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GOMIERP home and Andrew Allyn - NSF Fellow, Intercampus Graduate School of Marine Sciences and Technology, University of Massachusetts)....
March to May – Setting the dinner table for the summer
Longer days, warmer temperatures, and an increase characterize the beginning of spring in biological activity in the Gulf of Maine. Longer days increase the depth of the euphotic zone as light penetrates deeper down into the water column, providing a critical component required for photosynthesis and phytoplankton biomass growth. After being well mixed during the winter because of high winds and consistent, cool ocean temperatures throughout the water column, these newly illuminated waters are also rich with nutrients, adding another key item needed to support photosynthesis and the spring phytoplankton bloom. The final ingredient is added as the ocean surface waters warm, winds diminish and the water column becomes more stratified with vertical mixing decreasing. The increased stratification traps microscopic phytoplankton within the euphotic zone, abundant in light energy and nutrients. Armed with all of the necessary ingredients, the phytoplankton turn light energy and inorganic carbon (including carbon dioxide) into organic carbon compounds through photosynthesis. Their populations increase as the spring bloom commences, with phytoplankton biomass usually peaks around late-May to early-April. For some areas within the Gulf of Maine, this spring bloom occurs in waters that for most of the year are very unproductive, while other regions, such as coastal waters and the well-known Georges Bank, are fairly productive throughout the year.
The spring bloom provides much of the energy that will support the marine food web throughout the entire summer and it is no surprise that the diversity of marine organisms begins to increase during this vital time. Among these marine organisms, marine birds begin to return to their breeding colonies in the Gulf of Maine from late March through to early May. Arriving at just the right time, these migrating birds are able to key in on a variety of prey species, including zooplankton and forage fish, both of which are increasing in abundance as the amount of food available increases with the spring phytoplankton bloom. It isn’t just the breeding marine birds that arrive now, as later in May and April long distance non-breeding marine birds, such as the Greater shearwater, enter Gulf of Maine waters to take advantage of the nutrient rich waters while winter blankets their breeding grounds in the southern hemisphere.
May to July – Feasting and reproducing
The May to July period marks summer in the Gulf of Maine and the two things on most organisms minds are eating and reproducing. New phytoplankton growth has grinded to a halt in most areas throughout the Gulf of Maine as the exploding phytoplankton populations have used up most of the nutrients within the euphotic zone. The warm temperatures that stratify the water column prohibit the resupply of nutrients from deeper ocean waters, and as a result, phytoplankton biomass peaks and then begins to decline as predator populations’ increase taking advantage of the abundant phytoplankton. Among these predators are zooplankton, a key prey item for some fish, marine birds and mammals. For those fish-only marine organisms, the zooplankton may not be preferred prey items, but they serve a critical role in supporting the increase in abundance of forage fish species.
After replenishing depleted body reserves following the long winter and also possibly a long migration trip, many marine organisms quickly turn their attention to finding a mate, making a home, and reproducing. Most marine birds that breed in the Gulf of Maine are colonial nesters that exhibit high nest-site fidelity, regularly returning with the same partner to the same rock burrow or section of grass to raise their young. Their decision to breed is likely made many months before coming to the colony and once committed they will go to great lengths to ensure the survival of their young. For most species, survival rates are determined by a combination of food availability, weather, and predators. Even if food resources are abundant, an inopportune rainstorm or a visit by one of the many predators that frequent the colonies can quickly spell the end for marine bird chicks.
August to October – The fall bloom and choosing a winter location
(this is the time of our September 8th pelagic trip)
As the summer ends and fall begins [including the Sept 8 date of our trip], many areas in the Gulf of Maine see another spike in phytoplankton biomass. The shorter days, decreased temperatures and increased winds all support an increase in vertical mixing of the water column and nutrients are resupplied to the depleted euphotic zone. The increased nutrients, in turn, support a fall phytoplankton bloom [which provides nutrients all the way up the food chain, which attracts seabirds to these blooms and related upwellings]. Despite its usually smaller magnitude and duration as compared to the spring phytoplankton bloom, the increased food availability is vital during this critical time where many marine organisms are stocking up on body reserves before commencing their migrations to molting and wintering grounds.
For many species of marine birds, we still don’t know where these molting and wintering grounds are located. We do know, however, that no matter where they go, they need to find productive waters to survive the winter. These productive waters might be offshore or they could be thousands of miles south. Regardless of the location, individuals must make their trips relatively quickly as most undergo a fall molting period in the late fall. During the molt, individuals may remain flightless for extended periods (weeks to months) and consequently they need to have access to reliable food sources. Additionally, even for those species that may have different molting patterns, maintaining body condition during the winter is vital to long-term productivity as winter body condition is one of the dominant factors influencing the breeding success in the following season
November to February – Survival
For marine birds that breed in the summer in the northern hemisphere, the main goal during winter is survival, however, different species go about accomplishing this goal in different ways. Although more research is certainly needed, it appears that some of the alcid species (e.g., Atlantic puffins and Razorbills) that breed in the Gulf of Maine seek offshore waters, which maintain moderate levels of productivity throughout the year. These offshore waters are generally relatively close to the breeding grounds, at least when compared to the distances between breeding and wintering grounds for long distance migrants, such as the Arctic Tern. Instead of finding offshore waters near the breeding colonies, Arctic Terns from the Gulf of Maine embark on one of the longest migrations of any animal on earth, traveling all the way to Antarctica. There they arrive at the start of the summer in the southern hemisphere and they are rewarded for their travels with highly productive waters.
by Andrew Allyn
GOMIERP home
Gulf of Maine Integrated Ecosystem Research Program
