The current consensus is that both air and water temperatures will increase in the Northeast as a result of climate change. Predictions for how much temperatures will change are based on scenarios of greenhouse gas emissions and Gulf Stream circulation.
An annual average air temperature increase of 3-10° F in the Northeast by 2080 is possible, and the changes are expected to vary across seasons.

Most of the warming will be experienced in the winter, rather than summer, months. The frequency, intensity, and duration of cold air outbreaks is expected to decrease during this century. In the summer, the number of extreme heat days – those over 90° F – are expected to increase, although the increase is likely to be less along the Cape than in other locations in the Northeast. Furthermore, the character of heat waves is expected to change in the Northeast, becoming more frequent, intense, and prolonged.

Figure 1 (from the Union of Concerned Scientists report, “The Changing Northeast Climate – Our Choices, Our Legacy”) shows how changes in average summer heat index will strongly alter how summer feels to residents of the Massachusetts. Red arrows track what summers in Massachusetts could feel like over the course of the century if we follow a higher-emissions pathway. Yellow arrows track what states could feel like on a lower-emissions pathway, demonstrating that our emissions choices make a difference.

Predictions reported in the 2011 assessment by the Commonwealth of MA are shown in Table 2.

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Figure 1

Increases in air temperatures may impact the intensity of wind by changing temperature gradients. Higher winds can lead to more severe coastal erosion and sediment transport, which may impact shellfish resources.
Sea surface temperatures are also predicted to rise, by up to 4 to 8° F by end of the century. The MA EOEA (2011) assessment reported an average annual sea surface temperature of 53° F in coastal MA waters, which may increase to 55-56° F by 2050 and 57-61° F by 2100.

Coupled with warmer winters, winter ice cover is predicted to decline, although there will be variation from winter to winter.

  Recent Conditions
(average of observed data over 1961–1990)
2050 Prediction
(based on average of 2035–2064 predictions)
2100 Prediction
(based on average of end-of-century predictions)
Annual Temperature 46° F 50-51° F 51-56° F
Summer Temperature 68° F 72-73° F 72-78° F
Winter Temperature 23° F 25-28° F 27-33° F

Table 2.  Predictions reported in the 2011 assessment by the Commonwealth of MA (MA EOEA 2011).

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Water and Air Temperature Impacts Relevant to Shellfishing

Warming air and water temperatures may impact coastal embayments like Wellfleet Harbor in various ways:

  1. An increase in stratification of marine waters with respect to salinity and temperature.
  2. Depletion of oxygen levels, primarily during higher summertime temperatures, and changes in nutrient availability (MA EOEA 2011). Higher temperatures also lead to higher metabolic rates (including photosynthesis and respiration) for ectothermic organisms, but this effect can be moderated by temperature tolerance, nutrient availability, and other biological processes. Higher temperatures can also lead to increased energy demand of organisms to keep up with increase metabolic rates. Shellfish in oxygen depleted waters may have greater resilience than finfish.
  3. A general decline in primary productivity (phytoplankon), with one source estimating a decline of 2-20% by 2100.
  4. Warming may favor benthic predators feeding on bivalves. Increased temperatures may favor growth rates of predatory crustacean species over prey bivalve species.
  5. Rising sea temperatures may cause a decrease in the reproductive output of bivalve species.
  6. Rising sea temperatures may advance the spawning season for bivalves leading to increased mortality due to decreased resource availability (phytoplankton as a food source) for spat – this is referred to as a mismatch in trophic synchrony within communities.
  7. Warming air and water temperatures may increase the presence of marine diseases. For example, warmer temperatures may increase the spread of Dermo among oysters and may cause Dermo to become more prevalent farther north into New England states.
  8. Warming air and water temperatures may increase the prevalence, seasonal period, and geographical range of human pathogens, including Vibrio. Outbreaks of Vibrio parahaemolyticus (and other Vibrio spp.) have been associated with economic losses.
  9. Some fish and invertebrates will shift north as their preferred temperature ranges shift north. Warming will likely lead to invasion of ecosystems by southern species that displace native species. Another issue is the increased potential for “biofouling” organisms that can clog oyster growing bags and trays and smother quahogs by clogging nets over quahog runs.
  10. Oysters are habitat forming species – they form oyster reefs. If they are harmed by pathogens, decrease in food and nutrients, etc. key habitat will be lost for other species.
  11. Warming air temperatures will alter temperature gradients, thus leading to changes in wind patterns and speeds. Higher winds can exacerbate coastal erosion and alter sediment transport in the harbor.

Implications for Shellfishing

Warming air and water temperatures in Wellfleet Harbor may :

  1. Increase diseases and pathogens affecting both oysters and quahogs and selectively benefit predator species.
  2. Increase shellfish mortality due to summertime oxygen depletions.
  3. Increase exposure risks to those who work the shellfish beds.
  4. Decrease formation of ice and allow predators and pathogens to over-winter.
  5. Decrease economic revenue due to increased pathogens, shellfish diseases, and harmful algal blooms.
  6. Decrease economic revenue due to reduced reproductive rates.
  7. Decrease economic revenue due to incidents of human pathogens (e.g., Vibrio parahaemolyticus) or to the imposition of new rules to reduce risks of outbreaks.