There’s a quiet stirring afoot, a rustling of weathered brown spartina morning shrouded in the mist between afterthoughts of winter and anticipations of full-blown spring. The barely perceptible lengthening of days has set circadian clocks to ringing across the marsh and its attending waters. It is a time of awakenings and promise and we are all more than ready.
March typically is a month of singular transition, perhaps more than any other in the calendar year, in the estuarine cycle of life. Precluding aberrant weather such as a warmer than usual winter or late prolonged cold spell, water temperatures may rise ten degrees or more triggering a chain of actions, reactions and interactions among animal and plant species that will explode in a profusion of life over the following months.
March winds and waves break down the stands of dead spartina grass, the first step in converting the tough plant fiber into the most important commodity produced in the estuary, detritus. Tiny particles of detritus are the result of bacterial decomposition and are at the center of the estuarine food web.
Warming waters bring rising metabolisms and increased activity for cold blooded year round residents of the creeks and shallows and the return of others who over wintered in the deeper parts of the sounds and off shore.
Among those returning are the blue crabs primed for mating with peak activity occurring in April. Also during this time, post larval blue crabs (megalops) previously spawned off shore are entering the estuary for the first time. At less than 2mm and looking like a crab with a tail due to the fact that the abdominal plate has yet to fold under, the crablet (my word) is heavily dependent on detritus as a food source during this and subsequent early stages.
Commercial crabbing activity increases through the month as local watermen pursue the high profits of the soft shell crab season during which only female crabs seeking a mate are harvested.*
The current generation of white shrimp which vacated the estuary last fall to winter off shore is now spawning. Their post larval offspring will, like those of the blue crab, migrate to estuarine waters where they also depend on detritus as a primary food source.
By the end of the month the relatively clear water of winter begins to cloud as phyto (plant) plankton begin to bloom and more and more species ad their eggs sperm and larval offspring to the mix.
The estuary becomes a vast soup bowl of microscopic life with individuals feeding in frenzy on detritus and each other as they race to outgrow the intake capacity of as many hungry mouths as possible. The fry of offshore fish species that will call the estuary home while they grow large enough to increase chances of survival in open water are part of the mix. Black sea bass and red drum are two species sports fishermen prize that are dependent on the estuary as a nursery for their young.
March also means increased activity for Estuarium staff with the beginning of a new collecting season. It is my favorite time of year as each foray into the field brings the promise of surprise and thrill of discovery first experienced as a child and not forgotten. New creatures will soon be greeting Estuarium visitors along with new displays and the addition of a Children’s Corner and a touch tank.
I’m pleased to announce that all previous Estuarium Notes columns are now available on our web site listed below by clicking on Curator’s Corner.
* Some have raised concern in the past over the harvesting of female blue crabs for the commercial market. Please believe that the idea for the Soft Shell Crab Festival in Port Royal would not have originated with me if I were not certain, after discussing it with crustacean specialist with SCDNR, that it was a sustainable fishery. It is believed that a substantial number of the females harvested would not have been able to mate during the very short biological window of opportunity nature gives them to do so. This does not mean, however, that it’s okay to use a gravid female to make she-crab soup. By law, females showing eggs must be released.