Marine Biology & Global Change Part One

Marine Bio Exam 4

Incoming solar energy is balanced by

reflected and reradiated energy

The atmosphere’s loss of heat is balanced by

heat transferred from Earth to the atmosphere by evaporation, conduction, and re-radiation

The hottest year on record

2024 hottest year been in an increase in temp since 2014 breaking records each yr pretty much

Historic trends

• Reconstructed temperature

  from tree rings, ice cores, coral cores

• General negative trend until start of 1900’s

Every decade since 1960 has been

hotter than the previous one

Global Ocean Heat Content

energy absorbed and stored by the oceans

ocean heat content for 2022 for the upper 2,000 meters was

record high, surpassing the previous record set in 2021.

The regions of the North Pacific, North Atlantic, the Mediterranean, and southern oceans also had their highest

OHC since the 1950s.

Why does more than 90% of the heat accumulates in the ocean

because of its large heat capacity

Future trends

Models show an average warming of 1.8°, 2.8°, and 3.4°C for the low (Bl), medium (AIB), and high (A2) scenarios

On average, expect 3°C rise in SST by 2100

Marine heat waves

defined as any time the ocean temperature is above the 90th percentile for a specific length of time.

can last for weeks, months or years

Marine heat waves are ___ and __ over the past century

Marine heat waves are more frequent and last longer over the past century.

Biological impacts

Corals

• Bleaching

  Fish

• Physiology

• Life history

  Population & Community

  • Range shifts
  • Population declines

Coral bleaching

is the breakdown of symbiosis between coral and zooxanthellae

Coral polyps form obligate symbiotic relationship with

dinoflagellates of the genus Symbiodinium(zooxanthellae)

Heat stress due to rising SSTs can cause

mass bleaching events

decline in coral abundance

declines in the abundance of coral dwelling fishes an implication of bleaching

Implications of bleaching

• Proportionally greater losses of specialists than generalists

• Habitat specialists are thought to be more prone to extinction than generalists

Implications of marine heat waves on species

pos relationships with coral bleaching

neg relationship with seagrass density

neg relationship with kelp biomass

Fish physiology

Elevated temp increases

basal metabolic rate

Fish physiology

aerobic scope

difference between basal and maximal metabolic rates (B)

Impact on fish physiology

• Defines amount of aerobic energy that can be allocated to higher level activities

– Growth, reproduction, etc.

• Reduced aerobic scope in higher temperatures

How to measure aerobic scope in fishes

• Measure oxygen uptake at rest

  (MO2rest)
  and when swimming against current

  (MO2max)

• Abiotic factors can be modified

  • –  “Normal” 29 °C

  • –  Projected: 31 °, 32 °, 33 °C

Respirometry apparatus

• Oxygen uptake is a proxy for metabolic rate

What does aerobic scope do at high temps?

declines

Impacts on fish: life history

• Reduction in aerobic scope

  affects higher level functions

• Growth and reproductive rates decline beyond aerobic optimum

• Tropical species more susceptible due to narrower thermal range

Does growth decline at high temps?

Yes

• Independent effects of food and temperature

• Increased food does not ameliorate effects of high temperature at 31C

Reproductive failure at high temperatures are a result of

• Food and temperature influence multiple proxies of reproductive success

• Breeding pairs experience reproductive failure at high temperatures & low rations

Where are potential range shifts for coral reefs

(a) For species already living in the entire extent of coral reef development (a), range shifts are not expected (nowhere to escape – probably go extinct)
(c) For species living at equator, not at lat extent of coral, range shifts are expected towards the higher lat (b) For species living in mid latitude regions, reaching latitudinal extent of coral range, range contraction towards higher latitude expected.

(d) For species living in restricted ranges along the latitudinal extent of the coral range, range contraction poleward and range reduction expected, resulting in low population sizes – high risk of extinction.

Is the ocean experiencing more rapid seasonal shifts in climate than land

Yes fall is delayed in ocean relative to land and spring is advanced

causing range shift