Lagoon & Salt Marsh Part II Life in the Mud Or What the birds are eating … I broke the Salt Marsh Class into several sections. So it would be easier to load on the website. This is the second part … Looking at life in the mud, how shorebirds partition resources, what they’re eating and a little bit about ducks partition resources as well. Life in the Mud I first became enamored with mudflats and salt marshes learning about the creatures that lived in the salt pans and mudflats. One day, while out on the mudflats of Morro Bay sifting through mud samples and thinking about who I was finding and how I had to search for each critter (and if truth be told – how invasive it felt to be digging up these creatures to see who they were), I paused. Walking through mud takes a lot of energy – you need to skate-skate… pause … skate-skate … pause … if you don’t want to sink up to your hips and have to crawl or be hauled out. As I was resting and taking in the expanse of mud flats and drinking in the salt air, I found myself watching the birds. I experienced one of those moments when some previously described concept crystallizes. I actually sat back in the ooze and found myself saying, “Huh” out loud. I was watching long-billed curlews and marbled godwits and willets and western sandpipers and semi-palmated plovers and great egrets and great blue herons and a little raft of waterfowl feeding. The egrets and herons were lining the tidal channels. The curlews, godwits, willets and sandpipers were working the mudflats and edges of the salt marsh. The ducks were in the deeper water with their butts up in the air. I remember thinking – all these creatures I love so much – the polychaete worms and clams and sipunculids (peanut worms) and ghost shrimp and weenie worms were all bird food. What I was watching was the concept of resource partitioning in action. This is a pretty cool thing when this happens. In that moment, how deep a worm or clam burrows became intimately connected with the length of bird bills. Patchy aggregations of mud critters became linked to bird search patterns. Now all I need is a field guide to mudflat burrows. Shorebird Shapes To hammer in the idea … Look at all these body shapes and bill sizes and orientations. All (or many) of these birds “eat at the same table”. Some sort of resource partitioning must be going on! A little review of some of your more commonly seen shorebirds … Who are they? Resource Partitioning A couple of different versions of the same concept … Below is the classic picture from Ehrlich talking about resource partitioning. I like it because you can really get a sense of the size of the bird and the size of the bill. western sandpipers and semipalmated plovers both snatch invertebrates from the surface or near the surface. Western sandpipers are constantly searching whereas semipalmated plovers will run- run-run - pause and search - run-run-run - pause and search This is another way of resource partitioning. Even if you have a similar-sized bill and are searching for similar things, the way in which you search may act to partition resources. There is a great deal of patchiness in the distribution of creatures in the mud and sand. So, as the birders among you know, you are sometimes able to tell who a bird is just by watching it’s feeding behavior. So now lets talk a little bit about the creatures that captured my heart, caused me to quit my job and go back to graduate school. The mudflats are riddled with critters. And we don’t know much about them. Sampling mudflats, like sampling the ocean is really hard. We just can’t do it un-invasively at this point in time. And what we come up with is spotty, at best, in terms of giving us an idea of who lives there and how they live. It would be like taking a huge crane and flying above Tokyo and scooping up pieces of buildings and people and stores and saying we’re studying the Japanese. a) mud snails b) moon snails c) soft-shelled clams d) ghost shrimps e) fat innkeeper worms f) bent-nosed clams g) sandworms h) bamboo worms The majority of these creatures are particle feeders. Remember we learned that much of the base of the food chain in salt marshes and coastal wetlands is detritus. Even these small creatures living in and among the mud need to partition their resources … Particle Feeders Food is partitioned by: the size of the particles chosen ingesting particles suspended in water ingesting the substratum and extracting food from it actively pumping water through a burrow or themselves waving feather appendages in the current Let’s look at some of the cool creatures we can find living in the mud up close … First clams … which are amazing creatures! We find gaper clams and heart cockles, bent-nosed clams and more in and around Bolinas Lagoon. Gaper Clam (Tresus nuttalli) Incurrent siphon ? Excurrent siphon ? Gaper clams are large clams and can be used to demonstrate some basic clam anatomy. Most often what you see of these clams is there siphons, unless they are dead and you find a shell. They use their siphons to suck water (with food particles) in and expel water (and waste) out. Tresus nuttalli besides be called the gaper clam is also referred to as summer clam, big- neck clam, horse clam, otter shell clam, great Washington clam. Walking through a bed of gaper clams at low tide is a little like being in an upside down giant shower. Limantour Estero is one place where I’ve experienced this in full force. Gaper clam shells are often found around the edges of Bolinas Lagoon and on Bolinas Beach. The shell may be 20 cm long and clam can weigh up to 4 lbs. The siphon breaks off easily and can be found in the stomachs of shorebirds, halibut, rays. Young clams burrow actively. As the clam ages, its burrowing ability declines. People who dig for these clams (and geoducks) think that the clam can burrow really fast. Most often, what is happening is the clam is retracting its siphons. Clams are ciliary mucoid feeders. Some clams like the geoduck can burrow down 3-4 feet. The gaper burrows down 2-3 feet. As was mentioned above, as they get older, they become poor diggers and live in semi-permanent burrows. These clams can be quite long-lived – up to 10-15 years. At the anterior end of the visceral mass is the mouth between the pairs of labial palps. The mouth is followed by a short esophagus. The esohpagus leads into a larger stomach. On each side of the stomach are the greenish digestive glands. Ducts from the digestive glands open into the stomach. Inside the stomach there is a gelatinous rod called the crystaline style which extends forward into the stomach from a style sac in the posterior central region of the visceral mass. Clam feeding Cilia in the style sac rotate the crystalline style. The rotation of the style aids in pulling a food-laden mucous strand through the mouth into the stomach. The crystalline style dissolves at its anterior end releasing enzymes into the stomach. The stomach wall and the digestive glands may also release enzymes into the stomach. Food particles drop out of the mucous strand onto a sorting area. Coarse particles are rejected and are carried by cilia to the intestine. Finer food particles are carried by cilia to the ducts of the digestive glands. Once in the digestive glands food particles are digested intracellularly in food vacuoles within cells of the digestive gland. Think about this … all to remove nutrient-laden particles from their surroundings! A little something to ponder the next time you order that basket of steamed clams. How does a clam burrow? The muscles, hemocoel (basically the body cavity and fluid in it), and shell work together. 1. muscles relax and shell gapes 2. base of foot expands (blood sinus = hemolymph) and creates and anchor 3. adductor clamps down and water in mantle cavity shoots out into sand, saturating the substrate and facilitating digging 4. retractor repels and pulls shell towards anchored foot and they start over again … Macoma nasuta Bent-nosed Clam Macoma nasuta is small and hardy. It can be found in almost every possible mudflat between Kodiak and the southern tip of Baja. The bent-nosed clam can stand stale water and softer mud than many species of clams. It lies on its side up to a depth of 10-20 cm with the bend in its shell turned upward, following the upward curve of its separate yellow siphons. (It burrows at an angle, sawing back and forth like a coin sinking in water.) At high tide, the animal extends its incurrent siphon from the burrow and sweeps the bottom surface like a vacuum cleaner. Considerable sorting takes place in the gills and labial palps. California Indians made extensive use of this clam for food. Near Tomales Bay populations spawn in May and from September – November. Further south, spawning can occur year-round. Callianassa californiensis Pink Ghost Shrimp These are burrows commonly seen in Bolinas Lagoon mudflats. There is also another ghost shrimp (the blue ghost shrimp) that is found in sandier substrates than the pink. The animal digs its burrow with the claws of the first and second legs, which draw the sandy mud backward, collecting it in a receptacle formed by another pair of legs.