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OCH BLOG

What’s Love Got To Do With Us?: Sex in the Sea Book Spotlight

Sex in the Sea, a book written by Dr. Marah J. Hardt outlines how a variety of different species in our oceans reproduce and how certain environmentally harmful practices can alarmingly decrease reproductive rates. According to Hardt, reproduction rates affect “food security, human health, coastal development, climate change, and other global issues” (3). Thus, it is clear to see how important stabilizing the reproduction rates of key species is to maintaining balance in other vital processes of the world. Unfortunately, there are several commonly used practices that are making it harder for certain species to reproduce. Luckily, some of these practices such as overfishing and the multiple forms of pollution have yet to permanently damage reproduction numbers, so there’s still hope we can reverse these effects (209). 


One species that has been notably affected by human activity is the copepod (Copepoda). Copepod are crustaceans that are so tiny they can fit on the tip of a pencil. They are a major food source in the sea as they are eaten by “countless larval crabs, fish, and squid” (10). Copepod are found throughout different ocean ecosystems, and they need to breed frequently to support the species that rely on them as a food source. Since copepod are so small, water behaves in a unique way when they move through it. They move by pushing through the water, “leaving temporary tunnels of disturbed water behind” (11). This is how male copepod find females to reproduce with. Males follow these trails like footprints and in some species, females can actually release pheromones that make their trails smell stronger. This process occurs in specific zones of the ocean depending on water temperature and salinity. However, as climate change progresses, the surface temperature of ocean water increases which can “shift where those layers can occur, how much oxygen exists (warmer water holds less oxygen), and the availability of food within each zone” (12). This confuses the copepod as they try to reproduce and, if they fail to do so, can decrease the availability of a vital food source for other creatures.


Another species that has become affected by human activity over the years is the blue whale (Balaenoptera musculus). One major way that male blue whales find mates is through their singing. They use a unique set of sounds, whistles, and clicks to communicate with other blue whales and look for a mate. Female blue whales prefer deeper songs because it signals to them that the male is larger and the deeper baritone can actually travel farther in water. The challenge is that the oceans have become increasingly louder than they were in the past. According to Hardt, “Greater ship traffic, more oil and gas drilling offshore, increased naval activity that relies on sonar - all of these have contributed to a rising din throughout the global seas. And many of these machine-generated sounds occur right within the same frequency bands marine mammals tend to use for their own communication” (30). Since these uses of technology have invaded the audible aspects of the ocean, it is making it harder for females to hear when males are calling, decreasing the rates of reproduction.


Yet another animal affected by human activity is the slipper shell snail (Crepidula fornicata). Arguably the most important piece of their reproduction process has to do with female snails emitting a specific chemical scent that encourages juvenile hermaphrodite snails to stay males for longer than they normally would. These chemical cues are carried by small molecules that drift through seawater, but “change the chemistry of the water, say, by slightly lowering the pH, and the structure of the signal molecules change” (44). Additionally, “...a drop in pH could interfere with the receptor cells on an animal…reducing their capacity to ‘read’ the message” (44). Unfortunately for the slipper shell snail, the pH balance of the ocean is tampered by the release of carbon emissions. Part of the issue with large amounts of carbon emissions being released into the air has to do with the fact that the ocean absorbs a large portion of them. When the ocean does this, the seawater becomes more acidic. This is called ocean acidification. To add more barriers to the reproduction of this species and those like it, human populations are also constantly adding different chemical scents to the ocean. One common way this happens is through oil spills. Foreign substances like oil can actually mimic vital pheromones, affecting migration patterns of several species. It is also possible for pollutants to cover up natural odors. These threats to sea animal reproduction disrupt necessary avenues for communication that keep our sea life thriving.


Not only are these harmful practices affecting animals themselves, but they are also having a negative impact on entire ecosystems. According to Hardt, “Globally, coral reefs are one of the most endangered ecosystems on the planet, with a staggering 10 percent of all reefs already permanently lost and another 30 percent expected to decline in the next few decades” (202). These reefs are a lot more important to the human population than one would think. They provide an important source of protein and employment opportunities. In fact, “On a global scale, through tourism, construction materials, fishing, pharmaceuticals, and coastal protection services, coral reefs provide an estimated $375 billion annually” (202). For these reasons, it is of the utmost importance that corals successfully reproduce with genetically diverse colonies. Unfortunately, sedimentation, pollution, overfishing, and climate change generate less than optimal conditions for this important process to take place. As we urbanize, dirt and grit wash into coastal waters and force coral to release a substantial amount of energy in order to clear these compounds out of themselves. This leaves coral species with less energy to produce sperm and eggs and being more exposed to “heavy metals, herbicides, and other pollutants [that] can reduce the number of gametes and cause infertility or decreased egg size, sometimes for years after exposure” (204). This makes it harder for coral reefs to produce the benefits that humans and sea life desperately rely on.


Luckily, many of these adverse effects have not yet completely become permanent and many solutions have been developed to help. Beyond federal intervention, there are plenty of ways the public can help. One important contributor to the increase in marine repopulation in United States waters has been the establishment of Marine Protected Areas, or MPAs. These are designated spaces where marine life can recover and thrive undisturbed. For some time after their initial establishment in 2000, MPAs had not been maintained very well, but over the last decade this has changed. Recently, MPAs in general have become stricter on what type of human interaction is permitted and the level of enforcement for these restrictions. More countries have implemented their own version of MPAs, which has helped stabilize a variety of  species all over the world. MPAs also generate what is called a “spillover” effect when “the reproduction rate inside the reserve [is] high enough to also boost settlement of juveniles outside the reserve boundary…” (231), which in turn encourages the fishing community to support the MPA. In this way, the success within an MPA can be spread to wildlife that live outside of it. The public can help support MPAs by volunteering, donating, or just visiting an MPA local to them.


Another way researchers have been able to help facilitate successful reproduction and conservation efforts is through the use of new technology. For example, “smart” buoys can detect whale calls and listening stations that help define the intricacies of Nassau grouper (Epinephelus striatus) populations are key to accurately monitoring and studying the interactions between ocean life. This type of technology can also help governments identify and prosecute illegal fishing that may be occuring inside of an MPA. Advancements in the coral farming industry have also developed an active volunteer effort. According to Hardt, “As research improves coral propagation techniques, the cost of growing corals drops and farming becomes far more user-friendly” (227). In this way, people who visit can take an active role in coral reef growth and transplant programs. Additionally, eco-minded entrepreneurs have more opportunity than ever to create ocean-friendly businesses.


Although the current state of our ocean may be bleak, advancements in technology and interest in ocean conservation offer a great deal of hope and an accessible opportunity to alleviate some of the effects of unsustainable practices. Attempting to reverse adverse effects will take time and creativity, but with enough effort, key ocean populations will be able to recover. People around the world will have built themselves a society more focused around conserving our natural habitat, benefiting both civilization and the environment.

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