convert that biomass into more pods. Excess pods are easy and nutritious feed for fish, corals and inverts alike. However, copepod refers to an enormous subclass of crustaceans. There are 10 major copepod orders, each with a different general shape and each comprising thousands of different species. Copepods are found in most aquatic ecosystems and can function as grazers, predators or parasites.
Realization of the vast reality of pod diversity begs the question:
Desirable Characteristics of a Reef Tank Copepod
- Generalist Grazer: It is essential that a pod be capable of grazing on various forms of pests/detritus so that they can act as micro-cleanup crew. Various pod species have specialized mouthparts and movements which allow them to capitalize on different food items. Generalist feeders are best because not only can they feast upon changing arrays of detritus, algae, bacteria, cilitates etc...but they are not dependent on one particular food item, and thus, their populations can remain high and stable even if the tank looks spotless!
- Salt Tolerance: Copepod species intended to be seeded into a reef aquarium must be able to survive and reproduce at reef salinities (1.015-1.030 sg). Because of this, many commercial copepod species are euryhaline-- meaning that they are fit to survive over a wide salinity range. However, some pod species breed more at higher salinities than lower and vice versa. The nutritional quality of various pod species can also waver with salinity--a vital consideration for providing the best quality live-feed to the tank!
- Prolific Breeder: Copepod species which rapidly produce nauplii (offspring) are best for various apparent reasons. They colonize the tank quicker and require less seeding. Quicker colonization means a quicker reduction of available detritus and pests. It also means a greater surplus of nauplii, copepodites (juveniles) and adult copepods which can be consumed by the tank inhabitants without interrupting the greater pod population.
- Relatively Soft Bodied & Rich in Golden Fats: Some copepod species have evolved spikes and other protruding structures to deter predators. These sharp spines and edges can irritate/damage the mouths of corals and fish. Therefore, it is important to choose a species which has an edible shape at all parts of its life cycle. Most commercial pod species are relatively soft-bodied, making them juicy snacks. (Think eating a lobster vs an urchin with no hands). It is equally important that pods be able to retain and accumulate golden fats (PUFAs1) acquired through their diet. We recommend enriching pods and other live feeds with Golden Fat Isochrysis microalgae. In comparison to Artemia, which loses nearly all dietary PUFAs within 12 hrs of consumption, many pod species can retain PUFAs for days. However this is dependent on species, salinity and other environmental factors.
- Fit to Occupy the Ecology of the Tank: In nature, copepods occupy an infinite amount of ecological roles. For the most part, copepods function best in the reef aquarium as detritivores and generalist grazers. Because of this many pelagic, calanoid species used in commercial aquaculture (Parvocalnus crassioristris, Pseudodiaptomus pelagicus) are not suitable for seeding into a reef tank because they require lots of open water and are likely to be completely consumed within hours of introduction. They also reproduce relatively slowly and require live microalgal feed at all times. These species have their specific utility, yet the average reef aquarium is FAR better serviced by the introduction of harpacticoid (Tisbe, Tigriopus) or cyclopoid (Apocyclops) copepod species. These pods are able to cling to surfaces and crawl inside minute crevices. They are hardy to high ammonia and low oxygen levels and thus willingly colonize the foulest filter depths. They clean these sewage centers out and convert that waste into sweet delicious pod treats for your reef!
Tisbe was arguably the first genus of harpacticoid copepods to be the subject of aquaculture experimentation. In the wild, Tisbe copepods occupy a huge variety of temperate and tropical ecosystems, where they primarily act as detritivores and bacterial/algal grazers. Tisbe biminiensis is a tropical species that is EXTREMELY prolific, with each female capable of holding a few dozen eggs at a time. This species reproduces the quickest at higher temperatures (75F+) and salinities (1.025-1.030sg), making it a lover of reef ecosystems. This species benefits tremendously from Golden Fat enrichment by feeding species such as Isochrysis, and can store more PUFAs in their tissues for longer under higher salinities. However it should be noted that Tisbe pods specialize in the consumption of sunken particles. In Araujo-Castro et al 2005, it was demonstrated that Tisbe biminiensis adults preferentially consume benthic algae species and detritus over free-swimming algae and suspended particles. This is an incredibly efficacious benthic detritus-feeder that is best complimented by aggressive filter feeders.
Historically, Tigriopus californicus has been primarily studied through the context of tide pool ecology. The tide pools where this species evolved exposed it to extreme heat and UV radiation. As a result, the North American Tigriopus is perfectly capable of colonizing tropical reef tanks. This species is larger than Tisbe biminiensis, allowing it to eat larger pest species and to feed larger fish. However, they reproduce slightly slower as well. This species is capable of producing and assimilating massive amounts of the red pigment astaxanthin into its cells. Astaxanthin (what makes salmon red) acts as a natural sunblock and also provides a plethora of health benefits to fish and corals (most notably color enhancement). Weaver et al 2018, demonstrated that Tigriopus californicus was capable of converting lesser yellow pigments from its algal diet into the precious red astaxanthin pigment. This revelation offers the true worth of Tigriopus as a vehicle for superior color enhancement.
Though cyclopoid copepods have been the mainstay stapel of pond aquaculture for millenae, only in recent decades have they been directly applied to formal aquaculture. One of the first cyclopoids to be recognized was the Central American Apocyclops panamensis. This species somewhat couples the behavior of the benthic harpacticoid copepods (Tisbe, Tigriopus) with that of the free-swimming calanoids (Parvocalanus). Though spending a significant amount of time crawling on glass, rocks and other substrates, adults propel through the water column feasting on suspended detritus, bacteria, ciliates and algae. These open-water excursions make adult Apocyclops more available to fish and corals, which is fine because they have a rapid reproductive rate. Though there are higher-salinity strains of Apocyclops being developed, their natural preference is lower salinity (1.015-1.020). Being euryhaline, they still survive at higher salinities but will find best application in lagoon/brackish tanks. Because they are such a competent grazer of suspended prey items, they make an excellent coupling with benthic species like Tisbe.
Copepods are an enormously diverse and complex group of crustaceans. Commercial copepod species for the reef aquarium trade are united by shared characteristics such as high salt/temperature tolerance,
soft-bodied, ability to eat pests/waste and fast reproductive rate. Under these criteria, Tisbe, Tigriopus and Apocyclops are all fine candidates for seeding into a reef aquarium. Each has relative pros and cons associated with it, but these are best reconciled when two or more of the species are seeded together.
Combined with periodic enrichment feedings with Golden Fat Isochrysis microalgae, the ecology of various copepod species should synergize so as to maximize waste-removal and surplus live feed production in the coral reef aquarium.
1 Polyunsaturated fatty acids---EPA/DHA/ARA of particular interest; essential to short and long term health of many marine species
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Cruz-Rosado, L., Contreras-Sánchez, W. M., Hernández-Vidal, U., Perez-Urbiola, J. C., & Contreras-García, M. D. J. (2020). Population growth of a generational cohort of the copepod Apocyclops panamensis (Marsh, 1913) under different temperatures and salinities. Ecosistemas y recursos agropecuarios, 7(2).
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