Hatching Baby Cuttlefish

While with the MBA in Plymouth for work experience, I was given a chance to help in the facilities wet labs, an area of the building that is kept specifically to maintain experiments and studies that require live species. This may include breeding programs, testing new equipment, behavioural studies, and numerous other useful facets. Alix, the lab technician, needed our help moving cuttlefish eggs, bulbous sacs that grow of strips of organic matter like grapes on a vine, to a shallower tank where the baby cuttlefish could be more easily seen and cared for when they hatched. They need these cuttlefish as they are excellent subjects for tests, fairly adaptable and intelligent. 30 or so will be raised into adults each breeding cycle, and the rest will be released back into the ocean.

We place grape-like eggs into the tray.

The eggs contain tiny cuttlefish, identical to the adult animal in every way except for size, something which is fairly unusual in marine animals, most of which will go through an extensive larval stage. With a 5:1 male to female cuttlefish ratio, competition between males is high, often ending in confrontations and fights in which they will grapple each other, in an attempt to immobilise the competitor. Larger males will guard the females they have mated with in their dens, waiting for them to lay their eggs so they can find a new mate. Without this protection it is likely that other males would intercept the female and fertilise her, reducing the number of eggs in her brood belonging to the original male. Even with him standing guard, sneakier males can still slip by his defences, hiding their extra arms and changing their body colour in an attempt to disguise themselves as a female. The unsuspecting male lets them into his den, only for what it thought was another mate to fertilise the female and run. Interestingly, it seems that cuttlefish can learn about and adapt to their environment while still in the egg, showing a preference for food sources kept near the unhatched egg.

As we began picking the eggs of the rope they had grown on, and into a shallow tray of water, the cuttlefish (which were near ready to hatch) became stimulated by the movement and began to leave their eggs. The tiny animals would bite through the thin protective layer and push backwards out of the egg, using the water jets on the front of their face to propel themselves out into the water, searching for cover. We scooped up the newborns with a small net, placing them in a bucket for safekeeping. Sadly, one of the babies was born deformed, unable to properly float and would be likely to die very quickly in the wild. With a lot of suffering ahead of it, the technicians chose to put it down instead, placing it in a diluted tranquiliser before overdosing it, much like a vet would do to a suffering pet. By the time we had all the eggs, nearly 100 cuttlefish had hatched, and soon we had a tank of them whizzing about the water, hunting mysida shrimp we had caught for them earlier that day.

Seeing the baby cuttlefish come in to the world was amazing, as cuttlefish are some of the most intelligent and interesting animals in the ocean, with great social and behavioural capabilities. I really loved working with them, and hope that soon I’ll get a chance to see more cuttlefish up close.

Mysid Collecting

The MBA building is home to a large number of live animals which all require different and complicated things to survive. The biologists working with the live animals have been working to find the best ways to ensure that their specimens active and happy, not only for the creatures sake, but also to help improve the quality of the results their experiments yield. Cuttlefish are kept in the saltwater tanks, and the babies they breed require live prey to feed on. Mysida are an order of crustaceans, unique in their use of a kangaroo-like pouch to keep their live young in. Filter feeders, they prey on small planktonic species and pieces of organic debris, which they drag into their mouth using the front legs, and because of this are often a good sign of nutrient rich water, feeding heartily during algal blooms. In appearance, they are small shrimps, red or transparent in colour, and live around in world in both freshwater and saltwater.

This bag is utterly teeming with tiny Mysida.

Their size, abundance and high nutritional value makes them the perfect food for baby cuttlefish, and we were sent out to a nearby estuary to catch some. At low tide, the tiny Mysids are so common that you can barely wave your net through the water without catching some, and sweeping through a cloud will quickly gather up hundreds of tiny, wriggling bodies. Setting out with bags of fresh water, we quickly swept up as many as we could, conscious that spending to long or overfilling the bags would mean the Mysids would run out of oxygen and soon asphyxiate. Luckily it was a good day for gathering them, and after only 20 minutes we had enough to feed the new-born cephalopods. Although we sprung several leaks on the climb back up to the bank, perseverance meant we lost very little of our precious cargo. Triumphant, we rushed back to the MBA building, wanting to get the new feedstock in a tank as soon as possible.

Fish Larvae Dissection

While working on plankton with Dave, at the MBA labs, we were shown a collection of tiny larval fish, a mixture of pilchards and sprat, that had been previously captured and preserved in alcohol. To find out more about the lives of the fish in the sea, we need to understand the behaviour they show early in their lives. This includes what they eat. With a larger fish, this is as simple as catching it and recording the debris that falls out of their stomachs. On a larval fish, however, a dissection is not so easy, requiring a microscope, needles, steady hands and a lot of patience.

The guts are hanging out of this microscopic fish.

When the fish first go into the alcohol, they will often vomit up the contents of their bellies, leaving nothing behind for us to find except for lines of tubed intestine. Luckily, we couldn’t really spill the fish’s guts as we had never done it before, and it was harder than you might think. Dave himself has done thousands of such dissections and can now be considered a master. Looking under the microscope, I savagely ripped apart three tiny fish in search of the plankton that they were supposed to eat, finding it easier to take apart the smaller, squatter fish as their innards were visible from outside the fish, instead of stretched across the longer larvae. Eventually I managed to produce a small skeleton from one of the fish, the calcified remains of phytoplankton called cocoliths, the same type that form the chalk downs near my house, and the white Dover cliffs.

It was an interesting and challenging task, taking me several tries to yield even one measly plankton corpse, but with time and experience, people can find out what species these little fish consume, and tell us more about the miniature ecosystem that we can’t see.

Plymouth Plankton Study

The wonderful thing about studying plankton is that they are not a single species, but rather the collection of hundreds of creatures too small to move any great distance without the assistance of ocean currents. It’s like looking at a tiny ecosystem that exists in every cubic meter of the sea, comprising of plant-like phytoplankton, tiny hunting zooplankton and larvae of animals such as crabs, fish and bivalves. Every species is wildly different, with each tiny body under the microscope having a unique lifestyle.

Resident plankton expert of the MBA, Dave, took us out to observe the plankton life living in the Plymouth Harbour, just a stones throw away from the labs. Taking a fine, cone-shaped net attached to a high tech jam jar, he filtered a selection of plankton straight from the water. He only walked about 20m with the net in the water, and it wasn’t at all deep, but the wide variety of life we found under the microscope was astonishing. Even knowing that plankton were a diverse form of life, with around 5000 species in Plymouth alone, it was shocking to see the variety of each tiny lifeform.

High quality net, and an even higher quality jam jar.

Some species of plankton have extremely complex lifecycles, in particular the species of meroplankton, which are only planktonic for the first part of their lives, eventually turning into the larger sea species everybody commonly enjoys in their rock pools. The barnacle is an excellent example of this, living in two planktonic stages, a free-swimming nauplis which moults around 5 times before becoming a non-feeding cyprid which will use its oil energy reserves to burrow into an area of rock, ready to take root and become a sedentary adult. Looking down the microscope we saw such barnacle cyprids, comb jellyfish, which aren’t the same as true jellyfish, water fleas, algae and tiny fish.

It was extremely interesting to see what microscopic life was living in every cubic inch of water that covers the earth, a truly amazing prospect considering the size of our oceans. Countless billions of tiny organisms live around us, too small to see, and all too often out of mind.

Plymouth Fish Survey

Having spent a day surveying oysters on my MBA work experience week, my group and I went out to the Plymouth coast to look at some of the more charismatic denizens of the ocean. Where the estuary mouth meets the south coast, there is a remarkable selection of both freshwater and saltwater aquatic life living in the shallow bracken beaches. These areas are devoid of larger predators that would happily eat smaller marine life, and so make fantastic nursery grounds for young fish and crustaceans hiding in the sand. Taking our push and sweep nets in hand, we waded into the crystal waters to stir up fish life living under the surface.

We used two kinds of net to scour the estuary bed, large push nets which stirred up the sediment and captured the creatures that were revealed and smaller, finer sweep nets which could be used the capture smaller fish in clumps of seaweed or small rock formations. Spreading out and searching, we found a wide selection of flatfish in the knee deep water, as well as a wide selection of crabs, shrimp, sand eels, and, much to our delight, a large pipefish from among the short greenery. The flatfish were identified as a variety of young flounder and plaice, which look extremely similar apart from the small sharp spikes that can be felt on the sides of the flounder, setting it apart from the smooth plaice. We placed the animals into little trays while we collected, much like when I went pond thrashing with Matthew Smith, then chased the slippery customers about with our hands, trying to hold the still for measurements. The lesser pipefish, with it’s winding serpentine body and long nose was an immediate favourite – our catch of the day.

A lesser pipefish, held captive in a temporary tank, awaiting measurement.

We then moved onto the ocean itself, stretching out for mile upon mile of open blue. Ordinary nets would be of little use here, we’d be up to our necks in water before we saw anything, and so we brought out a huge weighted net. Three of the group brought the net out into the ocean, while the rest of us kept the net on the sea floor and near the shore, creating a semicircle of water, from which no fish could hope to escape from. Dragging the net in, we scrambled to seize the myriad of flatfish, such as flounder, turbot, plaice and brill, sandsmelts, baby sand eels and gobi.

It was a brilliant time out on the beach, and I learnt a huge amount about the fish species living around Plymouth. I feel sorry for all of the people on the beach building sandcastles and taking in the sun, instead of having such a good time with the marine life all around them.


Velvet Swimming Crab

While surveying the Pacific Oyster population on Batten Bay, Jack lifted several smaller rocks that littered the coastline, giving us a glimpse of the wildlife that was hiding under the seaweed forests that covered the lower shore. At first glance, most animals on the rocky landscape seemed stationary and with little diversity. Limpets and oysters dominated the rocky areas and on the sandy beaches tiny common crabs scuttled, giving the only sign of movement. The Plymouth coastline, however, is one of the most diverse habitats in Britain. Hidden beneath the sand, there is a wide range of snails, tiny nudibranchs, sea spiders and most noticeably, this creature:

A Velvet Swimming Crab, raising its claws in absolute fury.

The Velvet Swimming Crab is one of the largest crabs that can be found on the British coast, preferring areas of sheltered shore, such as the crannies of the large slate formations across Batten Bay. Commonly found across Europe in the North Atlantic and Mediterranean, easily identifiable by the blue and red stripes around the eyes and carapace, and the tiny hairs across the back that give it the ‘velvet’ part of its name. It’s paddle like back legs allow it to swim in high tides, rather than being forced to scuttle on the sea floor. Extremely aggressive for a crab of its size, it is little wonder that these crabs are sometimes called Devil Crabs, and even as I held it firmly from the back, I could feel it trying to turn and assault my fingers. This is an example of some of the larger creatures that make up the Plymouth aquaculture, but there are many other species hiding under rocks, just out off sight.

Batten Bay Oyster Survey

On the first day of my MBA (Marine Biological Association) work experience week at the Citadel Laboratory in Plymouth, we were taken down to a part of the Plymouth coastline called Batten Bay, a long shingle beach carpeted with a thick layer of brown buoyant seaweed. We headed out at low tide, when all of the large slate rock formations on the beach were open to the air, in search of a foreign species of oyster, called Crassostrea Gigas, or the Pacific Oyster. They grow around the rocky outcrops, and have in recent years been choking out the population of native European Flat Oyster.

The seaweed clogged Batten Bay, at low tide.

The Pacific Oyster is far larger than our native species, with short, sharp frills around the edges and a grey to pale-white colouration; it has a long oval shape that is distinct from the rounder European Flat. The species first came from estuarial areas of South East Asia and Japan, and was first brought into Europe because of its ability to grow to large sizes much faster than most types. It was believed that the waters around Britain would be too cold for them to successfully propagate, although they would be able to grow large enough for consumption. However, they soon adapted and started to take over areas of coast, which has made some ecologists concerned about the impact they are having on the European Flat. Pacific Oysters, like many other oyster species have sequential hermaphroditism, the ability to change their gender at will, in this case on a basis of food abundance. In times of plenty, the oysters become primarily female, in order to allow for a large number of eggs to be spawned so that the young can take advantage of the abundant food, while in times of famine, the oysters become mainly males so that the next generation will be smaller and thus use less of the limited food supply. Larval oysters are microscopic free swimmers, and will search for a new suitable area before permanently attaching themselves to that part of the rock.

The largest Pacific Oyster that we found that day, around 123mm in length. It even has a limpit growing on it for reference.

We separated into two groups, one taking the east side of the beach, and the other on the west side. With rulers and chalk in hand, we scanned the rocks searching for white oyster shells nestled in the rocks, noting down each one we found along with its length. Pictured above is the largest oyster that we found, 123mm long. I named him Ozzie. While Ozzie may be the largest we found that day, the Pacific Oyster can reach 400mm at the absolute most, but most are eaten before they survive that long. By measuring the length of the oysters, we hoped to check on how previous generations were faring, identifying cohorts (groups of oysters that attached to the rock at the same time) by their similar sizes. In addition we would see the success of the new generation, and be able to compare this to previous years, checking if the oysters are on the rise, and if older cohorts are surviving.

The survey was extremely fun, running about the coast and marking out oysters with the help of our extremely knowledgeable professional, Jack Sewell, who knew just about everything there was to know about the coastal ecology of Batten Bay. I look forward to comparing the data we gathered with that of previous years, and seeing how successful these foreign oysters really are.

MBA Work Experience

This summer, I have been selected by the MBA (Marine Biological Association) to spend a week in Plymouth doing work experience with them at their coastal Citadel Lab. Five other aspiring marine biologists and myself will be participating in various surveys across the Plymouth coast and estuary, spending time studying plankton in the laboratories, capturing feedstock for captive animals and going out into the Plymouth harbour to do boat work. I am extremely proud to have been chosen for this experience, and am excited to begin working at the MBA building as soon as possible.

The MBA Citadel Lab, located off the Plymouth Hoe.